Single-stage depressed collectors for gyrotrons

Journal Article · Sat Jun 01 04:00:00 EDT 1996 · IEEE Transactions on Plasma Science

DOI:https://doi.org/10.1109/27.532940· OSTI ID:377815

Piosczyk, B; Iatrou, C T; Dammertz, G ^[1]; Thumm, M ^[1]

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1. Forschungszentrum Karlsruhe-Association EURATOM-FZK (Germany). Inst. fuer Technische Physik

Two 140 GHz gyrotrons with a single-step depressed collector have been operated. The different position of the isolating collector gap in the stray magnetic field causes the electron motion in the retarding region to be in one case adiabatic and in the other case nonadiabatic. The kind of motion within the retarding field influences strongly the behavior of the gyrotron with a depressed collector. In the case of nonadiabatic motion a significant amount of transverse momentum is given to the electrons reflected at the collector potential. This causes the reflected electrons to be trapped between the magnetic mirror and the collector. The electrons escape from the trap by diffusion across the magnetic field to the body of the tube thus contributing to the body current. Despite the high body current there is no observable influence of the collector voltage on the RF output power. In the case of adiabatic motion the reflected electrons do not gain a sufficient amount of transverse momentum to be trapped by the magnetic mirror. They pass the cavity toward the gun and they are trapped between the negative gun potential and the collector. The interaction with the RF field by electrons traveling through the cavity enhances the diffusion in the velocity space thus enabling the trapped electrons to overcome the potential barrier and escape toward the collector. Therefore the body current stays at low values since in this case the reflected electrons do not contribute to it. However, at higher collector voltages a reduction of RF power occurred and some noise in the electron beam was observed. The main motivation for the development of gyrotrons in the frequency range above 100 GHz with power levels in excess of several hundreds kW per tube, is the application in magnetic fusion devices for plasma heating and for electron current drive.

• OSTI ID: 377815
• Journal Information: IEEE Transactions on Plasma Science, Journal Name: IEEE Transactions on Plasma Science Journal Issue: 3 Vol. 24; ISSN ITPSBD; ISSN 0093-3813
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ADIABATIC PROCESSES
BEAM DYNAMICS
DESIGN
ELECTRIC POTENTIAL
ELECTRON BEAMS
EXPERIMENTAL DATA
MICROWAVE AMPLIFIERS
OPERATION
THERMONUCLEAR DEVICES