ECAL LED monitoring system upgrade R&D status

1. ECAL LED monitoring system upgrade R&D status V. Egorychev, P. Shatalov, A. Zhokhov (ITEP, Moscow, Russia) E. Chernov, Yu. Guz, V. Obraztsov (IHEP Protvino, Russia)

2. Rad hard fiber – two options The 200/212µm rad hard fiber produced in Fryazino Russia (pure silica core) with metal coating. Total diameter of this fiber is ~ 240 µm This type fiber is used in CMS ~2 Euro/m for 30 km. 2x20 m samples sent us for tests. Found to be more rad hard than DRAKA. The 105/125µm rad hard fiber of DRAKA (pure-silica core/F-doped cladding) with acrylate coating+ black painting. Total diameter is ~ 258 µm ~0.8 Euro/m for 30 km. 300 m purchased from DRAKAto produce a test bundle

3. LED type selection The Multicomp “MegaBright Blue” LED was chosen. With this type of LED, fiber with core diameter of 100µm is already enough for ECAL calibration system: > 500 ADC channels for the Inner zone is expected. It is important to verify it on the calibrated ECAL: it is not easy to obtain the correct energy scale in the lab tests.

4. Production of a test bundle with 16 fibres - I • Procedure for Module end ( for every fiber in a bundle): • Remove the coating by a stripper on the length of about 12mm; • Cut the fiber end by a cleaver; • Glue the fiber into the connector; • control with a digital microscope, polish if necessary Module end connector LED end connector • Procedure for LED end (all the 16 (9) fibers): • Remove the coating by a stripper for every fiber; • Glue all fibers together into a brass tube 1.25 mm inner diameter; • polish with a polishing machine, controlling with a digital microscope; • gluing into the Plexiglas holder, together with a piece of 1.2 mm clear fiber (for PIN diode control).

5. Production of a test bundle with 16 fibres - II the 16 8m fibers are stretched at the table Gluing the fibers into end pieces control by digital 500x microscope, polishing if necessary cutting the fiber ends with a cleaver

6. Production of a test bundle with 16 fibres - III the LED end, view by microscope preparing the LED end: polishing quartz fiber bundle (16x8m) the LED end and module end connectors clear PSM fiberfor PIN diode the test bundle is ready, waiting for tests

7. Injection test The measurements were performed with a standard ECAL LED driver at max intensity with PMT LA4956 and Uctrl=1.53 V (HV=650 V). The setup included 50 cm clear fiber Ø1.2 mm, similar to that installed in each ECAL cell. Installation of the test bundle to ECAL and measurement at HV values corresponding to different ECAL zones is necessary to understand the calibration signal magnitude in FEBs and its variations.

8. Irradiation tests in Protvino During the ATLAS irradiation test in Protvino (22-31 March 2013) we were going to irradiate 10 m fiber sample(s) to 1-2 Mrad, working in “parasitic” mode. The goal is to see the transparency degradation for the blue light from our LEDs. The attenuation of the fiber was supposed to be continuously monitored with OceanOpticsSD2000 spectrometer, using blue LEDs as light source. The spectrometer has 2 inputs; two 10 m samples, DRAKA and Fryazino (“RUS”) were prepared for tests. They were installed near the end of the Absorber II, after ~2.7..2.9 λI. The thin film dosimeters (polykaproamide) were installed at the samples (G. Britvich et al, NIM B94 (1994) 338). The LED and spectrometer were installed in the barrack; 70 m long standard multimode (50/125 µm) optical cables were used to transport light to/from the samples. They were connected to the samples at ~ 30 cm from the beam line, out of the high dose area. LHCb samples Absorber I steel, 1 λI . Absorber II steel, 2 λI .

9. Irradiation tests in Protvino - preparations 10 m of fiber The “attenuation factor” of non irradiated samples was measured in the lab, as the ratio of light intensities with and without samples: 9.5 for DRAKA and 41 for “RUS” fibers. The main part of the loss occurs at the contact of 100 (200) µm core of sample fiber and 50 µm core transport cable, because of diameter mismatch. transport cables spectrometer “short” connectionof input and output sample LED boxes

10. Irradiation tests in Protvino samples beam Absorber-II the two samples (not on the photo) were installed between the steel sheets of the Absorber II .

11. Irradiation tests in Protvino • The plan of the test was the following: • beam adjustment • working at low intensity (~1-2·109p/spill) during 2 days (~1-2 Mrad at our samples expected). For us: recording main data, then removing and development of dosimeters. • switch to high intensity (few·1011p/spill). For us: ~50-100 Mrad expected at the samples position. Depending on the results from (2), either continue irradiation, or keep the samples away from the beam and observe their annealing. • However the things went wrong from the beginning. • The samples were installed before the beam adjustment. It turned out that the beam adjustment procedure requires working at maximum intensity. After ~ 6 hours, the transparency of our fibers degraded very significantly. No precise measurement therefore, only rough estimates. • The main conclusion is that the DRAKA fiber is less rad hard than the “RUS” one. • The latter is good enough for us, while with DRAKA we may be at risk (next slides). • Another surprise was that the transport cables showed strong degradation even staying out of the irradiation zone, at ~ 1.5 m from the beam line.

12. Irradiation tests in Protvino - results DRAKA RUS 1 2 3 4 5 2013-03-23 09:00 Start of the “beam adjustment” at high intensity. The transparency in the DRAKA line dropped to 0 during ~ 100 krad. The other one was always alive. 2013-03-23 16:00 Access to the zone. The samples were removed from irradiation area and placed ~1.5 m above the beam. Removal and development of dosimeters: ~2.5 Mrad on average. Start of working at low intensity. Annealing of our samples. 2013-03-25 05:00 Start of working at high intensity (part of time). Degradation and annealing periods seen in the DRAKA line, finally it drops to 0 (1.5 m from the beam line!). More smooth behavior of the other line, signal finally drops to ~30 ADC counts. 2013-03-26 13:30 Access to the zone. The both samples are disconnected, the transport cables are shorted and left at 1.5 m from the beam. The factor of ~10 degradation in the transport cables wrt their “fresh” state. 2013-03-29 08:00 End of the test. Another factor of ~10 degradation in the transport cables (kept 1.5 m away!).

13. Irradiation tests in Protvino - results ratio = 50(±10?) (cf 41 before irradiation) DRAKA RUS ratio >200 (cf 9.5 before irradiation) 1 2 3 4 only transport cables, 2 min later with samples • Deep damage-annealing cycles in DRAKA fiber; drop by factor of >100 after 100 krad • total damage with 2.5 Mrad received during 6 hours + 3 days of annealing (with some neutron exposure): • DRAKA: factor of >20 for 10 meters  ~25% per meter • RUS: factor of ~1.25...1.5 for 10 meters  < 4% per meter

14. Irradiation tests in Protvino • In spite of a very chaotic test, some conclusions can be made. • We need ~1% stability on a time scale of ~ 1 month (~ 100 krad in the Inner area after upgrade) • may be not safe to use DRAKA • to be safe, we can use the “RUS” fiber (in spite of higher price). • also, 200 µm core  no problem with amount of light for the Inner area • If we had a chance to redo the test: • lower intensity! • use more rad hard fiber for transport cables • have an extra measurement channel for transport cables’ degradation control • ...

15. cost estimate 40k Euro (DRAKA option) or 84k Euro (RUS option) + 24 man-months Can we afford the more expensive option?

16. preparation work at ITEP - status • Thermo-shrinkable tube – purchased and cut • Brass tube – purchased • Tools for cutting and drilling the brass tube – purchased. The work will start soon. • The plastic end pieces and nuts can be produced in August 2013 the earliest  connector production can start in September the earliest • Problems with money for 2013: matter of planning, more should be reserved for 2014