Construction of Region 2 Drift Chambers
Each of the 6 sectors of the Region 2 drift chambers is assembled and strung in several steps:

Preparation:

The two Stesalit endplates for the sector are taken out of storage and brought into the assembly room. Here, they are cleaned (with high-pressure water and alcohol) and all feed-throughs are inserted. (The feedthroughs are plastic inserts which reside completely inside the wire holes and serve to hold the crimp pins in place).


Preparation of a Region 2 wire chamber endplate

Lay-up:

In order to precisely align the two endplates with respect to each other, a high-precision lay-up structure (the "trapezoids") was build and surveyed in place at ODU.


Lay-up fixture (trapezoids) at ODU

The endplates are layed out on the "landing pads" and aligned with two precision pins. The front ("bow plate") and rear ("stern plate") connection members are attached. To make the whole structure rigid during stringing and transport, a number of cross members ("posts") are installed, both perpendicular to the endplates and diagonal ("exoskeleton"). Finally, the whole "box" is attached to a steel frame ("strong back") with wheels, allowing us to move it around easily.


A completely assembled wire chamber "box" on the trapezoids

Installation in stringing clean room

The finished box is moved into the clean room and installed on the stringing fixture.


Installation of a Region 2 drift chamber in the ODU clean room

Work in the clean room

As a next step, all "trumpets" are installed. These are small metal inserts on the inside of the endplate which allow the wires to take off at a 30 degree angle relative to normal in a controlled way. The endplates are then pretensioned with spring loaded cables down the center.


Partially strung nose section with pretension wires still in place

Afterwards, stringing begins in 2 shifts with 2 teams each. Presently, up to 600 wires (sense and field simultaneously) can be strung in a single day. Each crew tests the tension on all wires strung during a shift.

After all wires are strung and tested, gas bags are installed and the chamber is moved from the stringing clean room to the instrumentation clean room. There the HV and signal circuit boards are installed and field wires are ganged together (by wrapping wire around the crimp pins). After final tests, the chamber can be shipped out to CEBAF for installation.


Sector 3 in Installation Clean Room with HV circuit boards and cables

Installation consists of several steps: After checking the wire tensions and searching for broken wires one more time, the chamber is inserted in the installation cart. This device can position the chamber at the right angle so it can slide (on rails) into the CLAS cryostat. The chamber can then be attached to the cryostat via fixtures (on the upper side) and springs (on the lower side) and the springs are tensioned to take the load off the exoskeleton (this is checked with feeler gauges that measure a preset gap width in the posts). The posts and the strongback are then removed and tension is measured again.


Sector 0 being installed in CLAS. The insertion cart (yellow) carrying the Drift Chamber is visible to the right.

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