Journal article

Overview of TCV results

The TCV tokamak (R = 0.88 in, a < 0.25 in, BT < 1.54 T) is equipped with six 0.5 MW gyrotron sources operating at 82.7 GHz for second harmonic X mode ECH. By distributing the ECCD current sources over the discharge cross section, fully driven stationary plasmas with I-p = 210 kA, n(e0) = 2 x 10(19) m(-3), T-e0 approximate to 4 keV, were obtained for the full discharge duration of 2 s. Highly peaked electron temperature profiles with T-e0 up to 12 keV were obtained in central counter-current drive scenarios with off-axis ECH. Absorption measurements using a 118 GHz gyrotron have demonstrated the importance of suprathermal electrons for third harmonic absorption. A coupled heat-particle transport phenomenon known as 'density pumpout', which leads to the expulsion of particles from the plasma core, has been linked to the presence of m = I modes, suggesting that it is due to the existence of locally trapped particles associated with the loss of axisymmetry. Highly elongated discharges have been developed with ohmic heating (kappa < 2.8) and off-axis ECH. The latter exhibit considerably improved vertical stability due to current profile broadening. A 'gateway' for ELMy H modes has been discovered, which allows stationary ohmic ELMy H mode operation over a wide range of elongation, triangularity and density. Divertor detachment experiments suggest the existence of recombination pathways other than three body or radiative processes.


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