Solid hydrogen pellet injection into the Ormak tokamak

Foster, C.A.; Colchin, R.J.; Milora, S.L.; Kim, Kyekyoon; Turnbull, R. J.

doi:10.1088/0029-5515/17/5/017

Cited by 65 publications

(58 citation statements)

References 9 publications

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“…Fast electron cyclotron emission (ECE) and soft X-ray measurements have been used to study the effect of pellets on the electron temperature [6] and ion density [7]. The toroidal propagation of density away from the pellet was determined using microwave interferometry and found to be 2 X 10 6 cm-s- 1 [3,8].…”

Section: Introductionmentioning

confidence: 99%

Neutron and hard X-ray measurements during pellet deposition in TFTR

Heidbrink

Milora²,

Schmidt

et al. 1987

Nucl. Fusion

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ABSTRACT. Measurements of neutrons and hard X-rays are made with a pair of plastic scintillators during injection of deuterium pellets into deuterium TFTR plasmas. Three cases are investigated. During Ohmic heating in plasmas with few runaway electrons, the neutron emission does not increase when a pellet is injected, indicating that strong acceleration of the pellet ions does not occur. In Ohmic plasmas with low but detectable levels of runaway electrons, an X-ray burst is observed on a detector near the pellet injector as the pellet ablates, while a detector displaced 126° toroidally from the injector does not measure a synchronous burst. Reduced pellet penetration correlates with the presence of X-ray emission, suggesting that the origin of the burst is bremsstrahlung from runaway electrons that strike the solid pellet. In deuterium beam heated discharges, an increase in the d-d neutron emission is observed when the pellet ablates. In this case, the increase is due to fusion reactions between beam ions and the high density neutral and plasma cloud produced by ablation of the pellet; this localized density perturbation equilibrates in about 700 us. Analysis of the data indicates that the density propagates without forming a sharp shock front with a rapid initial propagation velocity (>2 X 10 7 cm -s" 1 ) that subsequently decreases to around 3 X 10 6 cm-s" 1 . Modelling suggests that the electron heat flux into the pellet cloud is much less than the classical Spitzer value.

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Section: Introductionmentioning

confidence: 99%

Neutron and hard X-ray measurements during pellet deposition in TFTR

Heidbrink

Milora²,

Schmidt

et al. 1987

Nucl. Fusion

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“…Pellets launched into the plasma are monitored by the spikes they cause in the D a radiation. The total amount of radiation can be assumed to yield an approximate measure of the deposited pellet mass [5]. Reduced intensities observed with some pellets are most probably due to mass losses on the external pellet path.…”

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confidence: 99%

“…This conclusion is further supported by the fact that reduced´f values were always accompanied by reduced ablation radiation. With the ablation radiation being assumed to be a good measure of the pellet mass [5], accordingly corrected´f values show a scatter reduced to 610% of the optimum value of ഠ0.7 for the HFS pellets. For LFS pellets, however, a strong reduction in efficiency takes place despite the fact even bigger ͑4 3 10 20 particles) and faster (1200 m͞s) pellets were injected using the centrifuge at high heating powers, penetrating deep into the plasma.…”

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confidence: 99%

High-Efficiency Plasma Refuelling by Pellet Injection from the Magnetic High-Field Side into ASDEX Upgrade

et al. 1997

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High-efficiency refuelling of ELMy H-mode tokamak discharges with solid deuterium pellets injected from the magnetic high-field side is demonstrated. Compared to standard low-field side injection, the fuelling efficiency was enhanced by a factor of 4, the pellet penetration more than 2 times. This experimental result can be qualitatively explained by the magnetic force pushing a diamagnetic plasma cloud towards lower magnetic field, causing rapid particle loss for shallow lowfield side injection, but enhancing fuelling efficiency and pellet penetration for high-field side injection.[S0031-9007 (97)03857-X] PACS numbers: 28.52.Cx, 52.55.FaNext generation fusion devices like ITER will have to operate at densities well beyond the Greenwald limit obtained in present day tokamaks with gas refuelling [1]. Though the detailed nature of this empirical limit is still under discussion, it was shown that it can easily be overcome by injection of frozen hydrogen isotope pellets penetrating much deeper than cold gas particles (e.g., Franck-Condon atoms from molecule disintegration) [2]. In discharges with high heating power and especially in type-I ELMy H-mode plasmas with high edge temperatures, a large fraction of the deposited material was rapidly expelled from the plasma column [3], resulting in significantly reduced fuelling efficiencies´f especially with shallow penetration [2,4]. In Ref. [4] it was shown that at least part of this mass was lost in the vicinity of the injection point along a trace aligned with the helical magnetic field (please note the correct sequence of Figs. 3(a) and 3(b) is reproduced in the corrigendum).In this and all previous experiments, pellets were injected from the magnetic low-field side (LFS), i.e., from the torus outside, which is easily accessible in a tokamak. It was therefore argued [4] that, because of the unfavorable toroidal curvature, part of the diamagnetic pellet plasma cloud could have been expelled before it was captured by the background plasma. If so, injection from the magnetic high-field side (HFS), i.e., the torus inside, should be much superior, since the same effect would help to transport the pellet mass deeper into the bulk plasma. In order to clarify this question, experiments have been conducted in ASDEX Upgrade where pellets were injected from both sides into H-mode plasmas and f as well as pellet penetration depths were compared. ASDEX Upgrade is a midsize divertor tokamak (tokamak radius R 0 1.65 m, plasma radius a 0.5 m, V plasma 13 m 3 , plasma elongation b͞a 1.6; singlenull divertor). Wall elements in contact with the plasma are covered by graphite tiles, the divertor target plates were tungsten coated. Calibrated valves mounted at the vessel midplane are used for gas puffing, and turbomolecular pumps with a pumping speed of 14 m 3 ͞s for D 2 (deuterium) gas to control particle exhaust.The experiments described here were carried out in D with plasma currents I p 0.8 1.2 MA, toroidal magnetic field jB t j 1.7 2.5 T, safety factor q 95 2.7 4.2, and additional bea...

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“…(1) and (2) that the ultimate attainable speed for an expansion to zero pressure is U max = 2eAl' -I).…”

Section: Principle Of Operationmentioning

confidence: 98%

Pneumatic hydrogen pellet injection system for the ISX tokamak

Milora

Foster

1979

Review of Scientific Instruments

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We describe the design and operation of the solid hydrogen pellet injection system used in plasma refueling experiments on the ISX tokamak. The gun-type injector operates on the principle of gas dynamic acceleration of cold pellets confined laterally in a tube. The device is cooled by flowing liquid helium refrigerant, and pellets are formed in situ. Room temperature helium gas at moderate pressure is used as the propellant. The prototype device injected single hydrogen pellets into the tokamak discharge at a nominal 330 m/s. The tokamak plasma fuel content was observed to increase by (0.5-1.2) x10(19) particles subsequent to pellet injection. A simple modification to the existing design has extended the performance to 1000 m/s. At higher propellant operating pressures (28 bars), the muzzle velocity is 20% less than predicted by an idealized constant area expansion process.

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Solid hydrogen pellet injection into the Ormak tokamak

Abstract: NOTICE This document contains information of a preliminary nature. I t is subject to revision or correction and therefore does not represent a final report.

Cited by 65 publications

References 9 publications

Neutron and hard X-ray measurements during pellet deposition in TFTR

Neutron and hard X-ray measurements during pellet deposition in TFTR

High-Efficiency Plasma Refuelling by Pellet Injection from the Magnetic High-Field Side into ASDEX Upgrade

Pneumatic hydrogen pellet injection system for the ISX tokamak

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