A CROWBARLESS HIGH VOLTAGE POWER CONVERTER FOR RF KLYSTRONS
Advances in power electronic components make feasible the production of switch-mode power converters in module sizes exceeding 100kW. The development of a power converter system in modular form for feeding high power CW RF klystrons will be described. It has the advantage that the stored energy at high voltage is so small that the conventional crowbar protection is unnecessary. Results of work to test the principle on a 50kW klystron used for power testing accelerating cavities at Daresbury will be presented.
HIGH-VOLTAGE MODULATOR WITH SMALL ENERGY ACCUMULATION IN THE OUTPUT FILTER
A compact power source for the Injector of neutral atoms designed for diagnostics of plasma in thermonuclear installations is described. It forms output voltage up to 55 kV with an output current up to 3A during the two seconds pulse. The power source is constructed by the module method. It consists of six identical cells. Each cell includes an IGBT inverter operating at a frequency of 5 kHz, a high-voltage transformer with a 1:20 transformation ratio, bridge diode rectifier and capacitance filter. Outputs of the cells are set up in series. The inverters are phased-in such a way that the main frequency of output voltage ripple equals to 5kHz*2*6=60kHz. A capacitance filter with accumulated energy less than 2 J is enough for decreasing of ripple amplitude to level less than 1% under the nominal load. Combination of such an output filter with comparatively low leakage inductance of the high-voltage transformers and high speed of response of protection circuits of IGBT inverters allowed reliable protection for the grid system of the Injector against a break-down without expensive crowbar switch. The report presents the features of technical realization of the power source and its experimental and operational characteristics.
Realization of the LEP power converters
After a phase of intensive and detailed preparation, which included preliminary inquiries to a wide variety of firms, more than forty contracts and large orders were placed with industry. They cover the power part of the converters for the magnet system, the RF klystrons and the vacuum pumps as well as the electronics for the supervision, control and local intelligence for these high-precision equipments. The first deliveries of the series production started in the second half of 1986 and by the end of 1987 most of the high-power units for the magnet system have been delivered to CERN. After thorough tests they are being installed in the LEP equipment buildings. This includes all the equipment necessary for the injection tests into LEP octant 1 to 2, scheduled for July ‘88. The tests on the prototype 100 kV, 40 A converter for the RF klystrons were successfully terminated with a full power run on the RF test string. The first sets of the series units are being delivered, tested and installed. An important aspect for obtaining high reliability lies in the automatic test procedures which are rigorously carried out, starting at the module level and ending at the complete equipment.