BEAM DIAGNOSTICS

The commissioning of the Accumulator and the Transfer Line has taken advantage of all the installed instrumentation, consisting of removable fluorescent screens, stripline beam position monitors (BPM), total transmitted current monitors in the Transfer Line, 4 stripline BPMs, 8 button BPMs, a total current monitor, a synchrotron radiation monitor, a beam loss monitor and the betatron frequency measuring system in the Accumulator.

The beam diagnostic instrumentation for the DAFNE Main Rings is operational; its main component is the beam position monitoring system, realized by means of electrostatic "button" pick-ups. Due to the peculiar shape of the vacuum chamber cross section, which may be circular, rectangular or elliptical at different positions in the rings, and to the need of measuring the position of the two beams at the same time in the interaction regions, where the two beams share a common vacuum vessel, there are 10 different kinds of BPMs. A prototype for each kind of monitor in the arcs has been calibrated with a wire technique. The single electrodes have been measured and grouped together in such a way that the capacitances to ground of the pickups in a single BPM differ by less than 0.01 pF. The control electronics has been built by industry, under very peculiar specifications, including the possibility of measuring the position of the stored beam or even its position at any single passage. It is also possible to gate the measurement in order to distinguish, within the same beam, the position of the bunches which cross the other beam from that of non interacting ones, thus allowing the optimization of the luminosity by means of the beam-beam deflection method. Orbit measurement software has been developed and implemented on the the Control System. It can deliver a complete orbit display (~50 horizontal/vertical beam positions) at a rate of 2Hz.

A crucial component of the DAFNE control is the timing system, consisting of programmable VME boards, which synchronize between each other the accelerating RF systems and the pulsed elements of the different accelerators in order to make possible the injection of a single bunch in any desired bucket of the two Main Rings, starting from the Linac gun and passing through the Accumulator, with an accuracyof few picoseconds. The system, entirely designed and realized at LNF, can program, on the basis of 20 ms "states", any sequence of events corresponding to the different operation modes of the Linac/Accumulator complex. It delivers also all the triggers (TTL on 50 Ohm, differential ECL and NIM) required for the beam diagnostic instrumentation.

The longitudinal feed-back system of the beam, based on parallel arrays of DSP processors, developed in collaboration with the SLAC-LBL group, is now installed and ready for commissioning.

M.Preger 29 JUN 1998