Description
Tokamak fusion plasmas must be confined at high temperatures and pressures to achieve optimum fusion power output, but such conditions may be compromised by the onset of the neoclassical tearing mode (NTM) instability. NTMs are characterized by the appearance of ‘magnetic islands’, modifications to magnetic field line topology that are detrimental to plasma confinement and may even prematurely terminate the plasma in a disruption event. The rapid stabilisation of NTMs is therefore critical for the operation of an efficient and stable fusion device. One of the most successful methods of NTM control has been to target the magnetic islands with electron cyclotron current drive (ECCD), driving current to counteract destabilising current perturbations. However in some designs of tokamak (e.g. MAST-U) the plasma is ‘overdense’, restricting the use of ECCD, thus incentivising the development of alternative NTM control schemes.
One such alternative is electron Bernstein wave current drive (EBWCD). As well as having the ability to drive current in overdense plasmas, EBWCD could also do so more efficiently [1], but requires a more complex and sensitive launch process. Before now, NTM control by EBWCD has also not yet been demonstrated in experiment or in simulation. By implementing parameters calculated by the EBW ray tracing code ‘Crayon’ into the NTM simulation code ‘co-mre’, we seek to investigate whether EBW current drive may plausibly stabilise simulated NTMs found in MAST-U discharges. The results of this investigation should inform the development of NTM control schemes in future fusion devices such as STEP.
[1] HP Laqua, H Maassberg, NB Marushchenko, F Volpe, A Weller, (W7-AS Team), W Kasparek, and (ECRH-Group). Electron-bernstein-wave current drive in an overdense plasma at the Wendelstein 7-AS stellarator. Physical review letters, 90(7):075003, 2003.