Qweak Final Design

Current Region 1 Tracking design

The current Region 1 tracking system design was accepted at the Qweak collaboration meeting on October 11, 2003. At that time a two stage primary collimator was centered at Z=(-543 cm) and the Region 1 tracking system was designed to be positioned in between the two stages. Below is a view of the collimator as seen by a scattered electron. A 10cm by 10cm detector would easily cover the collimator opening.

A milestone of September 2005 was established as the completion date for the construction of the ionization chamber identified above.

A detector positioning system was also design and has been constructed.

The current Jeopardy (2005) Design

The Qweak jeopardy proposal (PR-05-008) was submitted for review by the Jefferson Lab PAC-27 meeting in January of 2005. A basic three stage collimator design is illustrated in Figure 24 of the proposal which positions the Region 1 tracking system behind the first collimator stage. Unfortunately the size of the first collimator stage has been enlarged in the proposed collimator design designated as ``Version 5''.

The image below represents 3 possible locations of the Region 1 tracking system as positioned by the VT group. GEM1 is at Z=-584 cm, GEM2 is at Z=-567cm, and GEM3 is at Z=-552 cm.

The corresponding elastic electron profiles are shown below. Notice that GEM2 is located close to the location of the Region 1 tracking system that was accepted by the Qweak collaboration on October 11, 2003.

While a 10cm by 10cm active area detector will encompass most of the elastic electron flux there is a high Q² tail region (purple) of substatially smaller rate which will not be accepted by the detector unless it is moved radially outward.

It would not be possible to mount the recently completed detector support system behind the first collimator stage. As shown below, the system was designed to accomodate a radius of 29 cm. The final design has a measured radius of 25 cm. The current system would not be able to be positioned after the first collimator stage (GEM3; z=-552 cm) unless the ring gear is replaced at a cost of about 10,000 dollars.