Hydrogen and helium recycling in tokamaks with carbon walls

Ehrenberg, J.; Coad, P.; Kock, L. de; Erents, S.K.; Gondhalekar, A.; Goodall, Dominic; Hancock, John S; Harbour, P.J.; Jones, T. T. C.; McCracken, G.M.; Morgan, P. D.; Nicholson, C.; Neill, G. F.; O’Rourke, J.; Partridge, J.W.; Pick, M.; Simpson, J.; Sonnenberg, K.; Stevens, A.; Stamp, M.; Stott, P.E.; Summers, D.; Tagle, T.; Vince, J.

doi:10.1016/0022-3115(89)90258-4

Cited by 62 publications

(24 citation statements)

References 34 publications

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“…Defining T P ' = 0.3 a 2 /D x then gives the prediction TABLE VI. AMOUNT OF CARBON ON TOKAMAK WALLS [263] T IT' = (4.18) for the upper branch, which agrees well with the results, Fig. 45.…”

Section: A Simple Model For Particle Balancesupporting

confidence: 90%

“…where R, the global recycling coefficient, is defined by this equation (since r p and T* are experimentally measurable). Experimentally, it is often observed that N(t) scarcely decays when external sources are turned off, T* > 10 s not being uncommon, implying R = 1 [245,262,263]. In order to precisely establish the value of R, and of T P , it is necessary to measure $ as well as N (Eq.…”

Section: Measurements Of R Pmentioning

confidence: 99%

“…The hydrogen retention/release properties of metals appear to be reasonably well understood [1] and will not be further considered here. During the 1980s, many tokamaks [263] employed carbon extensively for limiters, divertor plates and walls; TFTR and JET, for example, each contained more than two tonnes of graphite, and the majority of the plasma exposed surface area was covered by carbon. Table VI indicates the carbon coverage in a number of devices [263].…”

Section: Fuelling Efficiency Wall Pumping Inventorymentioning

confidence: 99%

“…During the 1980s, many tokamaks [263] employed carbon extensively for limiters, divertor plates and walls; TFTR and JET, for example, each contained more than two tonnes of graphite, and the majority of the plasma exposed surface area was covered by carbon. Table VI indicates the carbon coverage in a number of devices [263]. The hydrogen retention properties of carbon are quite complex and are still imperfectly understood [216,263].…”

Section: Fuelling Efficiency Wall Pumping Inventorymentioning

confidence: 99%

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Plasma boundary phenomena in tokamaks

1990

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“…Defining T P ' = 0.3 a 2 /D x then gives the prediction TABLE VI. AMOUNT OF CARBON ON TOKAMAK WALLS [263] T IT' = (4.18) for the upper branch, which agrees well with the results, Fig. 45.…”

Section: A Simple Model For Particle Balancesupporting

confidence: 90%

Section: Measurements Of R Pmentioning

confidence: 99%

Section: Fuelling Efficiency Wall Pumping Inventorymentioning

confidence: 99%

Section: Fuelling Efficiency Wall Pumping Inventorymentioning

confidence: 99%

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Plasma boundary phenomena in tokamaks

1990

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“…This over-fueling situation is consistent with minimal wall conditioning performed before the startup campaign experiments were conducted (e.g. baking at 150 degrees C only, which is below the threshold to remove impurities from carbon 46 ). This result provides some additional confidence in our measurements of τ * p and τ p since the R they yield is consistent with plasma observations and the anticipated wall conditions during the startup campaign at W7-X.…”

Section: Global Recycling Coefficient In W7-xsupporting

confidence: 73%

Impact of magnetic islands in the plasma edge on particle fueling and exhaust in the HSX and W7-X stellarators

et al. 2018

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The edge magnetic structure in the Helically Symmetric eXperiment (HSX) and Wendelstein 7X (W7-X) stellarators has been shown to have a significant impact on the particle fueling and exhaust of the plasma main species (hydrogen) as well as impurity helium. For HSX, the plasma sourcing to exhaust ratio, quantified by the effective and global particle confinement times τ * p and τ p,H , respectively, increases when a magnetic island chain is located in the plasma edge. The fueling efficiency is reduced by 25% when the plasma boundary is deformed by the magnetic islands. The X-point geometry also yields higher plasma temperatures in front of the main recycling region. When the island is moved radially inward, both τ * p and τ p decrease by 10 − 25% depending on plasma density. The τ p,H results rely heavily on EMC3-EIRENE modeling which confirms reduced fueling efficiency due to more rapid ionization in the outward shifted island position. These findings suggest that for a helically optimized system like HSX, the plasma fueling from the recycling source, as well as from active gas injection, can be controlled by the magnetic island chain in the plasma edge-which is a basic requirement for a divertor system. This process is also effective for the control of effective helium exhaust times, as τ * p,He measured by perturbative gas puff experiments is reduced by up to 40% when the islands are shifted inwards. For Wendelstein 7-X, a similar reduction of τ * p,He was inferred when magnetic islands were moved from the far plasma edge into the confined plasma region. However, the effective confinement features of H as the main plasma species were not affected due to the non-optimal position of the magnetic islands with respect to the highly localized ionization domain during the limiter startup campaign.

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