The power supply and control system for the MM-2U neutral beam injector

Abstract

A single injector with one ion source has been constructed, which is provided for researching stability effect of sloshing ion distribution in the magnetic mirror experiment facility ( M M -2 U ) by oblique injection of neutral beam. The neutral beam injector (NBI) can deliver 80KW of neutral beam power at energy of 25 kev with 50ms for MM-2U.In the present paper, a testing power supply for neutral beam injector with injecting power up to 200KW is described. A thyristor switch modulator applied to an arc power supply ,it is capable of delivering 10 to lOOOA DC pulses at 20 to lOOv and pulse length up to 2s with a duty cycle of 1/100. Both switching-on and switching off times of the circuit are less than 0. 5ms. A high power vacuum tube TM-703F is used as the switch/regulator of the accel power supply ,specifications of the circuit are as follows: output pulse voltage 50KV, pulse current 30A, pulse wideth 50ms. Both the rise and fa11 times are less than 25,us,fluctuation of the pulse flattop less than 1%. A programmable comtroller by a DBJ-280 computer applied to control the sequence of the power supply. The power supply and control system have been operated for 5 years successf ully . I . INTRODUCTION The neutral beams are used to build up a sloshing ion distribution in the MM-2U axisymmetric plugs. The power supply (ps) system of ion source has been completed at the end of Oct. 1988 and testing of the ion source and installation of the injector has been carried out at the end of 1990 year. The NBI with ECRH system connected to MM-2U came in operation 1 1 : July 1992. For the first time experiment injected approximately 40KW of hydrogen neutrals into the plasma at energy 15Kev for 50ms. The 0-7803-14 12-3$04.00Q19941EEE 90 1 shutdown of MM-2U early August 1992 because of the vacuum system failure. Main power supplies of the MM-2U BNI system are the Failament , Arc, Accel , and Suppressor power supplies [l]. The PS also provides primary protection of the ion source. Fast-fault detection and turn-off of the appropriate power supplies due to sparkdowns in the accel grid, arc spots ,and other source failure modes are important operating features. The power supply system for the NBI is shown in Fig. 1 and the specification of each power supply is given in Table 1. The system consists of 8 power units, which can be used either PIG ion source or bucket ion source. . FILAMENT POWER SUPPLYThe filament supply consists of a three-phase variac ,a transformer and a silicon diode full-wave bridge rectifier set with an LC output filter ,the voltage is adjusted manually with raise-lower push buttons . A magnetic contactor is used to turn on the primary power with protective circuits which limit the total on time for a given pulse length. T o improve tungsten filament life, a wye-delta starter is used. the inrush of current during the first portion of the pulse is limited to twice the final value of current. The output is designed for 25v DC at the source terminals, 300A continuous duty, and 500A, 10s pulse length 10% duty.Under ...