Profile measurements in the plasma edge of mega amp spherical tokamak using a ball pen probe.
The ball pen probe (BPP) technique is used successfully to make profile measurements of plasma potential, electron temperature, and radial electric field on the Mega Amp Spherical Tokamak. The potential profile measured by the BPP is shown to significantly differ from the floating potential both in polarity and profile shape. By combining the BPP potential and the floating potential, the electron temperature can be measured, which is compared with the Thomson scattering (TS) diagnostic. Excellent agreement between the two diagnostics is obtained when secondary electron emission is accounted for in the floating potential. From the BPP profile, an estimate of the radial electric field is extracted which is shown to be of the order ∼1 kV/m and increases with plasma current. Corrections to the BPP measurement, constrained by the TS comparison, introduce uncertainty into the ER measurements. The uncertainty is most significant in the electric field well inside the separatrix. The electric field is used to estimate toroidal and poloidal rotation velocities from E × B motion. This paper further demonstrates the ability of the ball pen probe to make valuable and important measurements in the boundary plasma of a tokamak.
CCFE, Culham Science Centre, Abingdon,Oxon OX14 3DB, United Kingdom.
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Walkden
Institute of Plasma Physics of AS CR, v. v. i., Za Slovankou 3, 182 00 Praha 8, Czech Republic.
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Adamek
CCFE, Culham Science Centre, Abingdon,Oxon OX14 3DB, United Kingdom.
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Allan
Department of Physics, York Plasma Institute, University of York, Heslington, York YO10 5DD, United Kingdom.
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Dudson
CCFE, Culham Science Centre, Abingdon,Oxon OX14 3DB, United Kingdom.
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Elmore
CCFE, Culham Science Centre, Abingdon,Oxon OX14 3DB, United Kingdom.
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Fishpool
CCFE, Culham Science Centre, Abingdon,Oxon OX14 3DB, United Kingdom.
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Harrison
CCFE, Culham Science Centre, Abingdon,Oxon OX14 3DB, United Kingdom.
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Kirk
Institute of Plasma Physics of AS CR, v. v. i., Za Slovankou 3, 182 00 Praha 8, Czech Republic.
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Komm