Drift Chambers for CLAS12
-Mac Mestayer
• Context: how does it fit within CLAS12 ?
• Specifications:
physics a tracking specs. a design concepts a design
• Design concepts:
– ‘regions’ a superlayers a layers a cells
– ‘umbrella’ design: minimize Dfdead
– planar layout, triangular boxes: accuracy
• Simulations, Prototyping Issues
• Planned improvements and conclusion
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Drift Chambers for CLAS12
Toroidal magnet
∫ B dl ~ 3 T-m
6 “sectors”
between coils
3 “regions” of DC
1-2-3!
2 superlayers/region
6 layers/superlayer
112 wires/layer
24192 sense
wires
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Tracking: physics a design spec’s
• electron beam
– shift in Dq ~ 1 mrad a 2.5% shift in cross-sections
• small cross-sections
– L = 1035 /cm2/sec
• measure hadronic state (esp. excl. reactions)
– reject extra particles (missing mass)
• |dp| ~ 50 MeV/c, sinqdf p & dq p ~ 20 MeV/c
– other cuts: co-planarity, etc. a ~5 mrad
• forward-going particles
– 5o minimum lab angle
• broad coverage in center-of-mass
– minimize dead area
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Design Specification
Goals:
measure cross-section
accurately
select an exclusive
reaction; e.g. only one
missing pion
small
cross-sections
good acceptance
March 7, 2007
Specifications:
q ~ 1 mrad
dp/p < 1%
dp < .05 GeV/c
dq p < .02 GeV/c
sinq df p < .02 GeV/c
L = 1035/cm2/s
high efficiency
Df ~ 50% at 5o
CLAS12 Drift Chamber Review
Mac Mestayer
CLAS12 Drift Chambers
• measure charged tracks (5o – 40o)
DC’s: same concept
as present chambers
- but planar
•hexagonal cells
•6 sectors, 3 regions
•2 super-layers/region
•6 layers/super-layer
•112 wires/layer (24192)
•angled endplates
•on-board pre-amps
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Torus magnetic field
∫B∙dl ~ 3 T-m
highest field for
forward tracks
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Drift chamber layout
• Six sectors: Region
1
• Design Principles:
– large solid angle
(minimize dead area)
– accurate (250 mm
position accuracy)
– practical (install,
survey, calibrate)
– cost effective
March 7, 2007
~2m
central SVT and target
CLAS12 Drift Chamber Review
Mac Mestayer
Error Budget: individual sources < 25 mm
accurate construction
endplates, “boxes”
practical: install, survey,
calibrate, repair
–
–
–
–
planar chambers
identical cells
triangular boxes
self-supporting
Dave Kashy’s talk
March 7, 2007
Planar chambers
“triangular” shape
CLAS12 Drift Chamber Review
Mac Mestayer
Wire Layout
Staggered “Brick-Wall” Hexagonal
field
field
sense
field
field
sense
.
.
.
.
hit wires
shown in
yellow
circles represent
drift distances
.
sense
field
field
sense
field
field
6 sense layers, 2 guard layers, 14 field layers: 1 superlayer
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
DC design details
•
•
•
•
•
gas: Ar/CO2 (92:08)
gain ~ 5 ∙ 104 (sensitive to 2 - 3 ionization electrons)
drift velocity ~ 25 to 50 mm/ns
time windows: ~ 150, 200 - 500, 500 ns
material choices:
– wire: 30 mm W, 140 mm Al, 140 mm stainless steel
(SS)
– endplates: aluminum, Stesalit, aluminum
– Noryl plastic feed-throughs, SS insert
– gas system: SS, small sections of Nylon, Al-Mylar
– FR4 circuit boards
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Drift Velocity
Calculation
20 mm wire
2325 V
88:12 AR:CO2
30 mm wire
2475 V
92:08 AR:CO2
same gain
58% faster
- and more linear !
use 30 mm wire!
R3 cell
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Design based on “slanted” endplates
minimize
dead
area
8 mm
endplates
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Stiffening Frame: Extra Thickness where it Counts
minimize
dead
area
stiffening frame
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Circuit Board Placement
• large solid angle
(minimize dead area)
– small aspect ratio
pre-amp boards
– extend in z to
maximize azimuthal
coverage
– flanges stiffen frame;
do not extend dead
area
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Electronics: Chamber a TDC
drift chamber
75 ft. cable
Pre-amp
2 mV/mA
Post-amp
x 10 - x 30
30 mV disc.
1 mA
2 - 3 electrons
new circuit boards
Chris Cuevas’ talk
March 7, 2007
CLAS12 Drift Chamber Review
TDC’s
Lecroy 1877
Mac Mestayer
Forward Tracker: Expected Resolution
dp/p, dq,
df, dx
- plotted
versus p
- at 35o
dominated by
multiple
scattering
0.5 mrad
1%
0.5 mrad
100 microns
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Forward Tracking: Momentum Resolution
fractional
momentum
resolution vs.
momentum
March 7, 2007
different
configurations
CLAS12 Drift Chamber Review
Mac Mestayer
Forward Tracking: Momentum Resolution
fractional
momentum
resolution vs.
momentum
250 a 350 mm
250 a 350 mm
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Performance: efficiencies; resolutions
Latifa Elouadrhiri’s talk
• Rate studies:
– extrapolation from present CLAS
• decrease solid angle, time window, thickness of DC cells
– estimates of layer occupancy
• present studies show efficiency fall-off about 4%
• occupancy estimates don’t require track reconstruction
– generate tracks with background; reconstruct tracks
• the best method
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Performance: Drift Chamber Rate Capability
• Improved Rate Capability: relative to CLAS
– factor of 3: one cell’s angular size 1/3 as large
• 5 - 40o instead of 10 - 120o, 70% as many wires
– factor of 1.5: smaller time window
• thicker wire, higher field, faster gas
– factor of ~ 5: better shielding
• larger solenoid, better absorber
• Tracking will be efficient at 1035/cm2/s
Latifa Elouadrhiri’s talk
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Summary : specifications a design concepts
Specifications:
Design Features:
L = 1035/cm2/s
- high efficiency with
large backgrounds
small cells
six 6-layer superlayers
30 mm wires
dp/p < 1%
dq, df ~ 1 - 2 mrad
planar chambers
identical cells (easy to calibrate)
~linear drift velocity
+/- 6o stereo angle
good acceptance
flanged frame
low wire tensions
Df ~ 50% of 2p at 5o
reliability
self-supporting structure
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Drift Chamber Design Decisions
6x6 layers
+/- 6o stereo
planar; self-supporting
robust track-finding
112 wires/layer
enough for 1035 operation
faster, linear distance-vs-time,
strong, more reliable stringing
30 mm sense wire
92/08 Ar:CO2
low wire tension
on-chamber amplifiers
re-use hv, lv, ADB, TDC
March 7, 2007
better f resolution than CLAS
identical cells, easy to calibrate,
survey, repair
thinner endplates
good signal/noise
lots of spares; cost savings;
segmentation
CLAS12 Drift Chamber Review
Mac Mestayer
Design Plans: Drift Chambers
Features that require most design work
• Chamber “boxes” - especially attachments, relative
alignments, ease of installation and removal
• Region 2 attachment method;
– specifications for torus
• On-chamber PCB’s - small space
• Region 3: outer “skin”, inner posts
• Cable routing - mundane but important
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Prototyping Plans: Drift Chambers
New features that require prototypes
• smaller cells, thicker wire, less CO2
– higher voltages: leakage current, cathode emission
– higher electro-static forces
– less quenching
• pre-bowed endplate
– accuracy of wire placement
Stephen Bueltman’s
talk
• all-plastic feedthroughs
– is wire sensitive near feedthrough?
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer
Conclusions
• Design is a modest extrapolation
Latifa
George
Chris
Dave
Stephen
– still a challenge to improve
• basic design: robust track-finding; good design resolution
• shielding: factor of ten; study permutations (mis-steering)
• gas, utilities, TDC’s fine; want better segmentation
• on-board electronics: good design; small footprint
• mechanical: minimize Dfdead; design in tight specifications;
practical considerations: easy to install, survey
• prototyping: discover flaws; refine procedures
• construction: many details
We are ready for the challenge !
March 7, 2007
CLAS12 Drift Chamber Review
Mac Mestayer