Heiko Ehrlichmann (DESY, Hamburg, Germany)

1. 25 Years DESYII Beam Operation Heiko Ehrlichmann (DESY, Hamburg, Germany) More than 25 years ago, on the 22nd of March 1985, the first electron beam in DESYII was circulated. Since then, this synchrotron has been the central machine within the accelerator complex at DESY to deliver electron or positron beams with high stability and reliability up to 7GeV to the user facilities. History DESY’s first accelerator DESYI came in operation in 1964, first for high energy experiments directly at the synchrotron (until 1979), then also for delivering beam to the new storage rings DORIS (1974) and PETRA (1977). With HERA as a new project it was clear 30 years ago that for decades to come electron beams would be needed. Due to the combined function lattice of DESYI and the resulting horizontal anti-damped beam with a corresponding large emittance it was decided to split the upcoming needs for electron and proton pre-acceleration. A new separated function synchrotron DESYII for electron beams up to 10GeV was constructed, located in the same tunnel, using much of the existing DESYI infrastructure. In parallel to the DESYI routine operation in 1985 first beam tests with provisional power connection were performed. With the end of the PETRA collider program at the end of 1986, DESYI was irrevocably switched off for conversion into the proton synchrotron DESYIII. After the final connection of all transport lines and magnet circuits, from spring 1987 on, DESYII has delivered beam to DORIS, PETRA and detector test areas. Aerial view of the civil construction Tunnel view DESY Accelerator Complex DESY II Tunnel view The magnet system of DESYII consists of five circuits: the dipole. two quadrupole and two sextupole circuits, all synchronously oscillating with 12.5Hz. 24 horizontal and 24 vertical DC corrector coils allow some orbit manipulation at lower beam energies. The optical lattice is formed by 8 x 3 FODO cells. Eight 7-cell PETRA-type cavities are supplied by one 1MW HF station. One bunch of about 1010 electrons or positrons is injected (on axis) at 450MeV, shortly after the time of minimal fields, and accelerated to usually 6.3GeV, maximum 7GeV. For DORIS and PETRA the beam is extracted during acceleration at 2.0GeV, 4.5GeV or 6.0GeV, respectively. Three thin internal targets generate bremsstrahlung photons to be back converted into charged particles for test beam purposes. RecentImprovements During the past few years all six main power supplies (dipole DC, dipole AC, QD, QF, SD and SF) including the regulation concept have been renewed, as well as the resonance chokes. For the last several years, DESYII has been running in a completely automated operation mode without manual actions by the operators. Beam requests from all users (DORIS, PETRA and test beams) are detected to set all necessary parameters for the requested operation mode. For a further reduction of the outage risk, a second independent RF station is currently commissioned and will come into routine operation from autumn 2011 on. Snapshot of the beam requens and operation mode display Beam Operation 2011 With the top up operation mode of PETRAIII, DESYII has to deliver beam every few minutes. As a consequence DESYII has to run continuously. Maintenance periods are rather limited. At the same time the reliability and operation stability has to be very high. Although DESYII is still the central pre-accelerator within the accelerator complex and is planned to be used for further decades, infrastructure renovation is kept at a minimum. With the new power supplies the beam intensity variation could be significantly reduced, an overall efficiency of about 85-90% is typical. Usually an availability of 99% has been reached. Daily calculated Availability versus date Availability distribution: number of days with an availability greater than x(%) versus x (in blue: number of days with av. < 90%) Typical beam intensity history (console display snapshot): intensities in the transport line and in DESYII versus time DESYII is assigned to deliver beam quietly, without fanfare. This challenge has been continuously fulfilled. References G. Hemmie, “Die Zukunft des Synchrotrons”, DESY M-82-18 (1982) G. Hemmie, “A New Injector for the DESY Storage Rings PETRA and DORIS”, IEEE NS-30 (1983) J. Rossbach and F. Willeke, “DESY II Optical Design of a New 10GeV Electron-Positron-Synchrotron”, DESY M-83-03 (1983) G. Hemmie and J. Rossbach, “Eddy Current Effects in the DESYII Dipole Vaccum Chamber”, DESY M-84-05 (1984) J. Kouptsidis, R. Banthau and H. Hartwig, “A Novel Fabrication Technique for Thin Metallic Vacuum Chambers with Low Eddy Current Losses”, IEEE NS-32 (1985) G. Hemmie, “Status Report on the DESY II Synchrotron”, IEEE NS-32 (1985) G. Hemmie et al, “Design, Construction and Performance of the DESY II Magnets”, IEEE NS-32 (1985) U. Berghaus, W. Kriens and S. Pätzold, “Magnetic Field Measurements of the DESY II Magnets”, IEEE NS-32 (1985) W. Bothe and P.Pillat, “Magnet Excitation Circuits for DESY II” IEEE NS-32 (1985) The DESYII Collaboration, “Status of the DESY II Project”, DESY M-87-08 (1987) W. Bothe, “Resonant Excitation of Synchrotron Magnets”, DESY M-90-01 (1990)