The ISX-A graphite limiter experiment

Abstract

LE, ttAs part of t.ie ISX surface physics program and the TFTR materials research program, ATJS graphite rail iimiters were installed in the ISX tokamak in order to compare them with the existing stainless steel liniters and to investigate any deleterious effects arising from operation at elevated temperatures of the graphite. To facilitate the latter experiment, heaters were installed in the graphite liniters since the power deposition on the limiter in ISX was expected to be considerably less than for TFTR. The graphite liniters also contained thermocouples to monitor the bulk temperature. Ho large systematic differences werr observed in the electron temperature profiles, electron density profile;-nor Zeff between successive runs with the stainless steel (SS) limiters and graphite (G) limiters. There was, however, a xonotonic decrease in Zeff for both cases from i-5.6 in the first run following the installation of the graphite limiters to ^ 2.8 after a two week period when the experiment was terminated due to a scheduled shutdown. Normal incidence UV spejtroscopic measurements of C, II, 0, and H radiation showed a factor of 3-k greater hydrogen light for the S3 case over the 5 case, but no systematic differences in the impurity light. Arc tracks were cbserved on the graphite limiters upor. removal and 3EM analysis was performed so that the amount of material removed could be estimated. In the hot graphite limiter experiment, the temperature of one of the graphite liniters was increased on successive shots. The hydrocarbons formed, as determined by residual gas analysis (RGA), increased monotonically with increasing limiter temperature, e.g. mass 16 (presumed to be CHj,) increased about a factor of two as the temperature was raised from 150°C to SQO°C. CO and COg were also found to increase only slightly. The carbon impurity light was also observed to increase by a factor of two as the limiter temperature was raised from 150°C to 500°C. Further experiments using graphite liraiters are indicatec. before their application in beam driven tokamaks.

O–H charge exchange in cold, dense hydrogen plasmas

“…To date, there are no direct experimental tests of this model. Measurements of T e (a), n e (a), and n H o(a) have been performed on several tokamaks [5] with characteristic values being T e (a) ~ 5 -15 eV, n e (a) ~ 5 X 10 12 cm" 3 and n H o ~ 5 X 10 9 cm" 3 . These conditions should only result in a 1% O loss by O-H charge exchange.…”

Development of ultrahigh and extreme high vacuum technology for physics research

“…[78][79][80][81] Large scale tests of magnetic diverter structures for controlling the transport of both hydrogenic and impurities species were performed on the PDX tokamak at Princeton [82] and the ASDEX tokamak at Garching, Germany. [83] These two tokamaks, which became operational in the early 1980's, required very large vacuum vessels (~ 36 m 3 ) to contain the internal magnetic structures for the diverter and a ballast volume for pumping the plasma particles that were neutralized on the diverter target plate.…”