Recent advances in confinement and heating physics on EBT-S

Recent advances in experimental diagnostic capability and electron cyclotron heating (ECH) theory for the ELMO Bumpy Torus (EBT) have led to the development of a new picture of the electron heating and confinement. The diagnostic improvements include an improved, radially scanning Thomson scattering system, a new spectroscopic technique for measuring Tsub(e) using A1 ion line ratios, and soft X-ray and microwave interferometer measurements of plasma properties in the high magnetic field 'throat' region. The results indicate that the electron distribution (E<=2 keV) has two components: a cold isotropic collisional component (nsub(c)approx.=0.7x1012cm-3,Tsub(c)approx.=80 eV), and a warmer, collisionless, anisotropic tail component (nsub(w)/nsub(c)<=0.3,Tsub(w)approx.=600 eV). This result is in qualitative agreement with Fokker-Planck calculations of ECH in EBT, which indicate that most of the microwave power is absorbed by the warm tail electrons and that up to 50% of the absorbed power may be carried immediately to the walls by particles on unconfined drift orbits. A new closed bumpy field line device in the form of a square (ELMO Bumpy Square (EBS)) is proposed, which is predicted to have significantly better confinement properties than EBT. (author)