Experimental studies of plasma confinement in the Bumpy Torus

In the Nagoya Bumpy Torus (NBT) and the Elmo Bumpy Torus (EBT), the plasma is generated, stabilized and heated by high-power steady-state electron cyclotron heating (ECH). MHD stability is obtained by generation of intense, diamagnetic electron annuli by ECH in each sector. Even though plasmas are produced and heated at several frequencies ranging from 8.5 GHz to 28 GHz, a common set of physics exists between the two machines and can be used to define a generic device. Stable operation with both fundamental and second harmonic resonance present within the device or with fundamental resonance only depends critically on the ambient gas pressure, the ECH power and the ability to propagate the wave energy. In the fusion-relevant T-mode, a stable, clean, warm, moderately dense toroidal core plasma threads through the hot electron rings around the torus. Transport studies indicate that the electron particle and power balances are neoclassical for both machines. (author)