Regime of Improved Confinement and High Beta in Neutral-Beam-Heated Divertor Discharges of the ASDEX Tokamak

A new operational regime has been observed in neutral-injection-heated ASDEX divertor discharges. This regime is characterized by high β_p values comparable to the aspect ratio A (β_p<~0.65A) and by confinement times close to those of Ohmic discharges. The high-β_p regime develops at an injection power ≥1.9 MW, a mean density n̅ _e>~3×10¹³ cm^-3, and a q(a) value ≥2.6. Beyond these limits or in discharges with material limiter, low β_p values and reduced particle and energy confinement times are obtained compared to the Ohmic heating phase.