The Cyclotron Gas Stopper
The cyclotron gas stopper is based on a gas-filled weakly-focusing magnet and radiofrequency (RF) ion guiding techniques. Ions injected into the system will first interact with a solid degrader and then be slowed down in a helium gas at low pressure. The focusing properties of the magnet confine the ions in all dimensions during the deceleration process and the ionization can be distributed along a much longer path at lower pressure compared to linear gas stoppers. The ions are finally extracted by means of static electric fields, an RF carpet and ion guides.
A similar concept has been used for the production of antiprotonic, pionic and muonic atoms [1] and has also been discussed for the stopping of light ions [2]. The benefit of this concept for the stopping of intense rare isotope beams was first discovered in simulations performed at the NSCL/MSU [3].
References
[1] L.M. Simons, Hyperfine Interactions 81 (1993) 253.
[2] I. Katayama, M. Wada, Hyperfine Interactions 115 (1998) 165.
[3] G. Bollen, D.J. Morrissey, S. Schwarz, Nucl. Instr. Meth. A 550 (2005) 27.
Operation of NSCL as a national user facility is supported by the Experimental Nuclear Physics Program of the U.S. National Science Foundation.