ITER pressure gauges

The neutral gas outside the boundary of a fusion plasma has important influence on the plasma’s behaviour. An important parameter is the flux density of the neutral gas that crosses the plasma boundary or enters the pump ducts.

In order to achieve sufficient temporal and spatial resolution, the measurements have to be taken inside the plasma vessel. The harsh environment there is characterized by strong and varying magnetic fields, sources of strong background noise, neutral pressures ranging from 10^-4 to 20 Pa, and heavy vibrations.

The gauges foreseen for ITER are special hot cathode ionization gauges, known as “ASDEX pressure gauges”. They were first developed at IPP for ASDEX and were modified to meet the special requirements of ITER. This comprises in particular the extension of the operational parameter space to higher neutral gas pressures, higher magnetic fields and strong neutron and gamma radiation as well as extending their lifetime during long plasma discharges.

Current developments concentrate on the further extension of the measurement range to higher pressures up to 50 Pa and the optimization of the emitter in collaboration with the young investigator’s group plasma boundary models. These developments are motivated by the needs of a new generation of fusion experiments such as SPARC, with whom cooperation is coordinated through the project International Tokamak Collaboration (ITC).