The design of a collimator mechanism for the small angle mode K600 magnetic spectrometer

Abstract

The K600 (K is the kinematic factor) magnetic spectrometer at iThemba Laboratory for Accelerator Based Sciences (LABS) is a high resolution detector system, and is one of the kind in the southern hemisphere, first commissioned at iThemba LABS (then known as the National Accelerator Centre) in October 1991.The collimator of the K600 magnetic spectrometer defines the angular acceptance of reaction particles to be detected by the focal plane detection package of the spectrometer. For reaction measurements in the angular range of 6°-70°, the original collimator carousel with its six possible collimator positions works fine. However, the requirement to have the beamstop right next to the collimator in the small angle mode (to measure the 2° - 6° angular range) cannot be achieved by the use of carousel system. Small angle measurements require that a beamstop be positioned right next to the collimator and with the carousel it is not possible to perform such measurements because the carousel structure does not provide an internal beamstop position. To access the 2° - 6° angular range, the K600 has to be positioned at 4° since the spectrometer has a ±2° angular acceptance. For measurements at 4° a prototype small-angle mode vacuum chamber was used to connect the K600 to the scattering chamber. The problem with the carousel and the small angle mode was that, it required manual changing of collimators which caused loss of beamtime, and also posed a health risk to staff. The new design is remotely controllable from the data room, which protects employees from being exposed to high radiation level from manually operating the prototype when changing collimator position. The chamber was tested for any deformation through simulation software during the design stage and also during prototype installation to see if it is able to withstand the applied load. To remotely control the prototype, linear pneumatic motor was used coupled with electronics controls to ensure that the operator is able to get accurate positioning of collimator onto the beam line during experimental procedures. Linear potentiometer was used to lock position and also limit switches were utilised to avoid overshooting during positioning process. Air control valve was used to control the flow to the pneumatic motor. The manufactured mechanism was assembled and tested for vacuum and control systems. After installation of the prototype in the K600 vault, (with all the electrical and electronics components required) EPICS software codes were developed and tested at the K600 for remotely control.