Summer Student Project: ISIS-13

Building a high power analogue amplifier

The ISIS synchrotron uses magnets to steer and focus the proton beam. As the protons are all positive, they repel each other and the size of the beam profile increases. Quadrupole magnet pairs are used to squeeze the beam back together. The main quadrupole magnets are powered by a 90MW resonant circuit, which is difficult to adjust freely, so trim quadrupole magnets are added to the synchrotron to make small corrections.

These trim quads are powered with an arbitrary waveform, up to 300 A at 600 V. At present the trim quad power supply makes use of six IGBT H-bridges, each switching at 25 kHz but interlaced to give better frequency response. The resultant switching frequency is 150 kHz, which is seen in the magnet current. When the beam is going at a certain speed, this noise has an accumulative affect, adding to the beam on each revolution and causing beam instability.

I would like a student to investigate the suitability of using an analogue amplifier design to provide the arbitrary waveform. The student will research amplifier designs (Class A, Class AB, Class G and Class H) and suggest a suitable topology. They will also investigate how power can be shared between parallel semiconductor devices in order to achieve the high current. The student will then build a low power version of the circuit (up to 50A, 300V) to demonstrate it working.

The project is suitable for a placement between 4 to 12 weeks.

Supervisor: Johnny Ranner (

You might particularly like this if you are interested in any of these: electrical engineering, engineering, physics.

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