Summary on crystal damage from hadrons

Transcription

1 Summary on crystal damage from hadrons CMS crystals will be mainly exposed to: High ionizing radiation levels High hadron fluxes Effects: - changes in Light Transmission: YES, quantified through the induced absorption coefficient in Longitudinal Transmission (LT), µ IND (λ) = L ln LT 0(λ) LT (λ) i.e. LT (λ) LT 0 (λ) = e µ IN D(λ)L - Changes in Scintillation Emission: NO, in the investigated range and precision

2 Light Transmission (%) Transmission changes in PbWO4 for 20 GeV/c protons and 60 Co γ M.Huhtinen, P.Lecomte, D.Luckey, F.Nessi-Tedaldi, F.Pauss, Nucl. Instr. Meth. A545 (2005) and CMS Note The damage to Light Transmission as a function of wavelength is qualitatively different between proton - and γ-irradiated crystals A band-edge shift is observed with proton-damage (left), unlike for γ-damage (right) GeV/c protons Co γ Crystal a before irradiation Crystal c after 7.4 cm nm Crystal a after.3 3 cm -2 Crystal a after cm -2 t rec =25 d Intrinsic emission spectrum Wavelength (nm) ʻ ( ) indicates a second (third) irradiation of the same crystal Transmission (%) LTINIT t irr =27 h t rec =25 d Em. Spect t Wavelength (nm)

3 Transmission recovery in PbWO4 after proton irradiation 2 µ IND (420 nm, t REC )= A j i e t rec/τ i + A j 3 Damage can be globally fitted by with and τ = 7.2 days τ 2 = 650 days i=! IND (m - ) - Crystal c Crystal d Crystal G! IND (m - ) -2 Crystal b Crystal F Crystal E Crystal a Crystal h t rec (days) t rec (days)

4 Proton and γ damage vs. fluence in PbWO4 µ IND (m - ) - 20 GeV/c protons a F d h E G c b µ IND = 2.08E-3!.0049 After 50 days recovery 2 3 "! p ( 22 Na) (cm -2 ) Proton-induced damage increases linearly with fluence: it has a cumulative effect No flux dependence is observed µ ind (m - ) µ ind /µ std! ind Co γ Crystal u Crystal z Crystal w Crystal x Crystal t Crystal v Crystal y t irr (h at kgy/h) γ-induced damage saturates at a value only depending µ γ on the initial crystal quality std (given by IND obtained from the standard Hospital CMS γ-irradiation procedure)

5 Correlation between changes in LT and in Light Output in PbWO4 LO loss P.Lecomte, D.Luckey, F.Nessi-Tedaldi, F.Pauss, Nucl. Instr. Meth. A564 (2006) and CMS Note LY measurements performed with an XP2262B photomultiplier correlation could be different for APD and VPT, since ε( λ ) is different proton-irradiated crystals - µ IND (420 nm) (m - ) Correlation between μ IND (420 nm) and Light Output loss for crystals irradiated with protons a a b c d E F G h LO loss ! -irradiated crystals -! IND (420 nm) (m - ) Correlation between μ IND (420 nm) and Light Output loss for crystals irradiated with γ from a 60 Co source Within the accuracy of the measurement, the two correlations are compatible No additional, hadron-specific damage to the scintillation mechanisms observed t u v w x y z

6 Understanding of hadron damage mechanism in PbWO4 Specific features of proton damage: It grows linearly with fluence It only affects Light Transmission, and can thus be monitored The scintillation mechanism is not altered It has a Rayleigh-scattering behavior = scattering off dipoles with dimension < λ Observations consistent with the peculiarities of hadrons in PbWO4: Above ~20 MeV threshold, production of heavy fission fragments, stars, with up to μm range, typical E up to 0 MeV and energy loss along their path up to x mip (MeV/cm) de/dx Ionising Pb total de/dx Fe Pb Zr He Along their track, the crystal structure is changed permanently 2 H E (MeV)

7 Comparison between 24 GeV/c protons and 290 MeV/c π + in PbWO4 (420 nm) IND µ measured induced absorption coefficients W W3 Star density profiles from FLUKA simulation (mm) W 24 GeV/c p W3 W2 200 MeV! + W2 GeV! + - data rescaled to " =! 3 cm Depth in crystal (mm) Pion damage along crystal length is highest right after entrance into the crystal, then drops due to pion absorption, as expected Proton damage raises and then stays high. Beam LT (420 nm ) M. Huhtinen, XPG meeting 25-MAR-03 The damage profile is the same as the profile of star densities l W (W2) W3 Depth in crystal

8 Star density ratios as the scaling factor Compare the profiles of pion-to-proton induced absorption coefficient ratios with the profile of pion-to-proton star densities ratios The two ratio profiles agree within the accuracy of the data scaling of damage is determined by the ratio of star densities W IND (420 nm) W2 (420 nm)/! IND! - - star densities ratio (! / p ) data MonteCarlo Depth in crystal (mm) -2 P.Lecomte, D.Luckey, F.Nessi-Tedaldi, F.Pauss, D.Renker, Nucl. Instr. Meth. A587 (2008)

9 Implications for CMS from M.Huhtinen, P.Lecomte, D.Luckey, F.Nessi-Tedaldi, F.Pauss, Nucl. Instr. Meth. A545 (2005) and CMS Note Star density (cm -3 ) 3 2!=2.8!=2.6!=2.4!=2.2 3 cm -2 of 20 GeV/c protons!=2.0 µ IND (m - ) CMS EE values for 500 fb - - a F d h E G c b µ IND = 2.08E-3!.0049 After 50 days recovery Depth along crystal (cm) 2 3 "! p ( 22 Na) (cm -2 ) Recipe (from P.Lecomte, D.Luckey, F.Nessi-Tedaldi, F.Pauss, D.Renker, Nucl. Instr. Meth. A587 (2008) ) scale μind(20 GeV protons) by average star density ratio and luminosity ratio

10 Caveat from hadron energy spectrum before ECAL ECAL TDR, CERN/LHCC (997) p Pb and W need high-energy projectiles (rather > 0 MeV) to fission - Star densities calculated down to 20 MeV threshold, but fragments below ~200 MeV not very energetic nor ionizing (M. Huhtinen, comments to draft Radiation Hardness ECAL detector paper, Eds. I. Dafinei, P. Lecomte)

11 What could be expected in the CMS ECAL Caveats: - damage amplitudes 50 days after irradiation used (recovery from the τ = 650 days component not taken into account) - ECAL hadron spectrum might yield a different amount of energetic fission products than expected from star density ratios. η value vs. Ldt, at which μind(420 nm) = 2 m - η value vs. Ldt, at which μind(420 nm) = 2 m - is reached in EE is reached, in EB+EE LHC slhc shutdown slhc (using EB star densities from draft Radiation Hardness ECAL detector paper, Eds. I. Dafinei, P. Lecomte)

12 Reminder: integrated luminosity versus physics potential LHC slhc shutdown As a function of Ldt, η at which μind(420 nm) = 2 m - is reached - with the assumption mentioned - due to hadron damage As a reminder, plot by A. de Roeck and F. Moortgat showing, as a function of Ldt, the discovery potential of CMS.

13 Conclusions A hadron-specific, cumulative damage from charged hadrons has been observed in tests on PbWO4. All characteristics of the damage are consistent with it being due to an intense local energy deposition from heavy fragments. Within the explored flux and fluence ranges and the accuracy of the measurements, this contribution is observed to only affect Light Transmission, and thus can be monitored. Comparative PbWO4 irradiations with protons and pions have allowed to establish that the damage scales with the density of stars from FLUKA simulations The existing data can be used to estimate the expected damage to the CMS ECAL crystals during LHC and slhc operation. Fission damage in crystals can be avoided by using elements below Z=7 (Lutetium). A replacement of part of the EE could be considered for slhc During CMS running, it will be important, to accumulate monitoring data and to compare them with the Ldt delivered by LHC, to be able to extrapolate the crystals behavior for the following years.