Effect of RMPs on tokamak equilibrium and stability
Event details
| Date | 10.06.2015 |
| Hour | 10:30 › 11:30 |
| Speaker | Prof. C.J. Ham, CCFE, Culham Science Center, Abingdon, UK |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
Non-axisymmetric resonant magnetic perturbation (RMP) coils applied to mitigate or suppress ELMs produce a very small field compared to the axisymmetric magnetic field and yet they cause significant changes to both the equilibrium and stability of the plasma. Non-axisymmetric simulations are shedding new understanding on how these changes in stability influence the observed increase in ELM frequency or complete stabilization (suppression) of ELMs.
The required non-axisymmetric equilibria have been modelled using stellarator equilibrium codes. We have compared the stochastic structures and magnetic islands that form in HINT2 equilibria with VMEC, where nested flux surfaces are assumed. It is observed that displacement at the X-point, caused by the RMP field, is correlated to density pump out. We calculate the X-point displacement for an ITER equilibrium n=3 and n=4 RMPs applied. We also investigate potential experimental issues raised by applying RMP fields.
We have also calculated Mercier stability and infinite-n ballooning stability using COBRA. We find that Mercier modes can become unstable at rational surfaces due to the applied RMP fields. The most unstable ballooning mode becomes more unstable with RMPs applied. This indicates that RMPs act to destabilize ballooning modes and we would expect the ELM frequency to increase i.e. ELM mitigation.
This work was part-funded by the RCUK Energy Programme and the EU Horizon 2020 programme.
The required non-axisymmetric equilibria have been modelled using stellarator equilibrium codes. We have compared the stochastic structures and magnetic islands that form in HINT2 equilibria with VMEC, where nested flux surfaces are assumed. It is observed that displacement at the X-point, caused by the RMP field, is correlated to density pump out. We calculate the X-point displacement for an ITER equilibrium n=3 and n=4 RMPs applied. We also investigate potential experimental issues raised by applying RMP fields.
We have also calculated Mercier stability and infinite-n ballooning stability using COBRA. We find that Mercier modes can become unstable at rational surfaces due to the applied RMP fields. The most unstable ballooning mode becomes more unstable with RMPs applied. This indicates that RMPs act to destabilize ballooning modes and we would expect the ELM frequency to increase i.e. ELM mitigation.
This work was part-funded by the RCUK Energy Programme and the EU Horizon 2020 programme.
Practical information
- Informed public
- Free
Organizer
- Prof. P. Ricci
Contact
- Prof. P. Ricci