IAP/RAS, Nizhny Novgorod, Russia
We describe three works united by the idea of the non-resonant regime [1] providing an effective trapping in a beam with a great energy spread. In this regime, the "bucket" corresponding to the resonant electron-wave interaction passes through the electron layer on the energy-phase plane and traps a fraction of electrons. (I) Operability of this regime was demonstrated in the high-efficient 0.8 MeV Ka-band FEM-amplifier [2]. (II) In short-wavelength FELs the multi-stage trapping in several consecutive sections can be organized [3]. In each section a small e-beam fraction is trapped due to a weak electron-wave interaction. However, repetition of this process from section to section involves in the interaction almost the whole e-beam. We describe efficiency enhancement and improving the frequency wave spectrum in multi-stage SASE FELs. (III) The multi-stage amplification of a single-frequency wave signal can provide cooling of the electron bunch. In this regime, tapering of every section is provided such that the "bucket" goes from maximal initial electron energy down to the minimal one and moves down energies of trapped electrons.
[1] A.Savilov et al., Nucl. Instr. Meth. A, vol. 507, p.158, 2003
[2] A.Kaminsky et al., Int. Conf. IRMMW-THz 2018, art. 4057938
[3] S.Kuzikov, A.Savilov, Phys. Plasmas, vol. 25, p.113114, 2018
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
UCLA, Los Angeles, USA
Ariel University, Ariel, Israel
Shenkar College of Engineering and Design, Ramat Gan, Israel
We outline the fundamental processes of coherent radiation emission from a bunched charged particles beam [1]. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles N, a pre-bunched electron beam emits spontaneously coherent radiation proportional to N2 through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke’s [2]). The SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated-superradiance (ST-SR) in the presence of a seed injected radiation field. These coherent radiation emission processes are presented in term of a radiation mode expansion model, applied to general free electron radiation schemes: Optical-Klystron, HGHG, EEHG, and coherent THz sources based on synchrotron radiation, undulator radiation or Smith-Purcell radiation. The general model of coherent spontaneous emission is also extended to the nonlinear regime - Tapering Enhanced Stimulated Superradiance (TESSA) [3], and related to the tapered wiggler section of seed-injected FELs. In X-Ray FELs these processes are convoluted with other effects, but they are guidelines for strategies of wiggler tapering efficiency enhancement.
[1] A. Gover et al., Rev. Mod. Phys. https://arxiv.org/abs/1810.07566v3 (2019)
[2] R. H. Dicke, Physical Review 93, 99 (1954)
[3] N. Sudar et al., P.R.L. 117, 174801 (2016)
SLAC, Menlo Park, California, USA
ANL, Lemont, Illinois, USA