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SHMS GEM Tracker Status Update
× Overview
× Test results
× Summary
Hall C Coll. Meeting 2/21/2014
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12 GeV Upgrade
Hall C Coll. Meeting 2/21/2014
SHMS
HMS
In order to reach forward scattering angles of 5.5◦ and to increase the solid angle of the spectrometer, a 3◦ horizontal bend superconducting dipole magnet will be placed in front of the first quadrupole, at ~1◦ to the beam-line.
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�e SHMS Magnet
Dipole 18.4 Degree Bend Max Field: 4.76 T EFL: 2.85 m
Q2 Q3 Max Gradient: 14.4 T/m EFL: 1.61 m
Q1 Max Gradient: 10.63 T/m EFL: 1.86m
Bender 3 Degree Bend Max Field: 3.11 T EFL: 0.75 m
Collimator/Sieve
GEM Tracker
Ø An active collimation system is needed for the SHMS. Ø A pair of interchangeable collimator and sieve slit will be permanently attached in
front of the first quadrupole magnet. Ø In addition to the fixed collimators a GEM tracker will be added (can be inserted in
front of the horizontal bender). The GEM tracker is for optics calibration only, hence will be used for very low beam current (~10nA). The tracker defines the initial position of the particle trajectory entering the horizontal bend magnet and acts as an active sieve slit. The tracker and the sieve slit in front of the quadrupole magnet can be used to map out the transport properties of the entire SHMS within the geometrical acceptance defined by the fixed collimator.
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Gas Electron Multiplier (GEM)
Thin, metal-coated polymer foil is chemically pierced with a high density of holes. When applying a voltage difference, each hole acts as an individual proportional counter, and electrons released on the top side drift into the hole, multiply in avalanche, and get transferred to the other side.
Typical geometry: 5 µm Cu on 50 µm Kapton 70 µm holes at 140 µm pitch 50 - 100 Independent Proportional counters/cm2
F. Sauli, Nucl. Instrum. Methods A386(1997)531
70µm 140µm
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50 µm Kapton +5 µm Cu both sides Kapton 50 µm Copper 5 µm
U.V.
Photo-resist Mask
70 µm
50 µm
Double-mask photolitographic process
Metal etching by chemical solution
Kapton etching using Cu as mask
Low field (200 V/cm)
High field (2.5 kV/cm)
GEM Foils Construction
Hall C Coll. Meeting 2/21/2014 6
S. Bachmann et al, Charge amplification and transfer processes in the gas electron multiplier Nucl. Instr. and Meth. A438(1999)376
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Hall C Coll. Meeting 2/21/2014
GEM Detectors Principle
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Ø Charged particles ionize gas in the drift
volume
Ø Primary electrons drift to the GEM holes
following the E-filed lines
Ø Electron multiplication due to the strong
E-field in the holes
Ø Use of two to three layers in cascade
results in high gain (up to 105 in triple
GEM)
Ø Readout board collects charge
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Hall C Coll. Meeting 2/21/2014
GEM Readout
Electrons are collected on patterned readout boards. A fast signal can be detected on the lower GEM electrode for triggering or energy discrimination. All readout electrodes are at ground potential.
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Two orthogonal sets of parallel strips at 400µm pitch engraved on 50µm Kapton 80µm wide on upper side, 340µm wide on lower side (for equal charge sharing)
A. Bressan et al, Nucl. Instr. and Meth. A425(1999)254
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Hall C Coll. Meeting 2/21/2014
SHMS GEM Tracker
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Readout PCB
Drift Detector Base
GEM foils
Ø 3 GEM foils : 160mm x 160mm
(153.6mm x 153.6mm active area)
Ø External dimension: 240mm 240mm x 16mm
Ø Drift board
Ø Readout board 400µm pitch X and Y
Ø Panasonic connectors (128 pins per axis)
GEM tracker is a self-stretched triple GEM
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Hall C Coll. Meeting 2/21/2014
GEM Test
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Single channel test All channels connected to APV card
APV cards (Analog Pipeline Voltage )
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Ø Scalable Readout System (SRS)
developed by RD51 Collaboration (CERN)
Ø APV25 cards, ADC board, FEC card
Ø Data transferred through Gb Ethernet
Ø ALICE DAQ (DATE & AMORE)
GEM Readout System & DAQ
SRS ALICE DAQ
Hall C Coll. Meeting 2/21/2014 11
FEC
ADC
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GEM Test
Hall C Coll. Meeting 2/21/2014
APV25 raw data ADC analog signal
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Gas Mixture Ar/CO2 (70/30)
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Cosmic Test Results
Y-strips X-strips
Cluster: X-strips
charge distribution and cluster size distribution in X and Y strips
Cluster :Y-strips
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Hall C Coll. Meeting 2/21/2014 14
y-strips (340 mm)
x-strips (80 mm)
2-D Readout Strips
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GEM + APV Readout Map
Hall C Coll. Meeting 2/21/2014 15
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Front-end pad Back-end pad
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Hall C Coll. Meeting 2/21/2014
Correlation of Cluster Amplitudes
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X/Y strips charge sharing Correct map & high stat.
Charge sharing (correct map)
Charge sharing (incorrect map)
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Hall C Coll. Meeting 2/21/2014 17
2-D Hit Map from Cosmic Data
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Gap for separation of electrodes
Testing GEM Foils Ø Quality control (visual inspection)
Ø Understand sectoring and HV routing (notice small resistors called “surface mounts”)
Ø Place each foil in a sealed nitrogen- filled box and measure leakage current (~0.3 nA @ 400V)
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GEM & Shield Holder Lead shielding & box Boron-poly shielding Lead shielding & box
Rail (tracker can slide and retracted)
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Summary
Hall C Coll. Meeting 2/21/2014
Accomplished Ø Have correct mapping for both GEMs.
Ø SRS is set up with ALICE DAQ and working properly.
Ø GEM tracker test was successful and is ready.
Ø All foils for second GEM (spare) were tested and are good.
In progress
Ø Assembly of the GEM holder.
Ø Completing GEM tracker technical notes (located at my JLab webpage)*
Ø Assembly of the second GEM.
Ø Test of spare GEM.
Ø Integrating DATE into CODA
* https://userweb.jlab.org/~mitras/TechNotes.html
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Acknowledgement
Hall C Coll. Meeting 2/21/2014
² MEP group at MSU (D. Dutta)
² Colleagues at JLab (M. Jones, B. Sawatzky, S. Furches)
² UVA detector lab (K. Gnanvo, V. Nelyubin)
² Colleagues at CERN and FIT
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