Undulator superradiance effect and its applicability for the generation of multimegawatt terahertz pulses
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Undulator Superradiance Effect and Its Applicability for the Generation of Multimegawatt Terahertz Pulses N. S. Ginzburga,b, A. A. Golovanova, I. V. Zotovaa,*, A. M. Malkina, and V. P. Tarakanovc a
Institute of Applied Physics, Russian Academy of Sciences, Nizhni Novgorod, 603950 Russia b Lobachevsky Nizhni Novgorod State University, Nizhni Novgorod, 603950 Russia cNational Research Nuclear University “MEPhI,” Moscow, 115409 Russia *email: [email protected]nnov.ru Received April 22, 2014
Abstract—The generation of multimegawatt terahertz pulses based on the superradiance of picosecond elec tron bunches moving in a periodic magnetic (undulator) field is shown to be possible. The theoretical study of superradiance processes is based both on the method of an averaged ponderomotive force and on direct numerical PIC (particle in cell) simulations. The analysis is performed in the K' reference frame comoving with the electrons followed by the recalculation of radiation characteristics to the laboratory frame using the Lorentz transformations. Within the framework of the averaged approach, the electron bunch is represented as an ensemble of macroelectrons interacting between themselves through the radiation fields and Coulomb forces. The superradiance effect includes particle bunching followed by coherent emission of a single intense pulse from the entire volume of an electron bunch whose length exceeds considerably the wavelength. PIC simulations of this process based on the KARAT code have been performed for a more detailed analysis including the transverse inhomogeneity of the undulator field, the relativistic pattern of electron motion in this field, etc. A considerable simplification of the calculation procedure when passing to the comoving ref erence frame due to the commensurability of all spatial scales, including the radiation wavelength, the bunch length, and the length of the train of the pump wave into which the undulator field is transformed, is shown to be possible. DOI: 10.1134/S1063776114100021
1. INTRODUCTION In recent years, substantial progress has been achieved in the generation of intense electromagnetic pulses in the centimeter and millimeter ranges based on the superradiance (SR) of highcurrent kiloampere electron bunches [1–4]. This process includes particle bunching followed by coherent emission from the entire volume of an extended (in the wavelength scale) electron bunch. The SR pulses are distinguished by a recordhigh (gigawatt) peak power and an ultrashort (subnanosecond) duration. At moderate particle ener gies (up to 300 keV) and subnanosecond bunch dura tions, the Cherenkov mechanism is the most efficient SR pulse generation mechanism. Within the frame work of this mechanism, a rectilinearly moving extended electron bunch radiates into the backward wave propagating in a periodic slowwave structure [2–4]. The advancement of SR sources into shortwave ranges, including the terahertz one, can be considered as a natural outgrowth of these studies. The SR of elec tr
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