  At the FRS Ion Catcher (FRS-IC), projectile and fission fragments are
produced at relativistic energies, separated in-flight, energy-bunched, slowed
down, and thermalized in the ultra-pure helium gas-filled cryogenic stopping
cell (CSC). Thermalized nuclei are extracted from the CSC using a combination
of DC and RF electric fields and gas flow. This CSC also serves as the
prototype CSC for the Super-FRS, where exotic nuclei will be produced at
unprecedented rates making it possible to go towards the extremes of the
nuclear chart. Therefore, it is essential to efficiently extract thermalized
exotic nuclei from the CSC under high beam rate conditions, in order to use the
rare exotic nuclei which come as cocktail beams. The extraction efficiency
dependence on the intensity of the impinging beam into the CSC was studied with
a primary beam of 238U and its fragments. Tests were done with two different
versions of the DC electrode structure inside the cryogenic chamber, the
standard 1 m long and a short 0.5 m long DC electrode. In contrast to the rate
capability of 10^4 ions/s with the long DC electrode, results show no
extraction efficiency loss up to the rate of 2x10^5 ions/s with the new short
DC electrode. This order of magnitude increase of the rate capability paves the
way for new experiments at the FRS-IC, including exotic nuclei studies with
in-cell multi-nucleon transfer reactions. The results further validate the
design concept of the CSC for the Super-FRS, which was developed to effectively
manage beams of even higher intensities.
