A WATER COOLED, ACTIVE AND ADJUSTABLE APERTURE COLLIMATOR

摘要

The Isotope Production Facility at Los Alamos National Laboratory has embarked on a series of upgrades, one of which is to improve performance and functionality of the target collimator. The new collimator is segmented 4 ways circumferentially. This segmentation allows for the 'active' feature wherein each segment is electrically isolated and an induced voltage signal proportional to intercepted beam confirms beam position. Each segment is also monitored for temperature. Further, each segment is independently cooled. The graphite collimator arc segment is backed on the down-beam side with a cold plate with a water channel. To sustain the active feature, this stainless steel cold plate is electrically isolated from the graphite by a thin layer of Shapal™, a ceramic with high electrical resistivity but good thermal conductivity. This 3-layer sandwich is soldered together. Additionally, the through aperture of the collimator can be adjusted to accommodate different target sizes. The segments are attached to a flexure which acts as a spring. A stepper motor located exterior to the beamline is used to adjust the flexure tension and position, thus increasing or decreasing aperture. An additional 4-segment fixed collimator is upstream of the adjustable. This paper will describe the engineering details of these features, particularly as constrained by the available space defined by the pre-existing beam pipe diameter and limited access.