Supersonic gas-jet based beam profile monitor

• Main Author: Putignano, Massimiliano
• Other Authors: Welsch, Carsten
• Published: University of Liverpool 2012
• Subjects: 530; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579282

Ions and in particular antiprotons, stored and cooled at low energies in a storage ring or at rest in traps, are highly desirable for the investigation of a large number of basic questions on fundamental interactions, on the static structure of exotic antiprotonic atomic systems or of (radioactive) nuclei as well as on the time-dependent quantum dynamics of correlated systems. Such low energy, low intensity beams pose, however, new challenges on beam instrumentation, as they require least intrusive diagnostics operating at ultra-high vacuum pressures of the order of 10⁻¹¹ mbar. This work presents the design and commissioning of a novel transverse beam profile monitor that is based on a supersonic gas-jet screen for use under XHV conditions as well as at higher vacuum pressures in residual gas operating mode. The device has been optimized for operation in the Ultra-low energy Storage Ring (USR) at the future Facility for Low energy Antiproton and Ion Research (FLAIR) in Germany, but its flexible design also allows integration into other accelerator facilities. In this work the phenomenon of gas expansion is studied both analytically and numerically, and a novel theory of gas expansion is formulated to yield the gas target density and dimension at all points in its travel, as well as the residual gas pressures and required pumping speeds in all vacuum chambers. Furthermore, the technical and particle optical design and assembly of a dedicated experimental stand for the optimization and commissioning of the pro�le monitor is presented and discussed in detail. Finally, results from experimental tests are shown that successfully demonstrate the residual gas operation mode of the monitor, reporting a spatial resolution of about 65 μm and a current resolution of about 50 μA.