Onset and Control of Neo-classical Tearing Modes on JET

摘要

Neo-classical tearing Modes are aa critical issue for Next Step devices. They occur at #beta#_N>~2 in ELMy H-mode. The modes occur above a critical #beta#_N when an MHD perturbation, such as a sawtooth, triggers a seed island with large enough size. They degrade confinement and can elad to disruptions. Critical issues for Next Step devices are extrapolating onset criteria, which requires detailed understanding of the mechanisms involved, and developing control techniques, which are liekly to be reuired. NTMs have been clearly identified on JET in prevous work [1]. This paper reports on further experiments examining onsetcriteria, which requires detailed understanding ofthe mechanisms involved, and developing control techniques, which are likely to be required. NTMs have bee nclearly identified on JET in previous work [1]. This paper reports on further experiments examining onset mechanisms, with fast magnietic and ECE diagnostic, improving onset crieteria scaling data, and investigating control of the modes with IOn Cyclotron Current Drive. Present studies focus more on the 3,2 mode, which occurs at lower #beta#_N, than the more catastrophic 2,1 mode, and is therefore easier to study experimentally, and more likely to occur in Next Step devices.