Solid-State DC Power Supplies for Gyrotrons and NBI Sources

Modern Gyrotrons and NBI sources require highly efficient, reliable and compact DC sources. Based on high power broadcast modulator technology, solutions for various applications are available. Over many years, accel-sources for NBI using the PSM-design (Pulse Step Modulator) with GTO7apos;s (gate turn-off thyristors) have been operating in KFA, Julich, Germany very satisfactorily. Here the next generation of power supplies using recently available, very fast switching elements, will be discussed. For output currents up to 100 A DC and output voltages as high as 100 kV, such DC sources based on the already existing standard design allow good regulation at very low stored energy, thus avoiding crowbar systems. The individual switching power supply was developed for AM (amplitude modulated) broadcast transmitters and is hence available at reasonable cost as an off-the-shelf-item. In-built control and test systems on each switching module allow the safest operation. The DSP-based (digital signal processor) overall control system switches the individual switching units on and off, being series connected. Any desired output voltage, up to the nominal value can be obtained, with nearly no degradation of the overall efficiency (> 96%). Fast switch-off of all units removes the output voltage in a few micro seconds in case of flash overs in the source, or gyrotron, or other similar incidents, with no need for supplementary shorting devices, such as crowbar systems. The PSM-principle, furthermore, is characterised by a certain redundancy in case of loss of switching modules, and flexibility in structure, to match eventual future changes in application at reasonable cost. The key to such flexibility lies in the design of the DSP-controller of the whole power supply, with a very simple interface to the switching modules and a software based control algorithm. As a future outlook, some specific characteristics of such power supplies matching the eventually more complex requirements of future gyrotrons are also investigated.