Giuseppe Vismara

SIGNAL PROCESSING FOR BEAM POSITION MONITORS

At the first sight the problem to determine the beam position from the ratio of the induced charges of the opposite electrodes of a beam monitor seems trivial, but up to now no unique solution has been found that fits the various demands of all particle accelerators. The purpose of this paper is to help “instrumentalists” to choose the best processing system for their particular application, depending on the machine size, the input dynamic range, the required resolution and the acquisition speed. After a general introduction and an analysis of the electrical signals to be treated (frequency and time domain), the definition of the electronic specifications will be reviewed. The tutorial will present the different families in which the processing systems can be grouped. A general description of the operating principles with relative advantages and disadvantages for the most employed processing systems is presented. Special emphasis will be put on recent technological developments based on telecommunication ...

INTEGRATING WIRE CHAMBERS FOR BEAM TUNING IN THE CERN SPS EXPERIMENTAL AREAS

Abstract Wire chambers operating in the charge integrating mode are used for beam tuning in the SPS experimental areas. They are characterized by a wide dynamic rannge (10 4 –10 11 particle/s) and can be adapted for spatial resolution between 1 and 6 mm. This paper describes the charge integrator, the multiplexer and the readout system. Simultaneous display of beam profiles for four chambers in both horizontal and vertical planes, with 32 channels each or one chamber up to 16 times per beam burst, are possible. An account of the system performance, after fourteen months of operation, is given.

From narrow to wide band normalization for orbit and trajectory measurements

The beam orbit measurement (BOM) of the LEP collider makes use of a narrow-band normalizer (NBN), based on a phase processing system. This design has been working fully satisfactorily in LEP for almost 10 years. Development work for the LHC, requiring beam acquisitions every 25 ns, has led to a new idea of a so-called “wide-band normaliser” (WBN), which exploits most of the pickups differentiated pulse spectrum. In the WBN, the beam position information is converted into a time difference between the zero-crossing of two recombined and shaped electrode signals. A prototype based on the existing NBN unit has been developed and tested to prove the feasibility of this new idea. For this the bandpass filters and the 90° hybrids are replaced by lowpass filters and delay lines.

Drift chamber electronics with multi-hit capability for time and current division measurements

Drift chambers have been installed for luminosity measurements in intersection 5 of the SPS accelerator working in pp colliding mode. The required electronics is described. The system is able to process up to 16 hits per wire with a double pulse resolution of 40 ns; drift time and current division, with 1.25 ns and 1.6% resolution respectively, are recorded. Transconductance preamplifiers and discriminators are directly mounted on the chamber; 160 m of twisted-pair cable bring the signals to the digitizer unit. Coarse time is measured using RAM techniques, while fine time is obtained by means of a microstrip delay associated with a 100 K ECL priority encoder. Current division used a single 50 MHz Flash ADC which allows 26 dB dynamic range with 6 bit resolution. First operational results are reported.

Performance of the SPS beam spectrometer chambers under very high fluxes

Abstract Five beam spectrometers each consisting of four 100×100 mm 2 , 1 mm wire spacing, multiwire proportional chambers, are operational in the secondary beams of the CERN SPS. To determine the ultimate performance of the chambers and associated electronics, capable of working at a threshold of 0.5 ωA and transmitting signals on 500 m twisted pair cables at rates of 25 MHz/wire, we have studied the behaviour of the chambers under very high beam fluxes (∼10 7 particles/s). Up to 10 5 particles/(mm 2·s efficiencies as high as 90% can be reached.