Interaction of a modulated electron beam with a magnetoactive plasma

Experimental results concerning the interaction of a modulated electron beam with a magnetoactive plasma in the whistler frequency range are reported. It was shown experimentally that when a beam is injected into the plasma, waves can be generated by two possible mechanisms: Cherenkov emission of whistlers by the modulated beam, and transition radiation from the beam injection point. In the case of weak beam currents (N _b/N ₀)≪⁻⁴) the Cherenkov resonance radiation is more than an order of magnitude stronger than the transition radiation; the Cherenkov emission efficiency decreases at high beam currents. The transformation of the distribution function of the beam is investigated for the case of weak beam currents. It is shown that in the case of the Cherenkov interaction with whistlers the beam is retarded and the beam distribution function becomes wider and acquires a plateau region. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 378–382 (25 March 1998)     

Interaction of a modulated electron beam with a plasma

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 11, pp. 1351–1357, November, 1989.     

Excitation of waves in magnetoactive plasma by a strongly “spread” inhomogeneous electron beam

The stability of beam-plasma systems is studied assuming that the distribution of beam-electrons in the velocity space corresponds to the first period of the quasilinear relaxation. The necessary condition is derived for the usual quasilinear equations to be applicable within the whole period of quasilinear relaxation.The authors wishes to thank Dr. R. Klíma for his interest in this paper.     

Charged-particle acceleration by a modulated electron beam in a periodically inhomogeneous plasma

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 2, pp. 177–181, February, 1990.     

Transition radiation of modulated electron beam in strongly inhomogeneous plasma

A formula for the transition radiation of a modulated electron bean in a strongly inhomogeneous plasma is derived in a given-current approximation. Nonmonotonic variation of the transition-radiation power is detected when the inhomogeneity parameter for the beam emerging from the plasma is varied. The analytic results are confirmed by numerical calculations.Kiev State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 2, pp. 194–199, February, 1994.     

Nonlinear interaction of a modulated beam with plasma

Nonlinear evolution of h. f. instabilities excited by a premodulated electron beam in a magnetized plasma is investigated both theoretically and experimentally. Only the erenkov type of excitation (k_¦|v_b) of the upper branch of the electron plasma oscillations has been observed. The dynamics of excitation of the quasistationary fundamental wave (having the frequency of modulation) has been determined numerically. The wave absorption has been included into the theoretical model through an effective collision frequency. Numerical results agree well with the measured evolution of the amplitude and of the phase velocity of the fundamental wave along the system, as well as with the beam distribution functions. The observed bunching of beam electrons and characteristic features of plasma electrons heating are also reported. Broadening of the frequency spectrum and the occurrence of satellite waves with lower phase velocities have been observed downstream. Physical mechanism of spantaneous excitation of these satellites is suggested and their role in the process of the beam relaxation is discussed. More detailed studies of the nonlinearly excited waves have been performed by modulating the beam at two frequencies.It is a pleasure for us to thank Dr .Körbel who has kindly performed the numerical calculations.     

Propagation regimes of intense circularly polarized laser beam in magnetoactive plasma

This paper presents an analytical and numerical investigation of an intense circularly polarized wave propagating along the static magnetic field parallel to oscillating magnetic field in magnetoactive plasma. In the relativistic regime such a magnetic field is created by pulse itself. The authors have studied different regimes of propagation with relativistic electron mass effect for magnetized plasma. An appropriate expression for dielectric tensor in relativistic magnetoactive plasma has been evaluated under paraxial theory. Two modes of propagation as extraordinary and ordinary exist; because of the relativistic effect, ultra-strong magnetic fields are generated which significantly influence the propagation of laser beam in plasma. The nature of propagation is characterized through the critical-divider curves in the normalized beam width with power plane For given values of normalized density (ω_p/ω) and magnetic field (ω_c/ω) the regions are namely steady divergence (SD), oscillatory divergence (OD) and self-focusing (SF). Numerical computations are performed for typical parameters of relativistic laser-plasma interaction: magnetic field B = 10-100 MG; intensity I = 10¹⁶ to 10²⁰ W/cm²; laser frequency ω = 1.1 × 10¹⁵ s⁻¹; cyclotron frequency ω_c = 1.7 × 10¹³ s⁻¹; electron density n_e = 2.18 × 10²⁰ cm⁻³. From the calculations, we confirm that a circularly polarized wave can propagate in different regimes for both the modes, and explicitly indicating enhancement in wave propagation, beam focusing/self-guiding and penetration of E-mode in presence of magnetic field.     

Anomalous scattering of a relativistic electron beam in a beam created plasma

Measurements of the velocity angular distribution of a relativistic electron beam (0.8 MV, 6 kA, 150 ns) after propagation through hydrogen gas are presented. At a pressure of 25 Pa scattering of the beam electrons into a preferential angular interval is observed. At 190 Pa anomalously large scattering is observed, up to an angular width of 90°, during about 30 ns.     

Contribution to the theory of longitudinal instability of an electron beam in a waveguide with a magnetoactive dielectric

Conclusions Thus, our investigation shows that the character of the instability of an electron beam in a waveguide depends significantly on the state of the magnetization of the ferrite. Thus, in the case of an unsaturated ferrite the spectrum of the excited oscillations is unbounded, in contrast to the case of a longitudinally magnetized ferrite, when the spectrum of the waveguide harmonics is bounded by the frequency In the case of gyrotropic ferrite waveguide, the frequencies of the excited oscillations increase with increasing longitudinal magnetic field [see formula (21)], as is well confirmed by measurement results [8].The development of instability leads to a redistribution of the energy over the length of the beam (this effect was observed in experiment [8]), so that ferrite waveguides can be used for self-acceleration of intense electron beams.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 20, No. 3, pp. 444–450, March, 1977     

Oscillation interaction in a nonequilibrium magnetoactive plasma

Kharkov State University: Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 31, No. 6, pp. 675–679, June, 1988.