Dynamics of a high-current relativistic electron beam
- PDF / 850,932 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 204 Views
MA ELECTRONICS
Dynamics of a High-Current Relativistic Electron Beam P. S. Strelkova, V. P. Tarakanovb, c, I. E. Ivanova, and D. V. Shumeikoa a Prokhorov
General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia b Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya ul. 13-2, Moscow, 127412 Russia c National Research Nuclear University “MEPhI,” Kashirskoe sh. 31, Moscow, 115409 Russia e-mail: [email protected], [email protected], [email protected], [email protected] Received September 26, 2014; in final form, November 10, 2014
Abstract—The dynamics of a high-current relativistic electron beam is studied experimentally and by numerical simulation. The beam is formed in a magnetically insulated diode with a transverse-blade explosive-emission cathode. It is found experimentally that the radius of a 500-keV beam with a current of 2 kA and duration of 500 ns decreases with time during the beam current pulse. The same effect was observed in numerical simulations. This effect is explained by a change in the shape of the cathode plasma during the current pulse, which, according to calculations, leads to a change in the beam parameters, such as the electron pitch angle and the spread over the longitudinal electron momentum. These parameters are hard to measure experimentally; however, the time evolution of the radial profile of the beam current density, which can be measured reliably, coincides with the simulation results. This allows one to expect that the behavior of the other beam parameters also agrees with numerical simulations. DOI: 10.1134/S1063780X15060057
1. INTRODUCTION Relativistic microwave electronic devices usually operate with a high-current annular relativistic electron beam (REB) formed in a magnetically insulated diode. Due to the small thickness of the electron beam wall, the difference between the space charge potentials on the outer and inner sides of the beam wall is very low. This means that all electrons in the drift space have almost the same kinetic energy and can excite axisymmetric modes of the microwave electrodynamic system with equal efficiency. A thin-wall metal or graphite tube on the surface of which explosive emission occurs is usually used as a cathode. The emission current density is always limited; therefore, in such cathodes, a fraction of the side surface near the tube edge also emits electrons. In the initial stage of emission, the thickness of plasma on the surface of the annular cathode is small and the diameter of the electron beam is determined by the outer diameter of the cathode. Then, the plasma thickness above the cathode surface increases, the emitting boundary shifts outward, and the beam radius enlarges. The parameters of the electron beam in diodes with an annular cathode have been thoroughly investigated (see, e.g., reviews [1, 2]). It has been found that the cathode plasma from which the beam electron start to move rapidly expands in the longitudinal direction; how-
ever, the change in the transverse size
Data Loading...
