Automation

New sources now have a much wider range of choices for the development of control systems compared to the past, given the increasing number of commercial systems and collaborative projects, e.g. the EPICS system which was chosen by BESSY II because of the large amount of support available. More recently, ESRF/DESY are proposing a standard system that can be applied to both beamlines and machine, and which can be made available to other laboratories. It has been selected by the SOLEIL project and is under consideration also by the SLS, which is also considering a industrial-based system. Cheap multi-node controllers are also available, i.e., LONWORKS, which although too small for the main control system should be a feasible and cheap solution for systems such as vacuum control. The SRS has developed a new PC-based control system.

ELETTRA is developing a 1bm ("one button machine") program, which allows the controlled execution of modules, including existing modules, to perform routine operational sequences. Such an approach is of particular benefit for a machine with many different operating modes. Both the ESRF and ELETTRA have closed automatic closed orbit correction performed in the background every few minutes. An automatic program triggered by a beam loss to record beam parameters has proved useful in fault diagnosis at the ESRF.

ID Control by Users

Pressure from users to have control of ID gaps is generally growing. User control is now partially allowed at the ESRF over limited gap ranges, however changes are still supervised by the control room to prevent mis-use. The largest closed orbit effect is given by helical devices, however correction coils are used to reduce the changes to less than 10 % of the beam size. Changes to the coupling have also been observed due to some helical devices. Low energy machines are more sensitive to gap changes and ELETTRA is planning to allow a limited user control in the near future.

User Requirements

An important topic at the ESRF is the provision of different filling modes. Apart from single bunch and 1/3rd or 2/3rd filling, several "hybrid" modes have been developed. It was pointed out that there is interest for certain types of experiment also for a completely uniform fill, which may be an additional requirement for new light sources to consider. It is planned to try this at the ESRF using a Qs-splitting cavity to damp longitudinal coupled bunch modes. Such a requirement led to a discussion of ion trapping effects. It has been noted in the past that such effects have been observed at SRRC and ELETTRA, whereas they were absent from both the ALS and ESRF. In recent experiments at ELETTRA the original observation of ion trapping (1994) was no longer clearly seen, and it is assumed that the gas pressure during the commissioning phase lead to enhanced trapping effects.

It was pointed out that some beamlines need a stability better than 10 % of the beam size: this is required for example on the ESRF helical undulator which switches helicity about every 30 minutes.

A new type of non-destructive gas ionization photon detector has been developed by the KSRS group which is capable of giving information about both beam position and cross-section, as well as absolute intensity. First results of tests made at DCI were presented.

Fault Recovery

The high up-time of the current facilities generally indicates a satisfactory situation with regard to preventative maintenance, fault analysis and recovery. Comments were made on the usefulness of having on-line diagnostic tools to allow efficient recovery of faults. Internet products now exist for such purposes, for example at the APS. Control systems should be flexible enough to allow the easy build up of monitoring programs which are an essential feature of present day facilities. It was pointed out that the availability of spares is also important, particularly in view of components becoming obsolete.

Beam Loss Monitoring

At the ESRF it has been discovered that beam loss is mainly from the Touschek effect acting in the vertical plane, arising from the large vertical chromaticity which generates a large tune variation with momentum leading to resonant loss. As a result, narrow gap IDs cause increased bremsstrahlung in the beamline, activation of the ID vessels and radiation damage of the IDs. Possible solutions are a small vertical beta function at the IDs, removing the need for a large vertical chromaticity by means of higher conductivity vessels or use of feedback, and full protection of losses by use of two defining scrapers. At ELETTRA the distribution of losses during a beam dump, performed by momentarily removing r.f. power, is found to be non-uniform with preferential loss symmetrically placed about one point in the ring.

prepared by C.J. Bocchetta and R.P. Walker