Development of advanced tokamak operation scenarios in JT-60U and JT-60SA

Integrated high performance was achieved in a wall-stabilized reversed shear plasma, and the high values of HH98(y,2) = 1.7, βN = 2.7, fGW = 0.87, fBS = 0.9, and fNI = 0.95 were simultaneously realized at the ITER/DEMO-relevant value of q95 = 5.3. The βN value achieved was above the no-wall βN limit of 1.9 and close to the ideal-wall βN limit of 2.9 in that discharge. The βN was limited by the appearance of the Resistive Wall Mode (RWM) when the toroidal rotation velocity at the q = 3 surface decreased to below the critical velocity. Another discharge realized a fully relaxed current profile at the high value of fBS = 0.5 in a fully non-inductive Current Drive (CD) condition at q95 = 5.8 through use of a lower-hybrid CD and Neutral Beam (NB) CDs with bootstrap current. Integration of operation scenarios to ensure steady-state high performance is a major mission with the JT-60SA. A DEMO-equivalent value of βN = 4.3 is being aimed at utilizing highly shaped configurations, closely-placed conducting walls, low ripple rates, and RWM control coils. Steady-state q profiles can be maintained using an off-axis CD resulting from a negative-ion based NB and bootstrap current for 60-100 s. An operation scenario that supports building up the Ip with less consumption of the magnetic flux is a key issue in the realization of a compact DEMO SlimCS. Fully non-inductive buildup of Ip and recharging of the Ohmic coil current were demonstrated utilizing the JT-60U. Development of an overall operation scenario from the buildup of the Ip to steady sustainment of a high performance plasma is an important challenge with the JT-60SA. (author)