JT-60U Experimental Report No. 51 (December 7, 1998)

Sustainment of high normalized beta at low safety factor regime

On JT-60U, the normalized beta (β_N) of 2.5-2.8 at low safety factor (q) regime of about 3 which is required on the ITER was successfully obtained for long period (Fig.1), by increasing triangularity (δ) up to 0.46 (Fig.2) and optimizing the current and pressure profiles to improve the stability.

The β_N limit determined by the stability was previously observed as decreased with decreasing q in the low q regime. The value of β_N achieved was higher than that required in the ITER-FDR (=2.2). The results would give a promising prospect to the reduced design ITER which requires higher stability (β_N).

The typical waveforms (Fig.3: plasma current=1 MA, toroidal field=2.1 T, q=3.3) show that β_N, D-D neutron production rate etc. were constantly sustained for more than 10 times the energy confinement time.

Fig.1	Fig.3
Fig.2:A cross-section of a δ = 0.46 plasma (E32218).