Particle exhaust studies have been carried out with thepump limiter ALT-II in the TEXTOR tokamak, under ohmic conditionsas well as with NBI and with ICRF auxiliary heating, and the pumping effectivenessis shown to meet the requirements for a fusion reactor.Quantitative measurements of Dα emission,made with a CCD camera, have been used to determine the particle efflux from the plasma. Roughly one third of the Dα emission occurs in a diffuse `halo' that surrounds the limiter belt.The particle confinement time is less than the energyconfinement time by a factor of typically 4. Modelling in 2-D of plasma and neutral flows in the TEXTOR boundary has been performed.The source of D+ ionscan be related to the Dα emission by afactor that is found to depend on the location of the emission and on thedischarge density. The predicted total Dα emission agrees with the measurements withina factor of about 2.Pumping of ALT-II allows for density control;with NBI, the density can be increasedwell beyond the ohmic limit without the discharge ending in disruption.The plasma particle effluxand the pumped flux both increase with density as well as withheating power. The exhaust efficiency is typically ∼2%, withthe highest values observed in high density NBI discharges.Higher exhaust rates are observed with NBI than with ICRF.Plasma and neutral flows in the ALT-II scoops have been simulated,making use of a simple plasma model.The scoop may be viewed as a non-linear amplifier of the plasmaparticle flux; the amplification is found to range from about 2 to 3 for most cases.Flow reversal in the scoopis found in some of the NBI cases and particularly inthe highest density case.
Measurement of neutral density profile in a tokamak plasma using the principle of laser induced ionization