Electron Beam Dynamics
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.  
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. Mihalcea, 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. Lumpkin, 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. Guetg, 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. Wu
    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.
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.  
Beam Dynamics Optimization in High-Brightness Electron Injectors  
  • C.E. Mitchell, J. Qiang, F. Sannibale
    LBNL, Berkeley, California, USA
  Funding: This work was supported by the Office of Science of the U.S. Department of Energy under Contract Numbers DE-AC02-76SF00515, DE-AC02-05CH11231, and the LCLS-II project.
The next generation of X-ray free electron lasers requires beams with increasingly high peak current and low emittances at ~MHz repetition rates, placing increased demands on the performance of high-brightness electron photoinjector sources. To explore the high-dimensional parameter space associated with photoinjector design, global multiobjective optimization methods based on genetic algorithms or similar tools are playing an increasingly critical role. We review our experience with applying these tools both to understand and to optimize simulated injector beam performance for projects such as LCLS-II (at SLAC) and the Advanced Photoinjector EXperiment (at LBNL), including both challenges and successes.
slides icon Slides THB01 [13.103 MB]  
THB02 Non-Standard Use of Laser Heater for FEL Control and THz Generation 1
  • E. Allaria, L. Badano, M.B. Danailov, A.A. Demidovich, S. Di Mitri, D. Gauthier, L. Giannessi, G. Penco, E. Roussel, P. Sigalotti, S. Spampinati, M. Trovò, M. Veronese
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  The laser heater system is currently used at various FEL facilities for an accurate control of the electron beam energy spread in order to suppress the micro-bunching instabilities that can develop in high brightness electron beams. More recently, studies and experiments have shown that laser-electron interaction developing in the laser heater can open new possibilities for tailoring the electron beam properties to meet special requirements. A suitable time-shaping of the laser heater pulse opened the door to the generation of (tens of) femtosecond-long FEL pulses. Using standard laser techniques it is also possible to imprint onto the electron bunch, energy and density modulations in the THz frequency range that, properly sustained through the accelerator, can be exploited for generation of coherent THz radiation at GeV beam energies. Such recent results at the FERMI FEL are here reported, together with near future plans.  
High-Power, Narrow-Bandwidth THz Generation Using Laser-Electron Interaction in a Compact Accelerator  
  • Z. Huang, G. Marcus
    SLAC, Menlo Park, California, USA
  • K. Kan
    ISIR, Osaka, Japan
  • Z. Zhang
    TUB, Beijing, People's Republic of China
  We propose a method based on the slice energy-spread modulation to generate strong subpicosecond density bunching in high-intensity relativistic electron beams.* A laser pulse with periodic intensity envelope is used to modulate the slice energy spread of the electron beam, which can then be converted into density modulation after a dispersive section. In this paper, we study this method in a compact accelerator with electron energy on the order of 50 MeV. To interact with an infra-red laser, the modulation undulator is resonant with the laser at a harmonic frequency. We show the flexibility of this method to generate powerful, narrow-bandwidth radiation between 1-20 THz. The THz radiation can be generated at a very high-repetition rate that matches a high-repetition rate X-ray free-electron laser for pump-probe studies of novel materials.
* Z. Zhang et al., Phys. Rev. Accel. Beams 20, 050701 (2017).
Two-Color Beam Generation via Wakefield Excitation  
  • S. Bettoni, E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  Several beam manipulation methods have been studied and experimentally tested to generate two-color photon beams in free electron laser facilities to accommodate the user requests. We propose to use the interaction of the beam with an oscillating longitudinal wakefield source to obtain a suitable electron beam structure. The bunch generates two sub-pulses with different energies and delays in time passing through a magnetic chicane after its longitudinal phase space has been modulated by the wakefield source. According to this approach, the power of the emitted radiation is not degraded compared to the monochromatic beam, and the set-up in the machine is quite simple because the bunch is manipulated only in the high energy section where the beam is more rigid. We present the design applied to SwissFEL. We identified the parameters and the corresponding range of tunability of the time and energy separation among the two sub-bunches.
Reference: Phys. Rev. Accel. Beams 19, 050702 (2016)
Ion Effects in LCLS and LCLS-II  
  • T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  Funding: This work supported in part by the Department of Energy Contract DE-AC02-76-SF00515.
The effect of ions are evaluated in LCLS and LCLS-II. X-ray FEL's require high-brightness beams, that generate very high internal beam fields which can potentially lead to tunneling ionization. The FEL performance is sensitive to betatron mismatches which can arise from the focusing due to ions. In LCLS, both collisional and tunneling ionization may have an impact on single electron bunches while LCLS-II will have the additional complication of trapped ions in the MHz-rate multi-bunch trains. Analytic and simulation results for the LCLS and LCLS-II are presented and scalings are described to estimate the effects in other X-ray FEL's.