J.-F. Beche

An ionization chamber shower detector for the LHC luminosity monitor

The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the Large Hadron Collider (LHC) each absorb approximately 1.8 TeV of forward collision products on average per pp interaction (/spl sim/235 W at design luminosity 10/sup 34/ cm/sup -2/ s/sup -1/). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. A novel segmented, multi-gap, pressurized gas ionization chamber is being developed for sampling the energy deposited near the maxima of the hadronic/electromagnetic showers in these absorbers. The system design choices have been strongly influenced by optimization of signal to noise ratio and by the very high radiation environment. The ionization chambers are instrumented with low noise, fast, pulse shaping electronics to be capable of resolving individual bunch crossings at 40 MHz. Data on each bunch are to be separately accumulated over multiple bunch crossings until the desired statistical accuracy is obtained. At design luminosity approximately 2/spl times/10/sup 3/ bunch crossings will suffice for a 1% luminosity measurement. In this paper we report the first experimental results of the ionization chamber and analog electronics. Single 450 GeV protons from the SPS at CERN are used to simulate the hadronic/electromagnetic showers produced by the forward collision products from the interaction regions of the LHC.

High-speed nuclear quality pulse height analyzer for synchrotron-based applications

High-speed Nuclear Quality Pulse Height Analyzer for Synchrotron-based Applications J-F. Beche, J. J. Bucher, L. Fabris, V. J. Riot Abstract--A high throughput Pulse Height Analyzer system for synchrotron-based applications requiring high resolution, high processing speed and low dead time has been developed. The system is comprised of a 120ns 12-bit nuclear quality Analog to Digital converter with a self-adaptive fast peak detector- stretcher and a custom-made fast histogramming memory module that records and processes the digitized data. The histogramming module is packaged in a VME or VXI compatible interface. Data is transferred through a fast optical link from the memory interface to a computer. A dedicated data acquisition program matches the hardware characteristics of the histogramming memory module. The data acquisition system allows for two data collection modes: “standard” data acquisition mode where the data is accumulated and read in synchronization with an external trigger and “live” data acquisition mode where the system operates as a standard Pulse Height Analyzer. The acquisition, standard or live, can be performed on several channels simultaneously. A two-channel prototype has been demonstrated at the Stanford Synchrotron Radiation Laboratory accelerator in conjunction with an X-ray Fluorescence Absorption Spectroscopy experiment. A detailed description of the entire system is given and experimental data is shown. I. S UMMARY A fast high resolution and low dead time Pulse Height Analyzer (PHA) system for Synchrotron-based applications has been developed. This module is an addition to and completes the previously designed custom electronics for XAFS applications [1, 2]. The PHA system receives analog information from a low dead time pulse processing front-end section. The low dead time PHA system is comprised of a fast high resolution Analog to Digital Converter (ADC), a fast histogramming memory and a VME or VXI compatible interface. The VME-based system consists of one complete data acquisition channel. The VXI-based PHA system addresses the problem of simultaneous data acquisition from multiple channels. Both systems were tested at the Stanford Synchrotron Radiation Laboratory in conjunction with an X- ray Fluorescence Absorption Spectroscopy experiment. The block diagram of a single acquisition channel is shown in Fig. This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Science Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. J-F Beche, J. J. Bucher, L. Fabris and V. J. Riot are with E. O. Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (telephone: 510- 495-2327, e-mail: JFBeche@lbl.gov). The analog input section is built around a fast self-adaptive peak detector-stretcher described in [1]. The peak detector- stretcher includes all the necessary logic to provide pileup rejection and gating functions. The stretched signal is fed to a commercial ADC chosen to maximize throughput without compromising the differential non-linearity (DNL). This ADC is an 8Msps unit, providing 14 bit of resolution with no missing code over the full temperature range, and with an intrinsic DNL of ½ LSB. In order to improve the DNL (not adequate for nuclear spectroscopy applications), only the first 12 most significant bits are used. A 6-bit sliding scale correction [3] lowers the DNL to less than 1%. Including delays, the conversion time of the ADC is 120ns. The electronic pulse-processing amplifier, in its fastest version, shapes the energy events coming from the detector with a 250ns peaking time fourth-order, pseudo-gaussian shaping function. The conversion time of the ADC does not add to the dead time associated with the pulse-shaping amplifier. Data collection is either gated by an external synchronization signal such as an accelerator beam clock or a precise clock signal to time-stamp the data collection and measure count rates. After an analog to digital conversion has taken place, the ADC board control logic sends a request to the histogramming memory module. When the histogramming memory controller acknowledges the request, it uses the ADC data to increment by one the content of the corresponding address memory location. The entire operation lasts 130ns, which is less than the dead time of the pulse- processing amplifier. Therefore, the histogramming operation does not increase the overall event-by-event processing time of the entire system. The histogramming memory module is packaged in a VME or VXI compatible interface and is built around a dual-port static random access memory. One port is dedicated to data accumulation while the second port is mapped to the VME or VXI address and data buses. The transfer to the computer is controlled by either the synchronization signal in the form of an interrupt signal sent to the VME or VXI controller, or by the computer accessing the memory at regular time intervals. The former corresponds to the “standard” acquisition mode and the latter to the “live” mode. In standard mode the content of the histogramming memory must be erased (zeroed) before collecting any new data set.

High Speed Measurements of the LHC Luminosity Monitor

The LHC luminosity monitor is a gas ionization chamber designed to operate in the high radiation environment present in the TAN neutral absorbers at the LHC. One of the challenges is to measure the luminosity of individual bunch crossings with a minimum separation of 25 nsec. To test the time response and other aspects of a prototype chamber, we have performed a test using an x‐ray beam of 40–60 keV with pulse spacing of 26 nsec as an ionizing beam. The tests were made at BL 8.3.2 at the Advanced Light Source (ALS). This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DE‐AC02‐05CH11231.

The luminosity monitoring system for the LHC: Modeling and test results

Simulation results of the Beam Rate of Neutrals (BRAN) luminosity detector for the CERN Large Hadron Collider are presented. The detectors are intended to measure the bunch-by-bunch relative luminosity at the ATLAS and CMS experiments. Building up from experimental results from test runs at the SPS, RHIC and ALS we extend the simulated setup to the TAN neutral absorbers located at 140 m at both sides the IP1 and IP5 interaction points. The expected signal amplitudes are calculated for pp-collisions energies between 450 GeV and 7 TeV using the Monte Carlo package FLUKA and its graphical user interface FLAIR.