Upgrade of the LHCb ECAL monitoring system Yu. Guz (IHEP Protvino / CERN), on behalf of the LHCb collaboration 07/04/2014

Present ECAL LED system Y~7m X~8.5m Z~2.7m HCAL ECAL PS/SPD (LHCb Calorimetry System design: see talk of Xavier V. C.) The four LHCb calorimetry detectors, Preshower, ECAL and HCAL, are equipped with LED monitoring systems, which are used for: 1.control of PMT operation during maintenance at shutdowns 2.technical control during data taking 3.ECAL and HCAL: fine (%) monitoring of PMT gain during data taking, HV correction when necessary. Prompt correction is important to keep L0 trigger rate stable. Can be valid at a time scale of ~ 1 month, then the radiation degradation of the ECAL/HCAL modules themselves becomes noticeable, an offline calibration should be performed. The experience of the LHC Run I showed that, while (3) works well for HCAL, there are problems for ECAL caused by radiation degradation of clear fibers transporting LED light to PMTs. After LHCb upgrade, at x5 luminosity, these problems are expected to become more severe. It was decided then to replace the ECAL clear fibers to radiation tolerant quartz ones. Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 2

The 6016 ECAL cells are served by 456 LEDs (16 or 9 cells in one LED group) tunable LED flash magnitude and timing LED flash magnitudes are monitored by PIN photodiodes (1 per 4 or 2 LEDs) LED: red (630 nm) Ligitek LUR3333H: very bright and fast, found to be the best option, even though the photocathode QE~2-3% (design of 2003) PIN photodiode: HAMAMATSU S LED light is transported to PMTs and PINs through plastic fibers KURARAY clear-PSM Ø1 mm Present ECAL LED system Fragment of ECAL front face. The fibers of the LED monitoring system can be seen. The LED light is then delivered to each PMT via a dedicated clear fiber running parallel to the Shashlik structure ECAL modules, front caps are open. LED light inputs Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 3

( − monitoring box ) Present ECAL LED system the fibers are exposed to noticeable radiation dose at the ECAL front face LEDs, LED drivers, PIN photodiodes and their amplifiers are installed inside monitoring boxes above and below ECAL LED light is transported to PMTs through plastic optical fibers, KURARAY clear-PSM Ø1 mm For mechanical reasons, 8 out of 10 monitoring boxes are placed below ECAL. The fiber lengths range from 2 to 8 m. ECAL monitoring box The 6016 fibers are organized into 456 bundles, total length 28.6 km fiber lengths, mm Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 4

Expected (FLUKA) and measured doses at the ECAL front face in 2011 (1.2 fb -1 ) (M. Karacson, CERN) Max 100 krad*m for one year (2 fb -1 ) at 14 TeV. Doses at the ECAL front face After upgrade (LS2, ): lumi will increase x 5; but PS/SPD will be removed (see talk of Xavier), and doses will increase by less than x 2. Max 200 krad*m for one year (10 fb -1 ) at 14 TeV. Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 5 LHCb preliminary

The evolution of average LED responses in symmetrically placed areas is different, the reason is higher degradation of longer fibers (running from bottom to top). The KURARAY clear-PSM fiber degradation rate can be estimated to ~ -10% / m for ~7 krad at maximum. The LED system is of a limited use for online gain corrections (~% accuracy is desired). It is difficult to parameterize the degradation effect, also because of their annealing in LHC stops and accelerated degradation afterwards. -18% -4% 03-May – 06-Jun 2012, 0.36 fb -1 Radiation degradation of clear fibers longer fibers, 6 – 8 m shorter fibers 2 – 4 m Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 6

It was decided to replace the present plastic fibers to rad hard quartz ones (with < 1%/m transparency loss for ~100 krad). The work was planned for LHC LS1 (is being completed now, end of installation of new bundles ~ 15/05/2014). Component selection:  fiber: pure silica high-OH core is known to be best for blue light (e.g. CMS HF studies)  replace LEDS (present red Ligitek LUR3333H  blue: PMT QE will be increased by factor of ~10  present Ø1 mm HAMAMATSU Clear-PSM fibers can be replaced by a Ø 200µm quartz fiber  finally selected:  fiber Polymicro FVP (pure silica high OH core, F-doped quartz cladding, polyimide coating)  LED Multicomp OVL-5523 (460 nm) LED system upgrade (figure from the thesis of R.D. Thomas, Texas TU, 2004) Multicomp OVL-5523 LED 460 nm Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 7

* This test was supported by AIDA: FP7 Research Infrastructures project AIDA, grant agreement no Performed 25-Jun-2013 at UCL, Louvain-la-Neuve*. Two fiber types, both 200 µm q-q: FVP from Polymicro and MIS-166 (with copper coating) from Fryazino (Russia) (thanks to Yu. Chamorovsky for the samples). Each sample was 5 m long, in a Ø5.5 cm spool. Particles: protons Energy: 62 MeV dE/dx (quartz): 9 MeV / (g/cm 2 ) flux 2·10 8 p/cm 2 /s dose rate: 28 rad/s duration: ~10 hours irradiation zone Fiber irradiation test beam samples fiber spool is here Light source: LED Multicomp OVL-5523 (460 nm) Sensor: HAMAMATSU PIN photodiode S Continuous monitoring of attenuation, in DC mode. Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 8

As the dose rate in LHCb (< 0.01 rad/s) will be much lower than at the test (28 rad/s), the depth of the damage – annealing cycles during the LHCb operation is expected to be negligible. The expected attenuation values will be close to those measured at the test at the end of the annealing periods. 100 krad 300 krad 530 krad825 krad Blue light (460 nm) Fiber irradiation test Several min periods without beam were arranged during the test. Fast beam induced damage – annealing cycles, as expected (see e.g. CMS HF studies). The measurement of the depth of fast damage – annealing as a function of beam intensity is planned for 2014, again in UCL. The same sample (irradiated to 0.8 Mrad in 2013) will be used. Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 9

Status of work Preparation of new fibers (6016 fibers, organized into 456 bundles, 28.6 km of fiber): 01/11/2013 – 20/02/2014, finished bundlingpolishing LED (common) end module endfiber bundle Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 10

Status of work Installation onto ECAL: started 01/02/2014, half of ECAL successfully commissioned. Finish expected 15/05/2014. Fiber replacementWork on a LED boxECAL centre, new and old fibers Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 11

Conclusion The accuracy of the present LED monitoring system of the LHCb ECAL appears to suffer from radiation damage of the plastic clear fibers transporting LED light to PMTs The upgrade consisting in replacement of the clear fibers to radiation tolerant quartz ones will allow for the PMT gain following within % accuracy The upgrade work is ongoing, to be finished in May 2014 Yu. Guz CALOR2014 Upgrade of the LHCb ECAL monitoring system 12