Difference between revisions of "Results with the active collimator in the Hall B photon beam"

Revision as of 06:20, 7 April 2007

The Hall D active collimator prototype has been installed in the Hall B alcove. It is mounted on top of the total absorption counter (TAC) located just in front of the photon beam dump, as shown in the photos below. The motion controls of the TAC are used to position the active collimator in or out of the beam.

Photograph of the Hall D active collimator installed for beam tests on top of the Hall B total absorption counter.

Close-up photograph of the Hall D active collimator installed for beam tests in Hall B. The inner sectors shown disconnected in the photo are actually connected during the tests.

There are three positions of the TAC for these tests.

1. Home: both the TAC and the active collimator are out of the beam. This is the default position for photon beam running in Hall B.
2. Normalization: the TAC is in the beam and the active collimator is out of the beam. This is the position used for measuring the absolute tagging efficiency during special low-current (100pA) runs.
3. HD-AC: the TAC is out of the beam and the Hall D active collimator is in the beam. This position enables GlueX collaborators to test the response of the active collimator during normal photon beam running with CLAS.

The height of the detector on top of the TAC has been adjusted so that when the central hole through the collimator is at beam height, the TAC is completely out of the beam. Additional lead shielding bricks have been stacked below the beam to prevent any exposure to the TAC when it is in the HD-AC position.