Design and Testing of the 2 Mv Heavy Ion Injector for the Fusion Energy Research Program

The Fusion Energy Research Group at the Lawrence Berkeley Laboratory has constructed and tested a pulsed 2 MV injector that produces a driver size beam of potassium ions. This paper will describe the engineering aspects of this development which were generated in a closely coupled effort with the physics staff. The details of the ion source and beam transport physics are covered in another paper at this conference. This paper will discuss the design details of the pulse generator, the ion source, the extractor, the diode column, and the electrostatic quadrupole column. Included will be the test results and operating experience of the complete injector. INTRODUCTION The new 2 MV, 800 mA K+ injector for heavy ion fusion has been operational since January 1994. The injector utilizes electrostatic quadrupoles (ESQ) to simultaneously focus and accelerate the ion beam. Experiments in ion sources and beam emittance have been carried out during the past year. This paper will describe the engineering design and tests of the 2 MV Marx generator, the beam extraction and the acceleration ESQ column. The overall cross-section of the injector is shown on Fig 2. The pressure vessel is 25’ long and has an inside diameter of 64”. The left side houses the 38 stage Marx generator and is connected to the diode and ESQ column by the high voltage dome which houses the ion source. ION SOURCE ELECTRONICS The high voltage dome houses the hydraulically driven 400 Hz, 10 kVA alternator which powers all the source electronics including the telemetry system. Fig. 1 is a simplified block diagram of the source electronics. The source is an indirectly heated alumino-silicate coated on porous tungsten requiring 2500 watts. The source is biased at -80 kV and the extractor electrode is at dome potential inhibiting ion emission from the hot surface. Ion extraction is obtained by pulsing the source from a -80 kV to +80 kV with the step-up transformer driven by a tunable pulse forming network (PFN). The extractor waveform can be adjusted temporally in amplitude by + 5% simply by changing the coupled inductance of the PFN. The source filament transformer not only supplies the heater power, but is also a high voltage isolation transformer allowing the source to be biased at -80 kV. Trigger, timing, and diagnostics information is transmitted to and from the high voltage dome by fiber optics links. * This work was supported by the Director, Office of Energy Research, Office of Fusion Energy, U.S. Dept. of Energy, under Contract No. DE-AC03-76SF00098. Fig. 1