Characterization and investigation of the anomalous behavior of the immersed-Bz diode during operation at 4 to 5 MV

Rovang, Dean C.; Bruner, N.; Johnston, Mark D.; Madrid, E. A.; Maenchen, J.E.; Oliver, B.V.; Portillo, S.; Welch, D. R.

doi:10.1063/1.2980418

Cited by 4 publications

(1 citation statement)

References 27 publications

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“…The surface contaminants serve as a source for protons which are commonly found in experiments involving intense electron beam impact [21][22][23]. Simulations modeling a hydrogen anode plasma as described above show depletion of the plasma density as protons are drawn into bipolar flow, and plasma expansion does not occur.…”

Section: Model Parameters For the Smp Diodementioning

confidence: 97%

Anode plasma dynamics in the self-magnetic-pinch diode

Bruner

Welch

Hahn

et al. 2011

Phys. Rev. ST Accel. Beams

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The self-magnetic-pinch diode is being developed as an intense electron beam source for pulsed-powerdriven x-ray radiography. In high-power operation, the beam electrons desorb contaminants from the anode surface from which positive ions are drawn to the cathode. The counterstreaming electrons and ions establish an equilibrium current. It has long been recognized, however, that expanding electrode plasmas can disrupt this equilibrium and cause rapid reduction of the diode impedance and the radiation pulse. Recently developed numerical techniques, which enable simultaneous modeling of particle currents with 10 13 cm À3 densities to plasmas of near solid density, are applied to a model of the self-magnetic-pinch diode which includes the formation and evolution of anode surface plasmas. Two mechanisms are shown to cause rapid impedance loss, anode plasma expansion into the anode-cathode (A-K) gap, and increased ion space-charge near the cathode surface. The former mechanism dominates for shorter A-K gaps, while the latter dominates for longer gaps. Model results qualitatively reproduce the time-dependent impedances measured for this diode.

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Section: Model Parameters For the Smp Diodementioning

confidence: 97%

Anode plasma dynamics in the self-magnetic-pinch diode

Bruner

Welch

Hahn

et al. 2011

Phys. Rev. ST Accel. Beams

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

et al. 2010

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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.

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Compensational scintillation detector with a flat energy response for flash X-ray measurements

Chen

Ouyang

Liu

et al. 2013

Review of Scientific Instruments

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To measure the intensity of flash X-ray sources directly, a novel scintillation detector with a fast time response and flat energy response is developed by combining film scintillators of doped ZnO crystal and fast organic scintillator together. Through compensation design, the dual-scintillator detector (DSD) achieved a flat energy response to X-rays from tens of keV to several MeV, and sub-nanosecond time response by coupling to ultrafast photo-electronic devices. A prototype detector was fabricated according to the theoretical design; it employed ZnO:In and EJ228 with thicknesses of 0.3 mm and 0.1 mm, respectively. The energy response of this detector was tested on monoenergetic X-ray and γ-ray sources. The detector performs very well with a sensitivity fluctuation below 5% for 8 discrete energy points within the 40-250 keV energy region and for other energies of 662 keV and 1.25 MeV as well, showing good accordance with the theoretical design. Additionally, the detector works properly for the application to the flash X-ray radiation field absolute intensity measurement. This DSD may be very useful for the diagnosis of time-resolved dynamic physical processes of flash X-ray sources without knowing the exact energy spectrum.

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Characterization and investigation of the anomalous behavior of the immersed-Bz diode during operation at 4 to 5 MV

Cited by 4 publications

References 27 publications

Anode plasma dynamics in the self-magnetic-pinch diode

Anode plasma dynamics in the self-magnetic-pinch diode

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

Compensational scintillation detector with a flat energy response for flash X-ray measurements

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