Development of Penning ion gauge for in-situ measurement of neutral pressure in VEST

Abstract

A Penning Ion Gauge (PIG) has been developed to measure the responsive temporal changes of neutral pressure inside the magnetic fusion devices, and successfully operated in Versatile Experiment Spherical Torus (VEST). To check its reliabilities during in-situ operation, feasibility tests are conducted by specifically investigating both the penning discharge mode transition and the effect of magnetic field alignment on the penning discharge. The mode transition of penning discharge is clearly observed, confirming the developed PIG is applicable to the operation regime of VEST. The PIG is also designed to measure discharge current stably during magnetic field angle variation of upto 15∘. In addition, it has been verified that the operation range of PIG can be expanded by increasing inverse aspect ratio of the gauge cell geometry. Finally, the developed PIG is installed in VEST, measuring a millisecond-order temporal changes in neutral pressure within a range of 3×10−5 mbar to 1×10−3 mbar, under the magnetic field angle variation of up to 15∘. Finally, it is successfully measured rapidly evolving neutral pressures resulting from the plasma wall interaction during ohmic discharges in VEST.