Pellet-plasma interactions in tokamaks

Chang, C. T.

doi:10.1016/0370-1573(91)90053-o

Cited by 16 publications

(8 citation statements)

References 51 publications

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“…At this point, the pellet has just crossed the pedestal region and has lost there only about 20% of its initial mass (∼10 19 D-atoms). Form previous experience [15], the ablated material is quickly heated to a few electronvolts by parallel electron heat conduction, forming a local high pressure plasmoid, which expands along field lines at about the speed of sound, travelling a few metres only during this short time interval. In parallel, it is radially accelerated and displaced towards the core (high field side injection!)…”

Section: Optimization Of the Pellet Tool: The Pellet Mass Scanmentioning

confidence: 97%

ELM frequency control by continuous small pellet injection in ASDEX Upgrade

et al. 2003

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Injection of cryogenic deuterium pellets has been successfully applied in ASDEX Upgrade for external edge localized mode (ELM) frequency control in type-I ELMy H-mode discharge scenarios. A pellet velocity of 560 m s −1 and a size of about 6×10 19 D-atoms was selected for technical reasons, although even lower masses were found sufficient to trigger ELMs. A moderate repetition rate close to 20 Hz was chosen to avoid over-fuelling of the core plasma. Pellet sequences of up to 4 s duration were injected into discharges close to the L-H threshold, intrinsically developing large compound ELMs at a rate of 3 Hz. With pellet injection, these large ELMs were completely replaced by smaller type-I ELMs at the much higher pellet frequency, accompanied by a slight increase of density and even of stored energy. This external ELM control could be repeatedly switched on and off by just interrupting the pellet train. ELMs were triggered in less than 200 µs after pellet arrival at the plasma edge, at which time only a fraction of the pellet has been ablated, forming a rather localized, three-dimensional plasmoid, which drives the edge unstable well before the deposited mass is spread toroidally. The pellet controlled case has also been compared with a discharge at a somewhat lower density, but with otherwise rather similar data, developing spontaneous 20 Hz type-I ELMs. Despite the different trigger mechanisms, the general ELM features turn out to be qualitatively similar, possibly because of the similarity of the two cases in terms of ELM relevant parameters. The scaling with background plasma, heating power, pellet launch parameters, etc over a larger range still remains to be investigated.

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Section: Optimization Of the Pellet Tool: The Pellet Mass Scanmentioning

confidence: 97%

ELM frequency control by continuous small pellet injection in ASDEX Upgrade

et al. 2003

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“…The injection of a pellet into hot plasma generates a brief emission of electromagnetic radiation (e.g. Balmer Hα light) and results in transitory changes to plasma parameters such as electron and ion densities and temperatures, stored energy, etc [4]. It is also known to modify plasma turbulence [5].…”

Section: Introductionmentioning

confidence: 99%

“…These effects are observed in different devices and much of the underlying physics has been understood. For instance, effects include a cold wave preceding the pellet [6], cloud detachment from the pellet producing striations in ablation light profiles [7], fastelectrons incident on a pellet causing increased ablation or pellet rupture [4,8,9], and acceleration of a pellet by fast-ion impacts or by cloud pressure asymmetry [10,11]. Nonetheless, a full understanding of other transitory effects that have been observed remaining outstanding.…”

Section: Introductionmentioning

confidence: 99%

The interpretation of magnetic activity associated with pellet injections into plasmas created in the stellarator TJ-II

McCarthy¹,

Ascasíbar²,

Tamura³

et al. 2021

Nucl. Fusion

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Pellet injection into magnetic confinement plasma is widely employed for plasma fuelling and impurity transport studies. While post-injection effects include changes in density and temperature, several short-lived effects have been identified during and immediately after pellet ablation, e.g. pre-cooling of the plasma core or a strong reduction in fluctuations. Here, transitory effects observed in magnetic signals during and immediately after the injection of fuel and tracer encapsulated solid pellets into microwave and neutral beam heated plasma in the stellarator TJ-II are reported. One effect is the excitation of a clear, short-lived, magnetic instability during the ablation phase of a cryogenic pellet. Another effect is a brief reduction in broadband magnetic fluctuations immediately after an injection while a third effect is frequency jumps of already excited Alfvén eigenmodes (AE) when neutral beam heating is employed. The interpretation of these effects is facilitated by signals from 2 recently installed toroidal arrays of magnetic coils that follow the helicity of this device along one of its quadrants. It is concluded that interactions between outward drifting pellet particles and a low-order rational surface lead to the magnetic instability, that pellet-induced plasma cooling induces a transitory reduction in broadband magnetic fluctuations and that plasma mass density changes dominate jumps in AE frequencies.

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“…Pellet injection is able to deposit fuel deeper with a higher efficiency and the pellet fuelled plasma is purer, with less recycling. Also, for a tritium containing discharge, it is easier to control the inventory [1]. Pellet injection is the leading technology for deep fuelling of magnetically confined plasmas in controlled thermonuclear fusion research, and is regarded as a promising fuelling technology for the steady state fusion reactor of the future.…”

Section: Introductionmentioning

confidence: 99%

Pellet injection research on the HT-6M and HT-7 tokamaks

Yang

et al. 1999

Nucl. Fusion

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A multishot in situ pellet injection system has been constructed in the Institute of Plasma Physics. Single-and multi-pellet injection experiments were performed on the HT-6M and superconducting HT-7 tokamaks. The system proved to be convenient and reliable to operate. Pellets were fired into ohmically and LHCD and ICRF heated plasmas. Single pellet injection in ohmic discharge was found to increase the central density of HT-7 by about one half, while two pellet injection increased the central density in a step-like fashion by one half with each shot. Peaking of the electron density profile and a hollow electron temperature profile were obtained.

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Pellet-plasma interactions in tokamaks

Cited by 16 publications

References 51 publications

ELM frequency control by continuous small pellet injection in ASDEX Upgrade

ELM frequency control by continuous small pellet injection in ASDEX Upgrade

The interpretation of magnetic activity associated with pellet injections into plasmas created in the stellarator TJ-II

Pellet injection research on the HT-6M and HT-7 tokamaks

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