Active Alignment System for CLIC 30 GHz Modules in CTF2

The active alignment system is capable of positioning accelerator components of CLIC (Compact Linear Collider) with a few micron precision. An electronic processing and command system connects the micro-movers and sensors of this system to the CERN-PS complex control system

Active Alignment Electronic System for CLIC 30 GHz Modules in CTF2

The active alignment system is capable of positioning accelerator components of CLIC (Compact Linear Collider) with a precision of a few microns. An electronic processing and command system connects the micro-movers and sensors of this system to the CERN-PS complex control system

An Active Pre-Alignment System and Metrology Network for CLIC

The pre-alignment tolerance on the transverse positions of the components of the CLIC linacs is typically ten microns over distances of 200 m. Such tight tolerances cannot be obtained by a static one-time alignment because normal seismic ground movement and cultural noise associated with human and industrial activity quickly creates significant errors. It is therefore foreseen to maintain the components in place using an active-alignment system which will be linked to a permanent metrology and geodetic network. This report describes the overall philosophy and implementation of such a system and proposes one possible solution for active-alignment which uses stepping-motors to move components and stretched-wires as reference lines. Special sensors have been developed to measure the position of the components with respect to the reference lines, and to measure local tilt and relative vertical position. An in-depth analysis has been made of the repercussions on the alignment system of perturbing effects due to the attraction of the moon and the sun, and of the presence of nearby geological masses. The active-alignment system was used to maintain the components of the 30 GHz Two-Beam Test Accelerator in position in the CLIC Test Facility CTF2 as a practical demonstration of successful operation in an accelerator environment. The hardware and control system that was built for this application are described together with the results obtained

The effect of cooling water on magnet vibrations

The quadrupole magnets in the CLIC Test Facility II (CTF2) incorporate a water cooling circuit. In the frame-work of the CLIC stability study, the mechanical vibrations of the magnets were measured for different flows of cool-ing water. We present the results and compare them with simple theoretical estimates. It is shown that the vibra-tion requirements of the Compact LInear Collider (CLIC) quadrupoles with cooling water can basically be met

Closed orbit feed-back from low-β\beta quadrupole movements at LEP

Left and right of each of the four LEP interaction points superconducting low-beta quadrupole magnets are installed to squeeze the vertical beam size at the interaction points. These magnets are the dominant source of vertical closed orbit drifts at LEP because of their strength, the large vertical beta function and their support. Hydrostatic Levelling Systems and resistor-based position sensors were installed to measure the vertical movements of these magnets continuously. The correlation between the mechanical movements and closed orbit variations has been studied. The analysis has shown that the orbit can be kept stable by acting on one correction dipole per low-beta quadrupole pair. This has led to a feed-back system which uses the mechanical measurements to correct the closed orbit and to prevent large orbit variations

Determination of the Accuracy of Wire Position Sensors

An energy spectrometer has been installed in the LEP accelerator to determine the beam energy with a relative accuracy of 10-4. A precisely calibrated bending magnet is flanked by 6 beam position monitors (BPM). The beam energy is determined by measuring the deflection angle of the LEP beams and the integrated bending field. An accuracy of less than 10-6 m on the beam position is necessary to reach the desired accuracy on the LEP beam energy. Capacitive wire positioning sensors are used to determine the relative mounting stability of each BPM and to calibrate the beam position monitors. Two-dimensional sensors are attached to each side of every BPM support and provide a position measurement with respect to two stretched wires mounted on either side of the LEP beam pipe. The fixing points of each wire are monitored by additional reference sensors. The position information is digitised via a multiplexed high accuracy digital voltmeter and read out continuously during LEP operations. Wire position sensor accuracy was tested in the laboratory with a laser interferometer, while relative accuracy tests are performed in the LEP environment. Systematic effects of synchrotron radiation on the wire position sensor performance were studied

Status of the CLIC study on magnet stabilisation and time-dependent luminosity

The nanometer beam size at the CLIC interaction point imposes magnet vibration tolerances that range from 0.2 nm to a few nanometers. This is well below the floor vibra-tion usually observed. A test stand for magnet stability was set-up at CERN in the immediate neighborhood of roads, operating accelerators, manual shops, and regular office space. It was equipped with modern stabilization tech-nology. First results are presented, demonstrating signif-icant damping of floor vibration. CLIC quadrupoles have been stabilized vertically to an rms motion of (0.9 ± 0.1) n above 4 Hz, or (1.3 ± 0.2) nm with a nominal flow of cooling water. For the horizontal and longitudinal directions respectively, a CLIC quadrupole was stabilized to (0.4 ± 0.1) nm and (3.2 ± 0.4) nm

The CLIC Study of Magnet Stability and Time-dependent Luminosity Performance

The present parameters of the CLIC study require the collision of small emittance beams with a vertical spot size of 1 nm. The tolerances on vertical quadrupole vi-bration (above a few Hz) are as small as a few nm in the linac and most of the Final Focus. The final focusing quadrupole has a stability requirement of 4 nm in the horizontal and 0.2 nm in the vertical direction. Those tol-erances can only be achieved with the use of damped support structures for CLIC. A study has been set-up at CERN to explore the application of stabilization devices from specialized industry and to predict the time-dependent luminosity performance for CLIC. The results will guide the specification of required technological im-provements and will help to verify the feasibility of the present CLIC parameters

Status of the LEP2 Spectrometer Project

The LEP spectrometer has been conceived to provide a determination of the beam energy with a relative accuracy of 10-4 in the LEP2 physics region where insufficient polarisation levels prevent the application of the resonant depolarisation method. The setup consists of a steel bending magnet flanked by a triplet of Beam Position Monitors (BPM) at each side providing a measurement of changes in the bending angle when the beams are accelerated to physics energies. The goal for a 100 ppm relative precision on the beam energy involves a ± 1 micron BPM resolution and the calibration of the dipole bending strength to a 30 ppm accuracy. This paper reports on the results of the commissioning of the Spectrometer during the 1999 LEP Run and on the experience acquired on the behaviour of the several sub-systems with circulating beams