TUP —  Poster II   (22-Aug-17   15:30—17:30)
Paper Title Page
TUP002 Numerical Studies on RF-Induced Trajectory Variations at the European XFEL 1
  • T. Hellert, B. Beutner, W. Decking, N. Walker
    DESY, Hamburg, Germany
  At the European X-Ray Free-Electron Laser, superconducting TESLA-type cavities are used for acceleration of the driving electron bunches. Due to the high achievable duty cycle, a long radio frequency (RF) pulse structure can be provided, which allows to operate the machine with long bunch trains. The designated pointing stability of the FEL radiation places stringent restrictions on the acceptable trajectory variations of individual electron bunches. Therefore a transverse intra-bunch-train feedback system (IBFB) is located upstream of the undulator section. However, intra-bunch-train variations of RF parameters and misalignment of RF structures induce significant trajectory variations that may exceed the capability of the IBFB. In this paper we give an estimate of the expected RF-induced intra-bunch-train trajectory variations for different machine realizations and investigate methods for their limitation.  
TUP003 First Beam Halo Measurements Using Wire Scanners at the European XFEL 1
  • S. Liu, V. Balandin, B. Beutner, W. Decking, L. Fröhlich, N. Golubeva, T. Lensch
    DESY, Hamburg, Germany
  Beam halo measurements and collimations are of great importance at the European XFEL, especially for the operation at high repetition rates (27000 pulses/s). First beam halo measurements have been performed during the commissioning using the wire scanners installed before and after the ~200 m long post-linac collimation section. We present the measurement results and the comparison of beam halo distributions before and after the collimation section.  
TUP004 Longitudinal Phase Space Optimization for the Hard X-ray Self-Seeding 1
  • S. Liu, W. Decking, G. Feng, V. Kocharyan, I. Zagorodnov
    DESY, Hamburg, Germany
  • G. Geloni, S. Serkez
    XFEL. EU, Hamburg, Germany
  For the implementation of Hard X-ray Self-Seeding (HXRSS) at European XFEL, short electron-beam bunches (FWHM ≤ 50 fs) are preferred to mitigate spatio-temperal coupling effect and to fit to the seeding bump width. Therefore, operations with low charges (< 250 pC) are preferred. Longitudinal phase-space optimization has been performed for the 100 pC case by flattening the current distribution. Start-to-end simulations show that, with the optimized distribution, for the photon energy of 14.4 keV, the HXRSS output power, pulse energy and spectral intensity can be increased by a factor of approximately 2 as compared to the nominal working point.  
TUP005 Studies of the Transverse Beam Coupling in the European XFEL Injector 1
  • M. Scholz, B. Beutner
    DESY, Hamburg, Germany
  Coupling between the transverse plains leads to an increase of the horizontal and vertical electron beam emittances. The coupling can be measured with dedicated multi quadrupole scans while the correlations of the beam are observed on a screen. In this paper we show the results from first coupling studies in the European XFEL injector.  
TUP009 The Effect of Transverse Space Charge on Beam Evolution and Photon Coherence 1
  • Q.R. Marksteiner
    LANL, Los Alamos, New Mexico, USA
  An electron beam experiences a transverse electric field which tends to act like a defocusing force on the electron beam. This defocusing force will act with different strengths at different locations in the electron beam because the current varies along the beam. A simple, quasi-analytic method is presented to calculate the impact of this force on beam projected emittance. In addition, estimates are made regarding the degree to which this could degrade the transverse coherence of x-rays in an XFEL.  
TUP010 Double-Bunches for Two-Color Soft X-Ray Free-Electron Laser at the MAX IV Laboratory 1
  • J. Björklund Svensson, O. Lundh
    Lund University, Lund, Sweden
  • J. Andersson, F. Curbis, M. Kotur, F. Lindau, E. Mansten, S. Thorin, S. Werin
    MAX IV Laboratory, Lund University, Lund, Sweden
  The ability to generate two-color free-electron laser (FEL) radiation enables a wider range of user experiments than just single-color FEL radiation. There are different schemes for generating the two colors, the original being to use a single bunch and two sets of undulators with different K-parameters. A development of the scheme has recently been shown, where two separate bunches in the same RF bucket are used for lasing at different wavelengths. We here investigate the feasibility of accelerating and compressing a double-bunch time structure generated in the photocathode electron gun for subsequent use in a soft X-ray FEL at the MAX IV Laboratory.  
Preparation for the Two-Color FEL Experiment at SXFEL  
  • W.Y. Zhang, C. Feng, B. Liu, Z. Qi
    SINAP, Shanghai, People's Republic of China
  Generation of double ultra-short radiation pulses with different carrier wavelengths in the x-ray regime is of remarkable interest in the FEL user community. Applications exist over a broad range of wavelengths involving pump-probe experiments. This paper presents the design studies for the two-color FEL experiment at the Shanghai soft x-ray FEL test facility. An optical system has been built to produce the double pulse two-color seed laser. We show the design and measurement results of this seed laser system.  
TUP013 Experience and Initial Measurements of Magnetic Linearisation in the MAX IV Linac Bunch Compressors 1
  • S. Thorin, J. Andersson, M. Brandin, F. Curbis, L. Isaksson, M. Kotur, F. Lindau, E. Mansten, D. Olsson, R. Svärd, S. Werin
    MAX IV Laboratory, Lund University, Lund, Sweden
  • J. Björklund Svensson
    Lund University, Division of Atomic Physics, Lund, Sweden
  The MAX IV Linac is now in routine operation for injection into two storage rings, and as a high-brightness driver for a Short Pulse Facility (SPF). In short-pulse mode the electron bunch is created in a photo cathode gun and compressed in two double achromat bunch compressors that also linearize longitudinal phase space with the second order transfer matrix element T566. T566 in the compressors can be tweaked with weak sextupoles located at high dispersion. In this paper we present the current experience from operating the bunch compressors at MAX IV and results from initial measurements of longitudinal phase space using the zero-crossing method.  
TUP015 Coherent Transition Radiation from Transversely Modulated Electron Beams 1
  • A. Halavanau, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • S.P. Antipov, W. Liu, N.R. Neveu, J.G. Power, C. Whiteford, E.E. Wisniewski
    ANL, Argonne, Illinois, USA
  • A.I. Benediktovitch
    BSU, Minsk, Belarus, Belarus
  • S.N. Galyamin, A.V. Tyukhtin
    Saint Petersburg State University, Saint Petersburg, Russia
  • D. Mihalceapresenter, P. Piot
    Fermilab, Batavia, Illinois, USA
  • N.R. Neveu
    IIT, Chicago, Illinois, USA
  A transverse laser-shaping optical setup using microlens arrays (MLAs), previously developed and employed at Argonne Wakefield Accelerator (AWA), allows the formation of both highly uniform and modulated (patterned) beams. In the latter case, transverse modulation is imposed in the sub-millimeter scale. In the present study, we report the simulations of backward coherent transition radiation (CTR) emitted from a transversely modulated beam. We compare the case of a uniform round beam against different transverse modulation wavelengths by generating CTR on a steel target and measuring the autocorrelation function of the resulting radiation with an interferometer. We particularly focus on the differences between round and patterned beam distributions and discuss possible future applications of this setup in THz radiation generation.  
TUP016 Beam-Dynamics Analysis of Long-Range Wakefield Effects on the SCRF Cavities at the Fast Facility 1
  • Y.-M. Shin
    Northern Illinois University, DeKalb, Illinois, USA
  • K. Bishofberger, B.E. Carlsten, F.L. Krawczyk
    LANL, Los Alamos, New Mexico, USA
  • A.H. Lumpkinpresenter, J. Ruan, R.M. Thurman-Keup
    Fermilab, Batavia, Illinois, USA
  Funding: Work supported by the subcontract (contract No: G2A62653) of LANL-LDRD program and DOE contract No. DEAC02-07CH11359 to the Fermi Research Alliance LLC.
Long-range wakefields in superconducting RF (SCRF) cavities create complicated effects on beam dynamics in SCRF-based FEL beamlines. The driving bunch excites effectively an infinite number of structure modes (including HOMs) which oscillate within the SCRF cavity. Couplers with loads are used to damp the HOMs. However, these HOMs can persist for long periods of time in superconducting structures, which leads to long-range wakefields. Clear understanding of the long-range wakefield effects is a critical element for risk mitigation of future SCRF accelerators such as XFEL at DESY, LCLS-II XFEL, and MaRIE XFEL. We are currently developing numerical tools for simulating long-range wakefields in SCRF accelerators and plan to experimentally verify the tools by measuring these wakefields at the Fermilab Accelerator Science and Technology (FAST) facility. This paper previews the experimental conditions at the FAST 50 MeV beamline based on the simulation results.
High Resolution Method for Uncorrelated Energy Spread Measurement  
  • S. Bettoni, S. Reiche
    PSI, Villigen PSI, Switzerland
  The beam uncorrelated energy spread is a key quantity to characterize the electron bunch, especially in FEL facilities. This quantity is expected to be between 1 and 3 keV at the end of a typical photo-injector. A method based on the analysis of a streaked beam in a dispersive section does not typically reach the necessary resolution. A different approach, based on the coherent harmonic generation, demonstrated the capability of reaching a resolution in the range of a few keV. Following this idea, we propose to use the laser of the laser heater to generate a time-energy modulation on the beam and to measure the bunching downstream of a compressor as a function of the dispersion to determine the uncorrelated energy spread. We discuss here the validation of the method, after applying the reconstruction technique to the simulations of the measurements. We determine a discrepancy between the assumed and the reconstructed uncorrelated energy spread, which is below the order of 0.5 keV.  
High Energy Tunable THz Source Based on Wakefield Excitation  
  • S. Bettoni, P. Craievich, E. Ferrari, R. Ischebeck, F. Marcellini, C. Ozkan Loch, M. Pedrozzi, S. Reiche, V. Schlott
    PSI, Villigen PSI, Switzerland
  We plan to use the interaction of a beam optimized for the generation of FEL radiation with a dielectric waveguide as a pump source for pump and probe experiments in FEL facilities. This scheme provides several advantages to fulfill the user requirements for a radiation source, in particular synchronization with the hard x-ray pulses, tunability throughout the THz frequency range of interest and energy level. We present the optimization of this scheme for SwissFEL, where optimized beam optics matches into a small aperture dielectric waveguide allowing for the highest THz radiation energy. We also propose a method to further increase the THz radiation energy at higher frequencies by shaping the electron bunch.
Paper soon submittedto a journal
Optimization of PAL-XFEL's 3 Bunch Compressor Linac  
  • H.-S. Kang, H. Heo, C. Kim, C.-K. Min, H. Yang
    PAL, Pohang, Kyungbuk, Republic of Korea
  • D. Khan, T.O. Raubenheimer, J. Wu
    SLAC, Menlo Park, California, USA
  The Pohang Accelerator Laboratory X-Ray Free Electron Laser (PAL-XFEL) consists of a 10 GeV normal-conducting linac delivering an electron bunch to two undulator beamlines and FEL radiation between 0.1 nm (Hard XRay) and 4.5 nm (Soft X-Ray). To provide high quality FEL lasing, it is paramount to optimize the linac settings under the consideration of the collective effects a beam may experience during transport to the undulator. The PAL-XFEL linac consists of four S-band linac sections, an X-band harmonic linearizer proceeding the first linac section, and a three chicane bunch compression system (the very first of its kind in operation). The addition of the third bunch compressor opens the possibility of heightened mitigation of CSR during compression and an increased flexibility of system configuration. In this paper, we outline a procedure to optimize the PAL-XFEL linac under several compression configurations using the particle tracking code Elegant and present its results.  
Commissioning Procedure of Linac and Undulators in PAL-XFEL*  
  • H. Yang
    PAL, Pohang, Kyungbuk, Republic of Korea
  Funding: This work is supported by MSIP, Korea.
PAL-XFEL consists of the hard x-ray (HX) line with 4-10 GeV electron beam and the soft x-ray (SX) line with 3-3.5 GeV electron beam. The HX linac consists of four sections of S-band accelerating columns, three bunch compressors, an X-band linearizer, and a dog-leg line. HX and SX undulator lines have 20 and 7 undulators respectively. Also, phase shifters are installed between two undulators. We can control the gap of undulators and phase shifter and the vertical position of undulators. The HX line generates 0.1 nm FEL with 9.6-GeV and 140-pC electron beam. The electron bunch is compressed to 2.5 kA with 2 or 3 bunch compressors. We conduct commissioning the linac and undulators for PAL-XFEL. The Beam Based Alignment (BBA) of the linac is conducted by one-to-one to find the field center of quadrupole magnets. The quadrupole magent movers and Cavity Beam Position Monitor (CBPM) offsets in the undulator region are used for the BBA to align the trajectory of e-beam and FEL. The controlled parameters of undulators are optimized to maximizing FEL intensity. In this paper, we summary the commissioning procedure of linac and undulators and present the details.
poster icon Poster TUP021 [0.832 MB]  
TUP022 Modeling and Optimization of the APS Photo-Injector Using OPAL for High Efficiency FEL Experiments 1
  • C.C. Hall, D.L. Bruhwiler, S.D. Webb
    RadiaSoft LLC, Boulder, Colorado, USA
  • A.Y. Murokh
    RadiaBeam, Santa Monica, California, USA
  • P. Musumeci, Y. Park
    UCLA, Los Angeles, USA
  • Y. Sun, A. Zholents
    ANL, Argonne, Illinois, USA
  Funding: This work was carried out with support for the United State Department of Energy, Office of Scientific Research, under SBIR contract number DE-SC0017161.
The Linac Extension Area (LEA) is a new beamline planned as an extension of Argonne's APS linac. An S-band 1.6-cell copper photo-cathode (PC) RF gun has been installed and commissioned at the APS linac front end. The PC gun will provide a beam to the LEA for accelerator technology development and beam physics experiments, in interleaving with a thermionic RF gun which provides a beam for APS storage ring operations. Recently an experiment was proposed to demonstrate the TESSA high-efficiency concept at LEA. In support of this experiment, we have begun simulating the photo-injector using the code OPAL (Object-oriented Particle Accelerator Library). In this paper, we first benchmark OPAL simulations with the established APS photo-injector optimization using ASTRA and ELEGANT. Key beam parameters required for a successful high-efficiency TESSA demonstration are discussed.
Recent Developments and Plans for Two Bunch Operation with up to 1 μs Separation at LCLS  
  • F.-J. Decker, K.L.F. Bane, W.S. Colocho, A.A. Lutman, J.C. Sheppard
    SLAC, Menlo Park, California, USA
  Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
To get two electron bunches with a separation of up to 1 microsecond at the Linac Coherent Light Source (LCLS) is important for LCLS-II developments. Two lasing bunches up to 220 ns have been demonstrated. Many issues have to be solved to get that separation increased by a factor of 5. The typical design and setup for one single bunch has to be questioned for many devices: RF pulse widths have to be widened, BPMs diagnostic can see only one bunch or a vector average, feedbacks have to be doubled up, the main Linac RF needs to run probably un-SLEDed, and special considerations have to be done for the Gun and L1X RF.
TUP024 Stochastic Effects from Classical 3D Synchrotron Radiation 1
  • B.W. Garcia, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • R.D. Ryne
    LBNL, Berkeley, California, USA
  In most cases, the one-dimensional coherent synchrotron radiation wakefield gives an excellent approximation to the total coherent effect due to classical synchrotron radiation in bend magnets. However, full particle Liénard-Wiechert simulations have revealed that there is non-numerical, stochastic noise which generates fluctuations about the approximate 1D solution. We present a model for this stochastic term in which this noise is due to long-range interaction with a discrete number of synchrotron radiation cones. The nature of this noise and how it depends on the 3D dimensions of the beam are explored.  
Beam Shaping to Improve the Free-Electron Laser Performance at the Linac Coherent Light Source  
  • Y. Ding, K.L.F. Bane, W.S. Colocho, F.-J. Decker, P. Emma, J.C. Frisch, M.W. Guetgpresenter, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, A.A. Lutman, T.J. Maxwell, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J.J. Welch, F. Zhou
    SLAC, Menlo Park, California, USA
  A new operating mode has been developed for the Linac Coherent Light Source (LCLS) in which we shape the longitudinal phase space of the electron beam. This mode of operation is realized using a horizontal collimator located in the middle of the first bunch compressor to truncate the head and tail of the beam. With this method, the electron beam longitudinal phase space and current profile are re-shaped, and improvement in lasing performance can be realized. We present experimental studies at the LCLS of the beam shaping effects on the free electron laser performance.  
Dispersion Based Fresh Slice Scheme  
  • M.W. Guetg, Y.-C. Chao, F.-J. Decker, Y. Ding, A.S. Fisher, Z. Huang, A.A. Lutman, T.J. Maxwell
    SLAC, Menlo Park, California, USA
  This paper presents experimental studies of the dispersion based fresh slice scheme at LCLS. This scheme lead to pulse shortening resulting in pulse lengths below 10 fs. Careful orbit control allowed generating two colors with individual delay control and color separation of more than 3%. Unlike the dechirper based fresh slice scheme, the dispersion based fresh slice scheme does not require additional hardware. Another key benefit of this scheme is a strong spectral stability making the photon pulse energy independent of the electron energy jitter.  
TUP027 Cancellation of Coherent Synchrotron Radiation Kicks at LCLS 1
  • D. Khan, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  In this paper, we look at the cancellation of Coherent Synchrotron Radiation (CSR) induced emittance growth using a phase-advance manipulation technique pioneered by R. Hajima, and extended in the Courant-Snyder formalism by S. Di Mitri. Bending systems in a linear accelerator are essential for beam transport and bunch compression. With the ever-growing demands of high-energy, short wavelength free electron laser (FEL) drivers, the CSR effect has emerged to be a detrimental factor in emittance stability. Under linear approximation, it is showed that the CSR driven dispersive kicks in successive bending magnet systems can, with proper balancing of the linac optics, cancel each other to nullify transverse emittance growth. This technique of optics balancing in the constant bunch length regime is the focus of this paper. We will present our findings for the emittance measurements generated in Elegant simulations for the current LCLS-I dogleg system.  
TUP028 Approximated Expressions for the Coherent Synchrotron Radiation Effect in Bending Magnets 1
  • D. Khan, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  In this paper, we describe the development of simplified analytic expressions for the Coherent Synchrotron Radiation's (CSR) root-mean-square induced energy spread, typically found in the bending magnets of short bunch-length charged particle accelerators. The expressions are derived for a Gaussian longitudinal bunch distribution and compared with the full-rigor CSR wakefield integral expressions while entering, traversing and exiting a bending magnet. The validity of the expressions are then tested against ELEGANT with the simulation of an unchirped beam traveling across a bending magnet into a drift section, and the second stage bunch compressor (BC2) of the proposed LCLS-II beamline.  
TUP030 An Emittance-Preservation Study of a Five-Bend Chicane for the LCLS-II-HE Beamline 1
  • D. Khan, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  The Linac Coherent Light Source II (LCLS-II) is an upgrade intended to advance the great success of its predecessor, LCLS-I, to maintain its position at the forefront of X-ray science. The introduction of a niobium-metal superconducting linac for LCLS-II not only increases the repetition rate to the MHz level (from 120 Hz), but also boasts an average brightness many orders higher (~10,000) than that of LCLS-I. Though, these improvements do not come without a price: the peak brightness suffers by a factor of 10, owing its degradation to the impact of Coherent Synchrotron Radiation (CSR) diminishing the peak current of the beam in the second bunch compressor (BC2). In this paper, we discuss the impact of implementing a plug-compatible 5-bend chicane for BC2 on the beam's emittance dilution for a high-energy, low-emittance configuration of LCLS-II (LCLS-II-HE). The results are compared with that of a standard 4-bend chicane under various settings in Elegant and CSRTrack.  
TUP031 Design of a Dogleg Bunch Compressor with Tunable First-Order Longitudinal Dispersion 1
  • W.K. Lau, M.C. Chou, N.Y. Huang, A.P. Lee
    NSRRC, Hsinchu, Taiwan
  • J. Wupresenter
    SLAC, Menlo Park, California, USA
  A nonlinear bunch compressor has been designed for the proposed NSRRC VUV FEL facility. It is a double dog-leg configuration that provides a first order longitudinal dispersion function (i.e. R56) with a sign opposite to that of a conventional four-dipole chicane. A large variation in the bunch length or the peak current for various operation conditions can be done by tuning R56. This can be realized by changing the longitudinal positions of the outside dipoles and adjusting the quadrupoles and sextupoles settings for desired bunch compression. Residual energy chirp left after bunch compression as revealed from ELEGANT simulation can be corrected by a capacitive dechirper structure when the bunch is slightly over-compressed.  
Design of the Beam Distribution System for a Soft X-Ray FEL User Facility in Shanghai  
  • S. Chen, H.X. Deng, C. Feng, B. Liu, D. Wang
    SINAP, Shanghai, People's Republic of China
  A soft X-ray user facility will be upgraded from an existing soft X-ray test facility in Shanghai. One or more extended FEL undulator lines will be constructed parallel to the previous undulator line. For simultaneous operation of several undulator lines, a beam distribution system is required for spreading the electron bunches from linac to each undulator lines. In this work, the physics design of such a beam distribution system will be described.  
A Novel Way to Generate Ultrafast X-ray Free Electron Laser Pulses  
  • D. Huang, C. Feng, Q. Gu
    SINAP, Shanghai, People's Republic of China
  Recently, ultrafast X-ray free electron laser (XFEL) pulses have become a key tool in many fields of scientific research. In this paper, a novel method to generate ultrafast XFEL pulses based on the laser heater in a linear accelerator (linac) is proposed. Contrary to other proposed methods, this new method is merely parasitic in the laser heater operation. Thus, it has significant advantages over the others such as being non-destructive, simpler, less expensive, etc.  
TUP034 Novel Aspects of Beam Dynamics in CeC SRF Gun and SRF Accelerator 1
  • I. Petrushina
    SUNY SB, Stony Brook, New York, USA
  • T. Hayes, Y.C. Jing, D. Kayran, V. Litvinenko, G. Narayan, I. Pinayev, F. Severino, K.S. Smith, G. Wang
    BNL, Upton, Long Island, New York, USA
  • K. Mihara
    Stony Brook University, Stony Brook, USA
  • K. Shih
    SBU, Stony Brook, New York, USA
  Funding: DoE NP office, grant DE-FOA-0000632, NSF grant PHY-1415252.
A 15 MeV CW SRF accelerator had been commissioned at Brookhaven National Laboratory to test the coherent electron cooling concept. The accelerator consists of an SRF 113-MHz photoemission gun, two 500 MHz bunching cavities and a 704-MHz 5-cell SRF linac. In this paper we describe our experience with this system with focus on unusual phenomena, such as multipacting in the SRF gun. We also discuss issues of wakefields in the CeC accelerator.
TUP035 CSR Wake Fields and Emittance Growth with a Discontinuous Galerkin Time Domain Method 1
  • D. A. Bizzozero, H. De Gersem, E. Gjonaj
    TEMF, TU Darmstadt, Darmstadt, Germany
  Funding: Work supported by DESY.
Coherent synchrotron radiation (CSR) is an essential consideration in modern accelerators and related electromagnetic structures. We present our current method to examine CSR in the time domain. The method uses a 2D Discontinous Galerkin (DG) discretization in the longitudinal and transverse coordinates (z,x) with a Fourier decomposition in the transverse coordinate y. After summation over modes, this treatment describes all electromagnetic field components at each space-time coordinate (z,x,y,t). Additionally, by alignment of mesh element interfaces along a source reference orbit, DG methods can handle discontinuous or thin sources in the transverse x direction. We present an overview of our method, illustrate it by calculating wake functions for a bunch compressor, and discuss a method for estimating emittance growth from the wake fields in future work.
Group and Phase Velocity Matching in THz IFEL interaction  
  • E.J. Curry, S.S. Fabbri, P. Musumeci
    UCLA, Los Angeles, California, USA
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  Funding: Work supported by DOE grant DE-FG02-92ER40693 and NSF grant PHY-1415583.
We review results from the recent guided-THz IFEL experiment at the UCLA PEGASUS facility. Using a parallel plate waveguide, the group velocity of a near-single cycle THz pulse was reduced to match electron beam propagation in an undulator, resulting in a ponderomotive interaction sustained for 30 cm. With a 1-uJ THz pulse obtained by optical rectification in a LN source, the projected beam energy distribution increased from a full peak width of 30 keV to more than 100 keV. When using a long (multi-ps) electron beam, longitudinal phase-space measurements reveal the snake-like energy modulation from the ps-scale THz pulse. Using a short beam configuration, we also measure bunch compression, limited by the available drift length to a factor of two. Finally, we explore the application of this technique to amplification of the THz seed using the 1-D multi-frequency simulation code we have developed for this novel zero-slippage interaction scheme.
TUP038 Experiments in Electron Beam Nanopatterning 1
  • C. Zhang, W.S. Graves, L.E. Malin, J. Spence
    Arizona State University, Tempe, USA
  • D.B. Cesar, J.M. Maxson, P. Musumeci, A. Urbanowicz
    UCLA, Los Angeles, USA
  • R.K. Li, E.A. Nanni, X. Shen, S.P. Weathersby, J. Yang
    SLAC, Menlo Park, California, USA
  Funding: This work was supported by NSF Accelerator Science awards 1632780 and 1415583, NSF BioXFEL STC award 1231306, and DOE contracts DE-AC02-76SF00515 and DE-SC0009914.
We report on experiments in nanopatterning electron beams from a photoinjector as a first step toward a compact XFEL (CXFEL). The nanopatterning is produced by Bragg diffraction of relativistic electron beams through a patterned Si crystal consisting of alternating thick and thin strips to produce nanometer-scale electron density modulations. Multi-slice simulations show that the target can be oriented for a two-beam condition where nearly 80% of the elastically scattered electron beam is diffracted into the 220 Bragg peak. An experiment at the two-beam condition measurement has been carried out at the SLAC UED facility showing this effect with 2.26 MeV electrons. We successfully proved a large portion of the main beam is diffracted into 220 spot by tuning the orientation of the sample. Future plans at UCLA are to observe the nanopatterned beam, and to investigate various grating periods, crystal thicknesses, and sample orientations to maximize the contrast in the pattern and explore tuning the period of the modulation. The SLAC measurement results will be presented along with design of the UCLA experiments.
TUP039 Electron Beam Requirements for Coherent Electron Cooling FEL System 1
  • G. Wang, Y.C. Jing, V. Litvinenko
    BNL, Upton, Long Island, New York, USA
  • J. Ma
    SBU, Stony Brook, New York, USA
  Funding: DoE NP office, grant DE-FOA-0000632, NSF grant PHY-1415252.
In this paper, we present results of our studies in amplification of density modulation induced by co-propagating ions in the FEL section of a Coherent Electron Cooling system, as well its interaction with hadrons. We present a set of requirements for electron beam parameters to satisfy for necessary amplification of the density modulation, while preventing loss of the phase information and saturation.
TUP042 Determination of the Slice Energy Spread of Ultra-Relativistic Electron Beams by Scanning Seeded Coherent Undulator Radiation 1
  • J. Bödewadt, R.W. Aßmann, C. Lechner, M.M. Mohammad Kazemi
    DESY, Hamburg, Germany
  • L.L. Lazzarino, T. Plath, J. Roßbach
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  Modern high-gain free-electron lasers make use of high-brightness ultra-relativistic electron beams. The uncorrelated energy spread of these beams is upon creation of the beam in the sub-permille range and below the resolution of state-of-the-art diagnostics. One method to determine the slice energy spread is to use an external seed laser to imprint a coherent microbunching structure that gives rise to coherent radiation processes, different radiation sources such as transition radiation, synchrotron radiation, or undulator radiation and others. Here, we present a method and show measurements to determine the slice energy spread using an external seed laser with 266 nm wavelength to produce coherent undulator radiation at higher harmonics. The distribution of these harmonics allows retrieval of the electron beam slice energy spread with high precision.  
Passive Linearization of the Magnetic Bunch Compression Using Self-Induced Field and Without Any Active Higher Harmonic RF Structure  
  • G. Penco, E. Allaria, I. Cudin, S. Di Mitri, D. Gauthier, L. Giannessi, E. Roussel, S. Spampinati, M. Trovò
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • S. Bettoni, P. Craievich, E. Ferrari
    PSI, Villigen PSI, Switzerland
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  In linac-driven free-electron lasers, colliders and energy recovery linacs, a common way to compress the electron bunch to kA level is based upon the implementation of a magnetic dispersive element that converts the bunch energy deviation in path-length difference. The non-linearities of such a process are usually compensated by enabling a high harmonic rf structure properly tuned in amplitude and phase. This approach is however not straightforward for foreseen C and X-band linacs. In this work we report the experiment performed on the FERMI linac that has demonstrated the possibility to exploit the longitudinal self-induced field excited by the electron beam itself to passively linearize the compression process without any active higher harmonic rf structure. In this novel configuration, the FERMI electron bunch was compressed up to 700 A as in the nominal case and driven along the FERMI FEL-1 undulators, generating intense extreme-ultraviolet pulses that were provided to users for experiments.  
Generation of Sub-fs X-Ray Pulses at the European XFEL  
  • S. Serkez, G. Geloni, S. Karabekyan, M. Lederer, S.I. Tomin
    XFEL. EU, Schenefeld, Germany
  • G. Feng, V. Kocharyan, E. Saldin, I. Zagorodnov
    DESY, Hamburg, Germany
  • A. Kalaydzhyan
    CFEL, Hamburg, Germany
  Time-resolved studies of free electron lasers are of a great importance. The resulting temporal resolution of the user measurements is determined by FEL pulse duration. Here we investigate possibilities to obtain sub-fs-long pulses at the European XFEL. Installation of the drive laser, modulator and magnetic chicane before the baseline undulator is required.  
poster icon Poster TUP044 [0.680 MB]  
TUP045 Interference-Based Ultrafast Polarization Control at Free Electron Lasers 1
  • S. Serkez, G. Geloni
    XFEL. EU, Schenefeld, Germany
  • E. Saldin
    DESY, Hamburg, Germany
  We present a scheme to generate two distinct FEL pulses with different polarization properties and down to 50 fs-order temporal separation. The scheme is based on installation of two consecutive helical undulators, a corrugated structure and emittance spoiler on top of a baseline variable gap undulator, and is exemplified on the SASE3 beamline of the European XFEL. Good temporal coherence by either self or external seeding is preferable. Our schemes can be used for pump-probe experiments and in combination with the "twin-bunch" technique.  
poster icon Poster TUP045 [0.568 MB]  
Ultrafast Electron Diffraction Facility Based on an RF Photogun and Achromatic 90-degree Bends for Sub-100-Femtosecond Timing Jitter  
  • Y.U. Jeong, S. Bae, I.H. Baek, B.A. Gudkov, B. Han, K.H. Jang, H.W. Kim, M.H. Kim, Y.-C. Kim, K. Lee, S.V. Miginsky, J. Mun, J.H. Nam, S. Park, S. Setiniyaz
    KAERI, Daejon, Republic of Korea
  • R. Fabian, H. Ihee, J. Kim, K.Y. Oang, H. Yang
    KAIST, Daejeon, Republic of Korea
  • J.H. Han
    PAL, Pohang, Kyungbuk, Republic of Korea
  • H.W. Kim
    University of Science and Technology of Korea (UST), Daejeon, Republic of Korea
  • K.W. Kim
    Chung Buk National University, Cheongju, Republic of Korea
  • S.V. Miginsky, N.A. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  • S. H. Park
    Korea University Sejong Campus, Sejong, Republic of Korea
  • S. Park
    Kyungpook National University, Daegu, Republic of Korea
  We have developed a laboratory-scale ultrashort electron accelerator for investigating femtosecond dynamics of atoms or molecules with pump-probe experiments. This system includes an S-band radio-frequency (RF) photogun and four achromatic bends for compressing electron bunches. Two of them are for ultrafast electron diffraction (UED) experiments on solid and gas samples. The electron bunch duration at the UED beamlines was designed to be ~30 fs in rms. Our target value of the timing jitter between the pumping laser pulse and probing electron bunch is approximately 10 fs. The synchronization between the pumping laser oscillator and a master oscillator of the RF system was successfully performed with the extremely low timing fluctuation of ~10 fs during 24-hour operation*. We developed a high-intense terahertz pumping source with field strength of more than 0.5 MV/cm for THz-pump and electron-probe experiments. We are conducting three independent application experiments with superconducting and strongly-correlated materials and gas samples for ultrafast molecular dynamics.
* H. Yang et al., "10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources," Scientific Reports, 7, 39966, 2017.
A Linac-Based All-in-One THz-Pump and X-Ray-Probe Sources  
  • S. Setiniyaz, I.H. Baek, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, S. H. Park
    KAERI, Daejon, Republic of Korea
  • N.A. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  We describe a compact THz-pump and X-ray-probe beamline, based on an electron linac, for ultrafast time-resolved diffraction applications. Two high-energy electron (γ>50) bunches, 5 ns apart, impinge upon a single-foil or a multifoil radiator and generate THz radiation and X-rays simultaneously. The THz pulse from the first bunch is synchronized to the X-ray beam of the second bunch by using an adjustable optical delay of THz pulse. The peak power of THz radiation from the multifoil radiator is estimated to be 0.18 GW for a 200 pC well-optimized electron bunch. The optimization of radiator for X-ray generation, performed by using GEANT4, shows that carbon foils, with a total thickness of 0.5 - 1.0 mm, has the highest yield of 10 - 20 keV hard X-rays for a 25 MeV beam, which is approximately a few 103 photons/(pC electrons) within a few degrees of the polar angle. A carbon multifoil radiator with 35 foils (25 μm thick each) can generate close to 103 hard X-rays/(keV energy bin)/(pC electrons) within a 2° acceptance angle. The longitudinal time profile of X-ray pulse ranges from a few tens to hundreds of fs depending on the acceptance angle.  
Automatic Tuning of the Electron Beam Parameters to Enhance LCLS FEL Performance Using ES  
  • P.M. Anisimov, A. Malyzhenkov, A. Scheinker
    LANL, Los Alamos, New Mexico, USA
  We report on the design of the new automatic fine tuning system for the electron beam parameters using extremum seeking (ES) to enhance LCLS FEL performance. ES is the fastest multidimensional optimization algorithm for finding extremum. First, we demonstrate ES capability to find optimum Twiss parameters of the electron beam and FODO lattice delivering maximum radiation power in Genesis simulations. Then, we use ES for taper optimization and compare the optimum performance with no taper configuration but optimum Twiss parameters. Moreover, we combine these two techniques together for fine tuning to enhance FEL performance even further. Finally, we propose applying ES for fine tuning at LCLS experimentally: Once FEL is tuned to operate at desirable user parameters, electron beam parameters are changed to maximize radiation power, while the last one remains above the lowest border specified by user during each step of the optimization.  
An Optically Levitated Imaging System for X-Ray Free Electron Lasers  
  • A. Malyzhenkov, J.H. Bartlett, A. Castro, V. Lebedev
    LANL, Los Alamos, New Mexico, USA
  We propose an optically levitated imaging system for X-ray Free Electron Lasers. First, we report on the design of an in-vacuo optical levitation trap compatible with X-ray Free Electron Laser vacuum requirements and other technical conditions at the existing Free Electron laser facilities (LCLS, Spring-8, European XFEL, etc). Second, we propose to use this trap for holding a nano/micro particle which will serve as a lens for focusing the X-ray beam on a target. Such a lens can be accurately positioned with respect to the target and, moreover, the relative distance can be varied in time by the user to change optical properties of the X-ray beam on the sample. In particular, we discuss potential materials that can serve as an x-ray propagation media effectively yet also be trapped by optical tweezers. Finally, we discuss the possibility of holding the target in a separate optical trap which would allow target manipulation (position and orientation in space) relative to the X-ray beam and an X-ray detector.  
TUP050 Beam Driven Acceleration and RF Breakdown in Photonic Band Gap Travelling Wave Accelerator Structure 1
  • J. Upadhyay, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
  We report the results of an experiment to demonstrate excitation of wakefields and wakefield acceleration in a photonic band gap (PBG) accelerating structure. The experiment was conducted at the Argonne Wakefield Accelerator (AWA) facility. For modern X-ray free electron lasers (FELs), preservation of the electron beam quality during the beam acceleration is of crucial importance. Therefore, new accelerating structures must be designed with careful attention paid to the suppression of wakefields. PBG structures are widely studied due to their ability to exclude higher order modes. A 16-cell travelling-wave normal conducting PBG structure operating at 11.700 GHz is installed at the AWA beam line. We passed a high-charge single bunch or multiple bunch train through the structure that generated wakefields and evaluated the effect of these wakefields on a low-charge witness beam. We also passed high-charge multiple bunch trains through the structure that generated up to 100 MV/m accelerating gradient and studied the RF breakdown.  
Reaching High Peak Power X-Ray Radiation in Fels  
  • N.A. Yampolsky, D.C. Nguyen
    LANL, Los Alamos, New Mexico, USA
  Funding: This work has been supported by LANL LDRD Programm.
The output power in free electron lasers (FELs) such as MaRIE can be achieved through temporal compression of the output pulse. Such a compression can be achieved with conventional gratings in soft x-ray regime or Bragg crystals in hard x-ray regime. Currently, the use of compressing optics is limited due to high radiation fluences and the damage it causes to the grating. We investigate the possibility of reducing the local x-ray fluence at the grating through streaking the pulse transversely and designing optics which compress the streaked pulse. The streaking of the optical pulse can be achieved through streaking of the driving electron beam with a set of transverse deflecting cavities. The optical pulse shape mirrors the shape of the electron beam resulting in the streaked x-ray beam.
Demonstration of Cascaded Pre-Bunching for Complete Trapping of a Relativistic Electron Beam in a Strongly Tapered Undulator  
  • N.S. Sudar, I.I. Gadjev, P. Musumeci, Y. Sakai
    UCLA, Los Angeles, USA
  • M. Babzien, M.G. Fedurin, M.A. Palmer, I. Pogorelsky, M.N. Polyanskiy, C. Swinson
    BNL, Upton, Long Island, New York, USA
  Funding: US DOE Office of High Energy Physics DE-SC0009914 US Dept. of Homeland Security Grant 2014-DN-077-ARI084-01 US DOE Office of Science SCGSR Graduate Student Research Fellowship
We present results of an experiment recently performed at the Brookhaven National Lab's Accelerator Test Facility showing the first successful demonstration of a cascaded pre-bunching scheme. Two modulator-chicane pre-bunchers arranged in series and a high-power CO2 laser seed manipulate the longitudinal phase space of a 52-MeV electron beam, increasing the fraction of electrons initially trapped in the stable accelerating potential of a seeded, strongly tapered undulator interaction from 25% to 95%, accelerating up to 80% of the particles to the final design energy. These results represent an important step in the development of high efficiency tapered undulator interactions, both as advanced accelerators and as high peak and average power coherent radiation sources.
TUP053 The ACHIP Experimental Chambers at PSI 1
  • E. Ferrari, M. Bednarzik, S. Bettoni, S. Borrelli, H.-H. Braun, M. Calvi, Ch. David, M.M. Dehler, F. Frei, T. Garvey, V. Guzenko, N. Hiller, R. Ischebeck, C. Ozkan Loch, E. Prat, J. Raabe, S. Reiche, L. Rivkin, A. Romann, B. Sarafinov, V. Schlott, S. Susmita
    PSI, Villigen PSI, Switzerland
  • E. Ferrari, L. Rivkin
    EPFL, Lausanne, Switzerland
  • P. Hommelhoff
    University of Erlangen-Nuremberg, Erlangen, Germany
  • J.C. McNeur
    Friedrich-Alexander Universität Erlangen-Nuernberg, University Erlangen-Nuernberg LFTE, Erlangen, Germany
  Funding: Gordon and Betty Moore Foundation
The Accelerator on a Chip International Program (ACHIP) is an international collaboration, funded by the Gordon and Betty Moore Foundation, whose goal is to demonstrate that a laser-driven accelerator on a chip can be integrated to fully build an accelerator based on dielectric structures. PSI will provide access to the high brightness electron beam of SwissFEL to test structures, approaches and methods towards achieving the final goal of the project. In this contribution, we will describe the two interaction chambers installed on SwissFEL to perform the proof-of-principle experiments. In particular, we will present the positioning system for the samples, the magnets needed to focus the beam to sub-micrometer dimensions and the diagnostics to measure beam properties at the interaction point.
TUP054 Preparations for Installation of the Double Emittance-Exchange Beamline at the Argonne Wakefield Accelerator Facility 1
  • G. Ha
    PAL, Pohang, Republic of Korea
  • M.E. Condepresenter, D.S. Doran, W. Gai, J.G. Power
    ANL, Argonne, Illinois, USA
  Funding: This work is supported by Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
Preparations to upgrade the single EEX beamline at the Argonne Wakefield Accelerator (AWA) facility to a double EEX beamline are underway. The single EEX beamline recently demonstrated exchange-based longitudinal bunch shaping (LBS) which has numerous applications including high-energy physics linear colliders, x-ray FELs, and intense radiation sources. The exchange-based method can generate arbitrary LBS in the ideal case but has limitations in the real case. The double EEX beamline was proposed as a means to overcome the limitations of single EEX due to transverse jitter and large horizontal emittance. In this paper, we present the current status of beamline design and installation and simulation results for the planned experiments: collinear wakefield acceleration with tailored beams and tunable bunch compression without the double-horn feature.
Multi-Staged Enhanced SASE for Sub-Femtosecond, Terawatt Pulses  
  • J.P. MacArthur
    SLAC, Menlo Park, California, USA
  The peak power of an x-ray pulse from the LCLS is limited by saturation effects to a few tens of gigawatts. However, users looking at two-photon processes that scale with the square of the power need higher-power photon pulses. We investigate enhanced SASE for the production of high-power, sub-femtosecond pulses. This scheme can be used in a cascaded manner with the recently developed fresh-slice scheme to reach terawatt power levels.  
Generation of Two-Color X-Ray Free-Electron Lasers Using a Matching-Based Fresh-Slice Method  
  • W. Qin, Y.-C. Chao, Y. Ding, A.A. Lutman
    SLAC, Menlo Park, California, USA
  Two-color high intensity X-ray free-electron lasers (FELs) provide powerful tools for probing ultrafast dynamic systems. A novel concept of realizing fresh-slice two-color lasing through slice-dependent transverse mismatch has been proposed by one of the authors.* In this paper we present a feasible example following this concept based on the Linac Coherent Light Source parameters. Time-dependent mismatch along the bunch is generated by a passive dechirper module and controlled by downstream matching sections, enabling FEL lasing at different wavelengths with a split undulator configuration. Simulations for soft X-ray FELs show that tens of gigawatts pulses with femtosecond duration can be generated.
* Y. Chao, SLAC Report No. SLAC-PUB-16935, 2016.
Measurement of Short-Wavelength High-Gain FEL Temporal Coherence Length by a Phase Shifter  
  • G. Zhou
    IHEP, Beijing, People's Republic of China
  • W. Liu
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • W. Qin, T.O. Raubenheimer, J. Wupresenter, C. Yang
    SLAC, Menlo Park, California, USA
  • C.-Y. Tsai
    Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
  • B. Yang
    University of Texas at Arlington, Arlington, USA
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Short-wavelength high-gain free-electron lasers (FELs) are now well established as a source of ultra-fast, ultra-brightness, longitudinally partial coherent light. Since coherence is one of the fundamental properties of light source, so continual effort is devoted to high-gain free-electron laser coherence measurements. In this work, we propose a possible approach, employing a phase shifter to induce electron beam delay to measure the temporal coherence length. Simple analysis, numerical simulation and preliminary experimental results are presented. This approach can be robust and independent of frequency.
TUP058 Slippage-Enhanced SASE FEL 1
  • J. Wu, A. Brachmann, K. Fang, A. Marinelli, C. Pellegrini, T.O. Raubenheimer, C.-Y. Tsai, C. Yang, M. Yoon, G. Zhou
    SLAC, Menlo Park, California, USA
  • H.-S. Kang, G. Kim, I.H. Nam
    PAL, Pohang, Kyungbuk, Republic of Korea
  • B. Yang
    University of Texas at Arlington, Arlington, USA
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
High-brightness XFEL is demanding for many users, in particular for certain types of imaging applications. Seeded FELs including self-seeding XFELs were successfully demonstrated. Alternative approaches by enhancing slippage between the x-ray pulse and the electron bunch were also demonstrated. This class of Slippage-enhanced SASE (SeSASE) schemes can be unique for FEL spectral range between 1.5 keV to 4 keV where neither grating-based soft x-ray self-seeding nor crystal-based hard x-ray self-seeding can easily access. SeSASE can provide high-brightness XFEL for high repetition rate machines not suffering from heat load on the crystal monochromator. We report start-to-end simulation results for LCLS-II project and PAL-XFEL project with study on tolerance. Performance comparison between SaSASE FEL and self-seeding FEL in the overlapping frequency range is also presented.
TUP059 Alternative Electron Beam Slicing Methods for CLARA and X-ray FELs 1
  • D.J. Dunning, H.M. Castaneda Cortes, S.P. Jamison, T.A. Mansfield, N. Thompson, D.A. Walsh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • D. Bultrini, S.P. Jamison, N. Thompson
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • D. Bultrini
    University of Glasgow, Glasgow, Scotland, United Kingdom
  Methods to generate ultra-short radiation pulses from X-ray FELs commonly slice a relatively long electron bunch to feature one (or more) short regions of higher beam quality which then lase preferentially. The slotted foil approach spoils the emittance of all but a short region, while laser-based alternatives modulate the electron beam energy, improving potential synchronisation to external sources. The CLARA FEL test facility under development in the UK will operate at 100-400 nm, aiming to demonstrate FEL schemes applicable at X-ray wavelengths. We present new laser-based slicing schemes which may better suit the wavelength range of CLARA and provide options for X-ray facilities.  
Study of the Electron Transport in the COXINEL FEL Beamline Using a Laser-Plasma Accelerated Electron Beam  
  • T. André, I.A. Andriyash, F. Blache, F. Bouvet, F. Briquez, M.-E. Couprie, Y. Dietrich, J.P. Duval, M. El Ajjouri, A.M. Ghaith, C. Herbeaux, N. Hubert, M. Khojoyan, C.A. Kitegi, M. Labat, N. Leclercq, A. Lestrade, A. Loulergue, O. Marcouillé, F. Marteau, P. N'gotta, P. Rommeluère, E. Roussel, M. Sebdaoui, K.T. Tavakoli, M. Valléau
    SOLEIL, Gif-sur-Yvette, France
  • S. Bielawski, C. Evain, C. Szwaj
    PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
  • S. Corde, J. Gautier, G. Lambert, B. Mahieu, V. Malka, K. Ta Phuoc, C. Thaury
    LOA, Palaiseau, France
  The ERC Advanced Grant COXINEL aims at demonstrating free electron laser (FEL) at 200 nm, based on a laser-plasma accelerator (LPA). To achieve the FEL amplification a transport line was designed to manipulate the beam properties. The 10 m long COXINEL line comprises a first triplet of permanent-magnet variable-strength quadrupoles (QUAPEVA), which handles the large divergence of LPA electrons, a magnetic chicane, which reduces the slice energy spread, and finally a set of electromagnetic quadrupoles, which provides a chromatic focusing in a 2-m undulator. Electrons were successfully transported through the line from LPA with ionization-assisted self-injection (broad energy spectra up to~250 MeV, few-milliradian divergence).  
TUP062 Electromagnetic and Mechanical Analysis of a 14 mm 10-period NbTi Superconducting Undulator 1
  • F. Trillaud, G.A. Barraza Montiel
    UNAM, Cuernavaca, Morelos, Mexico
  • M. Gehlot, G. Mishra
    Devi Ahilya University, Indore, India
  Funding: DGAPA of UNAM, fund PAPIIT TA100617 SERB, India
A 14 mm - 10 period NbTi superconducting undulator for the next generation of Free Electron Laser has been stud- ied. The optimum electromagnetic pre-design was carried out using RADIA, an extension module of the commercial software Mathematica. For this pre-design, a variable gap was considered. Additionally, a thermo-mechanical study of one eighth of the superconducting undulator was conducted. This study utilized a thermal and mechanical contact model between the pancake coils and the carbon steel core. This coupled model allowed estimating the minimum pre-loading of the coil. This pre-loading ensures that the coil would remain stuck to its pole during cooling. Numerical results are presented for both studies.
* M. Gehlot et al., Nucl. Inst. and Meth. in Phys. Res., Sec. A, Vol. 846, p. 13-17, 2017.
** B.J.A. Shepherd et al., Proceedings of IPAC2014, WEPRI095, 2014.
*** J. Grimmer, R. Kmak, PAC 2005.
poster icon Poster TUP062 [1.355 MB]  
Laser-Plasma Accelerator Based Single-Cycle Attosecond Pulse Generation  
  • Z. Tibai, G. Almasi, J. Hebling, M.I. Mechler, A. Nagyvaradi
    University of Pecs, Pécs, Hungary
  • J.A. Fülöp, Gy. Tóth
    MTA-PTE High-Field Terahertz Research Group, Pecs, Hungary
  • A. Sharma
    ELI-ALPS, Szeged, Hungary
  A carrier-envelope-phase controlled single-cycle attosecond pulse source was proposed by us relying on a conventional linear accelerator.* Here, we demonstrate the feasibility of a related scheme, where a laser-plasma accelerator, rather than a LINAC is used. Pulses from a TW/PW-power laser are focused into a gas jet to generate a relativistic electron beam, which is then sent through a first quadrupole triplet to reduce its divergence. The reduction of the slice energy spread can be accomplished by a first chicane. The electron beam passes through a modulator undulator along with a TW laser beam (ELI-ALPS SYLOS).** Here, the interaction between the electrons, the magnetic field of the undulator, and the electromagnetic field of the laser introduces a periodic energy modulation. The electrons propagate through a second chicane which leads to the formation of a train of nanobunches. The nanobunched electron beam then moves through the radiator undulator consisting of a few periods and creates CEP-stable attosecond pulses According to our calculations, at 60 nm (100 nm) wavelength CEP stable pulses with 13 nJ (22 nJ) energy and 240 as (400 as) duration can be achieved at K=0.8.
* Z. Tibai et al., Phys. Rev. Lett. 113, 104801 (2014).
** online at http://www.eli-alps.hu for ELI-ALPS (The Scientific Case of ELI-ALPS (2015)).
TUP065 Dielectric Laser Acceleration Setup Design, Grating Manufacturing and Investigations Into Laser Induced RF Cavity Breakdowns 1
  • M. Hamberg, D.S. Dancila, M. Jacewicz, J. Ögren
    Uppsala University, Uppsala, Sweden
  • M. Karlsson, A. Rydberg, E. Vargas Catalan
    Uppsala University, Department of Engineering Sciences, Uppsala, Sweden
  • M. Kuittinen, I. Vartiainen
    UEF, Joensuu, Finland
  Funding: Work supported by Stockholm-Uppsala Centre for Free Electron Research.
Dielectric laser acceleration (DLA) is the technique utilizing strong electric fields in lasers to accelerate electrons in the proximity of nanoscaled dielectric gratings. The concept was recently demonstrated in experimental studies. Here we describe the experimental DLA investigation setup design including laser system and scanning electron microscope (SEM). We also present the grating manufacturing methods as well investigations into vacuum breakdowns occurring at RF accelerating structures.
TUP066 Luminosity Increase in Laser-Compton Scattering by Crab Crossing 1
  • Y. Koshiba
    Waseda University, Tokyo, Japan
  • T. Higashiguchi
    Center for Optical Research and Education, Utsunomiya University, Utsunomiya, Japan
  • S. Ota, T. Takahashi, M. Washio
    RISE, Tokyo, Japan
  • K. Sakaue
    Waseda University, Waseda Institute for Advanced Study, Tokyo, Japan
  • J. Urakawa
    KEK, Ibaraki, Japan
  Funding: Research Fellow of Japan Society for the Promotion of Science
Laser-Compton Scattering X-ray (LCS-X) sources have been expected as compact and powerful sources, beyond X-ray tubes. They will enable laboratories and companies, opening new X-ray science. It is well known that luminosity depends on the collision angle of a laser and electron beam. Head-on collision is ideal in the point of maximizing the luminosity, though it is difficult to create such a system especially with an optical enhancement cavity for a laser. In collider experiments, however, crab crossing is a promising way to increase the luminosity. We are planning to apply crab crossing to LCS to achieve a higher luminosity leading to a more intense X-ray source. Electron beams will be tilted to half of the collision angle using an RF-deflector. Although crab crossing in Laser-Compton scattering has been already proposed, it has not been demonstrated yet anywhere.* The goal of this study is to experimentally prove the luminosity increase by adopting crab crossing. In this conference, we will report about our compact accelerator system at Waseda University, laser system favorable for crab crossing LCS, and expected results of crab crossing LCS.
* V. Alessandro, et al., "Luminosity optimization schemes in Compton experiments based on Fabry-Perot optical resonators." Physical Review Special Topics-Accelerators and Beams 14.3 (2011): 031001.
Study on Cherenkov Laser Oscillator Using Tilted Electron Bunches  
  • K. Sakaue
    Waseda University, Waseda Institute for Advanced Study, Tokyo, Japan
  • M. Brameld, Y. Tadenuma, M. Washio, R. Yanagisawa
    Waseda University, Tokyo, Japan
  • R. Kuroda, Y. Taira
    AIST, Tsukuba, Ibaraki, Japan
  • J. Urakawa
    KEK, Ibaraki, Japan
  Funding: This work was supported by a research granted from The Murata Science Foundation and JSPS KAKENHI 26286083.
We have been studying a coherent Cherenkov radiation by using tilted electron bunches. Bunch tilting can enhance the radiation power about 10 times due to the wavefront matching of radiations. Recently, we investigated that this technique can produce high peak power THz pulses with sufficient pulse energy. Resulting pulse energy was more than 30 nJ/pulse and peak power was about 10 kW. Introducing the oscillator cavity with two concave mirrors, it would be possible to achieve lasing using tilted electron bunches. In the calculation, 1 uJ/micro-pulse and 100 uJ/macro-pulse broadband THz pulses are expected to be achieved, which are powerful THz sources compared with the existing THz FELs. In this conference, we will report the experimental results of coherent Cherenkov radiation, calculated results toward lasing and future prospectives.
TUP069 Simulating Beam Dynamics in Coherent Electron-Cooling Accelerator with WARP 1
  • K. Shih
    SBU, Stony Brook, New York, USA
  • Y.C. Jing, V. Litvinenko, I. Pinayev, G. Wang
    BNL, Upton, Long Island, New York, USA
  • K. Mihara
    Stony Brook University, Stony Brook, USA
  • I. Petrushina
    SUNY SB, Stony Brook, New York, USA
  Funding: DoE NP office, grant DE-FOA-0000632, NSF grant PHY-1415252.
Coherent Electron Cooling (CeC) is a novel cooling technique based on amplification of interaction between hadrons and electron by an FEL. If proven, this CeC could bring a revolution in hadron and electron-hadron colliders. A dedicated CeC proof-of-principle experiment is under way at RHIC collider (BNL) using a sophisticated SRF accelerator for generating and accelerating electron beam. This paper is dedicated to studies of beam dynamics in the CeC accelerator and specifically to emittance preservation in its ballistic compressions section. Two 500-MHz RF cavities are used for generating the necessary energy chirp leading in 1.56-MeV, 0.5-nsec-long electron bunched to compress them to 25-psec duration downstream. During the commissioning of the CeC accelerator we noticed that beam emittance can be strongly degraded when electron beam passes these 500 MHz RF cavities off-axis. We used a full 3D PIC code Wrap to simulate effect of the off-axis beam propagation through these
TUP070 Development of Mid-Infrared Photoacoustic Spectroscopy System for Solid Samples at Kyoto University Free Electron Laser Facility 1
  • J. Okumura, T. Kii, H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
  Photoacoustic Spectroscopy (PAS) enables IR absorption spectrum measurements of solid samples without preprocessing of samples. Its sensitivity and resolution depend on the intensity and spectral width of the infrared light, respectively. Mid-infrared free electron laser (MIR-FEL) is an intense, quasi-monochromatic and tunable laser in MIR region, so the method of PAS with FEL (FEL-PAS) was proposed.*,** However, the resolution was not so good since they used the direct FEL beam which has the spectral width of 1%. We considered that the resolution can be significantly increased by inserting a high-resolution grating monochromator before the PAS cell. Based on this consideration, a PAS system using an MIR-FEL with the monochromator is under development. We have already conducted preliminary experiments using a PAS cell which has been used in previous studies and successfully measured quite high PAS signals with this setup.*,** A demonstration of experiments to check the spectral resolution will be conducted soon. In this presentation, the progress of the development including the result of demonstration experiments will be reported.
* M. Yasumoto et al., Proceedings of the 2004 FEL Conference, 703-705 (2004).
** M. Yasumoto et al., Eur. Phys. J. Special Topics, 153, 37-40 (2008).
TUP071 Study on Second Harmonic Generation in SiC Using Infrared FEL 1
  • S. Tagiri
    Kyoto Univeristy, Kyoto, Japan
  • T. Kii, H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
  Mode-selective phonon excitation (MSPE) is an attractive method for studying the lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). In addition, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material (6H-SiC) with MIR-FEL (KU-FEL) by anti-Stokes (AS) Raman-scattering spectroscopy. Recently, we have certified that the Sum Frequency Generation (SFG) also occurs with AS Raman scattering. For distinguishing between the AS Raman scattering and SFG, we need to know the nonlinear susceptibility and transmittance. The coefficients can be measured by the Second Harmonic Generation (SHG) spectroscopy. In this paper, the outline of the measurement system and the preliminary results with a 6H-SiC sample are reported.  
Simulation of Phase Shifters Between FEL Amplifiers in Coherent Electron Cooling  
  • Y.C. Jing, V. Litvinenko, I. Pinayev
    BNL, Upton, Long Island, New York, USA
  • V. Litvinenko
    Stony Brook University, Stony Brook, USA
  Coherent electron Cooling (CeC) is a proposed advanced beam cooling method that has the potential of reducing the ion beam emittance in significantly shorter amount of time compared to existing cooling methods. A high-gain FEL, composed of three permanent magnet helical wigglers, is acting as an amplifier of the ion's signals picked up by electron beam in CeC. A self-consistent simulation which takes the space and possible phase shifts between wigglers into account is crucial in determining the performance of the FEL. The authors developed an algorithm based on the well-used GENESIS code to properly treat the propagation of particles and radiations in between wigglers and predicted the FEL performance with different beamline layouts. The authors will present their simulation setup and results and provide hardware requirements for future operations and research at CeC.  
Photoemission from Diamond Field-Emitter Arrays  
  • V.N. Pavlenko, H.L. Andrews, R.L. Fleming, A. Piryatinski, D.Y. Shchegolkov, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
  Funding: We gratefully acknowledge the support of the U.S. Department of Energy through the LANL/LDRD Program for this work.
We present experimental data on photoemission from diamond films, outlining future studies of diamond field emitter arrays (DFEAs) operation in photoemission mode. Nano-tipped field emitters are attractive types of electron sources for dielectric laser accelerators (DLAs),* whose ability to generate coherent electron bunches in laser-triggered mode has been successfully demonstrated.** To explore applicability of diamond field emitters to DLAs, we will measure spectral response (quantum efficiency vs photon energy) of DFEAs in the limit of low electric fields. We will compare the measurements on DFEAs with different densities and tip radii against bulk flat diamond photoemission. The results will be used to validate the a photoemission model that takes into account quantum confinement effects at the nano-tips of the pyramids.
* E. A. Peralta et al., Nature 503, 91 (2013)
** R. Ganter et al., Phys. Rev. Lett. 100, 064801 (2008); D. Ehberger et al., Phys. Rev. Lett. 114, 227601 (2015)