October 2005 Qweak Collaboration Meeting

Detailed Design of Shield House and Collimators wrt Backgrounds

Yongguang Liang

Just getting started – will probably take months to finalize!

1. Shield wall and entrance window design2. Strategy for detailed design of collimator: 2 bounce system3. Summary

October 2005 Qweak Collaboration Meeting

Possible Backgrounds Include

• background from target windows, beam pipe, collimators, …

• background from secondary reactions (Compton scattering Bremsstrahlung process, multiple scattering, …)

• background from inelastic reactions and Moller scattering

Only ep-elastic scattering in target and consider secondaries

October 2005 Qweak Collaboration Meeting

Shield Wall and Window Design

Goal: Minimize soft backgrounds near region III chamber while not introduce noise or dilution from showers

Consider:

1.Location, material, and thickness of the shielding wall location of main torus and region III chamber Z=330-430 cm 10 radiation lengths normal shielding concrete least 1.0 m thick MAX space ~ 70 cm 2. Shape and size of shielding entrance window Found we must address more basic issues (such as the source of the upstream background, design of a “two bounce system”) before we can design a suitable entrance window.

October 2005 Qweak Collaboration Meeting

Comparison of 0.5 m Wall to 1.0 m Wall case

Red: charged particles (mostly e-) Blue: neutral particles (mostly photon)

0.5m wall 1.0 m wall

October 2005 Qweak Collaboration Meeting

Source of Photon Background that hits the Quartz and Deposits > 5 MeV Energy

Primary collimator

X vs Z

x vs z

y vs z

October 2005 Qweak Collaboration Meeting

Photon Background (continued)

Significant amount of background from shower leakage at primary collimator E > 5 MeV signal at Quartz.

Based on VPI “final” primary collimator background ~0.08% But these studies: only ep elastic in target in the first octant Consider eight octants and inelastic reactions get larger AND difficult to measure

Reduce this background with “Two Bounce System” ie quartz NO direct line of sight to source

October 2005 Qweak Collaboration Meeting

View of Spectrometer from the Quartz

Looking upstream from Quart location along the central scattered electron trajectory:we see * inner lips of the primary collimator opening (yellow)

Qweak spectrometer is a “one bounce” system.

Modified to “two bounce” system in later slide

October 2005 Qweak Collaboration Meeting

Another view of the Spectrometer

Looking upstream from left edge of quartz tothe spectrometer:See *adjacent octant opening, *minitorus(violet), *upstream cleanup collimator (green).

October 2005 Qweak Collaboration Meeting

Block line of sight between quartz and primary collimator

October 2005 Qweak Collaboration Meeting

Demonstration of “Lintel Collimator” 60 cm downstream of Downstream Cleanup Collimator

Looking upstream from Quart location along the central scattered electron trajectory with * “lintel collimator” * primary collimator thickness 21.66 cm 5.25 cm

Defining collimator barelyseen

October 2005 Qweak Collaboration Meeting

From Left Edge of Quartz with “Lintel Collimator” 60 cm downstream of

Downstream Cleanup Collimator

October 2005 Qweak Collaboration Meeting

Elastic Collimator Detailed Design StrategyReduce background from the defining collimator two bounce system

1. Change primary collimator from Lead to Tungsten (W- Cu) Reduces the background from 0.08% to 0.04%

2. Cost management: reduce primary collimator thickness 21.66 cm 5.25 cm AND this 15 radiation lengths is sufficient

3. Cantilever a lintel from downstream collimator to block line of light between quartz and defining collimator

4. Move defining collimator slightly upstream if necessary (?)

5. Optimize primary collimator tilt angles (both x and y directions)

6. Finalize upstream cleanup and beam-defining collimation

Iterate with region I, II, III folks, VPI acceptance folks, and Neven to make sure we DON'T break anything.

Finally, Neven's background simulation needs to be repeated with the final collimator configuration.

October 2005 Qweak Collaboration Meeting

Summary

* We are just getting started on the detailed collimator design with respect to backgrounds using the outlined strategy * General shape of elastic e envelope will not change

* Work in Progess!