Abstract-Terahertz Undulator Radiation of Stabilized Dense Electron Beams

I. V. BandurkinI,  S. Kurakin, Yu. S. Oparina, A. V. Savilov, V. L. Bratman, N. Balal, Yu. Lurie

https://link.springer.com/article/10.3103%2FS1062873818120262

Dense short electron bunches produced by state-of-the-art photoinjector-based accelerators are used to create sources of powerful electromagnetic pulses of terahertz frequency range based on spontaneous coherent emission by these bunches. However, there is a problem of stabilizing the phase dimension of a bunch along the space of electron wave interaction. In this work, two means of such stabilization are considered that are based on using the intrinsic electromagnetic fields (quasi-static and radiation) of bunches.

Abstract-Energy enhancement and spectrum narrowing in terahertz electron sources due to negative mass instability

Yu. Lurie,1,* V. L. Bratman,1,2 and A. V. Savilov2 1
Ariel University, 40700 Ariel, Israel 2 Institute of Applied Physics, Russian Academy of Sciences, 603950 Nizhny Novgorod, Russia

https://journals.aps.org/prab/pdf/10.1103/PhysRevAccelBeams.19.050704

Simulations of coherent spontaneous undulator radiation in a waveguide demonstrate that the use of negative mass instability (NMI) for retaining longitudinal sizes of dense electron bunches, which are formed in laser-driven photoinjectors, allows one to increase power capabilities of a terahertz radiation source by many times. The NMI is realized in an undulator with combined helical and over-resonance uniform longitudinal magnetic fields due to nonisochronous longitudinal oscillations of electrons, whose frequencies increase/decrease with increasing/decreasing particle energy. In such conditions, an effective longitudinal size of the bunches can be preserved at long distance even at an extremely high electron density. Correspondingly, an energy extraction efficiency of more than 20% is revealed at a narrow frequency radiation spectrum, suggesting realization of a compact and powerful THz source.

Abstract-Gyrotron with a sectioned cavity based on excitation of a far-from-cutoff operating mode

I. V. Bandurkin1, Yu. K. Kalynov1, I. V. Osharin1 and A. V. Savilov1
http://scitation.aip.org/content/aip/journal/pop/23/1/10.1063/1.4940784
1 Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia
Phys. Plasmas 23, 013113 (2016); http://dx.doi.org/10.1063/1.4940784

A typical problem of weakly relativistic low-power gyrotrons (especially in the case of operation at high cyclotron harmonics) is the use of long cavities ensuring extremely high diffraction Q-factors for the operating near-cutoff waves. As a result, a great share of the rf power radiated by electrons is spent in Ohmic losses. In this paper, we propose to use a sectioned cavity with π-shifts of the wave phase between sections. In such a cavity, a far-from-cutoff axial mode of the operating cavity having a decreased diffraction Q-factor is excited by the electron beam in a gyrotron-like regime.

(This paper is focused basically on the problems of the gyrotrons operating at high cyclotron harmonics in the terahertz frequency range)

Abstract-Negative-mass mitigation of Coulomb repulsion for terahertz undulator radiation of electron bunches

N. Balal¹, I. V. Bandurkin², V. L. Bratman^1,2, E. Magory¹ and A. V. Savilov^2,3
 HIDE AFFILIATIONS
1 Ariel University, Ariel 40700, Israel
2 Institute of Applied Physics, Russian Academy of Sciences, 46 Ulyanov St., Nizhny Novgorod 603950, Russia
3 Lobachevsky State University of Nizhny Novgorod, 23 Gagarin Avenue, Nizhny Novgorod 603950, Russia
Appl. Phys. Lett. 107, 163505 (2015); http://dx.doi.org/10.1063/1.4934495

http://scitation.aip.org/content/aip/journal/apl/107/16/10.1063/1.4934495

It is proposed to utilize the effect of negative mass for stabilization of the effective axial size of very dense and short electron bunches produced by photo-injector guns by using combined undulator and strong uniform magnetic fields. It has been shown that in the “abnormal” regime, an increase in the electron energy leads to a decrease in the axial velocity of the electron; due to the negative-mass effect, the Coulomb repulsion of electrons leads to their attraction and formation of a fairly stable and compact bunch “nucleus.” An undulator with a strong uniformmagnetic field providing the negative-mass effect is designed for an experimental source of terahertz radiation. The use of the negative-mass regime in this experiment should result in a long-pulse coherent spontaneous undulator emission from a short dense moderately relativistic (5.5 MeV) photo-injector electron bunch with a high (up to 20%) efficiency and a narrow frequency spectrum.