Time evolution of the two-dimensional expansion velocity distributions of the cathode plasma in pulsed high-power diodes

Abstract

A combination of electrical and optical diagnostics has been used to investigate the time evolution of the two-dimensional expansion velocity distributions of the cathode plasma in pulsed high-power diodes. The perveance model based on the Child-Langmuir law was used to calculate the expansion velocity of the diode plasmas from voltage and current profiles. Additionally, a four-channel high speed framing camera was used to observe the formation and subsequent movement of the cathode plasma. More accurate and valuable information about the dynamics of the cathode plasma was also acquired by utilizing the digital image processing methods. Results from the experiments and theoretical analysis were compared. In this paper, the experiments have been performed using a high-voltage pulse generator with 200 kV output voltage and 110 ns pulse duration. Current densities up to 440 A/cm2were produced. The observation of the cathode plasma expansion in transverse direction indicated that the diode current was cathode-limited in the current rising stage (the first 60 ns of the current pulse). The perveance model should be modified taking in account the time dependent expanding plasma surface (i.e., not the whole cathode surface) for this period. The velocity in the direction parallel to the cathode surface (transverse velocity) was much larger than that in the direction perpendicular to the cathode surface (longitudinal velocity), and further, it dropped from 90 cm/μs to nearly 20 cm/μs rapidly. It was shown that, during the current flattop stage, the plasma filled out all the surface of cathode and the diode current was space-charge-limited. The values of the transverse velocity and longitudinal velocity were nearly the same and decreased relatively slowly. The satisfactory coincidence of experimental and calculated (both were in the range of 6–8 cm/μs) values of the cathode plasma expansion velocities was obtained.

Analysis of Landau damping in radially inhomogeneous plasma column

“…[1][2][3] Some important applications can be found in various areas such as high power microwave (HPM) devices, [4,5] industrial plasmas, plasma diagnosis [6] and plasma limiters. [7,8] The latter is used in protective devices against HPM and pulses with very short rising time. The wave-plasma interaction gives rise to different phenomena including absorption, reflection, scattering and transmission of the incident EM wave [9][10][11][12][13] as well as mode excitation, radiation and instability production in plasma.…”

Application of high speed frame camera on the intense electron beam accelerator: An overview

“…High speed framing camera (HSFC) is widely used in the areas of hypervelocity impact studies, ultrasonic flame propagation, laser ablation, sparks in electrical switches, and short time physics (Koing et al, 2005;Mark et al, 2010;Sun et al, 2013;Yang et al, 2013). So in the field of intense electron beam accelerator (IEBA), HSFC could be assembled to visualize the evolution of discharging and plasma generation phenomenon in nanosecond regime.…”

“…For the electrical delay method, a transmission line (TL) is usually used to delay the time of the electron emission, and the transmission time of TL should be larger than the compensated time (Yang et al, 2013). Now, if the load voltage of IEBA that is used to generate electron beam is used as trigger signal source, and to compensate the time (called compensated time), which is defined the sum of the trigger signal processing time and the IDT of the HSFC, there are two basic methods to realize the synchronization between HSFC and IEBA.…”