Shot-to-shot reproducibility of a self-magnetically insulated ion diode

Abstract

In this paper we present the analysis of shot to shot reproducibility of the ion beam which is formed by a self-magnetically insulated ion diode with an explosive emission graphite cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: the first pulse is of negative polarity (300-500 ns, 100-150 kV), and this is followed by a second pulse of positive polarity (150 ns, 250-300 kV). The ion current density was 10-70 A/cm(2) depending on the diode geometry. The beam was composed from carbon ions (80%-85%) and protons. It was found that shot to shot variation in the ion current density was about 35%-40%, whilst the diode voltage and current were comparatively stable with the variation limited to no more than 10%. It was shown that focusing of the ion beam can improve the stability of the ion current generation and reduces the variation to 18%-20%. In order to find out the reason for the shot-to-shot variation in ion current density we examined the statistical correlation between the current density of the accelerated beam and other measured characteristics of the diode, such as the accelerating voltage, total current, and first pulse duration. The correlation between the ion current density measured simultaneously at different positions within the cross-section of the beam was also investigated. It was shown that the shot-to-shot variation in ion current density is mainly attributed to the variation in the density of electrons diffusing from the drift region into the A-K gap.

Experimental evidence of energetic neutrals production in an ion diode

“…1) in the self-magnetically insulated diode in double pulse mode is very poor, the standard deviation is 20-25% in a set of 50-100 shots, whilst at the same time variations in the output parameters of the Blumlein generator do not exceed 10% [12]. Time interval between measurements was 10 s. However, the reproducibility of PIB energy density for the same diode is much better.…”

“…The preliminary research showed the insignificant correlation of the ion current density, formed in different parts of the strip planar diode simultaneously [12]. We measured the ion current density by two separate Faraday cups, installed at the equal distance from the planar diode, but at the distance from each other.…”

“…To analyze the composition of the ion beam formed by our diode, a time-of-flight diagnostic, based on a magnetically insulated Faraday cup was used [11]. The shot-to shot repeatability of acceleration voltage for a set of 100-200 pulses was good with the standard deviation not exceeding 6-7% [12].…”

“…The infrared imaging diagnostics allows one to measure the full energy and energy density distribution of the ion beam with a high space resolution, but a time interval between the measurements of 100 s is unavoidable. The shot to shot stability of the ion current density [12] was measured with the time interval of 9-10 s, which corresponds to normal pulse repetition rate of the TEMP-4M accelerator.…”

The influence of a shield on intense ion beam transportation

“…The shot to shot variation in the accelerating voltage for 100-200 pulses does not exceed 6-7% (Pushkarev et al, 2012b). The beam is composed of C + ions (80-85%) and protons; the beam energy density is 0.5-5 J/cm 2 (for different types of diode); the pulse frequency is 5-10 pulses per minute.…”