Effects of anode materials on the performance of explosive field emission diodes

Shiffler, D.; Luginsland, J.W.; Umstattd, R.; LaCour, A.; Golby, K.; Haworth, M.D.; Ruebush, M.; Žagar, Drago; Gibbs, Aimee; Spencer, Thomas A.

doi:10.1109/tps.2002.802146

Cited by 36 publications

(14 citation statements)

References 9 publications

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“…First, the SEM images show no evidence of explosive field emission, a fact consistent with previous experimental results 6,7 and with modeling and simulation efforts to be presented in future publications. 8 ͑Overheated or exploded fiber tips appear to have mushroomlike structure that will be discussed in Ref.…”

Section: Resultssupporting

confidence: 88%

Materials characteristics and surface morphology of a cesium iodide coated carbon velvet cathode

Shiffler

Heidger

Cartwright

et al. 2008

Journal of Applied Physics

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Cesium iodide (CsI) coated carbon fiber cathodes have shown promise as a cold cathode for microwave and x-ray devices. In particular, the cathodes have demonstrated over 1 000 000 shots lifetime at operating voltages at or in excess of 165 kV and current densities greater than 25A/cm2. While the vacuum emission characteristics have been well studied, the materials characteristics of the cathodes themselves, particularly after operation, have received little attention. Furthermore, while researchers at University of Wisconsin have demonstrated a reduction in work function of carbon due to the CsI coating, the details of the emission mechanism remain poorly understood. This article gives results of a series of materials diagnostics investigating the cathode surface morphology as well as the changes in the carbon fiber structure with cathode shot history. We demonstrate that the cathode surface undergoes several changes in relation to the bond line along the fiber-substrate interface as well as at the fiber tips. While the exact mechanisms leading to these changes have not been determined, we offer several possible explanations for the changes, as well as the means by which these mechanisms can be ascertained.

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Section: Resultssupporting

confidence: 88%

Materials characteristics and surface morphology of a cesium iodide coated carbon velvet cathode

Shiffler

Heidger

Cartwright

et al. 2008

Journal of Applied Physics

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“…The neutrals per electron plot, however, shows two roughly linear behaviors in this parameter range; the shots using the molybdenum mesh generated 0.38 neutrals per electron versus the 0.73 neutrals per electron for the shots using the carbon fiber anode. This significant difference in gas generation supports the conclusion [7] that the explosive emission cathode is not necessarily the largest source of outgassing in such a diode. These yields are possibly also a function of the incoming electron's energy, but this experimental setup did not allow us to accurately probe a wide enough parameter space to test this conjecture.…”

Section: Discussionsupporting

confidence: 75%

Gas evolution during operation of a CsI-coated carbon fiber cathode in a closed vacuum system

Umstattd

Schlise

Wang

2005

IEEE Trans. Plasma Sci.

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In order to quantify the gases generated during operation of an explosive emission cathode, residual gas analysis was performed on a closed vacuum system. Two different anode materials were tested using an identical CsI-coated carbon fiber cathode. For both the nearly transparent molybdenum mesh and the carbon fiber anode, the largest pressure increases were observed in hydrogen and carbon dioxide. Use of the molybdenum mesh resulted in the generation of approximately 0.38 neutrals per electron compared to 0.73 neutrals per electron while using the carbon fiber anode. While the background vacuum pressure was typically in the low 10 7 torr scale, it was found that gas generation during these explosive emission pulses led to local diode pressures of 0.5 mtorr up to several tens of mtorr. Such pressures are consistent with the ability to generate ion densities that can drastically effect the space charge-limited current.

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“…Over the pulse duration, the current variation is due to several factors which depend on the diode operation. These factors are the voltage increase, the changes introduced in the diode geometry by the expanding velvet plasma [27] and ion flow from the anode [28]. In our study, the hollowness of the anode and the large AK gap (17.2 cm) prevents ion flow from the anode during the time window of interest.…”

Section: Diode Resultsmentioning

confidence: 88%

High power electron diode for linear induction accelerator at a flash radiographic facility

Plewa

Bernigaud

Barnes

et al. 2018

Phys. Rev. Accel. Beams

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We investigated a new cathode design and beam transport with the EPURE axis-1 injector in order to increase the beam characteristics at 3.8 MeV, 80 ns FWHM from the 2.0 kA nominal current to 2.6 kA corresponding to an average current density of 82 A=cm 2 . Such current increase is highly desirable for improving the x-ray dose and hence radiographic performances. To achieve this, a time-dependent model based on the particle-in-cell method was developed in order to simulate the injector. Using results from calculations based on this model, a 17.2 cm AK gap diode with a larger radius cathode (3.175 cm) was designed, manufactured and tested. Experimental and calculated currents and emittances are qualitatively compared. The study provides a detailed understanding of the beam dynamics inside this type of high current, high energy injector.

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Effects of anode materials on the performance of explosive field emission diodes

Cited by 36 publications

References 9 publications

Materials characteristics and surface morphology of a cesium iodide coated carbon velvet cathode

Materials characteristics and surface morphology of a cesium iodide coated carbon velvet cathode

Gas evolution during operation of a CsI-coated carbon fiber cathode in a closed vacuum system

High power electron diode for linear induction accelerator at a flash radiographic facility

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