Online test of the FRS Ion Catcher at GSI

Abstract

At the FRS Ion Catcher at GSI, relativistic exotic ions produced by projectile fragmentation/fission are range-focused, slowed down and thermalised in a gas-filled stopping cell, extracted and made available to high-precision experiments with ions almost at rest. It is a prototype for a gas cell system at the Low-Energy Branch of the Super-FRS at FAIR. In an online experiment, the FRS Ion Catcher was commissioned successfully with relativistic nickel fragments. The overall efficiency of the system was measured as (1.8 ± 0.3)% and can be divided into a stopping efficiency of (5.0 ± 1.1)% and an extraction and transport efficiency of (35.8 ± 9.4)%. The overall efficiency is hence limited mostly by the stopping efficiency, which could be increased in the future by operating at higher gas cell pressures. From extraction time measurements of polyatomic ions formed in the gas cell extraction times of atomic ions of 20-50 ms can be derived. The potential of the system was illustrated by the half-life measurement of 54 Co with a short half-life of 193 ms only.

Design, construction and cooling system performance of a prototype cryogenic stopping cell for the Super-FRS at FAIR

“…A pioneering experiment with relativistic projectile fragments was performed earlier at the FRS Ion Catcher Facility at GSI, using a stopping cell operated at room temperature [11]. Based on the experience of this experiment, we have developed a second generation stopping cell.…”

“…For the stopping volumes of 0.5-2 Â 10 5 cm 3 [11,16,25,26] dictated by the high energies and emittances at in-flight separators, considering practical limits to the gas flow through the exithole that can be handled, gas flow is too slow for efficient ion extraction of short-lived isotopes. For example an exit-hole diameter of 1 mm, having a conductance of 0.45 l/s for helium gas at room temperature, combined with the stopping volume of 190 l for the cryogenic stopping cell described here, gives a helium gas refresh rate of once per 7 min.…”

The advanced trapping facility MATS at FAIR

“…[52] has served as a prototype for the gas cell to be installed at the end of the LEB at the Super-FRS for MATS. The results from an on-line commissioning experiment using ions from the FRS at GSI were published in 2008 [54]. The overall efficiency for a Ni-beam with a mean kineticenergy of about 260 MeV per nucleon 4 was 1.8± 0.3 %, divided into stopping efficiency (5.0± 1.1 %) and extraction-plus-transport efficiency (35.8± 9.4 %).…”

“Ion surfing” with radiofrequency carpets

“…In addition to ion transport along a line path there are situations in which transport over surfaces is required. This is of particular importance for stopping and thermalizing of energetic (MeV-GeV) rare isotopes produced by nuclear reactions or as recoils from nuclear decay [6][7][8][9][10][11][12][13][14]. In so-called gas stoppers or gas catchers fast multi-charged ions are initially slowed down in matter and finally stopped in a chamber filled with helium gas.…”