New Concepts
Paper Title Page
THOB02
 Transverse Gradient Undulator to Enhance the FEL Performance for a Laser-plasma Accelerator  
 
  • Z. Huang, Y.T. Ding
    SLAC, Menlo Park, California, USA
  • C.B. Schroeder
    LBNL, Berkeley, California, USA
  
  Compact laser-plasma accelerators can produce high energy electron beams with low emittance, high peak current but a rather large energy spread. The large energy spread hinders the potential applications for coherent FEL radiation generation. In this paper, we discuss a method to compensate the effects of beam energy spread by introducing a transverse field variation into the FEL undulator. Such a transverse gradient undulator together with a properly dispersed beam can greatly reduce the effects of electron energy spread and jitters on FEL performance. We present theoretical analysis and numerical simulations for SASE and seeded XUV and soft x-ray FELs based on laser plasma accelerators.  
slides icon Slides THOB02 [2.720 MB]  
 
THOB03 The Generator of High-power Short Terahertz Pulses 535
 
  • N. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  • Y.U. Jeong
    KAERI, Daejon, Republic of Korea
  
  The multi-foil cone radiator to generate high field short terahertz pulses with the short electron bunches is described. A round flat foil plates with successively decreasing radius are stacked, comprising a truncated cone with axis z. The gaps between foils are equal and filled by some dielectric (it may be vacuum). A short relativistic electron bunch propagates along the z axis from left to right. At high enough particle energy the energy losses and multiple scattering does not change the bunch shape significantly. Then, passing through each gap between foils, the bunch radiates some energy into the gap. After that the radiation pulses propagates radially. For the TEM-like waves with longitudinal (along the z axis) electric and azimuthal magnetic field there is no dispersion in these radial lines, therefore the radiation pulses conserve their shapes (time dependence). At the cone outer surface we have synchronous circular radiators. Their radiation fields forms the conical wave. The cone angle may be optimized, moreover, the nonlinear dependence of the foil plates radii on their longitudinal coordinate z may be used for the wave front shape control.  
slides icon Slides THOB03 [1.624 MB]  
 
THOB04 Use of Monocapillary X-Ray Optics as a Means to Reduce Linewidth and Fluctuations in SASE FELs 539
 
  • A.L. Lin, G. Travish
    UCLA, Los Angeles, USA
  
  Funding: UCLA
The Self Amplified Spontaneous Emission (SASE) operation of high-gain Free Electron Lasers (FELs) allows for amplification from "noise" when no suitable seed sources are available. While SASE FELs can achieve high powers and short radiation pulses within the X-ray region, they are hindered by large linewidths and fluctuations in amplitude and temporal profiles. Various approaches have been proposed to "clean up" the spontaneous emission and produce better effective seed signals. This paper presents the use of monocapillary X-ray optics as an alternative to current methods to improve SASE operation. A monocapillary tube placed at the beginning stages of the undulator can reduce the bandwidth and enhance a narrow band of the spontaneous emission amplified by the FEL. Monocapillary tubes guide radiation due to total external reflection, and the critical angle of the guiding is dependent on the frequency of the radiation (and indirectly on the surface profile and materials). 		 
slides icon Slides THOB04 [1.013 MB]  
 
THOBI01
 Improving Laser-plasma Accelerator Beam Quality for FELs  
 
  • E. Esarey, C. Benedetti, M. Chen, C.G.R. Geddes, W. Leemans, C.B. Schroeder, J. van Tilborg
    LBNL, Berkeley, California, USA
  
  Funding: This work was supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Present laser-plasma accelerator (LPA) experiments at LBNL produce up to 1 GeV electron beams in cm-scale plasmas using tens of TW laser pulses. Such beams have been successfully coupled to a conventional undulator, producing synchrotron radiation. Presently, beam quality limits FEL applications. In this paper we discuss methods of triggered electron beam injection into a laser-plasma accelerator to improve the beam quality. Laser-triggered injection, ionization injection, and the use of plasma density tailoring will be discussed. Short pulse, PW laser systems are presently under constructed, and future experiments using PW lasers aim at the production of 10 GeV electron beams accelerated over less than 1 m of plasma. We report on progress toward achieving compact 10 GeV electron beams using BELLA (Berkeley Lab Laser Accelerator). 		 
slides icon Slides THOBI01 [28.718 MB]  
 
THPD43 Progress on a Laser-driven Dielectric Structure for Use as a Short-period Undulator 630
 
  • J.M. Allen, G. Travish
    UCLA, Los Angeles, California, USA
  • H. Gong
    UESTC, Chengdu, Sichuan, People's Republic of China
  • R.B. Yoder
    Manhattanville College, Purchase, New York, USA
  
  A laser-powered dielectric structure, based on theμAccelerator Platform, has been design and offers undulator periods in the micron to millimeter range. This design was shown previously to potentially support a deflection field strength of several GV/m, equivalent to a magnetic undulator with field strength of about 40 T. In this paper, we address a previous problem in the design involving the junction between half periods of the undulator. Because the structure is resonant, flipping from one deflection direction to the opposite one required controlling the phase of the incident laser and reestablishing a new resonance. One solution to this 'phase flipping' problem involves the use of two lasers at different wavelengths to excite adjacent half-periods. This new approach is explored further here along with simulations of the beam trajectory and resulting undulator radiation. We also consider parameter sets that may be possible for these extremely short period undulators.  
 
THPD45 Beam Dynamics and Performance of ERL-driven X-ray FEL 634
 
  • Y.C. Jing, V. Litvinenko
    BNL, Upton, Long Island, New York, USA
  
  In this talk we present a self-consistent concept of ERL generated e-beam to drive an array of X-ray FELs. We use eRHIC multi-pass ERL design to explore all relevant beam dynamics. First, we study effects of incoherent and coherent synchrotron radiation on the e-beam parameters and present the set of parameters providing for the emittance preservation. Second, we present a sing bunch compressing scheme (similar to scheme described in [1]) with large compression ratio, which suppresses emittance growth caused by CSR. Finally, we present simulation result for soft- and hard-X-ray FELs driven by such electron beam. We compare projected performance of such facility with world's existing and proposed FEL facilities.
[1] Merger Designs for ERLs, V.N. Litvinenko, R.Hajima, D. Kayran, Nuclear Instruments and Methods in Physics Research A 557 (2006) 165 		 
 
THPD47 Progress on the Generation of Undulator Radiation in the UV from a Plasma-based Electron Beam 638
 
  • G. Lambert, S. Cordes, V. Malka, K. Ta Phuoc
    LOA, Palaiseau, France
  • A. Ben Ismail, E. Benveniste, A. Specka
    LLR, Palaiseau, France
  • F. Briquez, M.-E. Couprie, M. Labat, A. Loulergue
    SOLEIL, Gif-sur-Yvette, France
  • J.-M. Ortega
    CLIO/ELISE/LCP, Orsay, France
  
  Recently, at the Laboratoire d'Optique Appliquée, progresses have been made for the development of 5th generation light sources based on plasma-accelerator. Electron beams of tens of picocoulomb at about 200 MeV has been generated at the interaction of a 1 Joule, 30 fs laser focussed on a 3 mm long gas target at an electron density of 5 1018 cm-3. Then, the electron beam was refocused with a quadrupoles triplet inside a 60 cm long undulator composed of 34 periods of 18 mm with a deflection parameter equal to 1. In these conditions synchrotron radiation UV light has been measured. This constitutes a promising first step in the view of realizing FEL based on plasma acceleration in future.  
 
THPD48 Numerical Study of an FEL based on LWFA Electrons and a Laser-plasma Wiggler 642
 
  • R. Lehe, G. Lambert, A. Lifschitz, V. Malka, J.-M. Rax
    LOA, Palaiseau, France
  • X. Davoine
    CEA/DAM/DIF, Arpajon, France
  
  Recent works* have suggested that laser-wakefield acceleration (LWFA) may be used to produce the electron beam of an FEL. However, when using conventional magnetic wigglers, the requirements on the beam quality are very stringent, and are still challenging with current LWFA beams. An interesting alternative may be to use a laser-plasma wiggler (e.g. a plasma wave or a laser beam). Compared to a conventional one, a laser-plasma wiggler has a field amplitude several orders of magnitude higher - which can place lower constraints on the beam quality. Furthermore, since laser-plasma wigglers also have a typically much shorter period, their total wiggler length is correspondingly shorter, and it may therefore not be necessary to periodically refocus the beam along the wiggler. Taking into account these effects, we evaluate the range of wiggler properties (field, period) that would make the FEL process possible. From this analysis, the counterpropagating laser wiggler** seems to be one of the most promising solutions. We therefore extend the Ming Xie formula*** to a counterpropagating laser wiggler. We use this formula to evaluate the potential use of current state-of-the-art lasers.
* Nakajima, K., Nature phys. 4, 92 (2008)
** Bacci, A. et al., Nucl. Instrum. Methods Phys. Res. A 587, 388 (2008)
*** Xie, M., Nucl. Instrum. Methods Phys. Res. A 445, 59 (2000) 		 
 
THPD50 Steady State Microbunching for High Brilliance and High Repetition Rate Storage Ring-based Light Sources 646
 
  • D.F. Ratner, A. Chao
    SLAC, Menlo Park, California, USA
  • Y. Jiao
    IHEP, Beijing, People's Republic of China
  
  Modern accelerator light sources are based on either linac-FELs or storage rings. The linac-FEL type has high brilliance (microbunched beam) but low repetition rate. The storage ring type has high repetition rate (rapid beam circulation) but low brilliance. We propose to explore the feasibility of a microbunched beam in a storage ring that promises high repetition rate and high brilliance. The steady-state microbunched (SSMB) beam in a storage ring could provide CW sources for THz, EUV, or soft X-rays. We review several recently proposed SSMB concepts as promising directions for high brightness, high repetition rate light sources of the future.  
 
THPD51
 W-Band Cherenkov Maser Based on a Periodic Surface Field Structure  
 
  • A.R. Phipps, A.W. Cross, A. Phelps, C.W. Robertson, K. Ronald, C.G. Whyte, A.R. Young
    USTRAT/SUPA, Glasgow, United Kingdom
  • I.V. Konoplev
    JAI, Oxford, United Kingdom
  
  Funding: Work supported by EPSRC
Two-dimensional Bragg structures have been useful in producing distributed feedback in an FEM driven by an oversized annular electron beam [1]. The Bragg structures in this case act as frequency selective mirrors allowing the production of narrow band microwaves [2]. This structure can be observed using a hollow, copper, cylindrical waveguide with a sinusoidal grating machined into the walls where the diameter of the waveguide is much larger than λ. Localised surface fields are excited around the perturbations if the structure is radiated by an external electron beam [3]. The resultant eigenfield can be described as a superposition of a near cut-off volume field which synchronises the localised surface partial fields. A relativistic electron beam travelling close to the structure interacts with the spatial harmonics of the surface field propagating with υp< c. In this paper we demonstrate a novel high Q cavity operating at W band (75-110GHz), where there is coupling between a near cut-off TM0,6 volume field and an evanescent HE1,20 surface field, produced within the structure. Results of the numerical modelling of this device using the PIC code MAGIC will be presented.
1. N.S. Ginzburg, N. Peskov, et al, J Appl Phys, 92, pp. 1619-1629, 2002
2. I.V. Konoplev, et al, Appl Phys Lett, 92, 211501 2008
3. I.V. Konoplev, A. Maclachlan. et al, Phys Rev A, 84, 013826 2011 		 
 
THPD54 Dynamics of a Multi-beam Photonic Free Electron Laser 650
 
  • J.H.H. Lee, K.J. Boller, T. Denis, M.W. van Dijk, P.J.M. van der Slot
    Mesa+, Enschede, The Netherlands
  
  A photonic free-electron laser (pFEL) uses free electrons streaming through a photonic crystal (PhC) to generate tunable coherent radiation. Operation in different spectral regions can be obtained by scaling the lattice period while keeping the electron velocity the same. Increasing both the transverse dimension and the number of distributed electron beams increases the output power and results in a higher quality factor Pf2. Here, we consider a pFEL driven by a set of low energy (~ 10 keV), low perveance (< 0.1 μP) electron beams. A simple and robust PhC structure is used to slow down the phase velocity (match to electron velocity) of a co-propagating electromagnetic wave. The large transverse dimensions of the PhC result in an overmoded system, allowing many transverse eigenmodes of the PhC to interact with the electron beams. Using a particle-in-cell code, we numerically study the dynamics and calculate the small-signal growth rate and output power of the various modes. We show that for an appropriate design of the PhC and selective placement of the electron beams, single-mode operation is possible. We will also present results on the scaling with the number of electron beams.  
 
THPD56 Two-color FEL Generation based on Emittance-spoiler Technique 654
 
  • C. Feng, Y.T. Ding, Z. Huang, J. Krzywinski, A.A. Lutman
    SLAC, Menlo Park, California, USA
  
  Generation of two-pulse two-color x-ray radiation is attracting much attention within the free-electron laser (FEL) user community. Femtosecond x-ray pulses with variable durations and separation can be simply generated by the emittance-spoiler foil method* at the Linac Coherent Light Source (LCLS). In this paper, we describe three FEL schemes rely on the emittance-spoiler technique for the generation of two intense x-ray pulses with different colors. With a representative realistic set of parameters of LCLS, numerical simulations confirm that two femtosecond x-ray pulses at ten gigawatt level with different wavelengths around 1.8 nm can be generated by these schemes. The central wavelengths of the output pulses can be easily altered by changing strengths of the undulators.
*P. Emma et al., PRL 92, 074801 (2004). 		 
 
THPD57 Application of laser-plasma accelerator beams to Free-Electron Lasers 658
 
  • C.B. Schroeder, C. Benedetti, E. Esarey, W. Leemans, J. van Tilborg
    LBNL, Berkeley, California, USA
  • Y.T. Ding, Z. Huang
    SLAC, Menlo Park, California, USA
  • F. Grüner, A.R. Maier
    Uni HH, Hamburg, Germany
  
  Funding: This work was supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No.DE-AC02-05CH11231.
Plasma waves excited by high-intensity, short-pulse lasers are able to generate hundreds of GV/m accelerating fields, enabling extremely compact accelerators for applications such as radiation generation. Laser-plasma accelerators (LPAs) produce ultrashort (femtosecond), 0.1-1 GeV electron bunches with high-peak (kA) currents and low (sub-micron) normalized transverse emittance, with 6D beam brightness comparable to state-of-the-art RF linac-based sources. FEL applications are presently limited by the longitudinal phase space distribution of the LPA beam. Beam phase space manipulation is considered to enable the application of LPA beams to FELs. LPA beam decompression (such that the energy spread over a coherence length is less than the FEL parameter) is examined as a path toward realizing an LPA-driven VUV FEL. The possibility of using a flat beam, with an energy correlation with transverse position, in a transverse gradient undulator is also explored. Laser-based FEL seeding options for improved coherence are considered.