Minutes of HERA Meeting      28.10.2003

HERA

• HERA delivered several luminosity runs last week. Proton currents were up to 60mA, initial positron currents around 18mA. The efficiency was quite good. Beams were refilled relatively quickly. Background tuning took about 1 hour at the beginning of each fill. The proton background was quite high. The coupling is not yet understood. The specific luminosity was lower than the design value, about 1.4 10**30 cm-2 s-1 mA-2 at H1 and somewhat lower at ZEUS.
• There are several reasons for the large proton background and low specific luminosity. The vertical beam size of the positron beam at the IP is too small (bad for proton beam). The horizontal beam size is too large. The GA magnet power supply seems to be unstable, likely source for proton background spikes. The power supply electronics will be improved.
• The positron optics was improved. There was however no significant increase in luminosity.
• The positron current was still limited by beam pipe temperatures in order to avoid any further leaks due to synchrotron radiation. New temperature sensors were installed yesterday for better monitoring. The temperature limits will be increased. The positron current will then be limited by the RF power presently available.
• Saturday afternoon there was a failure of the cryo control system (failure of electronics board). The cryo system was without control. Warm air got into the system. The proton magnet temperature went up to 50K. Saturday to Sunday night HERA continued with positron operation. In order to speed up the cool-down it was decided Saturday afternoon to stop positron operation. Unfortunately, the cool-down speed was not increased.
• Another cryo failure occurred yesterday evening. Presently the proton magnet temperature is still up to 40K. Proton beam operation will not be possible before tomorrow.
• Yesterday HERA continued with positron machine studies and was planning to provide stable positron beam for HERMES and polarimeter studies.

ZEUS

• The calorimeter was repaired during the access yesterday. There are still some problems with the solenoid. It can be run without software checks. The new spare part is presently being calibrated.

• R.Yoshida discussed the background condition at ZEUS: CTD currents as a function of positron current scaled to Ip=60 and 100mA together with the current extrapolations. At present conditions the CTD limit is reached at Ip=60mA, Ie=35mA. Taking into account the expected improvements including a factor of 2 in proton vacuum, the maximum beam currents are Ip=100mA, Ie=55mA.
• Background plots Plot 1: CTD current scales by 20 Oct expectation, and the Ip and Ie during the same period. Looking at the CTD current and the proton lifetime, one has the impression that. a) HERA had a lot of trouble with protons and this is reflecting on the CTD currents b) The underlying condition of the background (i.e. if protons were not giving trouble) has been pretty constant.

  Plot2-5 are plots for the last 4 fills in plot 1.

  Plot2: 22-23 Oct.
  -e-particle background was relatively high at the beginning and improved when the positron was at about 10.5 mA
  -p-particle background was ok until about 10.5 mA, when it became suddenly worse.
  --which drove up the CTD current, and we couldn't continue to run.
  --there are indications that we began to get synchrotron radiation at about the same time.

  Plot2: 23 Oct
  -e-particle bg was ok until about 12.5 mA when it suddenly became worse
  -p-particle bg was high to begin with, and continued to get worse--is this correlated with vacuum readings at 3.5 m?

  Plot3: 24 Oct: this is the only "reasonable" fill of the 4.
  -e-particle was as expected
  -p-particle was somewhat high.
  -There was some periodic instability in the p-particle. This presumably causes spikes and frequent trips of the CTD.

  Plot4:
  -e-particle was high-ish but not catastrophic
  -p-particle was at the expected level at first, but quickly went out of control, causing the CTD to draw too much current. The fact that plot 2 and plot4, for runs with relatively high Ip have periods where the C5p is on the "expected" line probably means that the Ip dependence of the parameterization is ok.

  Conclusion: HERA is not yet in shape to consistently deliver clean beams where the background is dominated by the presently irreducible part (represented by the 20 Oct parameterization). Also, there are no signs yet that the irreducible part is getting better with time.
  The synchrotron radiation background is not visible anymore.

• Remarks by F.Willeke: The IP orbit bumps will be improved. Proton background will be reduced by increasing the positron vertical beam size and turning of the feedback system. Operators have to gain experience in background tuning.

H1

• Running conditions have been pretty good. 1.6pb-1 have been collected. HERA has to be congratulated for the short breaks between fills. Proton spikes were causing HV trips. Best running conditions were achieved 24.10.2003 0:00-8:00. There were no HV trips at all. (At the same time ZEUS was not able to turn on HV due to high backgrounds.)
• During the positron only fill the CJC current was lower than before. The present limit on the positron current is 30mA.

HERMES

• Was able to take data without any special background tuning.
• The positron current should be increased.

Schedule this week

• Finish cool-down of proton machine. First proton operation probably tomorrow.
• This afternoon and tonight: Positron studies (prepare new orbit files, reproduce bad positrons orbit and watch beam pipe temperatures, stable beam for HERMES and polarimeter studies).
• Continue luminosity operation
  • Improve proton background (Change electronics of GA magnet power supply, increase vertical, decrease horizontal positron beam size at IPs). Ip=60mA.
  • Increase positron current (raise temperature thresholds).
  • Some dedicated polarization studies may be needed in case parasitic studies take too long. Another energy scan is required.
• R.Klanner asked whether 12 positron pilot bunches, i.e. 10% of the positron current, are really needed.

Operation over Christmas and next year

• M.Bieler and F.Willeke looked at 4 different scenarios for operation over Christmas and in 2004, see transparency.
  Options: 1) continue operation over Christmas, 2) a short break (7 days off), 3) long break (14 days off) and 4) include pre-accelerator interlock tests (24 days off). Another option is to include the HERA interlock tests (about 6 week break).
  HERA would try to operate over Christmas if at least one of the experiments will take data. The interlock tests for all machines should be shifted to August/September, i.e. 6 week shutdown.
• H1 is in favor of running over Christmas (priorities: 1,2,3,4,5.) A Christmas shut-down should be avoided. A shut-down in August should be as short as possible.
• ZEUS will not be able to run over Christmas, experts will not be available. The preference is to start up at 2.01.2004. Starting shifts 29.12.2003 would be possible. There is however some risk that the detector will not be working properly without component experts. Options 1, 4, 5 are disfavored. The shutdown should be in August, not 2003/2004.
• HERMES will not be able to run shifts over Christmas. Starting up 2.01.2004 is possible. There should be no shut-down in the summer.

• A long break over Christmas is not favored. Interlock tests are manditory next year. It is unlikely that the interlock tests can be postponed until Dec 2004. In case the interlock tests are done in August, annual interlock tests will be done in the following summers. R.Klanner said that this would be in accordance with the end of HERA operation in summer 2007.
• The agreement was option 2): switch off 23.12.2003, turn on 29.12.2004 (power supplies and cooling towers will not be switched off) and to do the interlock tests in August, i.e. a shutdown of about 6 weeks in August/September.
• The machine group will check whether sufficient man power will be available.
• The schedule will be discussed in the directorate tomorrow.

                Uwe Schneekloth