New generation hadron colliders are going to reach unprecedented energies and radiation levels. Quartz has been identified as a radiation-hard material that can be used for Cerenkov calorimeters of the future experiments. We report from the radiation hardness tests performed on quartz fibers, as well as the characteristics of the quartz fiber and plate Cerenkov calorimeters that have been built, designed, and proposed for the CMS experiment

Akgun, U

Onel, Y

CERN Document Server

Available on CMS information server CMS CR 2006/075CMS Conference Report1 October 2006Radiation-Hard Quartz Cerenkov CalorimetersU. Akgun, Y. Onel (for CMS Collaboration)Department of Physics and Astronomy, The University of Iowa, 203 Van Allen Hall, Iowa City IA, 52242, USAAbstractNew generation hadron colliders are going to reach unprecedented energies and radiation levels.Quartz has been identified as a radiation-hard material that can be used for Cerenkov calorimetersof the future experiments. We report from the radiation hardness tests performed on quartz fibers, aswell as the characteristics of the quartz fiber and plate Cerenkov calorimeters that have been built,designed, and proposed for the CMS experiment.Presented in CALOR 2006, Chicago, June 20061 IntroductionThe future colliders are going to reach unprecedented energies and the experiments will experience huge particlefluxes. This requires developing and using radiation hard detector system technologies. For the CMS ForwardCalorimeter (HF) we have used quartz fibers as the active material, in light of a series of radiation-hardness testsperformed on quartz fibers. We report results from these tests. In this paper we summarize the test beam results onPre-Production Prototype (PPP-1) and HF, as well as the Geant4 simulations. The CMS detector has the CASTORcalorimeter behind HF to cover the forward region better. CASTOR has been designed to use Cerenkov light madein quartz plates. We review the design properties of CASTOR calorimeter. As a possible upgrade to the End-Cap Hadron calorimeter for the SuperLHC (SLHC) era, we have proposed to replace existing scintillators withradiation hard quartz plates. In the last section of this paper we give the preliminary results from R&D studies formaximizing the Cerenkov light collection efficiencies.2 Radiation Damage Studies on Quartz FibersThe simulations show that the CMS HF calorimeters are going to absorb, on average, 760 GeV energy per event.This is huge compared to only 100 GeV for the rest of the main detector. Moreover, this energy is not uniformlydistributed, but has a pronounced maximum at the highest rapidities. At η = 5 and integrated luminosity of5 × 105pb−1 (around 10 years of LHC operation), the HF will experience almost 1 GRad radiation [1]. Theneutron rates (En <= 14 MeV) at the front of the detector will be in the order of 10 8Hz/cm2. The chargedhadron rates will also be extremely high, especially at the shower maximum of the HF where the rate will reach1013 to 1016Hz/cm2. This hostile environment presents a unique challenge in particle detection techniques.Figure 1: The experimental setup. Figure 2: Attenuation for seven groups of fibers.Initial radiation damage studies on quartz fibers were performed at two different facilities; a 10 kW experimentalreactor, UTR-10 at ISU in Ames, Iowa, and the MGC-20E cyclotron at ATOMKI in Debrecen, Hungary. Thedetails of these tests can be found elsewhere [2]. The initial tests showed some radiation recovery for most silicafibers. For some quartz fiber types < 10 MRad gamma irradiation seems to have generated a similar type of opticaldamage as neutron irradiation at fluence of 1015n/cm2. After these initial tests we performed more radiationdamage tests on nine different high OH- quartz fibers by irradiating them with 500 MeV electrons from the LinacInjector of LEP (LIL) at CERN. The transmission of Xe light was measured in-situ in the 350-800 nm range. Theinduced attenuation at 450 nm is found to be 1.52± 0.15dB/m for a 100 Mrad absorbed dose. We observed somedarkening on the fibers, but the radiation did not change the tensile strength of the quartz fibers [3].In 2004, quartz fibers were exposed to strong neutron and photon radiation and tested for optical degradation. Thefibers were irradiated with pulses of high-energy neutrons produced by the Intense Pulsed Neutron Source (IPNS) atArgonne National Laboratory for a two-week period. Damage to the fibers was determined after 7.42×10 17n/cm2of fast neutrons, 17.6 Mrad of neutron and 73.5 Mrad of gamma radiation. The spectra of the irradiated fibers looksimilar to those from the non-irradiated fibers but were noticeably attenuated. The level of damage was wavelengthspecific (See Figure 1 and Figure 2). Recently, to complete our knowledge of radiation damage of the quartz fiberswe initiated a high level of irradiation with 24 GeV protons at CERN. The quartz fibers with 0.6 mm core diameterwere irradiated with 4.61016protons/cm2 corresponding to a 1.2 Grad dose. The attenuation measurements wereperformed in-situ. We tested quartz fibers with quartz cladding (qq) and with plastic cladding (qp). The light2Figure 3: α parameters for qq and qp fibers versuswavelength, where α is the attenuation in dB/m at 100Mrad.Figure 4: β parameters for qq and qp fibers versuswavelength.attenuation in the fiber is defined asA(λ,D) = α(λ)[D/Ds]β(λ)Where α and β are parameters for qq and qp fibers that are determined by fitting the ratios as a function ofwavelength and dose.I(λ,D)/I(λ, 0) = e−[(L/4.343)α(λ)(D/Ds)β(λ)]Choosing a scale factor Ds = 100 Mrad, a is the attenuation at 100 Mrad, in dB/m, L being expressed in m (seeFigure 3 and Figure 4). After 1.2 Grad of proton irradiation, the results are similar to the electron radiation tests[4]. Up to 0.8 Grad we do not observe a significant difference in attenuation versus dose between qq and qp fibers.Above 0.5 Grad there is no recovery of damage below 380 nm, and in the range of 580-650 nm quartz becomesopaque. We monitored the recovery over 4 months. The decrease of signal in fibers is very fast at the beginning:30% loss after 20 Mrad at 455 nm.3 Quartz Cerenkov Calorimeters of the CMS ExperimentThis part of the paper will cover three different radiation-hard Cerenkov calorimeters for the CMS experiment(Figure 5); i) Pre-Production Prototype (PPP-1) of the Forward (HF) calorimeter, ii) The Forward (HF) calorimeteriii) The CASTOR calorimeter. The PPP-1, and HF use quartz fibers while CASTOR uses quartz plate as the activevolume (Figure 6).3.1 Pre-Production Prototype (PPP-1)The PPP-I is an iron absorber matrix with embedded quartz fibers which serve as the active material. The ironmatrix is composed of 2.5 mm thick iron layers with grooves every 2.5 mm. The embedded fibers run parallel tothe beam and constitute the active component of the detector. The length of the absorber is 165 cm, 8.3 nuclearinteraction length (λint), with a cross sectional area of 18cm × 18cm. A single quartz fiber is inserted In eachgroove. In PPP-I, there are three different lengths of fibers to achieve a longitudinal segmentation. They are calledelectromagnetic (EM), hadronic (HAD), and tail catcher (TC). Long fibers sample all shower components whilethe shorter fibers are biased to the hadron component as the hadronic showers tend to penetrate deeper. There aretwo EM fibers for each HAD and TC fiber. The PPP-I is divided into nine physical regions called towers, eachwith a 6 cm 6 cm cross sectional area. At the center of each tower, a radioactive wire source-tube groove existsfor calibration [5].3Figure 5: The major components of the central part ofthe CMS detector.Figure 6: The major components of the forward re-gion of the CMS detector.At the test beam the detector was placed on a platform that could move in three dimensions with respect to the H4beam line at CERN. One of the factors that affect the calorimeters response is the non-uniformities in its structure.In PPP-I, this non-uniformity is the fiber spacing. In order to study the spatial uniformity of the PPP-I, a 120 GeVelectron beam was moved with 1.0 cm steps across the face of the detector. The energy resolution of a calorimeter,in general, can be parametrized as(σ/E)2 = (a/√E)2 + (b/E)2 + c2The first term is the sampling term and characterizes the statistical fluctuations in the signal generating processes.The second term corresponds to noise and includes the energy equivalent of electronic noise as well as pileup.The third term is the constant term and is related to the imperfections of the calorimetry, signal generation andcollection non-uniformity, calibration errors and fluctuations in the energy leakage from the calorimeter. In quartzfiber calorimeters the electromagnetic energy resolution is completely dominated by photoelectron fluctuations,therefore we drop the noise term for electromagnetic resolution definition (See Figure 7). The electromagneticenergy resolution was measured to be(σ/E)2 = (197%/√E)2 + (8%)2Where, E has units of GeV. The hadronic energy resolution was determined to be 18% at 1 TeV (Figure 8).3.2 The Forward (HF) CalorimetersThe HF calorimeters consist of two modules, located symmetrically at about 11 m from either side of interactionpoint. They cover the pseudorapidity range 3-5. The length along the beam is 1.65 m or 10 λ int. Each calorimeterconsists of a large steel block that serves as the absorber. Embedded quartz fibers in the steel absorber run parallelto the beam and constitute the active component of the detector. In order to optimize energy resolution for E andET flows and forward jets, the calorimeter is effectively segmented longitudinally by using two different fiberlengths.In this report we will summarize the results from tests performed on HF modules at the H2 test beam line atCERN, in 2004. And, the Geant4 simulation efforts to verify the test beam. The HF wedges were individuallyplaced on a remotely controlled table that could move horizontally and vertically with respect to the beam withbetter than 1 mm precision. The angular positioning of the detector on the vertical plane with respect to the beamline was also remotely controlled and varied from 0o to 6o to mimic the particle path in the CMS experiment. Thepurity of the beam depended on energy; in particular, high energy electron beams were contaminated with pionsand muons [6]. The simulations of the test beam, the physics of the electromagnetic and hadronic processes, areimplemented by using GEANT4 physics applications. Although electromagnetic physics used in the simulation isstandard GEANT4 electromagnetic physics, four different physics lists are used for the hadronic physics, LHEP,QGSP, QGSC, and FTFP [7]. Table 1 and Table 2 summarize the comparison of different Geant4 simulations with4Figure 7: The electromagnetic energy resolution ofPPP-1 as a function of 1/√E.Figure 8: The hadronic energy resolution of PPP-1 asa function of 1/√E.Figure 9: One of the completed HF calorimeters inCERN.Figure 10: The Forward region detectors.5the test beam. The test beam results showed that for the electromagnetic energy resolution, the stochastic term a is198% and the constant term c is 9%. The hadronic energy resolution is largely determined by the fluctuations inthe neutral pion production in showers, with a = 280% and c = 11%.Table 1: Test beam electromagnetic energy resolution and Geant4 results.Data 30 GeV 50 GeV 100 GeV 150 GeVTB04 0.396± 0.028 0.315± 0.022 0.231± 0.016 0.204± 0.014LHEP 0.421± 0.001 0.329± 0.001 0.239± 0.001 0.201± 0.001QGSP 0.420± 0.001 0.328± 0.001 0.240± 0.001 0.201± 0.001QGSC 0.421± 0.001 0.328± 0.001 0.239± 0.001 0.203± 0.001FTFP 0.422± 0.001 0.328± 0.001 0.238± 0.001 0.203± 0.001Table 2: Test beam hadronic energy resolution and Geant4 results.Data 30 GeV 50 GeV 100 GeV 150 GeVTB04 0.514 0.036 0.407 0.029 0.309 0.022 0.267 0.019LHEP 0.495± 0.001 0.380± 0.001 0.280± 0.001 0.241± 0.001QGSP 0.467± 0.001 0.368± 0.001 0.275± 0.001 0.234± 0.001QGSC 0.477± 0.001 0.373± 0.001 0.276± 0.001 0.236± 0.001FTFP 0.466± 0.001 0.372± 0.001 0.274± 0.001 0.232± 0.0013.3 CASTOR CalorimeterCASTOR [8] is a calorimeter that will measure the energy of particles emitted at very small angles, coveringthe polar angles from 0.1o to 0.7o with respect to the beam direction. The detector is an octagonal cylinder,approximately 1.5 m long with an outer diameter of 36 cm and an inner diameter of 3.8 cm (to contain the beampipe). It is subdivided into 16 sections in azimuth and 18 sections in depth. This fine segmentation allows it toimage the 3 dimensional texture of energy deposition for different particles. Because the energy of the incomingparticles is very high, the CASTOR spectrometer has to be very dense, which is achieved by using tungsten plates.For sensitivity to the angle of the incoming particles it is desirable to measure only the very fast positrons andelectrons produced at small angles with respect to the initial direction. This is done by using the Cerenkov effect,which results in emitted light created in an approximate electromagnetic equivalent to the shock front that causessonic booms. In its proposed location, the detector is expected to experience radiation exposure in the range of10-100 MGy. The quartz is arranged in thin plates, tilted at 45 o in order to efficiently capture the Cerenkov light.In order to increase the amount of light collected, many layers of tungsten and quartz are stacked together. Thelight from seven quartz plates is collected by an air filled light guide, covering 22.5o in azimuthal angle (see Figure11).Figure 11: The design of CASTOR.6The electromagnetic particles, photons and electrons, penetrate less deeply into the detector than the hadronicparticles, such as pions and protons. Therefore, the first 11.5 cm of the detector is segmented slightly differentlywith tungsten and quartz thicknesses of 3.0 and 1.5 mm, respectively, compared to 5.0 and 2.0 mm, in the remain-ing 1.25 m hadronic section of the device. With this design of quartz detectors, the diameter of the showers ofelectrons and positrons produced by hadrons is of the order of 1 cm for tungsten, compared to values orders ofmagnitude larger in other calorimeters. CASTOR will provide a very fast, high resolution measure of the azimuthaldistribution of energy in a region very close to the beam direction. The longitudinal segmentation will allow thisenergy to be differentiated into that carried by hadronic and electromagnetic particles and to allow study of exoticobjects that have been predicted to occur in this angular range [9]. In events with smaller occupancy, the energy ofindividual particles, as well as their hadronic or electromagnetic nature, can be determined with high accuracy.4 CMS HCAL Detector Upgrade Studies For SLHCThe Large Hadron Collider (LHC) is designed to provide, 14 TeV center of mass energy with proton-protoncollisions every 25 ns. After a few years of run, the conditions of LHC will be upgraded to operate at 10 timeshigher luminosity (L = 1035cm−2s−1) allowing new physics discoveries. This period is called SLHC. In thecurrent design, Hadronic EndCap (HE) calorimeters of the CMS experiment use Kuraray SCSN81 scintillatortiles, and Kuraray Y-11 double clad wavelength shifting fiber. These materials have been shown to be moderatelyradiation hard up to 2.5 MRad [1]. The scintillation photons are collected by wavelength shifting fibers which havethe geometry shown in the first picture at Figure 12. Under the SLHC conditions the lifetime radiation dose atthe HE will increase from 2.5 Mrad to 25 Mrad. The scintillator tiles used in the current design of HE will losetheir efficiency due to high radiation. As a solution to the radiation damage problem with SLHC conditions, wepropose to replace the scintillators with quartz plates. They will not be affected by the high radiation, but withquartz plates, the light comes from Cerenkov radiation which produces 100 times less light than scintillation. Ouraim is to find an efficient way to collect light from quartz plates. At the University of Iowa and Fermilab, we testedand simulated different sizes of quartz plates with different fiber geometries embedded in them to obtain maximumlight. After the test beams and simulations of different fiber geometries for their light collection efficiencies anduniformities we have constructed a quartz plate calorimeter prototype. The Geant4 simulations for the calorimeterprototype are still undergoing. We have test beams scheduled at Fermilab and CERN for the fall of 2006.Figure 12: Geant4 simulations of the Cerenkov light collection in quartz plates with different fiber geometries.5 AcknowledgementsWe would like to thank D. Green, J. Freeman, and A. Skuja of HCAL management, P. Bruecken, K. Cankocak, J.P.Merlo, T. Yetkin, IowaTurkish Universities Raddam Group. E. Norbeck, A.D. Panagiotou of the CASTOR group.This research is funded by DOE (DE-FG02-91ER40644), Iowa-Fermilab MOU for CMS construction and M&Oprojects, and The University of Iowa office of VP of Research and Graduate College.7References[1] The Hadron Calorimeter Project Technical Design Report, CERN/LHCC 97-31, CMS TDR 2, 20 June 1997.[2] A.S. Ayan, The CMS Forward Calorimeter Prototype Design Studies and Oc0 Search at E781 Experiment atFermilab, Ph.D. Thesis, The University of Iowa, 2004.[3] I. Dumanoglu et al., Radiation-hardness studies of high OH- content quartz fibres irradiated with 500 MeVelectrons, Nucl. Instrum. Meth. A 490, 2002, 444-455.[4] J.P. Merlo and K. Cankocak, Radiation-hardness studies of high OH- content quartz fibers irradiated with24 GeV protons, 2006, CMS CR 2006/005.[5] A.S. Ayan et al., Energy resolution and the linearity of the CMS forward quartz fibre calorimeter, J. Phys. G:Nucl. Part. Phys., 30, (2004), N33-44.[6] G. Baiatian et al., Design, Performance, and Calibration of the CMS Forward Calorimeter Wedges, CSMNOTE 2006/044.[7] T. Yetkin, Search for SUSY in Missing Transverse Energy Plus Multijet Topologies at vs = 14 TeV and Geant4Simulation of the CMS Hadronic Forward Calorimeter in the 2004 Test Beam, Ph.D. Thesis, Cukurova Uni-versity, 2006.[8] CASTOR: Centauro And Strange Object Research, http://cmsdoc.cern.ch/castor[9] E. Gladysz-Dziadus, CASTOR: Centauro and Strange Object Research Exotic Aspects of Forward Physics atthe LHC, Act. Phys. Pol. B, 37, 2006, 153-160.8

Radiation-Hard Quartz Cerenkov Calorimeters

Abstract

Similar works

Full text

Available Versions

CERN Document Server