Nonlinear theory of free-electron lasers and efficiency enhancement

Abstract

include, among other things, continuous frequency tunability, very high power of operatbios asid hiigh efficiency. Vic free electron laamr ;s charmeterized by a pump field; foi example., a spatially periodic magnetic filrd, which scatters from o, relativistic electron bkatn. The scattered radiation has a wavelength much smaller thaai the pump wavelength depending on the electron (Continued) DD ASTRACT (Continued),beoz energy. We present & general self-conulsteAt non-linear theory of the free electron lawe promess. The non4invar formulation of'the temporal steady state free electron laser problem results in -st of coupled differential Oquatirns govairiiip the spatWa ovolution of the ampl itudes and wavelength lrnf the radiation~ad space charge f&r1Ida These 1!quations are readily solved numerialy since the amnpltude and wavelength vtry on a Mpatla Scale which is comparable to a growth length of the output radiation. A itunaber of nuinerical/analytical illustrations are presenetd ranging from the optical to the stibmillllmter wavelunitth regime. Our non incear formulation in the linear regime is compared with lknsar theory and agrement is found to he excellent.. Analytical expressions for the saturated of ficiency and radiation amplitude ate als Shown to be in very good agreement with our non-linear numerical soiutiana. Efficiency curves are obtained for both the optical and submindimoter FEL examples with fixed magnetic: pump parameters. We show that these intrinsic efficiencie can be greatly enhanced by appropriately contouring the magnetic pump period~ciii the case of the optical FEL, the theoretical W4nge pals efficiency can be peter than 20% by'ã ppropriately decreasing the pump period and increasing th, pump magnetic field.

Mixing and space-charge effects in free-electron lasers

“…In the Compton case, relaxation proceeds as the particle distribution mostly revolves as a whole around itself in phase-space. 4 In the Raman case, however, relaxation is better described in terms of jets emanating from the core of the particle distribution, as in core-halo systems. 20 Jets are formed by charge density piling up, which creates regions of singular acceleration.…”

“…Raman regimes involve space-charge plasma waves, whose resulting forces acting on the electronic population are comparable to the forces produced by the ponderomotive potential well. [4][5][6][7][8] Space-charge effects in Raman regimes have been largely reported in the literature. Emphasis is mostly directed to issues related to instability and saturation levels of the electromagnetic mode, which are of central importance for FEL applications.…”

“…9,10 More complete views of FELs also include careful analysis of particle dynamics, especially in Raman regimes where collective space-charge effects become more prominent. 4 Relaxation in FELs occurs through dynamical mixing. If the charge is small, the ponderomotive well alone mainly drives the particle dynamics.…”

Design of a Compact Optically-Guided Pinched Megawatt Class FEL

“…In the optically guided, high gain regime the efficiency of conversion from electron beam power to optical power is given by [7] A.2 Ak _ "(2f +3f ) 1…”

Free electron laser instability for a relativistic annular electron beam in a helical wiggler field

“…For the most part, previous theoretical analyses of this instability have been carried out for an electron beam with uniform density, neglecting the influence of finite radial geometry. [3][4][5][6] Strictly speaking, a more accurate theoretical model of radiation generation by the free electron laser instability, including a determination of the optimum value of the beam radius RO, requires a linear stability analysis for perturbations about an annular electron beam propagating in a helical wiggler magnetic field. This paper develops a self-consistent theory of the free electron laser instability In Sec.…”