Particle-in-cell simulations for virtual cathode oscillator including foil ablation effects

Journal Article · Wed Jun 15 00:00:00 EDT 2011 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3595237· OSTI ID:21546970

Singh, Gursharn; Chaturvedi, S ^[1]

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1. Computational Analysis Division, B.A.R.C., Visakhapatnam-530012 (India)

We have performed two- and three-dimensional, relativistic, electromagnetic, particle-in-cell simulations of an axially extracted virtual cathode oscillator (vircator). The simulations include, for the first time, self-consistent dynamics of the anode foil under the influence of the intense electron beam. This yields the variation of microwave output power as a function of time, including the role of anode ablation and anode-cathode gap closure. These simulations have been done using locally developed particle-in-cell (PIC) codes. The codes have been validated using two vircator designs available from the literature. The simulations reported in the present paper take account of foil ablation due to the intense electron flux, the resulting plasma expansion and shorting of the anode-cathode gap. The variation in anode transparency due to plasma formation is automatically taken into account. We find that damage is generally higher near the axis. Also, at all radial positions, there is little damage in the early stages, followed by a period of rapid erosion, followed in turn by low damage rates. A physical explanation has been given for these trends. As a result of gap closure due to plasma formation from the foil, the output microwave power initially increases, reaches a near-flat-top and then decreases steadily, reaching a minimum around 230 ns. This is consistent with a typical plasma expansion velocity of {approx}2 cm/{mu}s reported in the literature. We also find a significant variation in the dominant output frequency, from 6.3 to 7.6 GHz. This variation is small as long as the plasma density is small, up to {approx}40 ns. As the AK gap starts filling with plasma, there is a steady increase in this frequency.

• OSTI ID: 21546970
• Journal Information: Physics of Plasmas, Vol. 18, Issue 6; Other Information: DOI: 10.1063/1.3595237; (c) 2011 American Institute of Physics; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABLATION
ANODES
BEAM-PLASMA SYSTEMS
CATHODES
ELECTRON BEAMS
FOILS
MICROWAVE RADIATION
OSCILLATORS
PLASMA DENSITY
PLASMA EXPANSION
PLASMA SIMULATION
PLASMA WAVES
THREE-DIMENSIONAL CALCULATIONS
TWO-DIMENSIONAL CALCULATIONS
VARIATIONS
BEAMS
ELECTRODES
ELECTROMAGNETIC RADIATION
ELECTRONIC EQUIPMENT
EQUIPMENT
EXPANSION
LEPTON BEAMS
PARTICLE BEAMS
RADIATIONS
SIMULATION