Design of the ITER neutral beam system beamline, United States concept

Abstract

Design of a neutral beamline for ITER (International Thermonuclear Experimental Reactor) is deerribed. The design incorporatee a barium surface conversion D-source feeding a linear array of accelerator channels. The q t e m usea a dc accelerator with electrostatic quadrupoles for strong focusing. A highvoltage power supply that is integrated with the accelerator ia presented as an attractive option. A gas neutralizer ia used and residual ions exiting the neutralizer are deflected to watercooled dumps. Cryopaneb are located at the accelerator exit to pump excess gas from the source and the neutralicer, and in the ion dump cavity to pump re-neutralized ions and neutralizer gas. AU the above componenta are packaged in compact identical, independent modules that can be removed for remota maintenance.The neutral beam eystem delivers 76 MW of Do into three porta with a total of nine modules arranged in stacks of three modules per port. To increase reliability each module is designed to deliver up to 10 MW at 1.3 MeV; this allows eight modules operating at partiaI capacity to deliver the required power in the event one module is removed from service. Radiation protection is provided by shielding and by locating critical components in the source and accelerator 36 m from the port into the tom. Neutron shielding in the drift duct providea the added feature of limiting conductance and thus reducing gas flow to and from the tow. Alternative component choices are ala0 discussed for the evolving design.the constraint that unanticipated reductions in power are lim-

A full transport treatment of ITER (International Thermonuclear Experimental Reactor) burn control scenarios

“…3MeV ITER neutral beams (optimized fortheTechnologyPhage machine where NB curreutdriveisone of the main goalsand forthatreasonlowerdensities are expected), cannot penetrate to the centerof the plasma. A series of stand-alone beam-penetrationcalculations with the Monte Carlo neutralbeam deposition code NFREYA[14]usingthe designparametersof the ITER beamline[15]and with MHD equilibrium generated by theNEQ codedemonstrates this verydearly:InFig.19,theNB deposition profile, H(_), isplotted versusthe normalizedpoloidal flux_, for different densities. It can be seen that for _ne) _)1.6x1020 m-S beam penetration is poor and the resulting heating profile is peaked off-axis.…”