Recent JET results and fast wave issues in divertor plasmas

Summary form only given. The interior of the JET tokamak has been extensively modified and a pumped divertor has been installed to study effective methods of power exhaust and impurity control. Due to its large size (R/sub 0/=2.96 m; a/sub p/=1 m; B/sub /spl phi//=3.4 T and I/sub p//spl les/6 MA) and proximity to reactor conditions, JET aims at providing physics support to ITER in the areas of divertor studies, energy confinement and fusion performance. The JET auxiliary equipment including heating and current drive systems (NBI=20 MW, ICRH=20 MW, LHCD=10 MW) permit a wide variety of operational modes including, most notably, the operation in D-T mixture and advanced tokamak operation with high /spl beta//sub p/, high boot-strap regimes with a central seed current. For the pumped divertor configuration, completely new ICRII antennas (A2) have been designed and installed to match the changed plasma profile. Also, current straps are grouped into 4-modules of 4-straps (toroidal extent /spl cong/1.8 m) each to improve the current drive capability. This required a new ICRH plant control electronics for automatic matching and phasing and features such as all immunity to cross-talk between different antenna modules have also been incorporated. The new ICRH system has coupled up to 15 MW of power to single-null, X-point divertor plasmas. A 26 MW of combined heating (15 MW of NBI) has produced ELMy H-modes in advanced tokamak regimes with /spl beta//sub p/=2.5, quasi steady-state H-factors (improvement over L-mode) of up to 2.5 and transient VII-modes with H=3.