A Technique for measurement of angular and time resolved energetic hydrogen flux to the walls in fusion devices

Abstract

A new type of diagnostic which directly measures the radial atomic hydrogen flux to the liner has been installed on TEXTOR. The diagnostic is based on hydrogen permeation through a well conditioned and characterized thin iron membrane. It can discriminate between molecular and atomic hydrogen species impinging on the liner. The permeant signal is proportional to the product of the sticking factor with the atomic hydrogen flux impinging on the upstream surface integrated over the energy spectrum of the incoming particles. The accuracy of the inferred flux magnitude to the liner is 20% for relative measurements and approximately threefold for absolute measurements. To date approximately 700 discharges have been monitored under typical tokamak operating conditions. Typical atomic fluxes are in the range 1013 to 1015 atoms cm−2 s−1 assuming a H0-on-iron sticking coefficient of unity. The probe time response is of the order of 0.3 to 0.6 s depending on the membrane operating temperature and the magnitude of the impinging flux. The dependence of the atomic hydrogen flux to the liner on the quantity of hydrogen, deuterium or methane injected into the plasma boundary region in the vicinity of the probe and on the RF heating power injected into the discharge are discussed.