Space Charge Wave with Broad Frequency Spectrum Formation in Transit Section of Klystron-type Two-stream FEL with Helical Electron Beam

Authors A.V. Lysenko1 , I.I. Volk1 , G.A. Oleksiienko1, A.A.Shmat’ko2

1Sumy State University, 2, Rimsky-Korsakov St., 40007 Sumy, Ukraine

2V.N. Karazin Kharkiv National University, 4, Svobody Sq., 61022 Kharkiv, Ukraine

Issue Volume 11, Year 2019, Number 5
Dates Received 23 July 2019; revised manuscript received October 2019; published online 25 October 2019
Citation A.V. Lysenko, I.I. Volk, et al., J. Nano- Electron. Phys. 11 No 5, 05022 (2019)
PACS Number(s) 41.60.Cr, 52.35.-g, 52.35.Mw
Keywords Two-stream instability, Two-stream superheterodyne free-electron lasers, Helical electron beam.

In the cubic non-linear approximation framework, the analysis of space charge wave formation with a wide frequency spectrum in helical two-velocity electron beams was performed. It was shown that the formation of a space charge wave with wide frequency spectrum in this kind of beams occurs on condition that the wave first harmonic frequency is much less than the two-stream instability critical frequency. We demonstrated that due to the linearity of the growing space charge wave dispersion characteristic, the condition of the three-wave parametric resonant interactions in helical two-stream relativistic electron beam fulfills for a significant number of such wave’s harmonics which frequencies are less than the critical frequency. Due to these resonances, the excitation of multiharmonic space charge wave occurs. This wave is amplified due to both the three-wave parametric resonances and the two-stream instability mechanism. As a result, the multiharmonic space charge wave forms, and its spectrum width is defined by the 1st harmonic frequency and the two-stream instability critical frequency. It is demonstrated that the frequency spectrum width of the multiharmonic space charge wave increases with the increase of the electrons input angle with respect to the longitudinal focusing magnetic field and it exceeds the frequency spectrum width of such waves in straight electron beams. It is also found out that the space charge wave saturation length in a helical electron beam is two and more times less than in straight electron beams. Therefore, the devices using two-stream helical relativistic electron beams would have less longitudinal dimensions. We proposed to use helical two-stream relativistic electron beams in multiharmonic two-stream superheterodyne free-electron lasers in order to increase the frequency spectrum width and to decrease the device’s longitudinal dimensions compared with devices using straight electron beams.

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