Due to an expected increase in radiation damage under super-LHC conditions, we propose to substitute the scintillator tiles in the original design of the hadronic endcap (HE) calorimeter with quartz plates. Quartz is proved to be radiation hard by the radiation damage tests with electron, proton, neutron and gamma beams. Using wavelength shifting fibers, it is possible to collect efficiently the Cherenkov light generated in quartz plates. This paper summarizes the results from various test beams, bench tests, and Geant4 simulations done on methods of collecting light from quartz plates, as well as radiation hardness tests on quartz material

Akgun, U

BrÃ¼cken, P

Cankocak, K

Cremaldi, L

Dumanoglu, I

Duru, F

Merlo, J

Onel, Y

Penzo, Aldo L

Winn, D

CERN Document Server

Available on CMS information server CMS CR-2008/056The Compact Muon Solenoid ExperimentMailing address: CMS CERN, CH-1211 GENEVA 23, SwitzerlandConference Report22 July 2008Quartz Plate Calorimeter as SLHC Upgrade toCMS Hadronic EndCap CalorimetersU. Akgun, P. Bruecken, K. Cankocak, F. Duru, J. Merlo, Y. Onel The University of Iowa, Iowa City IA, 52242,USA L. Cremaldi University of Mississippi, University, MS 38677, USA I. Dumanoglu Cukurova University,Adana, Turkey A. Penzo University of Trieste and INFN, Trieste, Italy D. Winn Fairfield University, Fairfield, CT06430, USAAbstractDue to an expected increase in radiation damage under super-LHC conditions, we propose to substitutethe scintillator tiles in the original design of the hadronic endcap (HE) calorimeter with quartz plates.Quartz is proved to be radiation hard by the radiation damage tests with electron, proton, neutron andgamma beams. Using wavelength shifting fibers, it is possible to collect efficiently the Cherenkov lightgenerated in quartz plates. This paper summarizes the results from various test beams, bench tests,and Geant4 simulations done on methods of collecting light from quartz plates, as well as radiationhardness tests on quartz material.Presented at CALOR 2008,May 2008,Pavia,Italy1 IntroductionThe Large Hadron Collider (LHC) is designed to provide 14 TeV center of mass energy with proton proton col-lisions every 25 ns. After a few years of running, the LHC will be upgraded to super-LHC (SLHC), that willoperate at 10 times higher luminosity (L = 1035cm−2s−1), thereby allowing new physics discoveries. In thecurrent design, the hadronic endcap (HE) calorimeter of the compact muon solenoid (CMS) detector uses KuraraySCSN81 scintillator tiles, and Kuraray Y-11 double clad wavelength shifting (WLS) fibers. These materials havebeen shown to be moderately radiation hard up to 2.5 MRad . The scintillation photons are collected by wavelengthshifting fibers lined close to the edge of the scintillators, which we defined as the HE-shape [1]. Under SLHC con-ditions the lifetime radiation dose in the HE calorimeter region will increase from 2.5 MRad to 25 MRad. Thescintillator tiles used in the current design of the HE calorimeter will lose their efficiency due to radiation damage.As a solution to the radiation damage problem in the SLHC era, we propose to substitute scintillators by quartzplates and carry out the light via UV absorbing, blue emitting WLS fibers. We performed radiation hardness testson various types of quartz material in the form of fiber, under electron, proton, neutron, and gamma radiation.Results show that quartz will not be affected by the radiation dose at the SLHC. In the first part of this report wesummarize these different radiation hardness studies performed by our group. Radiation damage to WLS materialswill be studied at a later date. However, when quartz plates are used, the detected photons come from Cherenkovradiation, which yields 100 times less light than the scintillation process. The focus of this study is to find an effi-cient way to collect light from quartz plates. At the University of Iowa and Fermi National Accelerator Laboratory,we tested and simulated different sizes of quartz plates with different fiber geometries embedded in them to obtainmaximum light. To make up for the reduction in light production, use the far-UV region to collect Cherenkovphotons since the number of generated Cherenkov photons increase as 1/λ2 [2]. The second part of this reportpresents the results from the studies performed on finding an efficient way to collect light from quartz plates.2 Radiation Damage Studies on Quartz FibersQuartz is known to be radiation hard in general. However, not all the quartz types have the same amount ofradiation hardness. Among the different types of quartz it is important to find the best option to replace the CMSHE calorimeter tiles. To investigate different fiber radiation damage properties under various radiation types thefollowing tests have been performed;2.1 Quartz Radiation Damage with ElectronsThe quartz radiation damage test with an electron beam has been tested on nine different high OH- quartz fibers,with hard plastic cladding (qp) and quartz cladding (qq) using 500 MeV electrons from the Linac Injector of LEP(LIL) at CERN. The transmission of Xe light was measured in-situ in the 350 to 800 nm range. The inducedattenuation at 450 nm found to be 1.52± 0.15 dB/m for a 100 Mrad absorbed dose. We observed some darkeningon the fibers, but the radiation did not change the tensile strength of the quartz fibers [3].We achieved a set of mechanical and optical tests for the properties after irradiation, of nine types of fused-silicacore fibers. We measured in situ the darkening and the recovery of two fibers at the same time. This arrangementallows us to make a direct comparison of the optical properties of two different fibers, independently of dose,injected light or electron beam fluctuations. The main results are: (1) there is no significant difference in opticalproperties between the polymer-clad (qp) fiber drawn by Polymicro Technology and the fluorine doped silica cladfibers drawn by Polymicro or Hesfibel from Heraeus performs under irradiation up to 100 Mrad. (2) Tensilestrength measurements show that Polymicro fibers exhibit highest tensile strength with minimum RMS. There isno significant radiation effect on the tensile modulus, which remains at 4.6± 0.4 GPa. (3) The quality of the corematerial strongly affects the fiber performance. We measured a very different attenuation in the fibers drawn, bya single company (Polymicro), where the preforms came from two different suppliers located in Germany and inRussia. (4) The attenuation and recovery as a function of time are well represented by two-parameter fits. (5) Themeasurement of quartz fiber darkening by attenuation of light transmission 14.4 s after the beam stop is insensitiveto short-lifetime luminescence induced by the Cherenkov UV emission or dose accumulation. Three bands ofluminescence have been observed in fused silica at 280, 470 and 650 nm with lifetimes around 4 ns; 210 ms;and 20 ms; respectively. The characteristics of the luminescence, mainly in the 470 nm band, in the fibers haveto be further measured in order to fully evaluate the effects of this band on the performance of the quartz platecalorimeter.2Figure 1: Typical behavior of induced attenuation versus wavelength for Polymicro qp fiber with 300 micron core,irradiated to 54 Mrad.2.2 Quartz Radiation Damage with ProtonsTo complete our knowledge of radiation damage in quartz fibers and to investigate their possible use at the SuperLHC (SLHC) we initiated high level irradiation with 24 GeV protons at CERN. About 1016protons/cm2 weresent onto 1.20 m of quartz fibers, corresponding to a dose of 1.25 Grad [4]. The fiber radiation damage induced byprotons exhibited the same well known behavior as with electrons: high light attenuation below 380 nm and in theband 550 to 680 nm, moderate attenuation in the band 400 to 520 nm and practically no attenuation above 700 nm.The damage varies exponentially with dose; fast in the first hours and slow after. Above 0.6 Grad we observe anew phenomenon: the radiation damage is not recoverable in the range 580 to 650 nm and below 380 nm. The twofibers tested, 0.6 mm quartz core diameter, one with hard plastic cladding (qp) and the other with quartz cladding(qq), were supplied by the US firm Polymicro Tech. Inc. (PT). The fibers were installed, with their light support, ona remote controlled table at the CERN facility IRRAD. Three loops of qq and qp fibers (40 cm long) were wrappedtogether and placed with a slope of 2.5% relative to the beam. The total irradiated length (L) was about 1.2 m.No material was inserted in front of the fibers as in the case of electrons. The 24 GeV proton beam at IRRADwas delivered as 34 sub-cycles in a 19.6± 3.0 s long supercycle. This beam delivers 1011protons/cm2/burst ina spot of 2 × 2cm2. The sub-cycle sharing changed during the irradiation. The number of protons delivered wasrecorded and the dose calibration was done using thin Al samples. We regularly checked the proton beam stabilityin position, width and time. The attenuation measurements were performed in-situ. We tested quartz fibers withquartz cladding (qq) and with plastic cladding (qp). The light 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, is the attenuation at 100 Mrad, in dB/m, L being expressed in m.Radiation damage due to protons and damage recovery are in agreement within errors with our previous results ofelectron irradiations with the same type of quartz used by Polymicro Technology Inc. The two types of irradiationwere quite different: 24 GeV protons compared to 0.5 GeV electrons, in different geometries. 1.25 Grad withprotons compared to 50 Mrad with electrons. As in electron irradiations we did not observe significant differencesin proton irradiation between qq and qp fiber up to 1 Grad. Near 450 nm the observed difference appears in the fitsat high dose and above 1 Grad there is a steep decrease of the transmitted signal in qp fiber. For doses above 0.5Grad there is no recovery of damage below 380 nm and in the range of 580 to 650 nm, the quartz becomes opaque.The PMTs detecting Cherenkov light are sensitive to the blue light (about 450 nm) emitted from the fibers where3Figure 2: Evolution of the transmitted light spectra from a 1.25m of qq fiber as a function of dose 0 rad (1), 240Mrad (2), 0.8 Grad (3) and 1.25 Grad (4).the effects are maximum. For a 2 m qp fiber we observed a decrease of 30% in light transmission resulting from adose accumulation of 20 Mrad, as well as an increase in light transmission by 22% 10 days after an irradiation of100 Mrad in 200 days.2.3 Quartz Radiation Damage with Neutron and GammaWe also performed radiation damage tests to measure the degradation of quartz optical fibers under neutron andgamma radiation, which is expected to be present in the CMS hadronic calorimeters at the LHC and even moreduring SLHC. For this purpose we selected seven different types of quartz material in the form of fiber fromPolymicro Technologies. The selected quartz types were FVP 300-315-345, FSHA 300-330-350, FDP 300-315-345, FBP 600-660-710, FVP 600-660-710, FVP 600-660-710 UVM, and FSHA 600-630-800 [5]. The fibers weretested for light transmission degradation after a large radiation dose. They were bombarded with pulses of high-energy neutrons produced by the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory for 313hours. Seven sets, of five fibers each, were placed in an irradiation tube about 25 cm away from the IPNS target.These fibers were irradiated for a two-week period during which the integrated current delivered to the IPNS targetwas 4456 µA − hrs. The fibers were exposed to a total of 17.6 MRad of neutron and 73.5 MRad of gammaradiation.The optical transmission of the fibers was then measured and compared to the baseline measurements. An OceanOptics PX-1 Xenon flash lamp and an Ocean Optics SD2000 spectrometer were used for these measurements.The light was sent into a bifurcated optical fiber and was split into two channels. The tests show that a specialradiation-hard solarization resistant quartz fiber (FBP 600-660-710) gives the best results. Solarization is definedas a phenomenon where a temporary change occurs to a material due to exposure to high energy electromagneticradiation. The response of this fiber to the radiation can be seen in Figure 3, where the solid line is the response ofthe quartz fiber before being subject to the radiation and the dotted line is the response after irradiation.4Figure 3: FBP 600-660-710 spectra before (solid) and after (dashed) radiation.3 Cherenkov Light Collection and a Quartz Plate Calorimeter3.1 Cherenkov Light Collection from Quartz PlatesAs stated before, our proposal is to collect the Cherenkov photons from the far-UV range to help make up forthe deficiency against scintillators [6]. For this purpose we selected Saint Gobain BCF-12 WLS fibers, which canabsorb photons down to 280 nm, and emit at 435 nm. In the current design of the HE plates, fibers collect thescintillation photons from the edges of the plates. This simple fiber geometry works well for the scintillators sincethe scintillation photons are generated in random directions. However, the Cherenkov photons are generated at afixed angle with respect to the momentum of the charged particle. Since the photons are scarce we cannot afford tomake them propagate to the edges of the plates. The fibers should be placed close to the photons for efficient lightcollection. We investigated the most uniform and efficient fiber embedding geometry to collect the Cherenkovphotons. For this purpose, various fiber embedding geometries were considered. Here we report the results for thefollowing geometries: Bar shape, HE shape, Y shape, and S shape (see Figure 4).All of the plates were wrapped with Tyvek, which is a very strong, synthetic material. The University of Iowabench tests showed that Tyvek is as good a reflective material as aluminum and Mylar in both the UV and visiblewavelength region [7]. In all the tests reported below Hamamatsu R7525-HA photomultiplier tubes (PMTs) [8]were used to measure the light at the end of the fibers.The calculations and simulated model for our system show that the amount of Cherenkov radiation in a quartz plateis around 1% of the scintillation photons from the same size scintillator tile. To collect the light in a more efficientway, we worked on different plates with different sizes and with different fiber geometries embedded in them.After many beam tests and bench tests we came to the conclusion that by using a quartz plate with the bar-shapefiber geometry, we can collect almost 70 percent of the light that the original HE tile would yield.Bar - shape HE - shape Y - shape S - shapeFigure 4: Fiber geometries embedded into quartz plates. The dotted lines of the bar-shape represent the fibers onthe other side of the plate.5The plate with the barshape fiber geometry is shown to be very uniform since the fibers are distributed uniformlythroughout the surface. To improve the light collection, a thick quartz plate with a small area, and many WLSfibers embedded in it should be used. It should be remembered that the space between the absorber layers of HEcalorimeter (9 mm) limits the thickness of the quartz plates. Simulations show that the surface non-uniformity oflight output is around 26% for the bar-shape and the ratio of collected light with respect to HE scintillator is about70%. The analyses of the mean arrival time showed that the light collection is extremely fast (¡ 5 ns) which makesquartz a good candidate for the SLHC era. Even if the 10 times higher luminosity is obtained by decreasing thebunch crossing to 12.5 ns, the photon arrival time for quartz plates will be well within the gate.0.5 1 1.5 2 2.5 3 3.5 4 4.5Light Collection Ratio (%)0102030405060708090100Light Collection Ratio (%)120 GeV, Quartz Plates66 GeV, Quartz Plates120 GeV, UVT PlatesS-shapeHE-shapeBar-shapeY-shapeFigure 5: The light collection ratios of quartz plates with different fiber geometries to the original HE scintillator.The variations in the response for different beam energies are due to lack of statistics at 66 GeV beam energy. Thetest results of the UV Transmitting Acrylic (UVT) are also marked.3.2 Quartz Plate Calorimeter Prototype I (QPCAL-I)Based on the R&D studies described above, we have built a quartz plate calorimeter prototype (QPCAL-I). Thecalorimeter consists of 20 layers of quartz plates with 20cm × 20cm × 5mm dimensions. The Cherenkov lightwas collected by Saint Gobain BCF-12 WLS fibers, with bar shape geometry. Hamamatsu R7525-HA PMTs wereused to collect the light from WLS fibers. The prototype was tested at the CERN H2 test area with 2 differentconfigurations; hadronic configuration with 7 cm iron absorbers between each layers, and electromagnetic (EM)configuration with 2 cm iron absorbers. The hadronic and EM configurations were tested with various energies ofpion and electron beams, respectively.QPCAL-I showed superior response linearity and uniformity (see Figure 6). QPCAL-I has a preliminary hadronicresolution of 18%. The preliminary hadronic and EM resolutions are shown in Figure 7.Figure 6: Hadronic (Left) and EM (Right) response linearity of QPCAL-1, versus beam energy.6Figure 7: Preliminary Hadronic (Left) and EM (Right) energy resolution of QPCAL-1, versus beam energy.4 AcknowledgementsWe would like to thank D. Green, J. Freeman, and A. Skuja of HCAL management, IowaTurkish Universities Rad-dam Group. This research is funded by DOE (DE-FG02-91ER40644), Iowa-Fermilab MOU for CMS constructionand M&O projects, and The University of Iowa office of VP of Research and Graduate College.References[1] The Hadron Calorimeter Project Technical Design Report, CERN/LHCC 97-31, CMS TDR 2, 20 June 1997.[2] G. F. Knoll, Radiation Detection and Measurement, 1989.[3] I. Dumanoglu et al., Nucl. Instrum. Meth. A 490, 444-455, 2002.[4] K. Cankocak et al., Nucl. Instrum. Meth. A 585, 20-27, 2008.[5] P. Bruecken et al., CMS IN-2006/014, 2006.[6] F. Duru et al., IEEE Trans. Nucl. Sci., 55, 734-740, 2008.[7] U. Akgun et al., IEEE Trans.Nucl.Sci.53:1547-1550,2006.[8] U. Akgun et al., Nucl. Instrum. Meth. A550:145-156,2005.7

Quartz Plate Calorimeter as SLHC Upgrade to CMS Hadronic EndCap Calorimeters

Quartz Plate Calorimeter as SLHC Upgrade to CMS Hadronic EndCap Calorimeters

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