Control of total voltage in the large distributed RF system of LEP

The LEP RF system is made up of a large number of independent RF units situated around the ring near the interaction points. These have different available RF voltages depending on their type and they may be inactive or unable to provide full voltage for certain periods. The original RF voltage control system was based on local RF unit voltage function generators pre-loaded with individual tables for energy ramping. This was replaced this year by a more flexible global RF voltage control system. A central controller in the main control room has direct access to the units over the LEP TDM system via multiplexers and local serial links. It continuously checks the state of all the units and adjusts their voltages to maintain the desired total voltage under all conditions. This voltage is distributed among the individual units to reduce the adverse effects of RF voltage asymmetry around the machine as far as possible. The central controller is a VME system with 68040 CPU and real time multitasking operating system. Event driven communication handlers allow fast reliable concurrent data communication with the remote units. The RF unit low level RF G64 equipment controllers use a VME 68030 CPU to achieve the necessary response time and reliability

Digital Design Of The LHC Low Level rf: The Tuning System For The Superconducting Cavities

The low level RF systems for the LHC are based extensively on digital technology, not only to achieve the required performance and stability but also to provide full remote control and diagnostics facilities needed since most of the RF system is inaccessible during operation. The hardware is based on modular VME with a specially designed P2 backplane for timing distribution, fast data interchange and low noise linear power supplies. Extensive design re-use and the use of graphic FPGA design tools have streamlined the design process. A milestone was the test of the tuning system for the superconducting cavities. The tuning control module is based on a 2M gate FPGA with on-board DSP. Its design and functionality are described, including features such as automatic cavity measurements. Work is ongoing on completion of other modules and building up complete software and diagnostics facilities

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

Operating Experience with the LEP200 Superconducting RF System

By the beginning of 1999, after several stages of installation, the RF system in LEP had gained a final total of 288 four-cell SC cavities. For 2000, the last year of LEP running, eight original LEP1 copper cavities were re-installed to bring their total to 56. During 1999 and 2000, the RF system was pushed to its absolute maximum limits for physics. By mid-2000 maximum total RF voltages of well over 3600 MV could be sustained, allowing beam energies of up to and even over 104 GeV for new particle searches. This corresponded to average gradients approaching 7.2 MV/m in the SC cavities, well above the design value of 6 MV/m. This level of performance was achieved due to the very successful high-field conditioning of the niobium-copper sputtered SC cavities, the many RF system improvements made in previous years and by a cryogenics system cooling power upgrade. Operation at very high energies however brought new difficulties, many related to the high fields and increased RF power levels. Running with the RF system at its limit required new operational procedures and facilities as well as constant follow up of cavity and RF system performance. LEP high energy running proved very successful, the beam energies and integrated luminosities obtained largely exceeded the most optimistic expectations. Finally, a vast amount of experience has been gained during the construction and operation of the LEP SC RF system. Some critical design issues in SC RF systems can be reviewed in the light of this experience

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

Commissioning of the 400 MHz LHC RF System

The installation of the 400 MHz superconducting RF system in LHC is finished and commissioning is under way. The final RF system comprises four cryo-modules each with four cavities in the LHC tunnel straight section round IP4. Also underground in an adjacent cavern shielded from the main tunnel are the sixteen 300 kW klystron RF power sources with their high voltage bunkers, two Faraday cages containing RF feedback and beam control electronics, and racks containing all the slow controls. The system and the experience gained during commissioning will be described. In particular, results from conditioning the cavities and their movable main power couplers and the setting up of the low level RF feedbacks will be presented

Plans for a Superconducting H−^{-} LINAC (SPL) at CERN

As part of the upgrade of the LHC injector complex at CERN, the construction of a 4 GeV Superconducting Proton Linac (the SPL, in fact an H- accelerator) is planned to begin in 2012. Depending upon physics requests, it should be upgradeable to 5 GeV and multi-MW beam power at a later stage. The construction of Linac4, its low energy front end, has started at the beginning of 2008. A full project proposal with a cost estimate for the low power version of the SPL aimed at improving LHC performance has to be ready for mid-2011. As a first step towards that goal, essential machine parameters like RF frequency, cooling temperature and accelerating gradient have recently been revisited and plans have been drawn for designing and testing critical components