High-Density Plasma Production by Hydrogen Storage Electrode in the Tohoku University Heliac

In the Tohoku University Heliac, a high-density plasma is produced by a vanadium electrode. The vanadium electrode is pretreated for hydrogen storage. In biasing experiments using the vanadium electrode, a high-density plasma is observed in not only argon plasmas but also helium plasmas. When the vanadium electrode is biased negatively, the radial distribution of the electron density steepens at the electrode position, and a strong negative radial electric field is formed between the electrode and the last closed flux surface. The E × B drift velocity is 30 km/s, and the estimated poloidal Mach number M_p is -20. The measured beta value exceeded 0.5% in the low-field discharges.