1. HERA 54th Meeting of the PRC October 30-31 2002 at DESY
F. Willeke, DESY MHE
Status of Operations and Present Performance Limitations
Accelerator Physics Progress and Issues
Strategy and Plans
11/21/2018
HERA, F.Willeke, PRC Oct30 02

2. Status of Operations and Present Performance Limitations
HERA Operations
Beam Current Limitations
Backgrounds
Luminosity
11/21/2018
HERA, F.Willeke, PRC Oct30 02

3. HERA Operations
Week of September 18: Luminosity Operation wit 60 bunches Ip Ie
HERA Operation is now more difficult than before (as stated in spring)
Aggressive Beam Optics with vulnerable Beam Stability
Uncompensated Solenoids
Poor support of the low-b quadrupoles in detectors
Strong influence of the detector iron on low-b quadrupoles
Sensitive detectors close to the beam
Background tuning much more tedious
 Operational toolbox needed to be adapted and extended
11/21/2018
HERA, F.Willeke, PRC Oct30 02

4. Operational Improvements
Orbit stabilization feedback
controls beam positions and synchrotron radiation during critical operation
Ramping, low-b squeeze, closing ZEUS Calorimeter implemented tested and used routinely with good success
Routinely Accelerated respectable e+ Beams of 20mA of Current
beam losses and uncontrolled irradiation avoided, interferences and poor magnet support compensated
Semi-automized SR Background Optimization implemented
Refinement of the Operational procedures: Many improvements since spring:
>> Operational procedures re-established
>> Operations automated to a large extent
>> new features: checking voltage vs currents of all magnets automatically
>> automatic file checking avoids accumulative errors in the operation system
>> improving archive features
Improved Communications
Electronic Logbook available (on-site or via VPN:
11/21/2018
HERA, F.Willeke, PRC Oct30 02

5. Remaining Operational Issues
Changes in Operational conditions require painfully long tuning
There is still not sufficient control to avoid occasional accidental irradiation of close-to-the-beam detectors by uncontrolled beam loss or uncontrolled synchrotron radiation in case of a faulty component,
While restrictive interlock systems would affect seriously operational effectivity
 This needs further work, thought and experience in routine running
11/21/2018
HERA, F.Willeke, PRC Oct30 02

6. Beam Current Limitations
p-injection
Beam currents in luminosity operations are limited by
experimental backgrounds and radiation damage considerations
Ip x Ie < 1000 mA2 (extrapolation)
( y2000 value is 5000 mA2; design is 8000 mA2)
Proton –Beam Intensity
PETRA made steady progress over the last years and has recently accelerated Design Intensity 40GeV/c
Injection and Acceleration Efficiency < 80% due to injection line aperture and HERA dynamic aperture restrictions
High proton beam intensity needs some beam conditioning of the cold vacuum
e-Beam Intensity
Intensity is limited at design currents by RF power
vacuum system has not seen much beam current >30mA  needs slow, steady conditioning
Besides backgrounds and radiation damage considerations, it should be possible to collide y2000 beam currents (need to work on it and test)
100ms/div
11/21/2018
HERA, F.Willeke, PRC Oct30 02

7. Experimental Backgrounds
There are four sources of backgrounds, all of which have been explored by experiments and by simulations
direct synchrotron radiation: tolerable after tuning
direct leptons noticeable contribution for e+ only runs, collimators not very effective for e+  need condition vacuum
backscattered synchrotron radiation shielding needs to be improved
direct proton background
beam gas scattering close to IP, related to vacuum, correlation with cold surface, gas composition unclear
Also unclear: what has changed since y2000?
11/21/2018
HERA, F.Willeke, PRC Oct30 02

8.  Report of the Chairman
Workshop on Synchrotron Radiation- and Particle Background in HERA
July at DESY in Hamburg
HERA, the electron proton collider at DESY in Hamburg turned on last year after a major upgrade of the interaction regions which should give at least a factor of 3 in luminosity in each of the experiments H1 and ZEUS.  While there where no unusual problems in recommissioning the accelerator, the background problems have been found more difficult than expected.  After the situation has been analyzed and studied, a point is reached where it appears to be desirable to review the HERA background problems and compare them to backgrounds at other accelerators.
For this reason, a short workshop is being organized which will be held at DESY on July 24-23
Review on  HERA Background and Vacuum Issues
October 21-23, 2002
at DESY
Room 459, building 30b
 Report of the Chairman
11/21/2018
HERA, F.Willeke, PRC Oct30 02

9.  Running with increased temperatures of 110K
HERA Vacuum Tests: What is the influence of the 40K cold Beam pipes in the IR’s?
 Running with increased temperatures of 110K
110K GG Beam pipe
Since October 10
Running with protons only:
Experimental backgrounds seem to be significantly lower
ep Running:
No improvements seen yet
Warmup
11/21/2018
HERA, F.Willeke, PRC Oct30 02

10. Vacuum Studies and Plans
Model and Understand Vacuum around the cold beampipes in the IR
Understand the production of Hydrocarbons in IR Vacuum
Increase IR Pumping: Improve Pumping port conductance and Install additional Pumps (f.e. cryo-pumps, Integrated IonP)
11/21/2018
HERA, F.Willeke, PRC Oct30 02

11. Luminosity Luminosity Test Data with variable Bunch-Charge and -Number normalized to nominal Bunch Number =180
Luminosity
[1031cm-2sec-1] 4 2
Design
Calc. from beam param.
H1 Measurements
ZEUS measurem.
2002 Goal
11/21/2018
HERA, F.Willeke, PRC Oct30 02

12. Accelerator Physics Issues
Full Understanding of Specific Luminosity beam-beam tune shift
Understanding of Nonlinear Resonances and synchro-betatron resonances and e-Beam stability in luminosity state
Beam Vacuum Interactions in the IR’s
Proton Dynamic Aperture at Injection
Proton longitudinal Emittance Preservation …
11/21/2018
HERA, F.Willeke, PRC Oct30 02

13. Beam-beam studies low intensity luminosity scans
using measured beam parameters
Specific Luminosity/1030cm-2sec-1mA-2
calculated from beam parameters
H1 max
H1 during hor Scan
H1 during vertical scan
H1 scan result
ZEUS max
ZEUS during hor scan
ZEUS during vertical scan
ZEUS scan result
luminosity measurements from luminosity scans and calculations in reasonable agreement
11/21/2018
HERA, F.Willeke, PRC Oct30 02

14. Beam-Beam Tuneshift & Specific Luminosity
Measured vs calculated beam beam tuneshift
Measured lepton beam-beam –tuneshift vs proton bunch current
Specific luminosity is above design for low and below design for large proton bunch charge
11/21/2018
HERA, F.Willeke, PRC Oct30 02

15. e+ Beam-Beam Limit tune footprint appears to be limited by 3rd & 4th order resonances
H1 and Zeus spec. lumi vs time
beams separated in South IP
luminosity in the North increases
3Qy
2Qx+2Qy
4Qx
11/21/2018
HERA, F.Willeke, PRC Oct30 02

16. Polarization Six tuning steps
Polarization without ZEUS and H1 solenoids on October measured at
Tpol & Lpol
40%
20%
Polarization
Six tuning steps
1) North &South Rotators flat, Solenoids off week41/42 ok
2) North & East Rotator on
3)North&South&East Rotator on
4) All Rotators+Solenoids on postponed to
5) All Rotators+Solenoids, large vertical emittance (3.5nm) Febr03
6) Polarization during Luminosity operation
11/21/2018
HERA, F.Willeke, PRC Oct30 02

17. Strategy and Plans Overall Plan: Understand the Background Problems,
Prepare Improvements
Shutdown to implement improvements
High Luminosity Running
11/21/2018
HERA, F.Willeke, PRC Oct30 02

18. Priorities until Shutdown
Strategy and Plans
Priorities until Shutdown
Fully understand the present background problems and develop credible plans for improvements, prepare the necessary changes
Demonstrate that HERA can deliver High Luminosity as planned
Provide Proton Beam for HERA-B
Demonstrate longitudinal Polarization for H1, HERMES, ZEUS
Deliver Beams for HERMES, ZEUS and H1
11/21/2018
HERA, F.Willeke, PRC Oct30 02

19. HERA Running until the End of the Year02
Deliver Colliding Beams with
20mA of protons in 180 bunches and 30mA of positrons in 190 bunches for all 4 Experiments
thereby
Consolidate Operations
Condition the IR vacuum with beam to verify expected improvements
Increase continuously the Beam Current to verify background extrapolations
Two days/week of Accelerator physics, Vacuum and Background Studies
per week reserved for dedicated studies
Collaborative, organized effort between Accelerator and experiments
11/21/2018
HERA, F.Willeke, PRC Oct30 02

20. Schedule (conditional)
02 Oct Accelerator Studies
Luminosity and Polarization
02 Oct.30-Dec21 Colliding Beam Operation with increasing Beam Intensities
Background and Accelerator Studies
as needed up to 2days per week
03 Jan02-Febr28 Colliding Beam Operation
Polarization Studies
03 March-June Shutdown
03 July Start-up HERA Run II
11/21/2018
HERA, F.Willeke, PRC Oct30 02

21. Summary
HERA has solved its operational problems to a large extent and is ready to deliver beams routinely
The background problems however are only partially solved and there is yet no final satisfactory solution
A major component in the backgrounds is the IR vacuum and a large effort is underway to provide more understanding and improvement
There is a strategy to solve the problems until March 03, to implement the improvements and start up HERA for physics running in July 03
11/21/2018
HERA, F.Willeke, PRC Oct30 02