### Abstract

The impact of resonant magnetic perturbations (RMPs) on the power required to access H-mode is examined experimentally on MAST. Applying RMP in *n* = 2, 3, 4 and 6 configurations delays the L-H transition at low applied fields and prevents the transition at high fields. The experiment was primarily performed at RMP fields sufficient to cause moderate increases in ELM frequency, f_{mitigated}/ f_{natural} ∼ 3. To obtain H-mode with RMPs at this field, an increase of injected beam power is required of at least 50% for *n* = 3 and *n* = 4 RMP and 100% for *n* = 6 RMP. In terms of power threshold, this corresponds to increases of at least 20% for *n* = 3 and *n* = 4 RMPs and 60% for *n* = 6 RMPs. This 'RMP affected' power threshold is found to increase with RMP magnitude above a certain minimum perturbed field, below which there is no impact on the power threshold. Extrapolations from these results indicate large increases in the L-H power threshold may be required for discharges requiring large mitigated ELM frequency.

Original language | English |
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Article number | 075013 |

Journal | Plasma Physics and Controlled Fusion |

Volume | 57 |

Issue number | 7 |

DOIs | |

Publication status | Published - 18 Jun 2015 |

### Keywords

- ELM frequency
- L-H power threshold
- L-H threshold
- mitigated ELM frequency
- resonant magentic perturbations
- RMP

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## Cite this

*Plasma Physics and Controlled Fusion*,

*57*(7), [075013]. https://doi.org/10.1088/0741-3335/57/7/075013