Analysis of the minimum duration of the runaway electron flow in an air electrode gap

Nikolay Zubarev, G.A. Mesyats, M.I. Yalandin, A.G. Sadykova, K.A. Sharypov, V.G. Shpak, S.A. Shunailov, M.R. Ulmaskulov, O.V. Zubareva, A.V. Kozyrev, N.S. Semeniuk
Institute of Electrophysics, UB RAS, Yekaterinburg, Russian Federation

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VT
Victor Tarasenko 2020-09-23 13:59
Thank you very much for your pterentation. Direct measurements of the beam current duration with a time resolution of 10 ps are very impressive. However only a small fraction of the beam electrons is recorded behind the small-diameter hole. When determining the duration of the real pulse of the runaway electron beam behind the entire surface of the anode foil, a collector with picosecond time resolution recorded the beam current at various points behind the all surface of the anode foil. Then, the actual duration of the beam pulse behind the anode was determined. Have you taken similar measurements? What was the duration of the beam current pulse when it exited through the hole, the diameter of which is equal to the diameter of your collector?
Do you know that, the duration of the runaway electron beam in air at atmospheric pressure of about 100 ns was recorded for the first time in 2005 at two experimental facilities in Yekaterinburg [Laser and Particle Beams, 2005, 23, 545–551.] and Tomsk [Technical Physics, 2006, Vol. 51, No. 5, pp. 637–643.]? It corresponded to the limiting resolution of the oscilloscopes used. As subsequent investigations showed, this duration corresponded to the real one recorded on such devices behind the entire surface of the anode foil.

NZ
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Nikolay Zubarev 2020-09-23 13:59
Victor Tarasenko 2020-09-22 16:09
Thank you very much for your pterentation. Direct measurements of the beam current duration with a time resolution of 10 ps are very impressive. However only a small fraction of the beam electrons is recorded behind the small-diameter hole. When


Thank you for interesting question.

The aim of this work was to determine the minimum duration of the runaway electron flows and (theoretically) to reveal the processes responsible for this duration. An increase in the window diameter, even in the case of a perfectly uniform RE flow, will increase the recorded duration of the current bursts due to the finite time of charge spreading from the collector. The real flow is inevitably inhomogeneous; moreover, it may include separate flows generated at different times in different sites of the cathode. This will also blur the recorded picture even more (for enlarged window), if we proceed from the purpose of the work, viz., determining the minimum duration of the runaway electron flow. I will not be surprised if the flow duration will reach 100 ps from the references you specified, ‚Äč‚Äčespecially without energy filtering.

To conclude, it is the use of a window of the minimum diameter that makes it possible to approach the consideration of the fundamental processes responsible for the generation and termination of the RE flow. Enlarging the collector window up to the entire surface of the anode foil only blurs this picture, which does not correspond to the purpose of the study.

VT
Victor Tarasenko 2020-09-23 16:35
Thank you very much for the reply.