Computerized precision control of a synchronous high voltage discharge switch for the beam separation system of the LEP e+/e- collider

Electrostatic separators are used to separate the beams in the LEP (Large Electron Positron collider). The counter-rotating beams are eventually brought into collision in the four low beta insertions, using switches to discharge simultaneously four high-voltage (HV) circuits. Each switch consists of four spark gaps mounted in a pressure vessel. A reduction of the gap widths below the self-ignition distance by electric motors results in the initiation of the discharges. Synchronization is ensured by the electrical coupling of the electrodes connected to ground. The design and performance of the computerized precision control of the discharge switch are described. The dynamic characteristics of the prototype switch are also presented. It is concluded that, with computerized precision control of the electrode motions of an HV discharge switch, it is possible to obtain better time accuracy than would have been the case with conventional analog servo feedback systems. In fact, the accuracy can be a fraction of the system time constant and allow large tolerances on the system parameters