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Boundary layer conditions in JET during RF heating

Journal of Nuclear Materials
Publication Date
DOI: 10.1016/0022-3115(87)90333-3
  • Langmuir Probes
  • Plasma Edge
  • Icrf


Abstract Profiles of density and temperature have been measured in the limiter scrape-off layer on JET using Langmuir probe arrays at the torus top and mid-plane positions. When ICRF heating is applied the local density, electron temperature and floating potential rise. Both particle flux and electron temperature show the characteristic exponential dependence on distance from the plasma edge but the e-folding length increases when ICRH starts. The particle flux e-folding length rises rapidly with ICRH power. Data from top and mid-plane probe arrays show good agreement when the field line compression is taken into account. The time response of particle flux to applied RF power is fast, 0.25–3 ms, however only low level RF voltages have been detected on the Langmuir probes suggesting that sheath rectification is not distorting the data. A change in perpendicular diffusion due to ICRH and ionisation of hydrogen molecules desorbing from the torus wall are considered as possible causes of the profile flattening.

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