Recent Changes in the Astron Fast Pulsing System

Two major changes were made in the Astron Fast-Pulsing System since June 1970. The hard-tube modulators used to charge the accelerator PFN´s have been changed to a resonant-charge system and completely rebuilt. While no comparative reliability records are available, it is obvious that the new system is at least ten times more reliable than the old system. The pulse-to-pulse regulation of the new system is not as good as was hoped for, but it seems to be adequate for reasonable performance of the accelerator. Furthermore, significant improvement should be simple and of negligible cost. The second major change was the building of a new power supply for the core-reset system. The old system had relatively poor voltage regulation (15 or 20%). Two problems existed - the power supply and cabling system were inherently poorly regulated, and an already too small substation was shared with another pulsed load of comparable size. Instead of about 90 small power supplies, the new system uses one large series-pass transistor supply, operated on its own 1.5 MVA substation. The new supply consists of a 340-V brute-force rectifier unit with a 1-F capacitor bank, followed by a series-pass transistor bank (about 2,000 transistors) feeding a distributed 1.3-F bank at 260 V. Rated output current is 7500 A. Output voltage is sensed at the most distant part of the load and a loop gain of 1,000 is planned for the system. The major components are completed and the substation and 13.