CLAS12 Drift Chamber Prototyping

CLAS12 Drift Chamber Prototyping

• Goals and Objectives– Validate Design– Test Assembly Techniques– Find Optimum Operating Conditions

• Status of Prototype Chambers

Stephen Bültmann - ODU JLab 12 GeV Upgrade Drift Chamber Review, March 2007

Design ObjectivesDrift Chamber Design and Operability

– Measure relative gain as a function of high voltage• Electric fields increased compared to CLAS DCs

– Validate choice of faster drift gas• Mixture of 92% Ar and 8% CO2 compared to old mixture of 90/10

– Measure particle detection efficiency along the wire• In particular close to the attachment point (wire feed-throughs)

– Verify low noise related to readout electronics or cathode emission

– Test and confirm wire tensions and wire deflections• Check for electrostatic oscillations


Mechanical ObjectivesDrift Chamber Construction and Assembly

– Measure deflections of chamber frame under load of wire tension and window bowing

• End-plates holding wire feed-throughs to be installed into pre-bowed chamber box frame

• Compare to Finite Element Analysis calculations– Validate procedure to survey wire positions and translation to

frame of DC• Validate alignment holes and fixtures on chamber framework

– Assembly• Chamber frame including tolerances• Chamber strong-back for handling and mounting• Wire feed-through placement• Wire stringing including fixtures and procedures• Circuit board attachment and contact to wires• Gas-tight window design and attachment


Electrical ObjectivesDrift Chamber Readout Electronics

– Validate new larger diameter sense wires (20 30 m)• Requires higher voltage between sense and field wires to

achieve gas gain of 5 ·104

• Measure HV plateau curve and noise levels– Measure leakage currents on readout boards

• Validate adequacy for higher voltage requirement resulting in about 10% higher electric fields

– Measure signal cross talk– Test new printed circuit board material

• Improved high voltage isolation and reduced water absorption by polyimide as compared to FR-4 (presently used)

HV and LV Cable – Frame patch panel on back-plane to route existing cables to

boards via smaller diameter on-chamber cables


Prototype Chambers• Full size sector of region 1 drift chamber

– Validate design and assembly techniques– Operate DC with varying voltages and gases– Test printed circuit board designs and materials

• Small drift chamber to test initially new all-plastic design wire feed-throughs and particle detection efficiency as a function of position along wire (Idaho State University)


Region 1 DC PrototypeExploded view of box frame and end-plates

Design Steve Christo and Richard Getz

Beam Line


Region 1 DC PrototypeBasic mechanical and electrical design as for the

current CLAS DC’s, but simpler geometry• Use same aluminum end-plate material and

thickness (7.9 mm)• Cell size comparable and sense wires slightly

thicker• Printed circuit board design using same

components

Design Steve Christoand Richard Getz


Region 1 DC PrototypeWire feed-throughs as used for CLAS region 1 DC• Metal trumpet insert molded into plastic holder• Crimp pin position defined by plastic holder

Design Steve Christo


Region 1 DC PrototypeMechanical design well advanced

• End-plates being fabricated• Design for frame close to being finished

Design of printed circuit boards for readout and high voltage sides are well advanced

Vendors for fabrication of wire feed-throughs with metal trumpets contacted• Enough feed-throughs on hand for prototype DC• Need to re-qualify manufacturer and process

Design and construction of assembly and stringing fixtures under wayDC will be assembled in ODU cleanroom


Region 1 DC PrototypeWire stringing of one sector of existing CLAS region 2 DC in ODU cleanroom


Wire feeding apparatus

New All-Plastic Feed-throughPossibility to improve detection efficiency on wire close to feed-through

• Improve detector acceptance at very small scattering anglesStudy electric field along wires close to feed-through

Potentially coat tip of feed-through (partially) with conductor



Small DC PrototypeInitial primary goal to test new all-plastic feed-through design Will be used for in-beam test at Idaho State UniversityMechanical design finished



TimelineRegion 1 DC prototype

• End-plates ordered (arrive middle of March)

• Box frame almost designed (should be available middle of April)

• DC mounting and handling fixtures ready middle of April

• Assembly and survey last week of April

• ODU cleanroom ready on April 1

• Begin stringing of wires at ODU middle of May for two months

• Printed circuit boards ready by end of June

• Gas system and DAQ ready by end of June

• Turn on DC in August


CLAS12 Drift Chamber Prototyping

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