COORminutes030701

Minutes of HERA/Experiment Coordination Meeting 01.07.2003

F.Willeke reported on the extensive shut-down activities of the machine group, see transparencies. Everything was completed except:

The absorbers 4 (N/SR11) were not exchanged. Coating of the new absorbers failed. The coated plates were damaged during brazing of the upper and lower halves.
The cooling of the GI/GJ magnets (N/SR) was not improved.
New electronics for the electron beam loss monitor system will be installed during maintenance days.
The wire position system will be installed during maintenance days.
The electron timing system was not modified. (HERMES had suffered from instabilities.) Maintenance of the glass fibers will be done. Components will be replaced in case of problems.
Experiments with cold surfaces (adsorption and desorption of residual gas) in the lab are in preparation.
The temperature of the GO/GG beam pipes cannot be decreased further without major changes of the GO/GG cryo system.

The proton ring magnets and superconducting electron cavities are cold. The H1 solenoid is being cooled down.
Most of the warm magnet power supplies were tested. A ground fault in the electron machine was found and repaired. A damaged coil of one of the BU magnets (vertical bent of the proton beam) NR75 is presently being repaired. The hope is to finish the repair by the end of this week.
A 120kV transformer failed yesterday during the re-commissioning of the electron RF system causing a fire in the modulator room in the south hall (6th floor). The transmitter SR will not be available for start-up. This does not cause a major problem. Without the transmitter the positron current is limited to 40mA at 27.5 GeV. The repair can be done during machine operation.
Survey and realignment of the IR magnets is in progress.

(See F.Willeke's transparencies and discussion below)

4 weeks of beam bake-out at 12GeV. GO/GG beam pipes will be warmed up 4 to 5 times. The gas load and gas composition will be recorded during the warm-up. Parasitic machine studies will be performed.
After 12GeV bake-out, 8 days of running at 27.5GeV for synchrotron radiation induced desorption is planned. Polarization studies will be done in parallel.

The goal is to optimize luminosity from the beginning of luminosity operation, scheduled to start 29.09.2003. Since the total beam currents will be limited by background conditions running with 120 bunches was proposed.
An integrated luminosity of 40pb-1 should be achieved until the end of luminosity operation (17.12.2003).
The positron bunch length at injection can be increased from 3 to 5mm in order to reduce higher order mode heating.

The cooling of the Central Inner Proportional chamber was improved. Defective electronics was exchanged. The CIP z-vertex trigger is expected to be fully effective.
The Central Silicon Tracker was repaired at PSI. The cooling was improved.
The Backward Silicon Tracker suffered severe radiation damage during the last running period. Defective sensors were replaced. New repeater electronics was installed. The BST is fully operational.
The radiation protection was improved: 2mm PB shield around beam pipe between C5a and C5b and new radiation monitors.
A new transition beam pipe with new C5b collimator and integrated ion getter pump was installed. Higher order mode losses were reduced by 15-30%. Water cooling was added. The beam pipe was pumped down again. The pressure readings of the new mass spectrometer and ion getter pump agree. The mass spectrum is as expected (no hydro-carbons).
The Very Forward Proton Spectrometer was installed. Commissioning with beam will be done in September. A bump in the proton orbit is needed for full acceptance.
After the background related improvements safe operation of the CJC should be possible at Ie*Ip = 55* 105 mA**2.

Two weeks of cosmics run from 4.07.
Collimators should be closed during the beam bake-out. Temperature, pressure and radiation will be monitored.
Luminosity operation should start when the background conditions allow to read 2000 peak luminosity (35 * 15 mA**2 in 60 bunches). The number of bunches should be increased, as total currents can be increased.
The positron beam should be polarized from the beginning of lumi operation. Start with right-handed positrons. One change of spin orientation before Christmas.

All shutdown activities are finished. The main work was the modification of collimators as presented in previous meetings and the repair of the Straw Tube Tracker. Friday the detector was closed to about 1/2m.
Yesterday work in the hall was interrupted by the fire on the 6th floor. The hall is still closed. Air samples are presently being analyzed.
The movement of the bridge magnets will be monitored by the survey group when the yoke is finally closed, scheduled for Thursday.
The diamond coated tungsten sample has not yet arrived.

The tracking chambers are being flushed with gas to prepare for cosmics.
The background conditions have to be optimized (beam orbits and collimator scans) before the 27.5GeV synchrotron radiation scrubbing.
The spin rotators should be set for right handed positrons.

All shutdown activities are finished. There were no changes, which could influence the beam. The alignment of the target region was improved.
The detector is ready for data taking.
Shifts will start 1.09.2003

HERMES will not take data during the 12 GeV beam bake-out. The statistics would be marginal.
The target magnet should be on during polarization studies.
Reducing the number of positron bunches during luminosity operation is not acceptable.
The positron beam should be polarized at the start of luminosity operation.
Would like to do end-of-fill running from the beginning of luminosity operation (increased target density 1 hour before beam dump).
Long term plans are to switch between electrons and positrons when the recoil detector is in operation and for some running at 12 GeV.

There were no objections to the schedule presented by F.Willeke: schedule
Two weeks are scheduled for the interlock test. (There is some uncertainty as it is the first time the inspection is done by the TUEV.)
Low current proton beam can be stored occasionally during the 12 GeV to monitor the proton background and for parasitic machine studies.
Luminosity operation will start with 120 bunches in order to maximize the luminosity as long as the beam currents are limited by the background conditions.
HERMES end-of-fill running does not have high priority at the start of luminosity operation.
The installation of the HERMES recoil detector is delayed. The installation date should not be in conflict with the overall HERAII schedule.
Dates of maintenance days: Thursday 7.08., 4.09., (Monday) 29.09., 6.11., 4.12.2003.

The date of the next coordination meeting is Tuesday, 09.09.2003 09:00hrs, seminar room 1.

Uwe Schneekloth