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

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

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

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: http://ttfinfo.desy.de/HERA/logbook/) 11/21/2018 HERA, F.Willeke, PRC Oct30 02

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

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 I=126mA @ 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

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

 Report of the Chairman Workshop on Synchrotron Radiation- and Particle Background in HERA July 23-24 2002 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

 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

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

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

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

Beam-beam studies low intensity luminosity scans using measured beam parameters Specific Luminosity/1030cm-2sec-1mA-2 calculated from beam parameters 2.40 H1 max 30.9. 2.24 H1 during hor Scan 1.99 H1 during vertical scan 1.7 H1 scan result 2.44 ZEUS max 30.9. 2.11 ZEUS during hor scan 1.50 ZEUS during vertical scan 1.87 ZEUS scan result 2.22 luminosity measurements from luminosity scans and calculations in reasonable agreement 11/21/2018 HERA, F.Willeke, PRC Oct30 02

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

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

Polarization Six tuning steps Polarization without ZEUS and H1 solenoids on October 17 2002 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

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

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

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

Schedule (conditional) 02 Oct 1-30 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

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