The First derivative probe technique for a correct evaluation of the plasma potential in the case of non‐Maxwellian EEDF is presented and used to process experimental data from COMPASS tokamak. Results obtained from classical and first derivative techniques are compared and discussed. The first derivative probe technique provides values for the plasma potential in the scrape‐off layer of tokamak plasmas with an accuracy of about ±10%. Classical probe technique can provide values of the plasma potential only, if the electron and ion temperatures are known as well as the coefficient of secondary electron emission. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, the advantages are presented and discussed of the first-derivative probe technique over the three- and the four-parameter conventional probe techniques for diagnostics of fusion plasmas. The conventional probe techniques for estimation of the plasma potential and the electron temperature and density can only be used when the electron energy distribution function (EEDF) is Maxwellian. The first-derivative probe technique can provide reliable results for the plasma potential and the real EEDF when the latter deviates from Maxwellian. To exemplify the application of the results obtained by different techniques, results on the parallel power-flux density distribution in the divertor region of the COMPASS tokamak, IPP.CR, are presented and discussed.

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