march 7, 2007 clas12 drift chamber review mac mestayer drift chambers for clas12 - mac mestayer...
TRANSCRIPT
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Drift Chambers for CLAS12-Mac Mestayer
• Context: how does it fit within CLAS12 ?• Specifications:
physics tracking specs. design concepts design
• Design concepts:– ‘regions’ superlayers layers cells
– ‘umbrella’ design: minimize dead
– planar layout, triangular boxes: accuracy
• Simulations, Prototyping Issues• Planned improvements and conclusion
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Toroidal magnet ∫ B dl ~ 3 T-m
6 “sectors” between coils
3 “regions” of DC 1 - 2 - 3 !
2 superlayers/region
6 layers/superlayer112 wires/layer
24192 sense wires
Drift Chambers for CLAS12
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
• electron beam – shift in ~ 1 mrad 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, sin p & p ~ 20 MeV/c
– other cuts: co-planarity, etc. ~5 mrad
• forward-going particles – 5o minimum lab angle
• broad coverage in center-of-mass – minimize dead area
Tracking: physics design spec’s
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Goals: Specifications:
measure cross-section accurately
~ 1 mraddp/p < 1%
select an exclusive reaction; e.g. only one missing pion
p < .05 GeV/c p < .02 GeV/c sin p < .02 GeV/c
small cross-sections
L = 1035/cm2/shigh efficiency
good acceptance ~ 50% at 5o
Design Specification
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
• measure charged tracks (5o – 40o)
CLAS12 Drift Chambers
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 m position accuracy)
– practical (install, survey, calibrate)
– cost effective
~2m
central SVT and target
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
accurate constructionendplates, “boxes”
practical: install, survey, calibrate, repair– planar chambers– identical cells– triangular boxes– self-supporting
Planar chambers“triangular” shapeDave Kashy’s talk
Error Budget: individual sources < 25 m
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Wire LayoutStaggered “Brick-Wall” Hexagonal
hit wiresshown in yellow
circles representdrift distances
fieldfieldsensefieldfieldsense
.
.
.
.
.sensefieldfieldsensefieldfield
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 m/ns• time windows: ~ 150, 200 - 500, 500 ns• material choices:
– wire: 30 m W, 140 m Al, 140 m 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 m wire 2325 V 88:12 AR:CO2
30 m wire 2475 V 92:08 AR:CO2
same gain
58% faster
- and more linear ! use 30 m wire!
R3 cell
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Design based on “slanted” endplates
endplates
minimizedead area8 mm
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Stiffening Frame: Extra Thickness where it Counts
minimizedead area
stiffening frame
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
• 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
Circuit Board Placement
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
1 A2 - 3 electrons
Pre-amp2 mV/A
Post-ampx 10 - x 3030 mV disc.
drift chamber75 ft. cable
TDC’sLecroy 1877
new circuit boards
Chris Cuevas’ talk
Electronics: Chamber TDC
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Forward Tracker: Expected Resolution
dp/p, d, d, dx - plotted versus p- at 35o
1% 0.5 mrad
0.5 mrad
100 microns
dominated bymultiplescattering
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Forward Tracking: Momentum Resolution
fractionalmomentumresolution vs.momentum
differentconfiguration
s
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Forward Tracking: Momentum Resolution
250 350 m
250 350 m
fractionalmomentumresolution vs.momentum
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Performance: efficiencies; resolutions
• 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
Latifa Elouadrhiri’s talk
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
• 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
Performance: Drift Chamber Rate Capability
Latifa Elouadrhiri’s talk
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Specifications: Design Features:
L = 1035/cm2/s- high efficiency with large backgrounds
small cellssix 6-layer superlayers30 m wires
p/p < 1% mrad
planar chambersidentical cells (easy to calibrate)~linear drift velocity+/- 6o stereo angle
good acceptance flanged framelow wire tensions ~ 50% of 2at 5o
reliability self-supporting structure
Summary : specifications design concepts
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Drift Chamber Design Decisions
6x6 layers robust track-finding
+/- 6o stereo better resolution than CLAS
planar; self-supporting
identical cells, easy to calibrate, survey, repair
112 wires/layer enough for 1035 operation
30 m sense wire 92/08 Ar:CO2
faster, linear distance-vs-time, strong, more reliable stringing
low wire tension thinner endplates
on-chamber amplifiers
good signal/noise
re-use hv, lv, ADB, TDC
lots of spares; cost savings; better segmentation
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
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
Design Plans: Drift Chambers
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
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
• all-plastic feedthroughs– is wire sensitive near feedthrough?
Prototyping Plans: Drift Chambers
Stephen Bueltman’s talk
March 7, 2007 CLAS12 Drift Chamber Review Mac Mestayer
Conclusions
• Design is a modest extrapolation– 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 dead; design in tight specifications;
practical considerations: easy to install, survey• prototyping: discover flaws; refine procedures• construction: many details
We are ready for the challenge !
LatifaGeorgeChrisDaveStephen