Extending the range of measurement of thermal imaging diagnostics of a high-intensity pulsed ion beam

Abstract

Thermal imaging diagnostics was used as a surface temperature mapping tool to characterize the energy density distribution of a high-intensity pulsed ion beam. This approach was tested on the TEMP-6 accelerator (200–250 kV, 150 ns). The beam composition included carbon ions (85%) and protons, and the energy density in the focus was 5–12 J/cm2. Targets of stainless steel, titanium, brass, copper, and tungsten were examined. Our observations show that the maximum energy density measured with the thermal imaging diagnostics considerably exceeds the ablation threshold of the targets. An analysis of the overheating mechanisms of each target was carried out, including metastable overheating of the target to above its boiling temperature during rapid heating; formation, migration, and the subsequent annealing of fast radiation-induced defects in the target under ion beam irradiation. This expands the range of energy density measurement for this thermal imaging diagnostics from 2–3 J/cm2 up to 10–12 J/cm2 but introduces error into the results of measurement. For a stainless steel target, this error exceeds 15% at an energy density of more than 4 J/cm2. A method of correcting the results of the thermal imaging diagnostics is developed for a pulsed ion beam under conditions of intense ablation of the target material.

Diagnostics of Pulsed Beams of Electrons, Ions, and Atoms (Review)

“…When the effect of an HPIB with a duration of 150 ns was simulated it was obtained that the threshold ablation energy density is 1.1 J/cm 2 for a titanium target, 2.75 J/cm 2 for a stainless-steel target, and 4.8 J/cm 2 for a copper target [31] (see Table 1). Radiation defects that are formed in the target by the beam increase the threshold ablation energy density to 4.8-7.4 J/cm 2 due to the migration of defects from the ablation region and the subsequent annihilation [18]. In our experiments, the HPIB energy density did not exceed 4 J/cm 2 ; therefore, the ablation of the target material had no effect on TID readings when using targets of different metals.…”

“…In addition, when a target is irradiated with an ion beam, its overheating depends on its size and thickness. When the thickness of a large brass target decreases its overheating increases from 220 to 435% [18]. Overheating of a small target reaches 350% and does not change when its thickness changes.…”

“…The calibration dependence that was obtained from measurements of the HPIB energy density [18,19] can be used to correct the results of TID of HPIBs under the conditions of intense ablation of the target material. To do this, it is necessary to measure the crosssectional distribution of the HPIB energy density, when the beam is attenuated by a metal grid (the total energy density) and without using a grid (the absorbed energy density) (Fig.…”