This paper presents the progress of performance tests of ITER gyrotrons developed at QST and the design of dual-frequency (170 GHz and 104 GHz) gyrotrons to enhance various operation scenarios in ITER, such as characteristics studies of H-mode/ELM at low magnetic fields. The major achievements in developing the ITER gyrotrons are as follows: (i) manufacturing of eight ITER gyrotrons and their auxiliary components has been completed. Performance tests at QST have been progressing and four of the eight gyrotrons achieved the required test criteria-1 MW/300 s/50%, 5 kHz modulation with 0.8 MW. Excitation of LP 01 mode having a purity of 95% was also successfully demonstrated using a 50 mm-diameter waveguide transmission line, satisfying the specification. (ii) The design of dual-frequency gyrotrons capable of 1 MW continuous-wave operation, was successfully completed.

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-

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High-power (1 MW), long-pulse operations up to 300 s were demonstrated by multi-frequency oscillations at 170 GHz, 137 GHz, and 104 GHz. A multi-frequency gyrotron based on the design of the ITER gyrotron has been developed and studied. By redesigning the built-in mode convertor and internal mirrors of the ITER gyrotron, the internal scattered power of the gyrotron was reduced while maintaining the same output beam size and beam direction for the three frequencies. In addition, the mirrors of a matching optics unit (MOU) were designed to efficiently couple the RF beam at 170 GHz, 137 GHz, and 104 GHz oscillations to a waveguide 50 mm in diameter, the same size that will be used in ITER. An HE11 mode content of ~ 94 % was achieved for the three frequencies. Output powers of 1 MW at 170 GHz and 137 GHz, and 0.9 MW at 104 GHz were demonstrated up to 300 s. These oscillation frequencies can facilitate in a wide range of toroidal magnetic field operations at ITER, including plasma start-up and electron heating and current drive.