Edge Localized Modes
The steep edge gradients (of density and temperature) associated with an H-mode lead to quasi-periodic violent relaxation phenomena, known as Edge Localized Modes (ELMs), which have a strong impact on the surrounding vessel. [1] [2]
Physical mechanism
The physical mechanism of ELMs has not been fully clarified. Several possible explanations have been put forward:
- Nonlinear interchange modes [3]
- Coupled peeling-ballooning modes [4][5]
- Self-Organised Criticality [6]
- Flux surface peeling [7]
- Peeling modes [8]
ELMs and machine operation
The occurrence of an ELM leads to a significant expulsion of heat and particles, with deleterious consequences for the vessel wall and machine operation. Although Quiescent H-modes exist (without ELMs), [9] they are generally considered not convenient due to the accumulation of impurities. To achieve steady state, an ELMy H-mode is preferred and this mode of operation is proposed as the standard operating scenario for ITER, thus converting ELM mitigation into a priority. [10]
References
- ↑ H. Zohm, Edge localized modes (ELMs), Plasma Phys. Control. Fusion 38 (1996) 105-128
- ↑ D.N. Hill, A review of ELMs in divertor tokamaks, Journal of Nuclear Materials 241-243 (1997) 182-198
- ↑ A Takayama and M. Wakatani, ELM modelling based on the nonlinear interchange mode in edge plasma, Plasma Phys. Control. Fusion 38 (1996) 1411-1414
- ↑ J.W. Connor et al, Magnetohydrodynamic stability of tokamak edge plasmas, Phys. Plasmas 5 (1998) 2687
- ↑ P.B. Snyder et al, Edge localized modes and the pedestal: A model based on coupled peeling–ballooning modes, Phys. Plasmas 9 (2002) 2037
- ↑ R. Sánchez et al, Modelling of ELM-like phenomena via mixed SOC-diffusive dynamics, Nucl. Fusion 43 (2003) 1031-1039
- ↑ E.R. Solano et al, ELMs and strike point jumps, Journal of Nuclear Materials 337-339 (2005) 747-750
- ↑ C.G. Gimblett, Peeling mode relaxation ELM model, AIP Conf. Proc. 871 (2006) 87-99
- ↑ K.H. Burrell et al, Advances in understanding quiescent H-mode plasmas in DIII-D, Phys. Plasmas 12 (2005) 056121
- ↑ M.R. Wade, Physics and engineering issues associated with edge localized mode control in ITER, Fusion Engineering and Design 84, Issues 2-6 (2009) 178-185