Relativistic Brillouin solutions have been derived for electron flow in crossed electric and magnetic fields. The application of these solutions to the high ν/γ diode is discussed and an approximate analytical expression for the anode current is derived. Measurements of diode current are compared to the theoretical and empirical expressions for diode current which have been developed.
The process of magnetic cutoff in diodes is investigated for several geometrical configurations. Generalized coordinates are used to show that the cutoff mechanism has certain basic properties which are common to all of the configurations considered. Theoretical solutions for two different one-dimensional flow patterns are compared and shown to have similar mathematical properties. Measurements are compared to theory for several types of magnetic cutoff.
Variations of the nature and pressure of the background gas used for neutralizing the charge of a relativistic electron beam have been observed to alter the current waveform of the propagating beam, the time delay before propagation begins, and the voltage and current waveforms of the diode which accelerates the beam. This interaction between the beam region and the diode occurs during the delay phase before beam propagation begins and can be explained by (1) the reflection of electrons back into the diode from a virtual cathode which exists in the beam region during the delay phase and (2) the flow of a significant positive-ion current in the diode during this same period. A theory describing positive-ion flow in the presence of multiply reflected electrons is developed and compared to experimental observations.
We report experimental and theoretical studies of an intense relativistic electron beam (REB) injection system designed for tokamak current drive experiments. The injection system uses a standard high-voltage pulsed REB generator and a magnetically insulated transmission line (MITL) to drive an REB-accelerating diode in plasma. A series of preliminary experiments has been carried out to test the system by injecting REBs into a test chamber with preformed plasma and applied magnetic field. REBs were accelerated from two types of diodes: a conventional vacuum diode with foil anode, and a plasma diode, i.e., an REB cathode immersed in the plasma. REB current was in the range of 50 to 100 kA and REB particle energy ranged from 0.1 to 1.0 MeV. MITL power density exceeded 10 GW/cm2. Performance of the injection system and REB transport properties is documented for plasma densities from 5×1012 to 2×1014 cm−3. Injection system data are compared with numerical calculations of the performance of the coupled system consisting of the generator, MITL, and diode.
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