SEE Facility:

Beam Diagnostics System

The beam diagnostics system is used to count the particles, collimate the beam, measure the beam energy, aid in the alignment the device under test, and shutter the beam.

In the picture below the beam would enter the image on the left through an entry port that is out of frame. The beam exits the diagnostics box through the exit port at the far right.

Beam Diagnostics Box

The beam first passes through a four element Photo Multiplier Tube ( Quad PMT ) arrangement. These PMTs are arranged in a diamond formation so that they are in the beam at all times but do not block the portion of the beam that hits the device under test.

Next the beam passes through a single PMT that is positioned in the center of the beam ( Center PMT ). This PMT is used to measure the exact intensity of the beam that will hit the device as well as to calibrate the Quad PMTs. During the actual tests, this PMT is moved out of the way.

The beam then passes through a five element collimating wheel . The collimators can be used to collimate or degrade the beam. Each collimator is 4 inches in diameter and can be easily changed or removed as desired.

Next in the beam line is a Solid State Detector (SSD). During tuning, the SSD is used to measure the purity of the various beams by measuring the beam energy of the particles. The SSD is moved out of the beam during an actual test.

Technician Using Beam Diagnostics Box

The beam will then pass by a Mirror Block . This mirror block and an aligned laser are used to position the devices directly in the center of the beam before testing takes place. The laser beam enters the box through the laser port and is split when it hits the mirror block. This creates a laser beam that is exactly in line with the particle beam that will be generated by the cyclotron. The mirror block is moved out of the way and the laser is turned off during an actual test.

And finally the beam passes by the shutter , through the exit port and into the vacuum chamber . Only if the shutter is open of course! The shutter is used to quickly stop the beam from hitting the device during testing. The shutter opens and closes quickly by using two solenoids at its base. These rotate the shutter plate out of the way.

Each beam diagnostic box element, except for the collimating wheel, is mounted on a sliding stage that allows it to be moved into and out of the beam as desired.