From tigwiki

TIGRESS has two modes of operation:

• High Efficiency - The front suppression shields are pulled back and not used, the Ge Clovers are pushed all the way forward to a source-to-detector distance of 11cm from the target. Compton-suppression is provided by the side and back catchers.

• Optimized Peak-to-Total - The Ge clovers are at a source-to-detector distance of 14.5cm. The front suppression shields are at 11cm from the target, fully collimating and suppressing the Ge. Compton-suppression is provided by the front, side and back catchers.

High-Efficiency Mode

Optimized Peak-to-Total Mode

Moving from one mode to the other should be done with 4 people and takes around 1 hour for 12 clovers.

[edit] Moving from High efficiency to optimized peak-to-total mode

Use hand tool for winding Ge in and out

Distance pin sets the distance

Hand tool for front suppressor plate

Align the 4 front suppressors in each position

Ensure the array closes without touching the chamber

• Open both hemispheres of TIGRESS.
• Using the hand tool wind all the clovers by their acme thread fully out to their stops. The hand tool should always be used as it reducing the vibrations experienced by the Ge.
• Change the Ge distance pin from 110mm to 145mm. There are two on each carriage.
• Wind all the front suppressor plates forward to 11cm from the target. There should be marks on the BGO guide rods to help you judge the distance. Line up the front collimators with the other three for the same position.
• Twin suppressors with two suppressors in the same frame pocket should always be wound in simultaneous with the ends never more than 2 inches apart.
• Once all front plates are inserted, visually inspect the alignment by looking into each position from the target side. You should be able to see light between the side suppressor and the front suppressors and this should be even on all sides. If it is not then there is a misalignment and you should contact an expert.
• The next step requires 3 people. One person shall be the spotter and will stand in the array and watch the Ge inside the front BGO plates (as was done in the previous step). This person shall shout out to STOP if the Ge or side catchers are touching the front suppressors at any point. The second person shall slowly wind in the Ge using the hand tool (Also read the instructions in the next step!). This person shall be constantly aware what the spotter is doing and if all is clear. This person will also be paying attention to one of the distance pins. The third person will be watching the second distance pin.
• The Ge should be wound in using the hand tool until one of the distance pins first touches the structure. This will be realized by either the person winding the Ge or the person watching the other distance pin. It is a good idea to be constantly wiggling the pin with your hand (Careful not to get your fingers trapped!). Once the pins first touch the structure, the Ge should be retracted by a small amount so that both distance pins are loose and able to wiggle. Do not allow the distance pins to be tight as this will change the alignment of the Ge.
• Once all Ges have been inserted, confirm the array is able to close without touching the vacuum chamber by slowly closing one hemisphere at a time with spotters all around the chamber. The lampshade front suppressor plates might need to be retracted by a small amount.
• Once it has been confirmed that the array will close without any detector touching the vacuum chamber, secure the stopping clamps on the lampshade front suppressors to prevent them from being wound in any further.
• Operation compete, make an elog entry.

[edit] Moving from optimized peak-to-total to High efficiency mode

• Open both hemispheres of TIGRESS.
• Using the hand tool wind all the clovers by their acme thread fully out to their stops. The hand tool should always be used as it reducing the vibrations experienced by the Ge.
• Change the Ge distance pin from 145mm to 110mm. There are two on each carriage.
• Wind all the front suppressor plates all the way out. They should be retracted all the way into the pocket of the support structure. The securing clamps should be loosened if they are in place.
• Twin suppressors with two suppressors in the same frame pocket should always be wound out simultaneous with the ends never more than 2 inches apart.
• The next step requires 3 people. One person shall be the spotter and will stand in the array and watch the nose of the Ge. This person shall shout out to STOP if the Ge or side catchers are touching anything at any point. The second person shall slowly wind in the Ge using the hand tool (Also read the instructions in the next step!). This person shall be constantly aware what the spotter is doing and if all is clear. This person will also be paying attention to one of the distance pins. The third person will be watching the second distance pin.
• The Ge should be wound in using the hand tool until one of the distance pins first touches the structure. This will be realized by either the person winding the Ge or the person watching the other distance pin. It is a good idea to be constantly wiggling the pin with your hand (Careful not to get your fingers trapped!). Once the pins first touch the structure, the Ge should be retracted by a small amount so that both distance pins are loose and able to wiggle. Do not allow the distance pins to be tight as this will change the alignment of the Ge.
• Once all Ges have been inserted, confirm the array is able to close without any detector touching the vacuum chamber by slowly closing one hemisphere at a time with spotters all around the chamber. The lampshade Ges might need to be retracted by a small amount.
• Operation compete, make an elog entry.