Confinement Studies In TFTR

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Abstract
The paper describes the present (end of February 1985) status of the plasma confinement studies in the TFTR tokamak with emphasis on those with neutral beam injection (NBI). Recent improvements in the device capabilities have substantially extended operating parameters: BT increased to 4.0 T, Ip to 2.0 MA, injection power (Pb) to 5 MW with H° or D° beams, ne to 5 × 1019 m−3 and Zeff reduced to 1.4. With ohmic heating (OH) alone, the previously established scaling for gross energy confinement time (τE ∝ ne) has been confirmed at higher Ip and BT, and the maximum τE of 0.4 sec has been achieved. With NBI at Pb, substantially (by factor > 2) higher than POH, excellent power and particle accountability have been established. This suggests that the less-than-expected increase in stored energy with NBI is not due to problems of power delivery, but due to problems of confinement deterioration. τE is observed to scale approximately as Ip Pb−0.5 (independent of ne), consistent with previous L-mode scalings. With NBI we have achieved the maximum τE of 0.2 s and the maximum Ti (o) of 4.4 keV in the normal operating regime, and even higher Ti(o) in the energetic-ion regime with low-ne and low Ip operation.