PNPI R&D on based detector for MUCH central part (supported by INTAS ) E. Chernyshova, V.Evseev, V. Ivanov, A. Khanzadeev, B. Komkov, L. Kudin, V.Nikulin, G. Rybakov, E. Rostchin, V.Samsonov, O.Tarasenkova, S. Volkov A.Khanzdeev, March_2009, GSI

Main steps of R&D at present stage: ■ Choosing the working gas ■ Radiation hardness of materials ■ Designing the beam test prototypes A.Khanzdeev, March_2009, GSI

GEM+MICROMEGAS MICROMEGAS+GEM based tracking detector is considered as candidate for central region. Pillars made by chemical etching from photo-resistant layer 4mm between pillars, diameter of each pillar - 300μm, height - 75μm GEM (5x5 cm 2 ) of CERN production For MICROMEGAS it was used rolled mesh of Russian production – stainless steel (wire - 32 μm in diameter, cell - 64μm). A.Khanzdeev, March_2009, GSI

Gas gain vs. voltage in the mesh-gem region Gas gain vs. voltage in the gem-cathode region A.Khanzdeev, March_2009, GSI Voltage into the drift gaps was always kept V/cm At previous R&D stage we worked with He/CO 2 and Ar/CO2 mixtures. New gas supply system for preparation of 3-component gas mixtures (designed and produced in the end of last year) allowed to study Ar/CO2/iC4H10, He/CO2/iC4H10, Ar/CF4/iC4H10, and He/CF4/iC4H10.

A.Khanzdeev, March_2009, GSI Small addition of isobutane gives huge effect. The same values of gas gain are reached at much lower HV. Almost twice less energy of discharge for the same value of gas gain ~ 100 Volts

A.Khanzdeev, March_2009, GSI β-source 90 Sr (~3∙10 5 counts/s) Spark probability was estimated as ratio of spark number (count of the signals laying above some high threshold and detected by the mesh) to number of total counts detected by the anode The mixture He/CF4/iC4H10 (90/8/2) showed much lower spark probability in comparing to 2-component mixture. Gas gain of 2∙10 7 is reached at 450 V applied to the mesh and GEM (visible spark problems occurred at 480 V). Current design of FEE supposes gas gain value of 2∙10 4 which is reached at 300 V. Last point that we tried to measure was at 350 V (gas gain of ~ 2∙10 5 ) and during 30 hours we did not detect any sparks (in the picture the last point is result of extrapolation). For Ar/CF4/iC4H10 (90/8/2) mixture sparks were observed at 380 V

σ d =k√x (μm), where x in cm For 5 mm drift distance σ d ≈ 100μm in the best case A.Khanzdeev, Martch_2009, GSI Why He and CF4? Transversal diffusion for He/CF4/iC4H10 almost twice less than for Ar/CF4/iC4H10 or He/CO2/iC4H10 calculations

A.Khanzdeev, March_2009, GSI Using He/CF4/iC4H10 (85/13/2) we can get collection time of ions in the mesh-anode gap plus drift time of electrons passing drift gaps at the level of ns

Drawback – number of produced pairs in He based gas mixture is ~4 times less than in Ar − inefficiency Looks reasonable to try He + Ar (20%, for example) A.Khanzdeev, March_2009, GSI Ar+ He+ He+10%Ar+ He+20%Ar+ Inefficiency ~0.5% ~3.8% ~2% ~1%

Radiation hardness of construction materials Co 60 (E=1.25 MeV) → two expositions of 390 krad and 5.3 Mrad After irradiation the emitted fractions were detected and analyzed by infrared spectroscopy method polyethyleneFR4kapton Red – 5.3 Mrad, blue -390 krad kapton (polyimid) norilflanFR4 polyethylene Radiation degradation Coefficient of radiation degradation after dose of 5.3 Mrad A.Khanzdeev, March_2009, GSI Prices of flan and kapton about 10 times higher than FR4 There is not cupper covered noril, noril is 2 times more expensive than FR4

Prototype for beam test A.Khanzdeev, March_2009, GSI

Schematics A.Khanzdeev, March_2009, GSI

Prototype chamber elements Mesh frames Anod boards Front-end electronics boards A.Khanzdeev, March_2009, GSI

Anode structure:  2048 pads;  Pad size 1.5x 3 mm 2 ;  Working area 102x109 mm 2 ;  Gap between pads 0.2 mm;  Mask-pad overlap mm;  Through hole diameter 0.5 mm;  Board thickness 1mm A.Khanzdeev, March_2009, GSI

Plans for this year ■ Try He+Ar based gas mixture ■ Measuring the collection time for chosen working gas ■ Building two prototypes (MICROMEGAS+GEM and MICROMEGAS+TGEM) for beam test ■ Preparing electronics for beam test ■ Would be nice to start beam test at PNPI accelerator A.Khanzdeev, March_2009, GSI