Recycling enhancement with ne and qeffin high density discharges on JT-60U

Quantitative studies of recycling, particle flux and divertor plasma parameters have been made in high density L mode discharges on the JT-60U tokamak, with the ion ∇B drift towards the divertor. The diagnostics used were H α /D α photon emission detectors and a Langmuir probe array. Deuterium particle influx Φ(D α ) and particle outflux Ψ probe measurements were in fairly good agreement in both the inboard and the outboard divertors. The relationship between the particle recycling and the divertor plasma parameters was investigated to clarify the conditions under which a cold and dense divertor plasma was formed. Ψ(D α ) was raised from 10 22 to 10 24 s -1 with increasing e and q eff . Recycling in the inboard divertor was amplified substantially owing to the appearance of a third peak in the local recycling profile, displaced from the separatrix. Numerical results from an interpretative divertor code showed that the particle amplification factor G div in the inboard divertor was larger than that in the outboard divertor, and that both increased with increasing q eff and e . These results explain the observed dependence of the recycling on the parameters n e and q eff . The maximum electron density e,div in the outboard divertor was (4-7) × 10 19 m -3 , exceeding n e for high q eff discharges. In the same discharges, the divertor electron temperature T e,div was reduced to about 20 eV before MARFEs were observed. High e and q eff operation was favourable for obtaining a cold and dense divertor plasma