Fuel retention in L and H mode experiments in JET

• The fuel retention has been studied out in JET in L mode, Type III and Type I ELMy H-modes using gas balance in series of repetitive pulses with an overall accuracy of about 1.2%. The short term (dynamic) retention is important for both L mode and Type III ELMy H-mode over the heating phases (respectively 13 and 17 sec) but decreases already significantly during the pulse. It becomes small already after 6 sec for the Type I ELMy H-mode conditions. In all the cases, the recovery after the pulse contributes for a weak part in the gas balance and in the overall fuel retention. The absolute long term fuel retention (on the time basis of typically 5 hours) for the different plasma conditions is between 1.3 and 2.8 1021Ds-1 (averaged over the plasma heating time) and in reasonable agreement with the value deduced from post mortem tile analysis of about 5 1020Ds-1 considering the additional long term outgassing, conditioning and disruptions included in the post mortem analysis. The increase of the long term retention observed from L mode to Type I ELMy H-mode is associated to the increase of the recycling flux and the ELM energy. This larger long term retention is attributed to an enhanced carbon erosion and transport in the SOL leading to stronger carbon deposition and fuel codeposition. The results confirm the strong concerns about fuel retention in a carbon clad tokamak and a possible full carbon wall ITER which could reach the T-inventory limit in only a small number of high performance shots. A reasonable ITER operation time depends thus on a significant reduced T codeposition under the different ITER material conditions (which has to be confirmed in a relevant tokamak experiment such as the JET ILW project) and an effective routine T removal technique.

Subject headings

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Keyword

Carbon

Fuels

Magnetoplasma

Plasma simulation

Sols

Publication and Content Type

ref (subject category)

kon (subject category)