FEL Theory
Paper Title Page
MOPSO04 Theoretical Analysis of a Laser Undulator-Based High Gain FEL 27
 
  • P. Baxevanis, R.D. Ruth
    SLAC, Menlo Park, California, USA
 
  The use of laser (or RF) undulators is nowadays considered attractive for FEL applications, particularly those that aim to utilize relatively low-energy electron beams. In the context of the standard theoretical analysis, the counter-propagating laser pulse is usually treated in the plane-wave approximation, neglecting amplitude and phase variation. In this paper, we develop a three-dimensional, analytical theory of a high-gain FEL based on a laser or RF undulator, taking into account the longitudinal variation of the undulator field amplitude, the laser Gouy phase and the effects of emittance and energy spread in the electron beam. Working in the framework of the Vlasov-Maxwell formalism, we derive a self-consistent equation for the radiation amplitude in the linear regime, which is then solved to good approximation by means of an orthogonal expansion technique [*]. Numerical results obtained from our analysis are used in the study of an example of a compact, laser undulator-based, X-ray FEL.
*P. Baxevanis, R. Ruth, Z. Huang, Phys. Rev. ST-AB 16, 010705 (2013).
 
 
MOPSO09 Investigation of a 2-Colour Undulator FEL Using Puffin 47
 
  • L.T. Campbell, B.W.J. MᶜNeil
    USTRAT/SUPA, Glasgow, United Kingdom
  • S. Reiche
    PSI, Villigen PSI, Switzerland
 
  The unaveraged FEL code Puffin* is used to investigate a 2 color FEL. In the scheme under investigation, undulator modules are tuned alternately to generate 2 frequencies quasi-simultaneously, which should result in greater stability than generating them consecutively. The advantage of using Puffin is that it provides the capability of modelling a broad bandwidth spectrum. For example, radiation at 1nm and 2.4nm is difficult to model simultaneously in standard averaged FEL codes. An unaveraged code like Puffin is able to model 2 (or more) wavelengths with a much wider spacing.
* LT Campbell and BWJ McNeil, Phys. Plasmas 19, 093119 (2012)
 
 
MOPSO17 The Present Status of the Theory of the FEL-based Hadron Beam Cooling 52
 
  • A. Elizarov, V. Litvinenko
    BNL, Upton, Long Island, New York, USA
 
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The coherent electron cooling (CeC)* device is one of the new facilities under construction in BNL. The CeC is a realization of the stochastic cooling with an electron beam serving as a pick-up and kicker. Hadrons generate electron density perturbations in the modulator section, then these perturbations are amplified in an FEL, and then, they accelerate (or decelerate) hadrons in the kicker by electric field with respect to their velocities. Here we present the theoretical description of the modulator sector**,***, where the electron density perturbations are formed and our new results on the time evolution of these perturbations in the FEL section, where they are amplified.
* V. N. Litvinenko, Y. S. Derbenev, Phys. Rev. Lett. 102, 114801 (2009).
** A. Elizarov, V. Litvinenko, G. Wang, IPAC'12, weppr099 (2012).
*** A. Elizarov, V. Litvinenko, IPAC'13, mopwo088 (2013).
 
 
MOPSO49 Numerical Accuracy When Solving the FEL Equations 82
 
  • R.R. Lindberg
    ANL, Argonne, USA
 
  Funding: U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357
The usual method of numerically solving the FEL equations involves dividing both the e-beam and radiation field into "slices" that are loaded one at a time into memory. This scheme is only first order accurate in the discretization of the ponderomotive phase because having only one slice in memory effectively results in a first order interpolation of the field-particle coupling. While experience has shown that FEL simulations work quite well, the first order accuracy opens the door to two possible ways of speeding up simulation time. First, one can consider higher order algorithms; unfortunately, these methods appear to require all the particle and field data in memory at the same time, and therefore will typically only be important for either small (probably 1D) problems or for parallel simulations run on many processors. Second, one may consistently solving the equations to some low order using faster, simpler algorithms (replacing, for example, the usual RK4). The latter is particularly attractive, although in practice it may be desirable to retain higher order methods when integrating along z. We investigate some of the possibilities.
 
 
MOPSO59 The Influence of the Magnetic Field Inhomogeneity on the Spontaneous Radiation and the Gain in the Plane Wiggler 97
 
  • K.B. Oganesyan
    ANSL, Yerevan, Armenia
 
  Funding: ISTC
We calculate the spectral distribution of spontaneous emission and the gain of electrons moving in plane wiggler with inhomogeneous magnetic field. We show that electrons do complicated motion consisting of slow(strophotron) and fast(undulator) parts. We average the equations of motion over fast undulator part and obtain equations for connected motion. It is shown, that the account of inhomogenity of the magnetic field leads to appearence of additional peaks in the spectral distribution of spontaneous radiation and the gain.
 
 
MOPSO60 Channeled Positrons as a Source of Gamma Radiation 101
 
  • K.B. Oganesyan
    ANSL, Yerevan, Armenia
 
  Funding: ISTC
A possibility of channeling of low-energy (5 / 20Mev) relativistic positrons with coaxial symmetry around separate crystal axes of negative ions in some types of crystals, is shown. The annihilation processes of positrons with medium electrons are investigated in details. The lifetime of a positron in the regime of channeling is estimated 〖10〗-6 sec which on a 〖10〗9/〖10〗8 times is bigger than at usual cases.
 
 
MOPSO61 Modulated Medium for Generation of Transition Radiation 105
 
  • K.B. Oganesyan
    ANSL, Yerevan, Armenia
 
  Funding: ISTC
It is shown on an example of amorphous quartz, under the influence of a standing microwave field, at its certain parameters, superlattice is created in the medium where difference in values of dielectric constants of neighboring layers can be up to third order. This superlattice exists during the nanosecond, however it is sufficient for using it as a radiator for generation of transition radiation by relativistic electrons.
 
 
MOPSO82 JLIFE: The Jefferson Lab Interactive Front End for the Optical Propagation Code 149
 
  • A.M. Watson, M.D. Shinn
    JLAB, Newport News, Virginia, USA
 
  Funding: Authored by Jefferson Science Associates, LLC and supported by the ONR, the Joint Technology Office, and the DOE under U.S. DOE Contract No. DE-AC05-06OR23177.
We present details on a graphical interface for the open source software program Optical Propagation Code, or OPC. [1] This interface, written in Java, allows a user with no knowledge of OPC to create an optical system, with lenses, mirrors, apertures, etc. and the appropriate drifts between them. The Java code creates the appropriate Perl script that serves as the input for OPC. The mode profile is then output at each optical element. The display can be either an intensity profile along the x axis, or as an isometric 3D plot which can be tilted and rotated. These profiles can be saved. Examples of the input and output will be presented.
[1] J. G. Karssenberg, P. J. M. van der Slot, I. V. Volokhine, J. W. J. Verschuur, and K.-J. Boller, “Modeling paraxial wave propagation in free-electron laser oscillators”, JAP 100, 093106 (2006).
 
 
WEICNO01
Harmonic Lasing in X-Ray FELs  
 
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
 
  Contrary to nonlinear harmonic generation, harmonic lasing in a high-gain FEL can provide much more intense, stable,and narrow-band FEL beam which is easier to handle if the fundamental is suppressed. We perform a parametrization of the solution of eigenvalue equation for lasing at odd harmonics, and present explicit expression for FEL gain length, taking into account all essential effects. We propose and discuss methods for suppression of the fundamental. We also suggest a combined use of harmonic lasing and lasing at the retuned fundamental wavelength in order to reduce bandwidth and to increase brilliance of X-ray beam. We discover that in a part of the parameter space, corresponding to the operating range of soft X-ray beamlines of X-ray FEL facilities, harmonics can grow faster than the fundamental. We suggest that harmonic lasing can be widely used in the existing or planned X-ray FEL facilities. LCLS after a minor modification can lase at the 3rd harmonic up to the photon energy of 25-30 keV providing multi-gigawatt power level. At the European XFEL the harmonic lasing would allow to extend operating range up to 100 keV, to reduce bandwidth and increase brilliance, etc.
Phys. Rev. ST-AB 15, 080702 (2012)
 
slides icon Slides WEICNO01 [1.558 MB]  
 
WEOCNO01
Simulation Studies of FEL Green Function and Its Saturation  
 
  • Y.C. Jing, Y. Hao, V. Litvinenko, G. Wang
    BNL, Upton, Long Island, New York, USA
 
  FEL amplifiers can be used for a number of applications ranging from the HGHG [1] , the coherent seed amplifying [2] or amplifier in Coherent electron Cooler [3]. Linear response of an FEL amplifier can be described using its Green function. In this paper we present results of detailed studies of the evolution and saturation of the Green function in FEL as function of its length. We are using time resolved mode of the code Genesis [4] for these studies, which include delta-function like seed and shot noise in electron beam. We simulate a statistically representative set of initial shot noise with and without the seed, and extract the Green function amplitude and phase evolution, as well as their fluctuation. We present results for three spectral ranges: the IR, the visible and the soft X-rays. We summarize our finding and compare them with a simple theoretical formula.
[1] L.H. Yu et al., science, 289 (2000)
[2] J. Feldhaus et al., NIMA, 1997
[3] V. N. Litvinenko et al., Phys. Rev. Lett. 102, 114801 (2009)
[4] S.Reiche, Genesis 2.0
 
slides icon Slides WEOCNO01 [0.479 MB]  
 
WEOCNO02
Echo-enabled Devices and Coulombian Diffusion  
 
  • G. Dattoli, E. Sabia
    ENEA C.R. Frascati, Frascati (Roma), Italy
 
  The mechanism of Echo-enabled FEL devices have been discussed by Stupakov and coworkers who have provided detailed analysis for an experimental implementation of their proposal. More recently the effect of the Coulombian diffusion as an element determining a dilution of the bunching coefficients has been studied by Stupakov, the problem has been treated using the diffusion equation coupled to a kind of ray tracing procedure. We propose a different approach based on the use of a Vlasov equation composed by two contributions accounting for the Liouville and diffusive part of the interaction. The equation is solved using simplectic integration procedures which provide an effective method of solution, easily implemented numerically, flexible and modular. The results which can be extended to different experimental conditions are confronted with those of earlier works.  
slides icon Slides WEOCNO02 [1.474 MB]  
 
WEOCNO03 3-D Theory of a High Gain Free-Electron Laser Based on a Transverse Gradient Undulator 481
 
  • P. Baxevanis, Y. Ding, Z. Huang, R.D. Ruth
    SLAC, Menlo Park, California, USA
 
  The performance of a free-electron laser (FEL) depends significantly on the various parameters of the driving electron beam. In particular, a large energy spread in the beam results in a great reduction of the FEL gain, an effect which is relevant when one considers FELs driven by plasma accelerators or storage rings. For such cases, one possible solution is to use a transverse gradient undulator (TGU) [*,**]. In this concept, the energy spread problem is mitigated by properly dispersing the e-beam and introducing a linear, transverse field dependence in the undulator. This paper presents a self-consistent theoretical analysis of a TGU-based high gain FEL, taking into account three-dimensional (3-D) effects and beam size variations along the undulator [***]. The results of our theory compare favorably with simulation and are used in fast optimization studies of various X-ray FEL configurations.
*T. Smith et al., J. Appl. Phys. 50, 4580 (1979).
**Z. Huang, Y. Ding, C. Schroeder, Phys. Rev. Lett. 109, 204801 (2012).
***P. Baxevanis, R. Ruth, Z. Huang, Phys. Rev. ST-AB 16, 010705 (2013).
 
slides icon Slides WEOCNO03 [3.217 MB]  
 
WEOCNO04
The Echo Scheme: An Efficient Alternative to Slicing on Storage Rings  
 
  • C. Evain
    SOLEIL, Gif-sur-Yvette, France
  • C. Evain
    PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
 
  Echo-enabled harmonic generation was proposed in Free Electron Lasers [1] in order to enhance dramatically the FEL radiation on very high harmonic orders. Two laser-electron interactions that modulate the longitudinal charge distribution at a harmonic number of the laser wavelength are required, before FEL radiation is produced in a last radiator. The scheme has been applied to a storage ring [2], in order to produce femtosecond pulses of soft x-ray coherent undulator radiation. The output photon flux is expected to be several orders of magnitude higher than in the case of the conventional slicing scheme. Analytical as well as numerical simulations are presented in the case of SOLEIL storage ring.
[1] G. Stupakov, PRL 102, 074801 (2009).
[2] C. Evain et al., New Journal of Physics 14, 023003 (2012).
 
slides icon Slides WEOCNO04 [2.067 MB]