ACTAR TPC: a new time projection chamber for radioactive beam experiments
The STAR Time Projection Chamber
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Transcript of The STAR Time Projection Chamber
JT: 1The Berkeley Lab
STAR
The STAR Time Projection Chamber
Jim Thomas Lawrence Berkeley National Laboratory
for the STAR collaboration
The Vienna Conference on Instrumentation
Thursday February 22nd, 2001
http://www.star.bnl.gov/
JT: 2The Berkeley Lab
STARThe Biggest in the World
The STAR TPC is the biggest TPC in the world
The biggest statue of Buddha in the world
– Under a wooden roof
– In a building without doors
– Under a concrete roof
– That rolls
JT: 3The Berkeley Lab
STARA TPC is at the heart of STAR at RHIC
ZCal
Barrel EM Calorimeter
Endcap Calorimeter
Magnet
Coils
TPC Endcap & MWPC
ZCal
FTPCs
Vertex Position Detectors
Central Trigger Barrel or TOF
Time Projection Chamber
Silicon Vertex Tracker
RICH
JT: 4The Berkeley Lab
STARTPC Gas Volume & Electrostatic Field Cage
• Gas: P10 ( Ar-CH4 90%-10% ) @ 1 atm
• Voltage : - 31 kV at the central membrane 148 V/cm over 210 cm drift path
420 CM
Self supporting Inner Field Cage: Al on Kapton using Nomex honeycomb; 0.5% rad length
JT: 5The Berkeley Lab
STARPixel Pad Readout
Readout arranged like the face of a clock - 5,690 pixels per sector
JT: 6The Berkeley Lab
STAROuter and Inner Sectors of the Pad Plane
60 cm
190 cmOuter sector
6.2 × 19.5 mm pads3940 pads
Inner sector2.85 × 11.5 mm pads
1750 pads
• 24 sectors (12 on a side)
• Large pads good dE/dx resolution in the Outer sector
• Small pads for good two track resolution in the inner sector
JT: 7The Berkeley Lab
STAR
Sector Operation for 20:1 signal to noise
Sector gas gain anodevoltage
inner 3000 1150outer 1100 1380
TPC Sector Detail
• Gating Grid
• Ground Plane of Wires
• Anodes– No field shaping wires
• Simple and reliable
– Individually terminated anode wires limit cross-talk
– Low gain
• Pad Plane
JT: 8The Berkeley Lab
STARTPC Front End Electronics
• FEE– 3rd generation
electronics
– very compact
– First chip is pre-amp, shaper & buffer
– Second chip is switched capacitor array & (slow) ADC
– Analog and Digital are not synchronous
– 512 time buckets per ch
– 32 channels per board
• Readout (RDO) board– Multiplex and tag data
– 6 RDOs per sector
– 144 total
– Data sent to DAQ on gigabit fiber link
JT: 9The Berkeley Lab
STARPixel Readout of a Pad Plane SectorA cosmic ray + deltaelectron
3 sigma threshold
JT: 10The Berkeley Lab
STARAu on Au Event at CM Energy ~ 130 GeV*A
Real-time track reconstruction
Pictures from Level 3 online display. ( < 70 mSec )
Data taken June 25, 2000.
The first 12 events were captured on tape!
JT: 11The Berkeley Lab
STARAu on Au Event at CM Energy ~ 130 GeV*A
Two-track separation 2.5 cm
Momentum Resolution < 2%
Space point resolution ~ 500 m
Rapidity coverage –1.5 < < 1.5
A Central Event
Typically 1000 to 2000 tracks per event into the TPC
JT: 12The Berkeley Lab
STAROffline Particle Identification by dE/dx
Aihong Tang (Kent State U)
Remaining issue : correlation of dE/dxbetween pad rows
No calibration 9 %
With calibration 7.5%
Design 6.7%
12
Kp
d
edE
/dx
(keV
/cm
)
0
8
4
Anti - 3He
dE/dx PID range:
~ 0.7 GeV/c for K/
~ 1.0 GeV/c for K/p
JT: 13The Berkeley Lab
STARDrift Velocity Control Using Lasers and Tracks
Alexei Lebedev, Bill Love, Jeff Porter (BNL)
Pressure (mbar)
5.44
5.45
Dri
ft v
eloc
ity
(cm
/s)
1010 1020
• Lasers for coarse value
• Fine adjustment from tracking matching both side of the TPC
See poster B24 by A. Lebedev
JT: 14The Berkeley Lab
STARSolenoidal Magnetic Field
• Magnetic Field
0.0 G
2.5 kG
5.0 kG
• Radial Uniformity
40 gauss
• Phi Uniformity
1 gauss
JT: 15The Berkeley Lab
STARB Field Map and Distortion Corrections
Field map allows parameter free calculation
Love, Foley (BNL), Trentalange (UCLA), JT (LBNL)
Calculated Distortion = E BrMeasured Br / Bz
20
60
100
140
-200 2000-100 100
180
Z (cm)
TPC fiducial volumeRad
ius
(cm
)
Br/Bz scale 0.8 %20
60
100
140
-200 2000-100 100
180
TPC fiducial volume
Z (cm)
Distortion scale 1 mm
Rad
ius
(cm
)
JT: 16The Berkeley Lab
STARElectric Field Distortions
• No wires at the boundary between the inner and outer sectors
– E field leak
• E field radial component
• ExB effect in R and
Outer sector Inner sector
Gating grid = -127 VGround plane = 0 V
1.6 cm
Pad row #10 20 30
Data
Res
idu
al (
mm
)
0.2
0.1
-0.1
0.
Res
idu
al (
mm
)
Calculation
gap
Inner sector Outer sector
Radius (cm)
Wieman, JT (LBNL), Long, Trentalange (UCLA)
JT: 17The Berkeley Lab
STARMany Small Effects – B, E, Clock, Twist, CM …
Hui Long, Steve Trentelange(UCLA), JT (LBNL)
All calculated distortions
20
60
100
140
-200 2000-100 100
180
Z (cm)
Rad
ius
(cm
)
Distortion scale 1.5 mm
Outer sectorInner sector
Tra
ck R
esid
ual
s (c
m) Before
> 200 m
Inner sector
Outer sector
Tra
ck R
esid
ual
s (c
m) After
< 50 m
JT: 18The Berkeley Lab
STAR Particle ID via Topology & Combinatorics
Secondary vertex: Ks + p +
+ + K e++e-
Ks + + - K + + K- p + - + + -
from K+ K- pairs
K+ K- pairs
m inv
m inv
same event dist.mixed event dist.
background subtracted
dn/dm
dn/dm
“kinks”
K +
JT: 20The Berkeley Lab
STARSummary of Performance Achieved to date
• Good particle separation using dE/dx– 7.5% dE/dx resolution
– -proton separation : > 1 GeV/c
• Position resolution– 500 m
– Function of dip angle and crossing angle
• 2-Track resolution– 2.5 cm
• Momentum resolution– 2%
• Unique features of the STAR TPC– 4 meter by 4 meter scale length– No field wires in the anode planes– Low gain– Very compact FEE electronics– Analog and Digital are not synchronous– Data delivered via optic fiber– Uniform B and E field– Distortions correctable to 50 m
• Lots of physics from the year 1 data – Collective flow– Identified particle spectra– Particle correlations– Event by event physics– Strangeness
• Future challenges– Achieve turn-key operation– Handle increased luminosity …
JT: 21The Berkeley Lab
STARTPC & Related Systems Project Leaders
• TPC Project Leader - Howard Wieman (LBL)
• Software - Iwona Sakrejda (LBL)
• Anode - Declan Keane (Kent State)
• Drift Velocity Control - Tom Trainor, Greg Harper (UW)
• Gas System - L. Kotchenda (PNPI), B. Stringfellow (Purdue)
• Slow Controls - Mike Cherney (Creighton)
• Laser - Alexei Lebedev ( MEPHI & BNL )
• Magnet - Ken Foley, Ralph Brown (BNL)
• Magnet Mapping - Steve Trentalange (UCLA),
• Trigger - Hank Crawford (UCB)
• CTB - Gary Epply, Ed Platner, Gordon Mutchler (Rice)
• FEE - Spencer Klein, Fred Beiser (LBL)
• DAQ - Mike Levine, Tonko Ljubicic (BNL)
• Gating Grid & Pad Plane Pulser - Vahe Ghazikhanian (UCLA)
• Mechanical Engineering - Russ Wells, Bill Edwards, Roger Stone, Ralph Brown