Operation for LHC Cryomagnet Tests: Concerns, Challenges & Successful Collaboration

The LHC construction phase is coming to a close, with installation work progressing rapidly and beam start-up foreseen by end 2007. For the testing of the 1706 LHC cryomagnets in cryogenic conditions and its successful completion by early 2007, considerable challenges had to be overcome since 2002 to assure certain semi-routine tests operation at CERN. In particular, the majority of staff for tests and measurement purposes was provided by India on a rotating, one-year-stay basis, as part of the CERN-India Collaboration for LHC. This was complemented by some CERN accelerator Operation staff. While only 95 dipoles were tested till 2003, the efforts and innovative ideas coming from the Operation team contributed significantly to the completion of tests of nearly all 1706 magnets by end-2006. These included the improvements and management of the tests work flow as well as the test rates. Amongst these, certain pivotal ideas to stream-line the tests methodology as proposed and implemented successfully by the Indian Associates deserve a special mention. An insight into this as well an overall view of the tests operation will be given, together with an indication of some of the operation-related results from the tests programme

Software for Beam Diagnostics Front-End Systems: Synchronization and Implementation Issues

Front-end software systems used for beam diagnostics at CERN's PS accelerator complex perform control and data acquisition of local hardware components in synchronization with specific accelerator events. The principal part of the software is generally hosted in a VME create, which drives all system components, provides interactivity with the general controls environment through networking and decouples the networking layer from the machine layer. Using three real-world examples of operational instrumentation systems, namely the beam intensity measurement between the PS-Booster and the PS, the AD Coherent Oscillations measurement and the PS Closed-Orbit Synchronization, the paper describes their synchronization to accelerator events and states. Sometimes these instrumentation systems are subject to complex real-time constraints and external conditions. The strategies to meet these requirements in the real-time software are discussed in the context of the general design and implementation in the PS control system environment

Tune measurement for the CERN proton synchrotron booster rings using DSP in VME

The CERN PS Booster (PSB) consists of 4 superposed rings supplied with protons from a 50 MeV Linac The CERN PS Booster (PSB) consists of 4 superposed rings supplied with protons from a 50 MeV Linac. The proton beam is then accelerated to 1 GeV and sent either to the 26 GeV Proton Synchrotron (PS) or to the ISOLDE facility. This is carried out in a multi-cycle mode every 1.2 s. For high-intensity beams, the working-point in the tune diagram needs to be changed considerably during acceleration from 50 MeV to 1 GeV and the repeated measurement of the tunes throughout the cycle is an important requirement. Up to now, tune values were obtained through calculations based on quadrupole currents. However, practical experience has shown the need for a direct tune measurement system. For this purpose, a classical kick technique is used. A fixed amplitude kick of duration equal to one revolution period excites coherent betatron oscillations. For fast treatment, a Digital Signal Processing (DSP) module in a VME-standard crate was selected. It carries out the Fast Fourier Transform (FFT) analyses of signals from position-sensitive pickups in both planes and evaluates the tunes. These measurements are carried out every 10 ms during the 450 ms acceleration ramp. The paper presents the novel features of this system, particularly the beam-offset signal suppression as well as the peak-search algorithm which yields the tune values

The New Digital-Receiver-Based System for Antiproton Beam Diagnostics

An innovative system to measure antiproton beam intensity, momentum spread and mean momentum in CERN's Antiproton Decelerator (AD) is described. This system is based on a state-of-the-art Digital Receiver (DRX) board, consisting of 8 Digital Down-Converter (DDC) chips and one Digital Signal Processor (DSP). An ultra-low-noise, wide-band AC beam transformer (0.2 MHz - 30 MHz) is used to measure AC beam current modulation. For bunched beams, the intensity is obtained by measuring the amplitude of the fundamental and second RF Fourier components. On the magnetic plateaus the beam is debunched for stochastic or electron cooling and longitudinal beam properties (intensity, momentum spread and mean momentum) are measured by FFT-based spectral analysis of Schottky signals. The system thus provides real time information characterising the machine performance; it has been used for troubleshooting and to fine-tune the AD, thus achieving further improved performances. This system has been operating since May 2000 and typical results are presented

Non-invasive single-bunch matching and emittance monitor

On-line monitoring of beam quality for high brightness beams is only possible using non-invasive instruments. For matching measurements, very few such instruments are available. One candidate is a quadrupole pick-up. Therefore, a new type of quadrupole pick-up has been developed for the 26 GeV Proton Synchrotron (PS) at CERN, and a measurement system consisting of two such pick-ups is now installed in this accelerator. Using the information from these pick-ups, it is possible to determine both injection matching and emittance in the horizontal and vertical planes, for each bunch separately. This paper presents the measurement method and some of the results from the first year of use, as well as comparisons with other measurement methods.Comment: 10 pages, 10 figures; added figure, minor textual additions; To be resubmitted to Phys. Rev. ST-A

Real-Time Control, Acquisition and Data Treatment for Beam Current Transformers in a Transfer Line

Particle beams are transferred from the 1 GeV Booster to the 26 GeV Proton Synchrotron and to an experimental area, ISOLDE. The characteristics of the beams and their destination change on a 1.2 s cycle basis. There are six beam current transformers to measure the beam intensities, i.e. the number of particles passing through the transfer lines. On each pulse of the Booster, a real-time system, called BTTR (Beam Transfer TRansformers), acquires the transformer values, selects the range, executes a calibration, and treats the data. Part of the treatment is the subtraction of the base-value, which includes systematic perturbations, acquired in the absence of beam. The system also handles asynchronous tasks, such as acquisition of base-value, readout of calibration factors and other diagnostic actions. The concept of the BTTR and its design are presented, as well as some practical results

Measurement of the mean radial position of a lead ion beam in the CERN PS

The intensity of the lead ion beam in the PS, nominally 4×108 charges of Pb53+ per bunch, is too low for the closed orbit measurement system. However, for successful acceleration it is sufficient to know the mean radial position (MRP). A system was thus designed for simultaneous acquisition of revolution frequency and magnetic field. The frequency measurement uses a direct digital synthesiser (DDS), phase-locked to the beam signal from a special high-sensitivity pick-up. The magnetic field is obtained from the so-called B-train. From these two values, the MRP is calculated. The precision depends on the frequency measurement and on the accuracy of the value for the magnetic field. Furthermore, exact knowledge of the transition energy is essential. This paper describes the hardware and software developed for the MRP system, and discusses the issue of calibration, with a proton beam, of the B measurement

Antiproton beam parameters measurement by a new digital-receiver-based system

The Antiproton Decelerator (AD) provides the users with very low intensity beams, in the 107 particles range, hence prompting the development of an innovative measuring system, which was completed in early 2000. This system measures antiproton beam intensity for bunched and debunched beams, together with momentum spread and mean momentum for debunched beams. It uses a state-of-the-art Digital Receiver board, which processes data obtained from two ultra-low-noise, wide-band AC beam transformers. These have a combined bandwidth in the range 0.02 MHz - 30 MHz and are used to measure AC beam current modulation. For bunched beams, the intensity is obtained by measuring the amplitude of the fundamental and second RF Fourier components. On the magnetic plateaus the beam is debunched for stochastic or electron cooling and longitudinal beam properties (intensity, momentum spread and mean momentum) are measured by FFT-based spectral analysis of Schottky signals. The system provides real-time information characterising the machine performance; it has been used for troubleshooting and to fine-tune the AD, thus allowing further improved performance. This system has been operating since May 2000 and providing beam intensity data to the users on a routine basis since late 2000. A dedicated software package was expressly developed to take care of the control, data acquisition and processing phases. It consists of three main codes, namely a GUI, a Real Time Task and a Low Level Code. This report gives an overview of both the hardware and software developed

Beam Measurement Systems for the CERN Antiproton Decelerator (AD)

The new, low-energy antiproton physics facility at CERN has been successfully commissioned and has been delivering decelerated antiprotons at 100 MeV/c since July 2000. The AD consists of one ring where the 3.5 GeV/c antiprotons produced from a production target are injected, rf manipulated, stochastically cooled, decelerated (with further stages involving additional stochastic and electron cooling and rf manipulation) and extracted at 100 MeV/c. While proton test beams of sufficient intensity could be used for certain procedures in AD commissioning, this was not possible for setting-up and routine operation. Hence, special diagnostics systems had to be developed to obtain the beam and accelerator characteristics using the weak antiproton beams of a few 10E7 particles at all momenta from 3.5 GeV/c down to 100 MeV/c. These include systems for position measurement, intensity, beam size measurements using transverse aperture limiters and scintillators and Schottky-based tools. This paper gives an overall view of these systems and their usage