Studies in JET divertors of varied geometry III: Intrinsic impurity behaviour
Impurity production and plasma impurity concentrations are surveyed over a wide range of operating conditions but with emphasis on ELMy H-mode operation using neutral beam heating. The Mark I divertor campaigns with carbon and beryllium targets are compared to the Mark II campaign which had carbon targets and a more closed divertor geometry. The beryllium target campaign has a significantly lower impurity level than those with carbon targets although the Z(eff) is still dominated by carbon. The divertor geometry appears to have little effect on the impurity level but it is found that the edge-localized mode (ELM) frequency has a marked effect on Z(eff), and the carbon and nickel concentrations, with maxima at an ELM frequency around 5 Hz to 15 Hz. This occurs whether the ELM frequency is varied by changing the plasma triangularity, the input power or by increasing the fuelling rate. The absolute impurity influxes from the inner and outer target and from the inner wall have been estimated from the CII and CIII line intensities. These fluxes are compared to the central carbon concentration and an attempt is made to correlate the influxes and the concentrations in the confined plasma both in their time evolution and in their absolute values.
Bibliographic Reference: Report: JET-P(98)21 EN (1998) 26pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon, OX14 3EA (GB)
Record Number: 199811099 / Last updated on: 1998-09-28
Original language: en
Available languages: en