Chopper control board check out: summary of chopper operation. PEP storage ring magnets and power supply system

Abstract

The chopper can be simplified by comparing its main SCR (or SCR's) to a switch being easily turned on with the main firing pulse (pulses) from the controller board. The commutator SCR is also a switch which turns on a ringing circuit that can shut off the main SCR and reset itself when given about 80 micro seconds to complete its cycle. Therefore, by operating the main SCR's for a longer or shorter time into a magnet and repeating this cycle many times a second so that the magnet smoothes out the variations in current, a regulated current can be maintained in the magnet. If the commutator firing pulse is delayed further in time the current in the magnet will increase. If the main pulse is followed shortly by the commutator pulse, current in the magnet will decrease. The increments of increase or decrease are very small due to the shortness of the cycle compared to the time constant of the magnet. The purpose of the pulse controller is then to deliver a main pulse trian and a commutator pulse train properly spaced for regulation in the 400A chopper. For the 1400 A chopper the main pulses must also be alternated between two SCR's so they can share the load current. The controller also establishes limits for the pulses to allow safe operation for the magnet and the chopper. The minimum pulse length to the magnet is 20% of the period at 2000 hertz. The maximum pulse length is 95% of the period at 2000 hertz. Some of the choppers run at 360 hertz, for this lower frequency the minimum pulse length is 1.8% of the period (the same number of micro-seconds), and the maximum length is 99% of the period. Note that the lower frequency gives a wider range at a sacrifice of frequency response.