Status of Superconducting Cavities in LEP

The upgrade of the Large Electron Positron collider (LEP) with superconducting cavities is nearing a successful completion. There are presently 240 superconducting cavities installed which, together with the original copper RF system, provide up to 2.6GV per turn. The majority of the superconducting cavities is of niobium sputtered on copper and runs at an operating gradient of 6MV/m. In 1997, LEP has operated routinely at an energy of 91.5GeV per beam and with a total current of over 5mA. The operation of the RF system has been very satisfactory, with only a few cavities limited in field. This paper will concentrate on describing the operation of this system during 1997, including new features, operational procedures and present limitations. Future plans, notably the work towards improving performance and the installation of the remaining cavities, will also be covered

Precision beam timing measurement system for CLIC synchronization

Very precise synchronization between main and drive beams is required in CLIC to avoid excessive luminosity loss due to energy variations. One possibility to accomplish this would be to measure and correct the drive beam phase. The timing reference for the correction could be the beam in the transfer line between the injector complex and the main linac. The timing of both main and drive beams will have to be measured to a precision in the region of 10 fs. The aim is to achieve this by means of a beam measurement at 30 GHz with the signal mixed down to an intermediate frequency (IF) for precise phase detection. The RF and IF electronics are being developed and tests will be carried out in CTF

CLIC Beam Position Monitor Tests

Prototype CLIC beam position monitors (BPMs) have been tested in the CLIC test facility (CTF) using a 50 MeV, 1 nC single bunch beam. The test set-up consisted of two BPMs and a charge normalization/phase reference cavity. The detection electronics consisted of a 5 channel super-heterodyne receiver to give charge independent horizontal and vertical positions in each BPM. Data were taken and processed at the full 10 Hz CTF repetition rate using a PC running LabVIEW. Both BPMs were mounted on 0.1 µm resolution micro-movers for displacement calibration. Separate tests in the lab of both cavities and electronics have shown that the potential resolution of the BPM system is less than one micron. An upper limit on resolution of ±4 µm has been demonstrated directly with the CTF beam. The measurement was almost certainly limited by the shot to shot angular jitter of the CTF beam

Performance of the LEP200 superconducting RF system

The LEP Superconducting RF system has reached its maximum configuration of 288 four-cell cavities powered by 36 klystrons. This has allowed the beam energy to be raised from 45.6 GeV where physics of the Z-particle was studied to well above 80.5 GeV the threshold of W pair production. The search for Higgs bosons and other new particles requires even higher beam energies. Currently the maximum operational energy achieved is 101 GeV with the RF system supplying a circumferential voltage of 3500 MV. This requires not only operating the cavities well beyond their design gradient but also demands a very high operational reliability from the entire system. The major developments necessary to achieve this performance are described

Ultimate Performance of the LEP RF System

The LEP Superconducting RF system reached its maximum configuration of 288 four-cell cavities powered by 36 klystrons in 1999. In 2000, this system, together with 56 cavities of the original copper RF system, routinely provided more than 3630 MV, allowing the beam energy to be raised up to 104.5 GeV. This not only required operating the cavities more than 15% above their design gradient, but has also demanded a very high operational reliability from the entire system. This paper will describe the operation of the LEP RF system during 2000, including new features, operational procedures and limitations