Real-time control of internal transport barriers in JET*

Abstract

In JET, advanced tokamak research mainly focuses on plasmas with internal transport barriers (ITBs) that are strongly influenced by the current density profile. A previously developed optimized shear regime with low magnetic shear in the plasma centre has been extended to deeply negative magnetic shear configurations. High fusion performance with wide ITBs has been obtained transiently with negative central magnetic shear configuration: H IPB98(y,2) ∼ 1.9, β N = 2.4 at I p = 2.5 MA. At somewhat reduced performance, electron and ion ITBs have been sustained in full current drive operation with 1 MA of bootstrap current: H IPB98(y,2) ∼ 1, β N = 1.7 at I p = 2.0 MA. The ITBs were maintained for up to 11 s for the latter case. This duration, much larger than the energy confinement time (37 times larger), is already approaching a current resistive time. New real-time measurements and feedback control algorithms have been developed and implemented in JET for successfully controlling the ITB dynamics and the current density profile in the highly non-inductive current regime.

Internal transport barrier triggering by rational magnetic flux surfaces in tokamaks

“…It is not yet clear which mechanism is acting to trigger the ITB. In any event, the role played by rational q surfaces supports the recent efforts undertaken to actively control the q profiles to trigger and sustain the ITB regime in tokamak [39].…”

Integrated scenario in JET using real-time profile control

“…This enhancement project undertaken under the European Development Fusion Agreement (EFDA) is now playing a decisive role in the operation of the JET device. In particular, ITER relevant plasma scenarios have been improved in JET in their reliability and stability thanks to the use of the real time control tools [8, 9,10]. This confirms that in ITER a very large effort will be devoted to the development of real time control tools.…”

Heating, current drive and energetic particle studies on JET in preparation of ITER operation

“…As a result, up to 3.4 MW of P LH was coupled in ITB plasmas with more than 15 MW of NBI and ICRF heating. This possibility to combine LH with strong additional power has allowed for the first time in JET, real-time control of ITB discharges for the duration of the heating pulse (up to 7.5 s) [21][22][23]. Quasi-stationary operation has thus been achieved in high performance discharges with a large bootstrap fraction.…”