Plasma expansion and impedance collapse in a foil-less diode for a klystronlike relativistic backward wave oscillator

Journal Article · Wed Dec 15 04:00:00 EST 2010 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3520072· OSTI ID:21532111

Renzhen, Xiao; Jun, Sun; Shaofei, Huo; Xiaoze, Li; Ligang, Zhang; Xiaowei, Zhang; Lijun, Zhang ^[1]

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1. Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

Klystronlike relativistic backward wave oscillator (RBWO) can produce microwave power exceeding 5 GW with a high efficiency larger than 40%. In the experiment of klystronlike RBWO, for about 1 MV peak diode voltages, increasing magnetic field from 1.43 to 1.89 T slowed the impedance collapse until it was suppressed completely. The introduction of a stainless steel obstructing ring aggravated the impedance collapse, whereas replacing the stainless steel obstructing ring with a flat stainless steel provided a more stable impedance variation during the pulse duration. These impedance collapses did not affect microwave generation seriously and may be attributed to the radial expansion of cathode plasma initialing from the cathode shank so that part of reverse currents were collected at the anode wall, contributing to the measured diode current. On the other hand, it was found that microwave generation shot-to-shot reproducibility was closely related to the diode impedance variation. When there was no or very low microwave measured, diode impedance collapse appeared at the latter of the pulse. The microwave generation shot-to-shot reproducibility was improved greatly after the electron collector was enlarged on radius with 1 mm. A possible explanation is that the anode plasma produced from electron collector expands axially and enters the diode region at a very high velocity of several mm/ns. The movement of the anode plasma in the beam-wave interaction region affects the microwave generation, which reduces the microwave power during the whole pulse duration significantly.

• OSTI ID: 21532111
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 17; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
DIODE TUBES
ELECTROMAGNETIC RADIATION
ELECTRON TUBES
ELECTRONIC EQUIPMENT
EQUIPMENT
EXPANSION
IMPEDANCE
KLYSTRONS
MICROWAVE EQUIPMENT
MICROWAVE RADIATION
MICROWAVE TUBES
OSCILLATORS
PLASMA EXPANSION
RADIATIONS
THERMIONIC DIODES
THERMIONIC TUBES