PULSER DEVELOPMENT FOR MBE-4

The Multiple Beam Experiment MBE4 is designed to accelerate four cesium ion beams from 200 kV to about 1 MV using an induction linac and to demonstrate the process of current amplification simultaneously with acceleration. The injected beam is obtained from a source using a Marx generator providing typically 10 mA/beam with a length of 1.6 meters. This is equivalent to a beam duration time of about 3 ..mu..sec. Twenty four acceleration gaps in groups of four are distributed along the length of the machine which will be some 16 meters long when completed. Each group of four acceleration gaps with appropriate quadrupoles form one section of the machine, identified as A through F. Careful tailoring of the acceleration voltage waveforms at each gap is required to accelerate the beam, amplify the current and provide longitudinal focusing. Ideal voltage waveforms for each gap were generated for a gap voltage limit initially set at 30 kV. These waveforms are shown in Fig. 1. The waveforms for the first 4 gaps are triangular with an approximate width of 3 ..mu..sec, becoming flatter and shorter at subsequent gaps as the beam bunch velocity increases. Ninety two nickel-iron tape wound cores capable of 6.8 mVsec/core and twenty six silicon steel tape wound cores capable of 24 mVsec/core were available. Groups of cores at the first eight gaps have been used in conjunction with an appropriate number of pulsers to provide the necessary accelerating voltage waveforms together with the pulser waveforms at every fourth acceleration gap which provides the longitudinal focusing of the beam. This paper will deal with the performance of the pulsers for the first eight gaps of acceleration and expectations for the next four, currently under construction

MBE-4: an induction linac experiment for heavy ion fusion

The multiple-beam induction linac approach to a heavy ion fusion driver features continuous current amplification along the accelerator and a minimum of transverse beam manipulation from source to pellet. Current amplification and bunch length control require careful shaping of the accelerating voltages. This driver approach exploits developments in electron induction linac technology that have occurred within the last 15 years at LBL, LLNL and NBS. MBE-4 is a four beam induction linac that models much of the accelerator physics of the electrostatically focused section of a considerably longer induction accelerator. Four parallel Cs/sup +/ beams are electrostatically focussed and will be accelerated from 200 keV to approximately one MeV when the experiment is complete in the spring of 1987. The current in each of the four beams will increase from 10 to 40 mA due to both increase in beam speed and shortening of the bunch length. Results of experiments with the injector and first eight accelerating gaps are presented

Multi-beam injector development at LBL

LBL is developing a multi-beam injector that will be used for scaled accelerator experiments related to Heavy Ion Fusion. The device will produce sixteen 0.5 Amp beams of C+ at 2 MeV energy. The carbon arc source has been developed to the point where the emittance is within a factor of four of the design target. Modelling of the source behavior to find ways to reduce the emittance is discussed. Source lifetime and reliability is also of paramount importance to us and data regarding the lifetime and failure modes of different source configurations is discussed. One half of the accelerating column has been constructed and tested at high voltage. One beam experiments in this half column are underway. The second half of the column is being built and the transition 2 MV experiments should begin soon. In addition to beam and source performance we also discuss the controls for the injector and the electronics associated with the source and current injection. 3 refs., 2 figs