Speaker
Dr
Florian Koechl
(Vienna University of Technology, Institute of Atomic and Subatomic Physics)
Description
The dynamics of the access to and exit from high QDT regimes in the H-mode confinement regime in ITER is expected to be qualitatively different to present experiments: neutral fuelling is much less effective, Psep/PL-H < 2.0 even in stationary QDT ~ 10 burning conditions, the density evolution determines not only PL-H but also Palpha which in turn affects dWth/dt after a transition, and plasma position control may be challenging in case of an unexpected back transition to L-mode. In addition, the presence of W may impose additional operational constraints due to possible core accumulation and increased radiation during transients (possibility of a sudden return to L-mode confinement, plasma-wall contact and/or a disruption). To determine under which conditions the transition to stationary high QDT H-mode regime and its safe termination can be achieved, how the plasma evolution to/from H-mode can be optimised, and to assess the problem of possible core W accumulation, modelling studies have been carried out with the JINTRAC suite of codes, simulating the core and core+SOL plasma evolution for the entire period of density evolution following transitions to/from H-mode in the ITER 15 MA/5.3 T and 7.5 MA/2.65 T scenarios.
Simulation scans for the L-H transition have been performed with varying target waveforms for the density evolution, applying a feedback on pellet fuelling. Depending on boundary and operational conditions, limits for the density ramp rate and/or a delay time before the application of increased fuelling could be established. Below these limits, the plasma remains in dithering conditions with Psep~PL-H for a long while before it enters a good quality H-mode regime at Psep>PL-H, leading to increased flux consumption and a significantly reduced burn duration. In extreme cases, the plasma never reaches high performance H-mode and returns back to L-mode.
The back transition to L-mode has also been assessed. The fast reduction in core energy would cause Psep to remain close to PL-H. The plasma would then not immediately reach L-mode but stay in H-mode for a while, followed by a dithering phase before the ETB completely disappears. The energy loss could become accelerated though by an immediate transition to dithering mode e.g. after a strong MHD event. Subsequent W accumulation could then lead to an immediate transition to L-mode and a disruption.
| Country or International Organisation | Austria |
|---|---|
| Paper Number | TH/P3-24 |
Primary author
Dr
Florian Koechl
(Vienna University of Technology, Institute of Atomic and Subatomic Physics)
Co-authors
Dr
Alberto Loarte
(ITER Organization)
Dr
Alexei Polevoi
(ITER Organization)
Dr
Andrei S. Kukushkin
(ITER Organization)
Dr
Gabriella Saibene
(Fusion for Energy Joint Undertaking (F4E))
Dr
Roberta Sartori
(Fusion for Energy Joint Undertaking (F4E))
Dr
Vassili Parail
(CCFE)
