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In the edge plasma of magnetically confined devices such as tokamaks, the electron distribution is not necessarily Maxwellian, and may consist of a small number of electrons characterised by a hot temperature, T(eh), with the bulk of the electrons at a colder temperature, T(ec). In a strong magnetic field, there is no satisfactory theory for interpreting the IV characteristic above floating potential, and so usually only the high energy electrons in the distribution are used to deduce T(e). It is shown that the value of T(e) extracted from the Langmuir Probe characteristics in this way yields T(eh), unless the hot component is extremely small. Langmuir probes therefore tend to overestimate T(e) in magnetically confined devices. This effect may also be relevant to observations of (apparently) very low sheath heat transmission coefficients in tokamaks.

Additional information

Authors: STANGBY P C, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(95)14 EN (1995) 7 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199511443 / Last updated on: 1995-11-03
Original language: en
Available languages: en