ICRF system in the JET pumped divertor configuration

After one year of operation the new A2 ICRF system installed for the pumped divertor phase of JET has achieved a coupled power of 16 MW, a coupled energy of 70 MJ, and combined heating with NB of 32 MW, each in ITER relevant high density, highly radiating, ELMy H-mode plasmas. The generators and antenna system now operates over 30 kV, with rapid, on-line matching and phase control of four coupled current straps. The coupling to the plasma and heating efficiency are phase dependent-coupling improves but heating efficiency falls with decreasing k/spl par/; good heating in monopole phasing has been observed after installation of a new separator between the set of antennae in one of the modules. Cross-coupling between straps enhances the imbalance in plasma coupling of the inner and outer straps of the array due to a mismatch in the feed lines. Modifications to reduce this imbalance and improve low k/spl par/ operation are described. The A2 array is similar in size to one row of the current ITER in-port antenna design. The implications for such a design are discussed.