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

Stutzman, Brooke S.; Luginsland, J.W.

doi:10.1109/tps.2010.2051460

Cited by 16 publications

(6 citation statements)

References 33 publications

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“…A number of theoretical investigations have been carried out to understand the radiation cutoff in MILOs including simulating the impact of backscattered electrons, ion flows, and finite background gas pressures. [13][14][15] While these studies have motivated design changes resulting in measurable improvements, the radiation pulse duration in MILOs and other HPM devices is still much less than typical input power-pulse durations, particularly at higher operating voltages.…”

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confidence: 99%

Electrode-plasma-driven radiation cutoff in long-pulse, high-power microwave devices

et al. 2013

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The impact of electrode plasma dynamics on the radiation production in a high power microwave device is examined using particle-in-cell simulations. Using the design of a compact 2.4 GHz magnetically insulated line oscillator (MILO) as the basis for numerical simulations, we characterize the time-dependent device power and radiation output over a range of cathode plasma formation rates. These numerical simulations can self-consistently produce radiation characteristics that are similar to measured signals in long pulse duration MILOs. This modeling capability should result in improved assessment of existing high-power microwave devices and lead to new designs for increased radiation pulse durations. V C 2013 American Institute of Physics.[http://dx.doi.org/10.1063/1.4794955] High-power microwave (HPM) devices are capable of producing directed, sustained radiation pulses. 1 The formation of electrode plasmas in these devices has been identified along with a shortening of the radiation pulse and other effects. [2][3][4][5][6][7][8] Through the use of electromagnetic (EM) particle-in-cell (PIC) simulation codes, device designs have been optimized for efficient power output 1 although these simulations have generally not been able to model measured impedance collapse or radiation cutoff. In the case of magnetically insulated line oscillators 9,10 (MILOs), long pulse operation (typically greater than $100 ns) is hampered, reducing the potential peak radiated energy from these devices. 11,12 A MILO is essentially a coaxial transmission line that relies on the selfgenerated magnetic field due the current flowing in the center conductor to insulate an electron flow as it passes through a slow wave structure. The electron flow only becomes insulated from this anode structure once the current reaches a critical value. Therefore relatively fast rising power pulses are required to achieve insulation before electron bombardment of the anode leads to anode plasma formation and ion currents. In a MILO, the cutoff of the radiation pulse is often associated with a partial impedance collapse. A number of theoretical investigations have been carried out to understand the radiation cutoff in MILOs including simulating the impact of backscattered electrons, ion flows, and finite background gas pressures. 13-15 While these studies have motivated design changes resulting in measurable improvements, the radiation pulse duration in MILOs and other HPM devices is still much less than typical input power-pulse durations, particularly at higher operating voltages.Recent computational modeling developments have been utilized to examine the impedance collapse in a number of highpower devices, including charged-particle-beam diodes 16,17 and high-power transmission lines. 18 These models for electrode plasma generation are applied here to study the impedance evolution in a MILO and the associated radiation cutoff. The results of this study suggest that modest plasma formation rates (and modest monolayer contaminant levels) can strongly influen...

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Electrode-plasma-driven radiation cutoff in long-pulse, high-power microwave devices

et al. 2013

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“…Previous work has shown that not only does the presence of ions in a crossed-field gap increase the electron excursion toward the anode region 1 , but electron scattering and ionization of the background species exacerbate this crossed-field migration. 2 We have also shown that the farther into the gap the scattering or ionization occurs, the greater the maximum excursion of the scattered or created electron. 3 In this work, we will break down the scattering problem further by looking at the scattering due to elastic collisions and excitation events separately.…”

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confidence: 75%

Electron excursion versus scattering mechanism in a cross-field diode

Stutzman

Verboncoeur

2014

2014 IEEE 41st International Conference on Plasma Sciences (ICOPS) Held With 2014 IEEE International Conference on High-Power P

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The operation of high-power microwave sources in relativistic magnetrons, magnetically insulated transmission lines for pulsed power systems, and Hull thrusters for space propulsion all rely on cross-field diodes. Electron migration from the cathode to the anode should be eliminated due to magnetic insulation, however, many electrons still transit the gap. This leads to the excitation of undesired modes and/or pulse shortening. Previous work has shown that not only does the presence of ions in a crossed-field gap increase the electron excursion toward the anode region 1 , but electron scattering and ionization of the background species exacerbate this crossed-field migration. 2 We have also shown that the farther into the gap the scattering or ionization occurs, the greater the maximum excursion of the scattered or created electron. 3 In this work, we will break down the scattering problem further by looking at the scattering due to elastic collisions and excitation events separately. We will use a 1D PIC code 4 to compare the electron excursions based on scattering mechanism and scattering site. We will further compare the collision type with the expected energy change due to the collision mechanism.

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“…However, the startup, from a non-oscillating state to an oscillating state, of a magnetron or CFA remains incompletely understood [6]. Characterizing the behavior of electron flows in crossed-field gaps is of great interest for reducing the noise in CFAs [2], [3] and improving CFD startup and operation [6], [15].…”

Section: Introductionmentioning

confidence: 99%

“…Electron flows in crossed-field gaps with various conditions have been studied in space-charge-limited regimes with or without magnetic insulation [2], [3], [15]- [23]. In some cases, the critical behavior of the electron flows under a certain condition can be described by modifying the one-dimensional (1D) classical Child-Langmuir (CL) law for space-charge limited current density (SCLCD) for a onedimensional (1D), planar geometry, given by…”

Section: Introductionmentioning

confidence: 99%

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Electron Trajectories and Critical Current in a Two-Dimensional Planar Magnetically Insulated Crossed-Field Gap

Zhu,

Wright,

Harsha

et al. 2024

IEEE Access

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The critical current in a one-dimensional (1D) crossed-field gap is defined by the transition from a cycloidal flow to a near-Brillouin (nB) state characterized by electron flow orthogonal to both the electric and magnetic fields and uniform virtual cathode formation. Motivated by recent studies on spacecharge-limited current in non-magnetic diodes, we assess the meaning of critical current in a two-dimensional (2D) crossed-field geometry. Particle-in-cell (PIC) simulations demonstrate that binary behavior between a laminar and turbulent state does not occur in 2D because the virtual cathode is nonuniform. Rather than a distinct nB state above the critical current as in 1D, there is an increase in Brillouin contribution with the presence of cycloidal components and noise even at low currents. To evaluate the electron flows in a 2D crossed-field gap in the absence of a binary transition, we developed two metrics to assess the Brillouin and cycloidal components in a 2D planar crossed-field gap for various emission widths and injection current densities by comparing the phase space plots from PIC simulations to analytical solutions for cycloidal and Brillouin flow. For a smaller emission width, less Brillouin contribution occurs for a given injection current, while maximizing the cycloidal noise requires a larger injection current. Once the virtual cathode starts to form and expand with increasing injection current, the cycloidal noise reaches its peak and then decreases while the Brillouin components become significant and increase.INDEX TERMS Brillouin flow, cycloidal flow, crossed-field amplifiers (CFAs), crossed-field devices (CFDs), electron emission, high-power microwave, magnetrons, particle-in-cell, space-charge-limited current, vacuum tubes.

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

Cited by 16 publications

References 33 publications

Electrode-plasma-driven radiation cutoff in long-pulse, high-power microwave devices

Electrode-plasma-driven radiation cutoff in long-pulse, high-power microwave devices

Electron excursion versus scattering mechanism in a cross-field diode

Electron Trajectories and Critical Current in a Two-Dimensional Planar Magnetically Insulated Crossed-Field Gap

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