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 (~235 W at design luminosity of [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, multigap, 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 x [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. Index Terms--Ionization chamber, luminosity monitor, shower detector.