An overview of recent results from the TCV tokamak

The TCV tokamak (R=0.88 m, a < 0.24 m, B < 1.54 T) program is based on flexible plasma shaping and heating for studies of confinement, transport, control and power exhaust. Recent advances in fully-sustained off-axis electron cyclotron (EC) current drive (CD) scenarios have allowed the creation of plasmas with high bootstrap fraction, steady-state reversed central shear and an electron internal transport barrier. High elongation plasmas, k = 2.5, are produced at low normalized current using far off-axis EC heating (ECH) and ECCD to broaden the current profile. Third harmonic heating is used to heat the plasma center where the second harmonic is in cut-off. Both second and third harmonic heating are used to heat H-mode plasmas, at the edge and center, respectively. The ELM frequency is decreased by the additional power but in separate experiments can be controlled by locking to an external perturbation current in the internal coils of TCV. Spatially resolved current pro- files are measured at the inner and outer divertor targets by Langmuir probe arrays during ELMs. The strong, reasonably balanced currents are thought to be thermoelectric in origin. (author)