Calibration and test of CsI scintillator ion detection system for tokamak magnetic field diagnosis based on laser-driven ion-beam trace probe (LITP)

As a new diagnostic method of core electromagnetic field, the laser-driven ion-beam trace probe (LITP), is expected to realize the first application of the advanced laser accelerator in magnetic confinement fusion. The detector of the LITP directly measures the distribution of the dispersed pulsed ions after they have passed through the core plasma (Yang 2014 Rev. Sci. Instrum.85 11E429). In such an environment of high temperature and radiation, the response and lifetime of the ion detector is very crucial. In this work, we have verified the feasibility of the LITP ion detection through systemic experiments. A CsI(Tl) scintillator coupled with an imaging system composed of optical lens and optical fiber array was calibrated on both the 4.5 MV Electrostatic Accelerator and the Compact LAser Plasma Accelerator (CLAPA) at Peking University. We found that the detectable proton density limit is achievable by using a tens of TW level laser system. The CsI(Tl) scintillator system was also tested on the HL-2A tokamak device to measure the real background noise caused by the hot plasma electrons and radiation. It was not damaged by the harsh environment after being placed in the tokamak for three days, and the background noise was completely suppressed when using an ultrafast camera and microsecond shutter. These calibrations and tests verified the feasibility of the LITP detector.