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

26/5/2005J. Keil : HERA Status2 Contents  Operation of HERA 04/05 with Electrons  Luminosity Performance  Major technical Problems  Polarization  Improvements  Schedule 2005  Conclusions

26/5/2005J. Keil : HERA Status3 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): 1.Set up/check HERA-e with positrons 2.Move magnets in IR 3.Continue with electrons 4.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 to limited space in GO magnet on left side  Delay in schedule: –Quadrupole GN NL20 had a burnt coil –Vacuum leak at GI07 NR

26/5/2005J. Keil : HERA Status4 Trajectories for e - /p and e + /p in IR BO GJ GI GO,HO GG,HG GI GJ GI p-beam for e + p beam for e mm e - -beam e + -beam GM ee p Radial orbit shift at IP of 7.5 mm between electron and positron operation

26/5/2005J. Keil : HERA Status5 Parameters of Run ‘04/05 with Electrons ParameterElectronsProtons Energy E / GeV Max. current I / mA (design for n b =180)58 / / 102 Number of bunches n b 180 / 63  126  / 60  120  150 Number of colliding bunches n c 174 / 57  114  147 Hor. beam emittance  x / nm  rad 20 / < 26 ?5.1 / 4.7 Ver. beam emittance  y / nm  rad 3.0 ?5.1 / 4.7 Hor. beta function at IP  x * / m Ver. beta function at IP  y * / m Bunch length  p / m / 0.21 Hour glass factor R0.924 / Specific luminosity L / cm -2  s -1  mA / 1.9  2.2 Peak luminosity L / cm -2  s / 2.5  4.5 For p: Long. instability Beam-Beam effects Design 2005 with e - For e - : Vacuum, RF For p: Pre-accelerators Hour glass factor included in design!

26/5/2005J. Keil : HERA Status6 Beam Currents  Peak currents for run ‘04/05 with electrons (150 bunches):  I p max = 102 mA  I e max = 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!

26/5/2005J. Keil : HERA Status7 Specific Luminosity  High specific luminosity with electrons for 2004/05 run: L s =  cm -1 ·s -1 ·mA -2  Specific Luminosity is larger than the design value of L s = 1.84  cm -1 ·s -1 ·mA -2  One reason for higher specific luminosity compared to last year with positrons (  ) 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

26/5/2005J. Keil : HERA Status8 Integrated Luminosity 04/05  Integrated luminosity is 95.3 pb -1 in 156 days (start: Dec. 17 th, 2004)  Best run delivered 1.1 pb -1 within 14 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 of L= 5.07  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!

26/5/2005J. Keil : HERA Status9 Integrated Luminosity Luminosity production rate with electrons in 2005 is higher than 2004 for positrons! (ZEUS)

26/5/2005J. Keil : HERA Status10 HERA e - -Lifetime Lifetime event  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

26/5/2005J. Keil : HERA Status11 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.

26/5/2005J. Keil : HERA Status12 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)

26/5/2005J. Keil : HERA Status13 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!

26/5/2005J. Keil : HERA Status14 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 14 th Nov. ‘05) Collimator beam loss rate

26/5/2005J. Keil : HERA Status15 Polarization Colliding bunches: 40% Non-colliding bunches: ~50%  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

26/5/2005J. Keil : HERA Status16 Mirror Tunes

26/5/2005J. Keil : HERA Status17 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 Checked magnet 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

26/5/2005J. Keil : HERA Status18 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

26/5/2005J. Keil : HERA Status19 Longitudinal Multi-Bunch Feedback  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 Schematic principle

26/5/2005J. Keil : HERA Status20 Schedule 2005  Schedule –Start of luminosity operation: 17 th Dec. ’04 –Start of shutdown: 14 th Nov. ’05 –End of shutdown: End of Jan. ’06 –Luminosity operation: 2 nd week in Feb. ’06  Expectations for integrated luminosity –Until now: L i = 95 pb -1 in 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: L i  200 pb -1 ? –Can be even more, if hardware problems happen not so frequently and 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

26/5/2005J. Keil : HERA Status21 Conclusions  High luminosity production with electrons; performance of HERA has greatly improved  Integrated luminosity up to now with electrons has already exceeded the value with positrons of year 2004  Background conditions are usually good after source of p-background spikes has been found; but there was again a vacuum leak in north!  Polarization with max. 40% disappointing  investigation of mirror-tunes has started  Availability of HERA components and operational efficiency is still too low  HERA will continue luminosity operation until winter shutdown (14 th Nov – Jan./Feb. 2006)