Expected Performance

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The cyclotron gas stopper concept offers superior performance compared to the classical linear gas cell concept:

  • Faster extraction time (<10 ms) for practically all beams, matching the advantages of fast-beam production.
  • A beam rate limit higher than 108/s, compatible with beam intensities available at next-generation facilities.
  • The capability to stop beams of light to heavy ions with a mass-to-charge ratio A/Z of 1.75 < A/Z < 3 with high efficiency.

The key feature of the cyclotron gas stopper, the separation of stopping and extraction regions, is illustrated in the figure. In this example, a 100 MeV/nucleon beam of 78Br is degraded to about 610 MeV and then stopped inside a gas-filled 2 Tesla magnet with a field index of 0.2 (for details see [1]). For a helium gas pressure of 10 mbar the ions stop after a path length of about 60 m. A spatial separation is observed between the stopped-ion distribution in the center and the region at larger radii where the energy deposition and ionization rate is maximal. The spatial separation of the two regions is key to minimizing ion loss due to space charge effects.

Once stopped, the ions are guided to an extraction orifice. This is done with electrostatic fields combined with an RF carpet . For a guiding field of 10 V/cm towards the center of the carpet, ions can be brought to the extraction orifice in less than 5 ms. This is possible because of the low helium-gas pressure and the short distance to the extraction orifice.


Figure 1: Energy loss densities in the cyclotron gas stopper for the slowing of a 100 MeV/nucleon beam of 78Br after being slowed to about 610 MeV in a solid degrader. The spatial separation between the stopping region and the stopped ion distribution reduces space charge effects.


Figure 2: Trajectories of ions in the cyclotron gas stopper for the slowing of a 100 MeV/nucleon beam of 78Br after being slowed to about 610 MeV in a solid degrader.

Reference
[1] G. Bollen, D.J. Morrissey, S. Schwarz, Nucl. Instr. Meth. A 550 (2005) 27.