march 7, 2007 clas12 drift chamber review mac mestayer drift chambers for clas12 - mac mestayer...

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


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


• 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


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


• 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


Torus magnetic field

∫B∙dl ~ 3 T-m

highest field for

forward tracks


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


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


Wire LayoutStaggered “Brick-Wall” Hexagonal

hit wiresshown in yellow

circles representdrift distances

fieldfieldsensefieldfieldsense

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.sensefieldfieldsensefieldfield

6 sense layers, 2 guard layers, 14 field layers: 1 superlayer


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


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


Design based on “slanted” endplates

endplates

minimizedead area8 mm


Stiffening Frame: Extra Thickness where it Counts

minimizedead area

stiffening frame


• 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


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


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


Forward Tracking: Momentum Resolution

fractionalmomentumresolution vs.momentum

differentconfiguration

s


Forward Tracking: Momentum Resolution

250 350 m

250 350 m

fractionalmomentumresolution vs.momentum


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


• 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


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


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


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


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


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

march 7, 2007 clas12 drift chamber review mac mestayer drift chambers for clas12 - mac mestayer...

Documents

design principles

field layers

cellsumbrella design

drift chamber75

dead areaaccurate

present chambers

sinqdf p dq p

guard layers