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HERA Status

HERA Status. Joachim Keil, DESY (MPY). 59 th Meeting of the Physics Research Committee May 26 th , 2005. Contents. Operation of HERA 04/05 with Electrons Luminosity Performance Major technical Problems Polarization Improvements Schedule 2005 Conclusions.

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HERA Status

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  1. HERA Status Joachim Keil, DESY (MPY) 59th Meeting of the Physics Research Committee May 26th, 2005

  2. Contents • Operation of HERA 04/05 with Electrons • Luminosity Performance • Major technical Problems • Polarization • Improvements • Schedule 2005 • Conclusions J. Keil : HERA Status

  3. Re-Commissioning with Electrons • HERA electron operation: • More synchrotron radiation (for design currents: 26 kW 36 kW) • Different orbits for e and p in IR • Successful re-commissioning strategy (Oct.-Dec. ‘04): • Set up/check HERA-e with positrons • Move magnets in IR • Continue with electrons • Beam-based alignment; check of optic and correction; … • Start with electrons was smooth: No big problems found! • But: It was necessary to move H1 by x=7 mm due tolimited space in GO magnet on left side • Delay in schedule: • Quadrupole GN NL20 had a burnt coil • Vacuum leak at GI07 NR J. Keil : HERA Status

  4. Trajectories for e-/p and e+/p in IR GM GM GM GM GG,HG 7.5 mm GI - GO,HO p beam for e- p + p-beam for e+ e--beam - - GI GI + e+-beam + + GJ - GJ BO e Radial orbit shift at IP of 7.5 mm between electron and positron operation J. Keil : HERA Status

  5. Parameters of Run ‘04/05 with Electrons Design 2005 with e- For e-: Vacuum, RFFor p: Pre-accelerators Beam-Beam effects For p: Long. instability Hour glass factor included in design! J. Keil : HERA Status

  6. Beam Currents • Peak currents for run ‘04/05 with electrons (150 bunches): • Ipmax = 102 mA • Iemax = 40 mA • Proton single bunch current is high:Would be 123 mA with 180 bunches! • Electron current was limited first by H1 background (vacuum) • No progress increasing the electron beam current in the last monthsslow conditioning of RF cavities, transmitter problems and vacuum • Switch to 180 bunches if 40 mA electrons can be routinely filled; but dust trapping probability will be higher! J. Keil : HERA Status

  7. Specific Luminosity • High specific luminosity with electrons for 2004/05 run: Ls = 1.8 - 2.2 1030 cm-1·s-1·mA-2 • Specific Luminosity is larger than the design value of Ls = 1.84 1030cm-1·s-1·mA-2 • One reason for higher specific luminosity compared to last year with positrons (1.2 -1.61030) is the smaller proton emittance and bunch length • Calculated specific luminosity based on measured beam parameters can describe the measurements of H1 and ZEUS sufficiently good overestimated J. Keil : HERA Status

  8. Integrated Luminosity 04/05 • Integrated luminosity is 95.3 pb-1 in 156 days (start: Dec. 17th, 2004) • Best run delivered 1.1 pb-1 within14 hours • On average 0.61 pb-1/d (number for last year: 0.41 pb-1/d) • Mid of May was best so far:HERA delivered 1.17 pb-1/d • New record peak luminosity ofL= 5.071031 cm-2·s-1 was achieved • But: high proton background and many spikes until BU SR coil was identified as the culprit fixed in April! J. Keil : HERA Status

  9. Integrated Luminosity Luminosity production rate with electrons in 2005 is higher than 2004 for positrons! (ZEUS) J. Keil : HERA Status

  10. HERA e--Lifetime • Again: Sudden lifetime reduction and lifetime recovery during electron operation • At the same time increased beam loss measured • Observed for I > 30 mA since January ‘05; but number of events is fortunately rare at the moment • Theory: trapping of positive ionized dust particles by the negative charged electron beam • Source of dust: Ion getter pumps (dipole pumps were already replaced in shutdown 1997/98) • If the number of bunches is increased, the probability of dust trapping gets higher Lifetime event 4.5.2005 J. Keil : HERA Status

  11. HERA Operational Statistics 2005 Relative large amount of faults is reducing the efficiency of operation; fraction for e- and p-injection times have decreased, fraction of luminosity-run increased since ‘04. Main problems for faults and delays in ‘05 were due to magnet problems, cryogenics, power supplies, PETRA and problems with the proton quench protection. J. Keil : HERA Status

  12. Major technical problems • Nov. 2004: • Burnt coil of proton quadrupole magnet GN NL 20 Coil exchanged • Dec 2004: • GI NR 7 vacuum leak; broken feed through of NEG pump • Jan. 2005: • Ground fault proton quadrupole magnet GN NL 23 Coil exchanged • Feb. 2005: • Cryogenic compressor failure quick repair but p-ring warmed up (1 week) • Apr. 2005: • Periodic p-background spikes shorted coil of BU-magnet SR; coil exchanged (4 days) • May 2005: • Vacuum leak in p-chamber between GM proton quadrupoles NR welding of seam; bad vacuum (since 1 week) J. Keil : HERA Status

  13. GN Magnet Problem • During recommissioning in Nov. ‘04 the magnet GN NL20 failed (cooling problem) • GN magnet: vertical focussing low beta quadrupole for protons; 12 magnets • Damaged lower inner coil had to be exchanged (six days lost) • In January ‘05 also the magnet GN NL23 failed with ground fault; all four coils were replaced (1 week) • Possible reason: Magnets have been operated with 1638 A during power supply tests in October last year exceeding the manufacturer limit of 1600 A Measures: • Current of power supply limited to 1470 A (max. value for luminosity run) • New coils ordered! J. Keil : HERA Status

  14. BU Magnet Problem • Since January ‘05: Periodic background spikes in combination with vertical orbit movements; not all the time • Reason was shorted coil of BU magnet SR; April:coil exchanged (4 days) • BU bend the protons upwards at end of straight sections; 18 magnets • Six BU-coils in NL (last shutdown) and one coil in SL were already exchanged • Candidate for another short: BU OL Measures: • Measurement of voltage drop of coils • Exchange of all remaining BU coils in next shutdownShutdown delayed until all ordered coils are delivered (shutdown starting at 14th Nov. ‘05) Collimator beam loss rate J. Keil : HERA Status

  15. Polarization Non-colliding bunches: ~50% Colliding bunches: 40% • Even after long tuning polarization is dis-appointing low • Colliding bunches reaches 40% only at end of run (but non-colliding have 55%!) • Influence of beam-beam effect: Polarization is rising due to growth of proton emittance and declining proton intensity • Energy and harmonic bumps are optimized • Problem: Tunes are not optimal for electrons and polarization! Measures: • Electron intensity related effects allows to decrease the tunes at lower electron currentBut: e-background spikes at H1! • Possible solution: Mirror tunes started test with mirror tunes last week! Polarisation History of polarization and single bunch polarization J. Keil : HERA Status

  16. Mirror Tunes J. Keil : HERA Status

  17. Improved e--Transfer Efficiency • Transfer efficiency of El-Weg between PETRA and HERA-e: • HERA I : never reached 100% • HERA-II: sometimes only 30-40% and non-reproducible! • Better efficiency faster filling, less radiation during injection process Measures: • Calculation of a new matched optic for the EL-Weg adapted for HERA-II injection optic • Installation of 6 beam position monitors in last summer shutdown • Checkedmagnet rolls by survey ok! • Measurement of response matrix of the EL-Weg  large error in optics • Measurement of quadrupole calibration curve calibration wrong! • Now: • Transfer efficiency >70% • Efficiency more stable than before • Remaining losses: PETRA extraction J. Keil : HERA Status

  18. Improvement: Proton Tune Controller • Energy ramp of protons is demanding: • Induced eddy currents in super- conductors  Time varying dipole and sextupole fields • Tunes near coupling resonance • Control of beam parameters is done manually by operators watching beam signals and turning knobs; needs much experience! • Nevertheless p-beam often get lost Measure: • Semi-automatic control of tunes was developed; ramping between 70 GeV and 920 GeV and electron refill are now far easier than before! • Coupling and chromaticity control under development J. Keil : HERA Status

  19. Longitudinal Multi-Bunch Feedback Schematic principle • Proton-bunch lengthening due to longitudinal coherent multi-bunch instability • Longer bunches smaller specific luminosity („Hour glass effect“) • Happens during proton ramping Measure: • Installation of an longitudinal multi-bunch feedback system for protrons • Status: Feedback cavity arrived; first measurements done • Installation in next shutdown • Goal: Reduction of bunch length at 920 GeV from 1.6 ns to 0.7 ns (FWHM); realistic? Feedback Cavity J. Keil : HERA Status

  20. Schedule 2005 • Schedule • Start of luminosity operation: 17th Dec. ’04 • Start of shutdown: 14th Nov. ’05 • End of shutdown: End of Jan. ’06 • Luminosity operation: 2nd week in Feb. ’06 • Expectations for integrated luminosity • Until now: Li = 95 pb-1in 156 days • Conservative assumption: Average increase of 0.61 pb-1/d • This includes hardware faults, maintenance days, … • 176 days remaining  Additional 107 pb-1 • Lower bound for 2005: Li 200 pb-1 ? • Can be even more, if hardware problems happen not so frequentlyand electron current can be increased! • Plans for hardware changes in the shutdown • Exchange of all remaining BU coils • Installation of the longitudinal proton feedback cavity J. Keil : HERA Status

  21. Conclusions • High luminosity production with electrons; performanceof HERA has greatly improved • Integrated luminosity up to now with electrons has alreadyexceeded the value with positrons of year 2004 • Background conditions are usually good after sourceof p-background spikes has been found; but there was againa vacuum leak in north! • Polarization with max. 40% disappointing investigation of mirror-tunes has started • Availability of HERA components and operational efficiencyis still too low • HERA will continue luminosity operation until wintershutdown (14th Nov. 2005 – Jan./Feb. 2006) J. Keil : HERA Status

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