Abstract
The electron-beam ion trap (EBIT) charge breeder of the ReA post-accelerator, located at the National Superconducting Cyclotron Laboratory (Michigan State University), started on-line operation in September 2015. Since then, the EBIT has delivered many pilot beams of stable isotopes and several rare-isotope beams. An operating aspect of the ReA EBIT is the breeding of high charge states to reach high reaccelerated beam energies. Efficiencies in single charge states of more than 20% were measured with ${^{39}\mathrm{K}}^{15+}$, ${^{85}\mathrm{Rb}}^{27+}$, ${^{47}\mathrm{K}}^{17+}$, and ${^{34}\mathrm{Ar}}^{15+}$. Producing high charge states demands long breeding times. This reduces the ejection frequency and, hence, increases the number of ions ejected per pulse. Another operating aspect is the ability to spread the distribution in time of the ejected ion pulses to lower the instantaneous rate delivered to experiments. Pulse widths were stretched from a natural $25\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ up to $\ensuremath{\sim}70\text{ }\text{ }\mathrm{ms}$. This publication reviews the progress of the ReA EBIT system over the years and presents the results of charge-breeding efficiency measurements and pulse-stretching tests obtained with stable- and rare-isotope beams. Studies performed with high sensitivity to identify and quantify stable-isotope contaminants from the EBIT are also presented, along with a novel method for purifying beams.
Highlights
The ReA post-accelerator of rare isotopes at the National Superconducting Cyclotron Laboratory (NSCL), located at Michigan State University (MSU), currently accelerates beams up to ∼6 MeV=u for light ions and ∼3 MeV=u for heavy ions
Compared to other techniques such as the use of stripper targets or electron cyclotron resonance ion sources, electron-beam ion sources (EBISes) and electron-beam ion trap (EBIT) have been increasingly recognized over the past decades as the best alternatives to charge breeding owing to their high efficiencies in single charge states, small emittances, and high beam purity
In previous measurements performed with an electron-beam current of 800 mA, the Q=A separator was used to measure the energy spread of 16O7þ and 39K15þ beams ejected from the ReA EBIT to be 31 eV=e × Q and 25 eV=e × Q, respectively
Summary
The ReA post-accelerator of rare isotopes at the National Superconducting Cyclotron Laboratory (NSCL), located at Michigan State University (MSU), currently accelerates beams up to ∼6 MeV=u for light ions and ∼3 MeV=u for heavy ions (see [1,2,3,4,5] and Fig. 1). ReA ended the commissioning phase and started on-line operation in the fall of 2015 It is the unique post-accelerator reaccelerating rare isotopes thermalized in a gas cell after production by fast projectile fragmentation [6]. EBIS/T. systems are currently in operation at other rare-isotope facilities such as CARIBU (ANL) [7], TITAN (TRIUMF) [8], and ISOLDE (CERN) [9,10]. The ReA EBIT was brought on-line for the first time as part of commissioning in late 2013 [17] It began on-line operation in September 2015 with the addition of an ion beam cooler and buncher (BCB) device for injection of pulsed beams. This publication reviews the progress of the ReA EBIT over the years It presents the results of efficiency measurements, recent developments on stretching the pulse width of ejected. Beams, high-sensitivity measurements of ion-beam contaminants, and a new technique to reduce the level of contamination in beams delivered to experiments
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