HERA Status

1
HERA Status
59th Meeting of the Physics Research Committee
May 26th, 2005

• Joachim Keil, DESY (MPY)

2
Contents

• Operation of HERA 04/05 with Electrons
• Luminosity Performance
• Major technical Problems
• Polarization
• Improvements
• Schedule 2005
• Conclusions

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 ?x7 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

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
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!
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Beam Currents

• Peak currents for run 04/05 with electrons (150
  bunches)
• Ipmax 102 mA
• Iemax 40 mA
• Proton single bunch current is highWould 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!

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Specific Luminosity

• High specific luminosity with electrons for
  2004/05 run Ls 1.8 - 2.2 ?1030
  cm-1s-1mA-2
• Specific Luminosity is larger than the design
  value of Ls 1.84 ?1030 cm-1s-1mA-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
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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 farHERA delivered 1.17
  pb-1/d
• New record peak luminosity ofL 5.07?1031
  cm-2s-1 was achieved
• But high proton background and many spikes until
  BU SR coil was identified as the culprit? fixed
  in April!

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Integrated Luminosity
Luminosity production rate with electrons in 2005
is higher than 2004 for positrons!
(ZEUS)
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HERA e--Lifetime

• Again Sudden lifetime reduction and lifetime
  recovery during electron operation
• At the same time increased beam loss measured
• Observed for I gt 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
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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.
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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)

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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!

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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
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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
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Mirror Tunes
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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 gt70
• Efficiency more stable than before
• Remaining losses PETRA extraction

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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

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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
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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-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 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

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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)