H-alpha photon yield in fuelling of tokamaks

Mcneill, D. H.

doi:10.1016/0022-3115(89)90315-2

Cited by 54 publications

(38 citation statements)

References 11 publications

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“…As a monitor for the pellet ablation we adopt the diode recorded ablation radiation D α signal. This radiation intensity is known to represent fairly well the time-varying pellet particle ablation rate dmP dt ≡ṁ P [13]; this approximation was also well confirmed by our earlier pellet ELM pacing and fuelling studies [14]. For this study we simplify the picture assuming in the ELM case the Mirnov signal is stemming from the mode activity in the edge region closest to the coil.…”

Section: Resultssupporting

confidence: 71%

Investigation of pellet-triggered MHD events in ASDEX Upgrade and JET

et al. 2008

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To get deeper insight into the MHD activity triggered by pellets we extended our previous analyses of standard type-I ELMs to pellets injected into discharge phases of the following types: Ohmic, L-mode, type-III ELMy H-mode, ELM-free, radiative edge scenarios with type-I ELMs, the quiescent H (QH)-mode regime. It turns out that pellet injection generally creates a strong, local perturbation of the MHD equilibrium in the ablation region and even beyond. Regarding the triggering of ELMs, this initial perturbation can damp out, indicating that the plasma is stable in the corresponding regime even for finite-size perturbations. This behaviour is observed not only in Ohmic and L-mode phases but also in the QH-mode where the edge harmonic oscillations (EHO) appear to keep the edge within or at the boundary of a stable regime. In case the plasma is prone to ELM growth, the large amplitude of the pellet perturbation can trigger the event even in situations where modes appear to be still linearly stable.The non-linear character of the ELM trigger process is highlighted also by the subsequent explosive growth of these events. For edge plasma conditions characterised by higher resistivity the growth time of spontaneously occurring ELMs increases when the plasma changes from the type-I into the type-III regime. Pellet-triggered ELMs, however, maintain the fast rise times otherwise typical for the hot edge type-I regime. In the discussion section we attempt to relate these observations also to core mode activity like neoclassical tearing modes or snakes. Data were taken from ASDEX Upgrade and JET.Pellet triggering of mode activity can be shown to be a quite universal phenomenon, which, however, only for the case of ELMs can be unambiguously attributed to prompt direct excitation by the pellet.

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Section: Resultssupporting

confidence: 71%

Investigation of pellet-triggered MHD events in ASDEX Upgrade and JET

et al. 2008

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“…It is clear that pellets trigger ELMs irrespective of their injection path as also LFS injection was found to trigger ELMs. A perturbation strength monitor is provided by the D α ablation radiation measured proportional to the pellet particle ablation rate dN/dt(t) [13]. Using the information derived by a fast framing camera system on the pellet motion in the plasma or by comparing the measured dN/dt(t) with modeling results it is possible to derive dN/dt( r) (with r(t) the pellet position) [14].…”

Section: Local Impact and Elm Dynamics Featuresmentioning

confidence: 99%

Local 3D perturbation experiments for probing the ELM stability

Lang¹,

Hobirk²,

Horton³

et al. 2005

Czech J Phys

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Empirical estimates indicate that the transient divertor power load induced by type-I ELMs in the standard H-mode ITER scenario might result in intolerably short target life times. Significant experimental effort has been put on the exploration of recipes to avoid or at least mitigate the ELM size by external intervention. Experimental ELM mitigation studies (and related modeling) are of interest from different points of views. First, the active intervention gives access to new, externally controlled ELMy discharge scenarios and ELM diagnostic techniques. Second, the ELM response on the type and amplitude of the applied perturbation provides additional hints on the ELM stability. Third, mitigated ELMs, possibly different from spontaneous ones, and their scaling are of interest 'per se', in case that mitigation is to be finally applied in ITER. In this contribution we report on ELM mitigation results in ASDEX Upgrade, where we further restrict the scope to those methods involving 3D, local non-axisymmetric perturbations.Perturbations applied were cryogenic pellet injection, localized supersonic pulsed injection of D gas and laser blow off from targets carrying C or Al micro pellets. The corresponding perturbations differ strongly both in the space and time domain and provide an instrument to probe the local stability. Varying the parameters of the external * ) perturbations by e.g. changing the amount of injected material or the injection speed we mapped out the ELM trigger threshold with high spatial and temporal resolutions. : 52.55.Fa, 52.35.py, 52.55.Rk PACS

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“…The time evolution of the pellet ablation is monitored by the D α radiation from the ablation cloud [5]. So far we observe that every injected pellet triggers its own type-I ELM which occurs on a short time scale (t os of the order 100 µs) after the pellet crosses the plasma edge.…”

Section: Experimental Approachmentioning

confidence: 99%

Investigations on the ELM cycle by local 3D perturbation experiments

Lang

Gál

Hobirk

et al. 2006

Plasma Phys. Control. Fusion

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An experimental study is performed to investigate the underlying physics of ELM triggering by imposing local perturbations at the plasma edge. Deuterium is injected during type-I ELMy H-mode phases by solid small pellets or as a supersonic gas jet. In both cases the repetition rate is small compared to the intrinsic ELM frequency, aiming for a small perturbation of the intrinsic ELM cycle. Active triggering of ELMs requires a density perturbation in the gradient region about 1 cm inside the separatrix (measured at horizontal mid plane), a condition that is achieved by pellets of any size and speed but not even by the strongest available gas jets. The pellet-induced triggering of ELMs occurs always when pellets reach the H-mode barrier region. A density perturbation produced by a gas jet remains localized at the separatrix, and even if larger by a factor of at least 100, it is not sufficient to trigger an ELM. No significant dependence was found of the ELM size on the ELM onset time, measured from the onset of the previous ELM.

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H-alpha photon yield in fuelling of tokamaks

Cited by 54 publications

References 11 publications

Investigation of pellet-triggered MHD events in ASDEX Upgrade and JET

Investigation of pellet-triggered MHD events in ASDEX Upgrade and JET

Local 3D perturbation experiments for probing the ELM stability

Investigations on the ELM cycle by local 3D perturbation experiments

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