sPHENIX GEM Tracker R&D at BNL

Craig Woody BNL

sPHENIX Design Study Meeting

September 7, 2011

C.Woody, sPHENIX Design Study, 9/7/11 2

Basic Guidelines

• Want a low mass gas tracking system that can provide multiple coordinate measurements with a resolution ~ 50-100 m

• Use in conjunction with the silicon tracking system to provide additional track finding capability (particularly in heavy ion collisions) as well as improved momentum resolution

• Probably want a cylindrical geometry in the central region and a planar geometry in the forward direction

• Low mass is especially important for eRHIC (particularly in the electron direction)

C.Woody, sPHENIX Design Study, 9/7/11 3

Two Approaches1. Design and build a cylindrical GEM detector capable of working

in heavy ion collisions (readout can also work for planar chambers)

– Cylindrical GEM trackers have been built and operated ( KLOE). However, KLOE cylindrical GEM tracker was designed for very low multiplicity e+e- collisions (XV strips read out only on ends)

– sPHENIX detector must work in high multiplicity HI collisions Readout must deal with high local occupancy – Want to provide multiple layers of coordinates with lowest possible mass “MicroTPC” configuration can provide multiple coordinates with a single readout plane. Need to study various types of readout planes.

2. Investigate the design of a fast, compact TPC that could be used in either the central region and/or possibly the forward direction (depending on the configuration of the magnetic field)

– TPC would provide the most number of tracking coordinates with the lowest possible mass

Important for measuring low energy electrons in the forward direction at eRHIC

C.Woody, sPHENIX Design Study, 9/7/11 4

Cylindrical GEM Tracker for KLOE-2

Cylindrical tracker • Rinner = 12.7 cm, Router = 23

cm• r ~ 200 m, z ~ 500 m• 5 KHz/cm2 rate capability

Prototype has been built with small (200x240 mm2) double-mask foils

C.Woody, sPHENIX Design Study, 9/7/11 525 May 2010

XV readout

A second prototype (same dimensions) will be

assembled with the final KLOE-2 readout: XV strips-pads with 650 μm pitch on

a kapton substrate.

C.Woody, sPHENIX Design Study, 9/7/11 6

Line and Pad 2D Readout R.Majka (Yale)R.Majka (Yale)

Concept: Have both X & Y readout on the same single layer Normal strips in one direction on top Connect pads to strips on bottom with vias for other direction Can also do with 3 coordinates

Concept: Have both X & Y readout on the same single layer Normal strips in one direction on top Connect pads to strips on bottom with vias for other direction Can also do with 3 coordinates

300 m line-pad produced by Tech Etch300 m line-pad produced by Tech Etch

X

Y

C.Woody, sPHENIX Design Study, 9/7/11 7

Chevron Readout with Floating Strips

No floating stripsFloating strip patternsPattern Resolution

Fine Chevron (no Floating Strips) 128.2 μm

Coarse Chevron (no Floating Strips) 183.8 μm

Fine Chevron (with Floating Strips) 97.6 μm

Coarse Chevron (with Floating Strips) 104.5 μm

Intermediate -

Straight Strips 113.3 μm

Provides good precision coordinate in one direction (e.g., r-) and allows for coarser segmentation in other direction (e.g., z) to minimize channel count

~ 100 m

C.Woody, sPHENIX Design Study, 9/7/11 8

MicroTPC Operation of MPGDs

Edrift 300V/cm Vdrift ~2cm/sVmesh 570 V

ATLAS Muon Tracker Trigger Upgrade V.Polychronakos, G.De Geronimo (BNL)

Can do the same with GEMs !

Problem with Inclined TracksoResolution degrades with tan(theta)oFine for tracks at small angles (detectors can be inclined to mitigate the effect)oImpractical for larger coverage

FurthermoreoInduced charge footprint rather large, need better double track resolutionoConstruction of large area chambers is labor intensive

Use time of arrival of ionization to reconstruct trackNeed both amplitude and time measurement

MicroMega

C.Woody, sPHENIX Design Study, 9/7/11 9

• 64 channels• adj. polarity, adj. maximum charge (0.11 to 2 pC), adj. peaktime (25-200 ns)• derandomizing peak detection (10-bit) and time detection (1.5 ns)• real-time event peak trigger and address• integrated threshold with trimming, sub-threshold neighbor acquisition• integrated pulse generator and calibration circuits• analog monitor, channel mask, temperature sensor• continuous measurement and readout, derandomizing FIFO• few mW per channel, chip-to-chip (neighbor) communication, LVDS interface

VMM1 ASIC for MicroMegas for ATLASVMM1 ASIC for MicroMegas for ATLAS

peaktime25,50,100,200ns

stop at1st cnt

timeCA SA

Neighbor enable(channel or chip)

AADC 10-bit

TADC 6-bit

TACamplitude

6-bit counter

Clock (10MHz)

Trigger in

enable

tstop

(rejects data if no

trigger after X counts)

200ns conv.

capacitance2pF-200pF

4-bit countercoarse time 100ns

trigger identifier

fine time 1.5ns

amplitude

FIFO32-bit

x3x16

address

tstart

channel

input charge range0.11, 0.33, 1.0, 2.0 pC

ADDR 5-bit

2x peak/time detector derandomizer

PD/TD

DSC

4-bit counter

Trigger outAddress out

BNL Instrumentation

Division (G.DiGeronimo)

C.Woody, sPHENIX Design Study, 9/7/11 10

VMM1 Chip Design

Design nearing completionFirst submission anticipated by Nov 2011

C.Woody, sPHENIX Design Study, 9/7/11 11

Beta Source Test Stand

• Use Sr-90 source to produce collimated beam of electrons• Emax = 2.3 MeV (enough to pass through many cm of gas)• Can produce sub-millimeter collimated beam• Need to suppress background from ’s and ’s• Can rotate to various angles• Easier and faster than cosmic rays• Use for preliminary studies before going to test beam for higher precision measurements

6 mCi 90Sr source

Brass collimator with 0.8 mm hole

C.Woody, sPHENIX Design Study, 9/7/11 12

CERN Scalable Readout System (SRS)

Crate with one Front End Card and one ADC arrived at BNL in July - Capable of reading out ~ 2000 channels 10x10 cm GEM detector with COMPASS readout also arrived in July Currently setting up to to run in Gas Detector Lab at BNL

Hybrid card with APV25 chip

SRS crate in Martin’s office....

10x10 CM GEM with COMPASS readout

C.Woody, sPHENIX Design Study, 9/7/11 13

GEM TPC Test Stand

in BNL Gas

Detector Lab

Fast Drift TPC Development

Double GEM Readout

Designed and built by BNL Instrumentation Division

GEM Readout TPC for the Laser Electron Gamma Source (LEGS) at BNL

Custom ASIC • 32 channels - mixed signal• 40,000 transistors• low-noise charge amplification• energy and timing, 230 e-, 2.5 ns • neighbor processing• multiplexed and sparse readout• Basis for ATLAS VMM1 chip

G. De Geronimo et al., IEEE TNS 51 (2004)