Neutral pressure measurement in TCV tokamak using ASDEX-type pressure gauges.

Abstract

Probing the neutral gas distribution at the edge of magnetic confinement fusion devices is critical for plasma exhaust studies. In the TCV tokamak, a set of ASDEX-type hot ionization pressure gauges (APGs) has been installed for fast, in situ measurements of the neutral pressure distribution in the TCV chamber. The APGs have been calibrated against Baratron pressure gauges (BPGs) for pressures ranging from less than one mPa to several hundred mPa. A correction to account for the residual pressure in the pumped torus is proposed to improve the measurement accuracy at low pressures. APG measurements in a series of plasma discharges with varied density ramp rates are analyzed and compared with the BPG pressure measurements. APG measurements feature a significantly faster time response and extend the BPG measurement range to lower pressures. Systematically higher neutral pressures measured with APGs compared to BPGs connected to the same TCV port are attributed to the BPG's slower time response and a nonuniform neutral distribution in gauge ports during the plasma discharge. The initial APG operations in TCV have been proven successful, which validates the APG as an adequate pressure measurement technique for the upcoming TCV divertor upgrades.