Microstrip PSD detectors C Fermon V Wintenberger G

Microstrip PSD detectors C. Fermon, V. Wintenberger, G. Francinet, F. Ott, Laboratoire Léon Brillouin CEA/CNRS Saclay 1

Outline n Present state of the art at the LLB – – n micro-strip detectors (MS) geometry electronics performances projects, problems and improvements Projects within TECHNI – large size (300× 300 mm²) detectors 2

Principle: charge division n Position determination : Qa Qb 3

Microstrip geometry n Typical voltages: – Anode 1000 -1200 V Cathode 400 V VAC max = 1000 V; avalanche gain ~ typ. 106 (105 - 107) n Use of the ILL geometry; line resistance = 6 k. W Pitch 0. 5 mm or 1 mm n Size : 100× 100 mm² or 200× 100 mm² Possible to make 200 × 200 mm² 4

Detector casing n 100 × 100 detector 5

Gas n Maximum pressure in the casing is 10 bars – n Typically – – n n n Þ Flat Al window, 4 -5 mm thick 1. 5 bar CF 4 2 -4 bar 3 He (depending on the wavelength) Use of indium seals (Cu or Al did not work) Pumping down to 10 -7 mbar + etuvage at 80°C Purification of the gas: Þ nitrogen trap while filling the detector (for 3 He) Þ fractional distillation for CF 4 In the future, use of oxygen getter (provided by SAES) 6

Preamplifiers n n “Home made” charge amplifier (based on OPA 621) associated with a 50 W line driver. Gain: 10 m. V/f. C (with an input capacitance of 20 p. F) – – n n Output noise 15 m. V Typical avalanche gain = 106 (at VAC = 900 V) – n n Small detector (100 x 100 mm²): 20 p. F Large detector (100 x 200 mm²): 40 p. F Output signal = 1 V Rise time 1. 3 µs; Signal length = 5 µs tests of (8) integrated charge amplifiers (from Delft, van Eijk): smaller signals because of the high input capacitance 7

Anodes and Cathode signals Anode 1 Anode 2 500 m. V 5 µs Anode 1 500 m. V 250 m. V 5 µs Cathode 1 5 µs 8

Signals outputs dispersion n Counts (a. u. ) Anode 1 Anode 2 Cathode signal Dispersion 8% Width 15 -20% Discrimination levels Energy (a. u. ) 9

Translation scan Scan over 100 mm with a 0. 5 mm slit Intensity (counts) n Position (mm) 10

Detector linearity (w/o correction) 11

Overall characteristics n Spatial resolution: – – n Background noise: – n 0. 2 count per minute over whole detector (because of the good discrimination) Maximum counting rate: – – n 1. 3 mm on the small detector 2 -2. 5 mm on the large detectors 104 n/s without deformation of the peak. 105 n/s if one allows a 5% error on the total counting. Efficiency : 95% (2. 5 bars at 0. 4 nm) 12

Time and flux stability n Time stability: Small detector has been under vacuum for under 18 months: è no deterioration of the output signals (amplitude nor energy spectrum) – n High flux illumination – has sustained a flux of 3× 107 n/s for over 1 month (fluence of 2× 106 n/s. cm²) 13

Detector cost (w/o manpower) n 14

Short term projects (year 2000) n Use of the detectors (200× 100) for the reflectivity spectrometer PRISM. (and later for EROS) n Building of a banana shaped set of 12 detectors for 7 C 2 (liquid and amorphous materials on the hot source) n Validation of the long term stability while in operation (but in a limited flux environment however) 15

Problems and improvements n Large spread of performances between the MS plates: – – n n gain varying by a factor of ten between plates no explanation yet Building of a standard interface (hardware and software) with the LLB electronics (Daffodil) => swappable devices Improvement in the signal conversion: integration or averaging. Band pass filters Use of FPGA components for processing and linearisation (to replace the use of EPROMs. ) 16

Project within TECHNI n Project: use of multidetectors for Very Small Angle Neutron Scattering n Large size (300× 300 mm²) detectors set at a distance of 8 -10 m : – angular opening of 0. 03 rad = 1. 7° – angular resolution of 2× 10 -4 rad (= 0. 02°) (Dq = 5× 10 -5 nm-1 óobjects sizes of 1 µm) n Solutions – – assembly of smaller detectors (200× 100 mm²) use of GEM and resistive plate 17