Role of Ions in a Crossed-Field Diode

Abstract

The effect of ions in a magnetically insulated crossed-field gap is studied using a single particle orbit model, shear flow model, and particle-in-cell simulation. It is found that, in general, the presence of ions in a crossed-field gap always increases the electrons' excursion toward the anode region, regardless of the location of the ions. Thus, the rate at which the electrons migrate toward the anode, which is a measure of the diode closure rate, is related to the rate at which ions are introduced into the crossed-field gap. This anode migration of electrons is unrelated to crossed-field ambipolar diffusion. The implications of these findings are explored, such as pulse shortening in relativistic magnetrons and bipolar flows in pulsed-power systems.

Plasma physics and related challenges of millimeter-wave-to-terahertz and high power microwave generation

“…In HPM devices, dense beam impact on the anode or collector surfaces leads to release of adsorbed gases 111,117 and ultimately plasma production that limit the achievable operating pulse length. 47,118 In compact mmw-to-THz high power sources, dense beam impact on the circuit or collector can lead to irreparable, single-shot damage, even with short pulses during initial device testing.…”

Loss of Magnetic Insulation in a Crossed-Field Diode: Ion and Collisional Effects

“…We applied a −5000-V dc bias to the cathode while keeping the anode grounded; the cathode bias is ramped from 0 to −5000 V in 25 ns. All of these values were chosen to compare with [23]. The maximum number of particles for each species considered is 5 × 10 5 , and the number of physical particles per computer particle is 1 × 10 8 for pressures ranging from 1 × 10 −6 Torr to 1 × 10 −4 Torr.…”

“…It has been shown that this can cause changes in the relativistic magnetron resonance condition which leads to pulse shortening and/or excitation of undesired modes [11], [18]- [22]. Furthermore, it has been conjectured that this electron migration results from the formation of an unintentional plasma in high-power crossed-field devices [11], [14]- [18], [22], [23]. The exact origin and role of these plasma ions have not been unambiguously determined [23].…”

“…Furthermore, it has been conjectured that this electron migration results from the formation of an unintentional plasma in high-power crossed-field devices [11], [14]- [18], [22], [23]. The exact origin and role of these plasma ions have not been unambiguously determined [23].…”

“…Once the basic physics is understood, the complexity of the models is extended to the high-dimensional relativistic regime reflective of actual device geometry. As such, the role of these aforementioned ions in a crossed-field diode was investigated by Lau et al using the single particle orbit theory and 1-D particle-in-cell (PIC) simulation where a sheet of ions was used to represent a plasma in the gap [23]. This showed that when a sheet of ions was placed near the anode, the electrons feel only a fraction of the acceleration potential of the sheet.…”