Development and Test Results of a Modified Crystal Cathode Pressure Gauge for KSTAR

Neutral pressure measurements in the tokamak divertor region can support to control the heat flux and help to understand the plasma behavior in the divertor region. In addition, as KSTAR has recently replaced carbon-based divertors by tungsten-based ones, similar to ITER, understanding how neutral pressure in the divertor region of KSTAR affects the plasmas can provide valuable information to develop ITER operation scenarios. For these reasons, six crystal cathode pressure gauges (CCPG) [Wenzel, U., et al., Rev. Sci. Instrum. 89 033503 (2018)] are planned to be installed in the KSTAR divertor region. Since accessibility to these CCPGs will be limited after installation of the new divertors, we have modified the conventional LaB₆ crystal cathode with the aim of achieving better mechanical stability. Due to its higher heat capacity compared to the conventional one, the modified cathode has a slower response time for controlling the electron emission rate, which adversely affect the measurements. We are developing an improved feedback control algorithm to compensate for the slower response time and will present the test results together with the modified cathode design.