Progress in development of ITER diagnostic pressure gauges and status of interfaces with ITER components

Abstract

Neutral gas pressure is one of the main parameters for a basic control of ITER operation. Diagnostic Pressure Gauges (DPGs) shall provide pressure measurements in the range from 10−4 Pa to 20 Pa with an accuracy of 20% and a time resolution of 50 ms. In total 52 DPG sensor heads will be installed in 4 lower ports, 4 divertor cassettes and 2 equatorial ports. The overall DPG system has 15 interfaces with various systems and components of ITER. The DPG system is being developed including sensor head and front-end electronics. A test campaign aiming at validation of the system baseline design is currently ongoing. The measurement performance of a DPG sensor head prototype has been investigated for various parameters, such as electrode potentials, transparency of the acceleration grid and electron emission current demonstrating the possibility to measure pressures up to 20 Pa. Emission properties of several material candidates for the filament (hot cathode) have been studied during approximately three months of continuous operation. Filament samples made of tungsten with 2% doping of ThO2and tungsten alloy with 26% of rhenium coated with Y2O3 demonstrated most promising results. These cathodes required lowest heating currents for fixed electron emission current. Mechanical tests of these samples showed no detectable deformations for maximum heating currents in transient magnetic fields of up to 8 T. The already obtained as well as future test results will be used for further design optimization and integration of the DPG system into the ITER environment.