Fast Electron Transport during Ecrh in Text-U

The 2nd harmonic extraordinary mode ECE spectrum was measured through a nearly vertical chord in the TEXT -U tokamak. Near the second harmonic frequency the spectrum was dominated by emissions from thermal electrons. Relativistically -downshifted emissions were due to suprathermal electrons. The spectrum was measured during both ohmic and ECRH discharges. There were three classes of ohmic discharge: thermal, runaway and slideaway. During thermal discharges the low frequency spectrum was dominated by reflections of emissions from other parts of the plasma. In runaway type discharges low frequency emissions were proportional to the runaway source rate. Finally, in the slideaway regime enhanced emission by suprathermal electrons was due to the Parail -Pogutse instability. The emission spectrum during ECRH was consistent with the presence of low density suprathermal electrons. By comparing the experimentally measured ECE spectrum with the results of a comprehensive Fokker-Planck calculation, the diffusion of fast electrons has been measured in the plasma core of TEXT-U during electron cyclotron heating. The simulation includes the effects of both magnetic and electrostatic fluctuations on the transport of fast electrons. The experimental spectra were best fit by spectra that include magnetic fluctuations with b = (2.5{-}5)times10 ^{-5} (~ b{ equiv}|{delta B_ r over B_phi}|). The addition of an electrostatic fluctuation term did not significantly change the results and the electrostatic term by itself could not explain the experimentally measured data. Uncertainties in the level of RF power, internal toroidal electric field, Zeff profile and transport due to sawteeth limit the accuracy of this measurement. However, this measurement indicates that an upper limit can be placed on b in the core of between 2.5times10^{-5} and 5times10^{-5}. This is in fair agreement with measurements made outside of the TEXT limiter using magnetic probes and with measurements of runaway electron diffusivity in the outer edge of the plasma. Since a magnetic fluctuation level of 10 ^{-4} would be necessary in order to explain transport in the core plasma, the magnetic fluctuation levels inferred here are unlikely to be the dominant cause of the transport of thermal electrons in TEXT-U.