Proton Synchrotron Division Introduction Following the celebration of the 40th anniversary of the PS at the end of 1999, the synchrotron this year entered its fifth decade of operation as CERN’s workhorse accelerator. The Division was once again fully occupied supplying its usual multitude of beams to the users, nevertheless finding time to work on other exciting subjects not directly linked to today’s beams, and including essential R&D aimed at the very long- term future of CERN. Nowhere else in CERN does one find such a diversity of topics being studied and machines being operated, which is what makes the Division so attractive. In April the ISOLDE technical team was welcomed into the Division, it having been decided by the CERN management that PS would be a more logical home for ISOLDE operation and development than its former home, EP Division. Then at the end of the year a group of RF experts from SL Division was also welcomed into the Division. Since it was no longer necessary to coax the best performance from LEP’s superconducting cavities after the closure of that machine, this team will become the nucleus for the construction of the new CTF3 test facility. The highlights of the year with regard to beams were the commissioning of the Antiproton Decelerator (AD) and the start-up of the neutron Time-Of-Flight (nTOF) facility. Both had been eagerly awaited by the physicists, who obtained exactly what they were expecting, although perhaps with just a slight delay. The year also saw the end of a decade of electrons/positrons in the PS for LEP, and the best run ever for heavy ions. This latter run was scheduled originally as the last, but it has now been agreed that ions will come back again in 2002/3, and of course later for the LHC. Work continued on improving the proton beam needed in the future by the LHC, and during this time a new intensity record was established for protons in the PS, and extracted from it. In summary, the year 2000 was an excellent one for the PS and for the Division. Operation Operating statistics for the different particle beams in the PS Complex in 2000 are presented in the tables below. Proton Synchrotron Division 185 Operational statistics for lepton operation in 2000 Total number of hours scheduled for lepton operation, including expt. areas 6787 h Total number of hours achieved for lepton operation 6573 h Hours scheduled for lepton production for SPS/LEP, including setting up in PS 5242 h Hours achieved for lepton production for SPS/LEP 5041 h Electrons supplied to SPS/LEP 1.50 × 1017 Positrons supplied to SPS/LEP 1.38 × 1017 Operational statistics for proton operation in 2000 Total number of hours scheduled for proton operation 6477 h Hours scheduled for setting-up and machine development 441 h Hours scheduled for proton production for SPS 4038 h Hours achieved for proton production for SPS 3832 h Protons produced for SPS (at PSB extraction) 1.76 × 1019 Protons produced for SPS (at PS extraction) 1.59 × 1019 Protons for machine studies (at PSB extraction) 1.99 × 1018 Protons for AD (at PSB extraction) 2.62 × 1018 Protons for East Hall test beams (at PSB extraction) 7.74 × 1017 Hours scheduled for ISOLDE operation 3224 h Hours achieved for ISOLDE operation 3136 h Protons supplied by PSB for ISOLDE operation 8.73 × 1019 Operational statistics for Pb-ion operation in 2000 Hours scheduled for ion production for SPS 1184 h Hours achieved for ion production for SPS 1138 h Total charges of Pb53+ ions for SPS (at PSB extraction) 1.91 × 1016 Total charges of Pb53+ ions for SPS (at PS extraction) 1.4 × 1016 Operational statistics for AD operation in 2000 Hours scheduled for AD operation for physics 1482 h Hours achieved for AD operation for physics 1272 h The Proton Run from March to September The PS Complex started up at the beginning of March as usual, following the annual shutdown. The LPI machine was the first into action, but the proton Linac 2, the PS Booster and the PS itself were not far behind. Leptons were injected into the PS on 13 March with the protons following soon after. However, it quickly became apparent that there were some timing or synchronization difficulties affecting all machines. These problems were soon traced to an unforeseen instability in the TG8 timing units, which had been modified during the shutdown; the PS Complex has about 250 of them. When laboratory tests revealed that the problem could not be resolved easily, it was decided to go back to the old hardware/software configuration for each of 186 Proton Synchrotron Division the 250 units. Thanks to a big effort from the Controls group this change was made in less than a week, and the delivery of beam to users was not delayed. LEP began operation on 3 April, and the East Hall beams were delivered as planned a week later. ISOLDE was also scheduled to begin operation then, and for ISOLDE this start-up was an important one as it was their first as part of PS Division. All went as planned and the PSB beams at 1.0 and 1.4 GeV, with nominal intensity up to 3 × 1013 protons/pulse, were sent to the ISOLDE target by mid-April. ISOLDE started by using the GPS target station, but one of the big priorities for the first half of 2000 was to complete the commissioning of the second separator (the HRS). This is important if 400 shifts of beam time are to be delivered to the ISOLDE users per year, as promised. This important milestone was passed at the end of May when the first scheduled HRS physics run took place. The SPS proton physics programme was scheduled to start a week after Easter, but this did not mean that the SPS was idle until then. The PS had to supply a number of specialized Machine Development (MD) beams to the SPS machine physicists as part of the preparation of the SPS for LHC. On 2 May, the SPS began fixed- target physics operation with protons. This operation normally uses the standard five-turn proton extraction at 14 GeV from the PS. However this year, the SPS scheduled a two-week physics run to test some components of LHC detectors. These tests required the SPS to extract beam at 450 GeV, with the LHC-style 25 ns bunch spacing. As this bunch spacing is established in the PS, it was decided to perform this test run using a test version of the LHC beam in the PS, instead of the standard SPS proton beam. This mode of operation was extremely successful and will probably be repeated for similar runs in the future. AD commissioning started on time although there had been a serious vacuum leak on a stochastic cooling kicker, and some alignment and vacuum problems with the electron cooler. However, this did not stop the AD team making excellent progress, and the goal of decelerating antiprotons to 100 MeV/c using both stochastic and electron cooling was successfully achieved by July. The AD requires two beams from the PS. First the machine is set up using 3.5 GeV/c protons, which are injected in the ‘wrong’ direction around the AD machine (i.e. they circulate anticlockwise). This has the advantage that the AD can be optimized for deceleration with a relatively intense proton beam rather than with low-intensity antiprotons. However, the beam cooling systems do not work in this mode. Therefore, the transverse emittance of the 3.5 GeV beam has to be very delicately controlled in the PSB and the PS, to allow subsequent deceleration in the AD. Then, to produce antiprotons, the AD needs a high-intensity 26 GeV proton beam incident on the antiproton production target. This beam is produced by injecting four PSB bunches into half of the PS circumference and then compressing them into a quarter of the circumference, just before ejection from the PS. This new scheme was made operational during the PS start-up and 1.5 × 1013 protons at 26 GeV were available for antiproton production for AD right from the start. Every 12 weeks or so, the PS main power supply needs some regular maintenance because it is rotating machinery (and is now more than 30 years old). A 10-hour technical stop was scheduled for 7 June, in the shadow of which other interventions were carried out, including a large amount of scheduled (and unscheduled) vacuum work on Linac 2, the PSB and the PS. All the PS Complex water stations were also stopped for routine maintenance and inspection. In spite of the large amount of work carried out, all the beams were back again by early evening. For the PS, this was simply a continuation of what had been already operational: protons for SPS, leptons for SPS/LEP, slow extracted beams for DIRAC and the other East Hall experiments, the AD production beam, and a number of MD beams for both PS and SPS studies. At the Proton Synchrotron Division 187 Booster, the ISOLDE programme at the GPS station was in full swing and, throughout June and July, the commissioning tests of the HRS continued. During June, a lot of effort was put into completing the commissioning of the AD machine, in order to meet the re-scheduled deadline for starting AD physics on 10 July. By 14 July, the ASACUSA team was able to announce that it had made ‘a complete scan of a 597 nm resonance’.