During the period from 1/1/99 to 31/12/99, 686 shifts were allocated to the Users, i.e., 5488 hours (excluding the shifts for radiation tests and PSS tests). Subtracting the 189 hours due to failures (3.4%) and the 63 hours of dead time necessary for the refills (1.1%), 5236 hours of beam time were indeed delivered for experiments. This represents an average beam availability of 95.4% during 1999, a new record (Figure 133). The other figure of merit, the Mean Time Between Failures, has reached 31.9 hours, a slight improvement on that achieved in 1998 (Table 1). Thanks to a new method of testing the Personal Safety System (PSS) on the beamlines, only one shift per period of six months is dedicated to PSS tests instead of the habitual five shifts in the past.

Modes

The multibunch modes remain predominant with 65% of the time allocated to the 2/3 filling modes (Figure 134). The 1/3 filling mode has now completely disappeared and left its place to the 2/3 filling mode which, in turn, has now given up its place to the 2 x 1/3 filling mode. This new mode consists of two trains of 330 bunches spaced by a gap of 1/6th of the ring. It has all the advantages of the 2/3 filling, i.e., an intensity of 200 mA and a 65 hours lifetime whilst having the time structure needed for some experiments. Although the hybrid mode has not been abandoned, a general trend clearly is developing for separate shifts of single and multibunch modes in preference over the hybrid mode. The disappearance of the 32-bunch mode is simply explained by the fact that this mode was considered as a fallback position mode when several RF fingers problems were encountered last year. Although not fully solved at this time, the study of the RF fingers behaviour has dramatically progressed (thanks to a bench test installed on the Storage Ring) and we can once again consider working in 16-bunch mode.

During six User Service Mode (USM) shifts, the beam was delivered at 4 GeV for the first time. This energy led to a record in low emittance values: ex = 1.7 nm.rad and ez = 12 pm.rad. It was possible to achieve 100 mA with a lifetime of 10 hours. Several beamlines took advantage of the beam to perform experiments up to 30 KeV (using very high ranking harmonics from the undulator).

Failures Analysis

The longest beam interruption occurred during run 99-4: the feed through connector of an ion pump in Cell 23 broke and the corresponding cell was brought to atmospheric pressure. This incident may result from ageing combined with extreme working conditions (high voltage within a small volume of air). Fortunately, the incident happened the day before the start of a Machine shutdown. Although the repair was done in record time (12 hours), the lifetime after the intervention would have been so short (less than 1 hour) that the decision was taken not to return to USM. The full interruption therefore lasted 27 hours.

The second longest failure happened during run 99-2 and interrupted the Machine for 18 hours when an RF finger melted upstream of the in-vacuum undulator. A gap between the fingers and the sleeve, due to a mounting problem, was discovered. With the exception of this incident, the RF finger problems have almost disappeared thanks to an exhaustive control of the RF finger ­ by performing in situ radiogammagraphies ­ followed by the systematic replacement of any suspicious-looking assemblies at each vacuum intervention.

Among the eight failures which lasted more than two hours, we note five cooling problems. Although corrosion of the copper by the de-ionised water (producing copper oxide) is unavoidable, it appeared that an abnormally high rate of copper oxide was present in the water circuitry. This copper oxide accumulated on the calibrated fittings of magnets, hence reducing the water flow rate and stopping the corresponding power supply. The only short-term solution consisted of inserting special resins to trap these oxides. This proved to be efficient. However it has since been discovered that these resins saturate quickly and so their regular renewal is necessary. Since run 99-02, a test on the water circuitry is regularly carried out during Machine Dedicated Time in order to detect the first signs of blockage. This problem is partially at the origin of a degradation in the FE equipment's Mean Time Between Failure. It should also be noted that, following many problems of radiation effects on the flexible pipes, all of the magnets' and vacuum vessels' water cooling pipes have been replaced by those made of an improved radiation-proof material.

Although it remains the most fragile piece of equipment accounting for 40% of the failures, the MTBF of the Radio Frequency system has improved by 10% compared to last year.