Development and installation of a radio frequency quadrupole cooler test

Abstract

A Radio Frequency Quadrupole Cooler (RFQC) prototype was adapted for insertion into a high uniformity magnetic field, with Bz up to 0.2 T, to improve radial confinement. While the RFQC purpose is to reduce (by gas collisions) the energy spread and emittance of a beam of radioactive nuclei, to finely select ion mass in nuclear physics, the prototype is tested in a setup including a stable ion source, a pepper pot emittance meter, and two Faraday cups; this makes a precise characterization of the RFQC feasible. The ion extraction was studied in detail by simulations, both to match it to the emittance meter granularity and to verify the effect of the typical nonuniformity of the longitudinal electric field Ez inside the RFQC; an average motion description (including friction force from gas collisions) was used, introducing the ballistic and diffusive regimes. With a preliminary optimization of the electrode shape, buffer gas pressure pg, and radio frequency voltage, the ion beam can be extracted with a significant cooling margin.

Ion transport and gas collision effects in a radio frequency quadrupole cooler: installation in the Eltrap solenoid and beam calculations

“…But ray tracing can treat only the friction force (Cavenago et al. 2019), and not the diffusion (or straggling) arising from collisions. The theoretical analysis presented in the following allows us to approximately describe the diffusion with the time evolution of its correlations, which can be added to the ray-tracing solver, obtaining a so-called ‘augmented solver’.…”

“…A preliminary study of the overall ion trajectories (from the source to the emittance meter EMI1) was given in Cavenago et al. (2019) considering the friction force, but not straggling effects. Here, we approximately include straggling, that is, tensor effects.…”

“…The RFQC insertion inside the Eltrap machine was described elsewhere; for example, see figure 1 of Cavenago et al. (2019). The Eltrap machine features a high uniformity magnetic solenoid (1.5 m long) optimized for experiments with a Malmberg–Penning trap (Amoretti et al.…”

“…The extraction line (Cavenago et al. 2019) is actually cantilevered on this RFQC box, which lies on a 2 m girder (or support bar), where the injection line also sits; the girder is rigidly connected to a CF250 flange, forming a so-called ‘plugin’ module.…”

“…1992; Li & Werth 1992; Beu, Hendrickson & Marshall 2011; Cavenago et al. 2019) and the injection and extraction phases. In these tests, natural Cs ions with a typical 100 nA current are provided by a commercial surface ionization ion source, IS1.…”