Understanding the effect resonant magnetic perturbations have on ELMs

Kirk, A.; Chapman, I. T.; Evans, T.E.; Ham, Christopher; Harrison, J.; Huijsmans, G. T. A.; Liang, Y.; Liu, Y. Q.; Loarte, A.; Suttrop, W.; Thornton, A.

doi:10.1088/0741-3335/55/12/124003

Cited by 49 publications

(67 citation statements)

References 83 publications

(161 reference statements)

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“…Vacuum calculations have been used to design the in-vessel coil set, suggesting that the RMPs in ITER will be able to achieve the empirical conditions found to be necessary for achieving ELM suppression in present day devices [29]. The effect of RMPs on ELM behaviour and the pedestal structure has been investigated in many tokamaks in a wide range of pedestal conditions, summarised in references [30] and [31]. It is important to understand why ELM mitigation is achieved at high collisionality plasmas [17,10] -that is to say the ELM frequency increases significantly and peak heat flux reduces commensurately, but ELM events persistwhereas at low collisionality, complete ELM suppression has been achieved.…”

Section: Understanding the Effect Of Resonant Magnetic Perturbationsmentioning

confidence: 99%

Advances in understanding and utilising ELM control in JET

Chapman

Luna²,

Lang

et al. 2016

Plasma Phys. Control. Fusion

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Edge localised mode (ELM) control may be essential to develop ITER scenarios with a reasonable lifetime of divertor components, whilst ELM pacing may be essential to develop stationary ITER scenarios with a tungsten divertor. Resonant magnetic perturbations (RMPs) have mitigated ELMs in high collisionality plasmas in JET. The efficacy of RMPs in mitigating the ELMs is found to depend on plasma shaping, with the change in magnetic boundary achieved when non-axisymmetric fields are applied facilitating access to small ELM regimes. The understanding of ELM pacing by vertical kicks or pellets has also been improved in a range of pedestal conditions in JET (T 0.7 ped = -1.3 keV) encompassing the ITER-expected domain (1.4 N β = -2.4, H 98(y, 2) = 0.8-1.2, f 0.7 GW ∼ ). ELM triggering is reliable provided the perturbation is above a threshold which depends on pedestal parameters. ELM triggering is achieved even in the first 10% of the natural ELM cycle suggesting no inherent maximum frequency. At high normalised pressure, the peeling-ballooning modes are stabilised as predicted by ELITE, necessitating a larger perturbation from either kicks or pellets in order to trigger ELMs. Both kicks and pellets have been used to pace ELMs for tungsten flushing. This has allowed stationary plasma conditions with low gas injection in plasmas where the natural ELM frequency is such that it would normally preclude stationary conditions.

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Section: Understanding the Effect Of Resonant Magnetic Perturbationsmentioning

confidence: 99%

Advances in understanding and utilising ELM control in JET

Chapman

Luna²,

Lang

et al. 2016

Plasma Phys. Control. Fusion

Self Cite

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“…Extrapolation from present measurements suggest that the natural ELM frequency in ITER will vary from ~ 1 Hz for discharges with a plasma current I P = 15MA to ~7Hz for I P = 5MA. Avoidance of both damage to Plasma Facing Components (PFC) and Tungsten (W) accumulation leads to a requirement that the ELM frequency is increased by a factor of ~3-40 over the natural ELM frequency as I P is increased from 5-15MA (see [2] and references therein). Hence a mechanism is required to either increase the ELM frequency or to eliminate ELMs altogether accompanied by sufficient particle transport in order to avoid W accumulation.…”

Section: Introductionmentioning

confidence: 99%

Effect of resonant magnetic perturbations on low collisionality discharges in MAST and a comparison with ASDEX Upgrade

Kirk¹,

Suttrop²,

Liu³

et al. 2015

Nucl. Fusion

145

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Sustained ELM mitigation has been achieved on MAST and AUG using RMPs with a range of toroidal mode numbers over a wide region of low to medium collisionality discharges. The ELM energy loss and peak heat loads at the divertor targets have been reduced. The ELM mitigation phase is typically associated with a drop in plasma density and overall stored energy. In one particular scenario on MAST, by carefully adjusting the fuelling it has been possible to counteract the drop in density and to produce plasmas with mitigated ELMs, reduced peak divertor heat flux and with minimal degradation in pedestal height and confined energy. While the applied resonant magnetic perturbation field (b r res ) can be a good indicator for the onset of ELM mitigation on MAST and AUG there are some cases where this is not the case and which clearly emphasise the need to take into account the plasma response to the applied perturbations. The plasma response calculations show that the increase in ELM frequency is correlated with the size of the edge peelingtearing like response of the plasma and the distortions of the plasma boundary in the Xpoint region. In many cases the RMPs act to increase the frequency of type I ELMs, however, there are examples where the type I ELMs are suppressed and there is a transition to a small or type IV ELM-ing regime.

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“…Various techniques have been envisaged for the purpose of mitigating or suppressing type-I ELMs, such as the pellet pacing [2], the vertical kicking of the plasma position [3], and finally the application of resonant magnetic perturbation (RMP) fields [4]. So far RMPs are probably the most exploited technique, having been applied for ELM control on many present day tokamak devices where H-mode plasmas are achieved [5].…”

Section: Introductionmentioning

confidence: 99%

Toroidal modelling of RMP response in ASDEX Upgrade: coil phase scan, q₉₅ dependence, and toroidal torques

et al. 2016

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. A systematic investigation is carried out, considering various plasma and coil configurations as in the ELM control experiments. The low q plasmas, with q 95 ∼ 3.8 ( q 95 is the safety factor q value at 95% of the equilibrium poloidal flux), responding to low n (n is the toroidal mode number) field perturbations from each single row of the ELM coils, generates a core kink amplification effect. Combining two rows, with different toroidal phasing, thus leads to either cancellation or reinforcement of the core kink response, which in turn determines the poloidal location of the peak plasma surface displacement. The core kink response is typically weak for the n = 4 coil configuration at low q, or for the n = 2 configuration but at high q (q 95 ∼ 5.5). A phase shift of around 60 degrees for low q plasmas, and around 90 degrees for high q plasmas, is found in the coil phasing, between the plasma response field and the vacuum RMP field, that maximizes the edge resonant field component. This leads to an optimal coil phasing of about 100 (-100) degrees for low (high) q plasmas, that maximizes both the edge resonant field component and the plasma surface displacement near the X-point of the separatrix. A strong parallel sound wave damping moderately reduces the core kink response but has minor effect on the edge peeling response. For low q plasmas, modelling shows that both the resonant electromagnetic torque and the neoclassical toroidal viscous (NTV) torque (due to the presence of 3D magnetic field perturbations) contribute to the toroidal flow damping, in particular near the plasma edge region. For high q plasmas, however, significant amount of torque is also produced in the bulk plasma region, and the contributions from the electromagnetic, the NTV, and the torque associated with the Reynolds stress, all play significant roles.

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Understanding the effect resonant magnetic perturbations have on ELMs

Cited by 49 publications

References 83 publications

Advances in understanding and utilising ELM control in JET

Advances in understanding and utilising ELM control in JET

Effect of resonant magnetic perturbations on low collisionality discharges in MAST and a comparison with ASDEX Upgrade

Toroidal modelling of RMP response in ASDEX Upgrade: coil phase scan, q₉₅ dependence, and toroidal torques

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Understanding the effect resonant magnetic perturbations have on ELMs

Cited by 49 publications

References 83 publications

Advances in understanding and utilising ELM control in JET

Advances in understanding and utilising ELM control in JET

Effect of resonant magnetic perturbations on low collisionality discharges in MAST and a comparison with ASDEX Upgrade

Toroidal modelling of RMP response in ASDEX Upgrade: coil phase scan, q95 dependence, and toroidal torques

Contact Info

Product

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Toroidal modelling of RMP response in ASDEX Upgrade: coil phase scan, q₉₅ dependence, and toroidal torques