Measurement of hydrogen permeation due to atomic flux using permeation probe in the spherical tokamak QUEST

Abstract

Particle retention and recycling in plasma fusion devices are generally associated with the diffusion of atomic hydrogen into the materials. The resulted permeation of atomic hydrogen is known as plasma driven permeation (PDP). This permeation may also be significant, even in the walls, which are not directly exposed to the plasma. Under similar conditions, the permeation flux ( Γ perm) of hydrogen through a 30 μm thick Ni membrane heated at 412–575 K has been measured in the spherical tokamak QUEST. Γ perm is being measured during the scans of different operating parameters like RF power ( P RF), chamber pressure ( P chamber), discharge widths ( τ dis) and vertical magnetic field ( B Z). Simultaneously edge plasma density and spectral intensities of atomic (Balmer) lines and molecular (Fulcher) bands have been compared with the permeation measurements. A linear relationship has been established between the time integrated Γ perm i.e. permeation fluence ( Q perm) and the time integrated H α intensity i.e. H α fluence ( Q α). Q perm also shows a strong relationship with the edge plasma density and various spectral fluences. The obtained results are discussed for exploring the applicability of the permeation probes in measuring the atomic flux near the first walls.