Facility For Low-energy Antiproton And Ion Research Research Articles

Beam life time studies and design optimization of the Ultra-low energy Storage Ring

The Ultra-low energy electrostatic Storage Ring (USR) at the future Facility for Low-energy Antiproton and Ion Research (FLAIR) will provide cooled beams of antiprotons in the energy range between 300 keV down to 20 keV. Based on the original design concept developed in 2005, the USR has been completely redesigned over the past few years by the QUASAR Group. The ring structure is now based on a ’split achromat’ lattice. This ensures compact ring dimensions of 10 m × 10 m, whilst allowing both, in-ring experiments with gas jet targets and studies with extracted beams. In the USR, a wide range of beam parameters shall be provided, ranging from very short pulses in the nanosecond regime to a coasting beam. In addition, a combined fast and slow extraction scheme will be featured that allows for providing external experiments with cooled beams of different time structure. Detailed investigations into the dynamics of low energy beams, including studies into the long term beam dynamics and ion kinetics, beam life time, equilibrium momentum spread and equilibrium lateral spread during collisions with an internal target were carried out. This required the development of new simulation tools to further the understanding of beam storage with electrostatic fields. In addition, studies into beam diagnostics methods for the monitoring of ultra-low energy ions at beam intensities less than 10 6 were carried out. This includes instrumentation for the early commissioning of the machine, as well as for later operation with antiprotons. In this paper, on overview of the technical design of the USR is given with emphasis on two of the most important operating modes, long term beam dynamics and the design of the beam diagnostics system.

Beam instrumentation for the Ultra-low energy Storage Ring (USR)

The electrostatic Ultra-low energy Storage Ring (USR) at the future Facility for Low energy Antiproton and Ion Research (FLAIR) will make available antiprotons from 300 keV down to 20 keV beam energy. This multipurpose machine puts challenging demands on the beam instrumentation due to the varied bunch structure (ultra-short bunches of 1–2 ns up to a quasi-DC beam structure on the other), together with variable very low beam energies, ultra-low currents of down to 1 nA (or even less in the transfer lines which means less than 2 × 107 particles). Thus, the development of new diagnostic devices is required as most of the standard techniques are not suitable. Within the QUASAR Group, the necessary beam instrumentation for the commissioning phase and standard operation of the USR, as well as advanced techniques such as a gas curtain-jet beam profile monitor, have been developed and prototypes of all devices have been built up. This paper presents the design of all beam diagnostics devices for the USR and summarizes the results from first measurements.

Ultra-low energy storage ring at FLAIR

The Ultra-low energy electrostatic Storage Ring (USR) at the future Facility for Low-energy Antiproton and Ion Research (FLAIR) will provide cooled beams of antiprotons in the energy range between 300 keV down to 20 keV and possibly less. The USR has been completely redesigned over the past three years. The ring structure is based on a “split achromat” lattice that allows in-ring experiments with internal gas jet target. Beam parameters might be adjusted in a wide range: from very short pulses in the nanosecond regime to a Coasting beam. In addition, a combined fast and slow extraction scheme was developed that allows for providing external experiments with cooled beams of different time structure. Detailed investigations of the USR, including studies into the ring’s long term beam dynamics, life time, equilibrium momentum spread and equilibrium lateral spread during collisions with an internal target were carried out. New tools and beam handling techniques for diagnostics of ultra-low energy ions at beam intensities less than 106 were developed by the QUASAR Group. In this paper, progress on the USR project will be presented with an emphasis on the expected beam parameters available to the experiments at FLAIR.

Electrostatic ultra-low-energy antiproton recycling ring

There is a strong need to push forward developments in the storage and control of ultra-low-energy antiproton beams to enable important scientific research. To this end, a small electrostatic ring, and associated electrostatic acceleration section, is being designed and developed by the QUASAR group. The ring will be placed on the MUSASHI beamline at the CERN-AD. It will serve as a prototype for the future ultra-low energy storage ring (USR), to be integrated at the facility for low-energy antiproton and ion research (FLAIR) and will enable various components of the USR to be tested and optimised. A reaction microscope will be integrated in the ring to enable partial ionisation cross section measurements to be made. This small recycler ring will be unique due to its combination of size, electrostatic nature and energy and type of circulating particles (ca 3–30 keV antiprotons). A short electrostatic accelerating section is also being developed, which will be placed between the beamline and the ring to accelerate the antiprotons from the trap extraction energy (typically 250 eV) to the final required (re-circulating) energy. The AD recycler project will be described, including ring design, accelerating injection section and the inclusion of a reaction microscope and the experiments it will enable.

Present status of the USR project

The Facility for Low-energy Antiproton and Ion Research (FLAIR) and a large part of the wide physics program decisively rely on new experimental techniques to cool and slow down antiprotons to 20 keV, in particular on the development of an ultra-low energy electrostatic storage ring (USR). The whole research program connected with anti-matter/matter interactions is only feasible if such a machine will be realized. For the USR to fulfil its key role in the FLAIR project, the development of novel and challenging methods and technologies is necessary: the combination of the electrostatic storage mode with a deceleration of the stored ions from 300 keV to 20 keV, electron cooling at all energies in both longitudinal and transverse phase-space, bunching of the stored beam to ultra-short pulses in the nanosecond regime and the development of an in-ring reaction microscope for antiproton-matter rearrangement experiments. In this contribution, the present status of the USR project is summarized and the new machine lattice is presented.

Preliminary design studies of an extraction of the USR

The next-generation Facility for Low energy Antiproton and Ion Research (FLAIR) at GSI is going to be a dedicated research facility for ion research in the keV range. These ion beams will allow to explore fundamental properties in matter-antimatter research at ultra-low energies of only 20 keV/q in hitherto impossible experiments. To provide these very low energy beams, the Ultra-low energy Storage Ring (USR), an electrostatic synchrotron, will play a major role within the FLAIR complex. It combines the electrostatic storage mode with deceleration from an initial energy of 300 keV/q down to 20 keV/q—as well as an efficient beam cooling. To fulfill its role as a multi-purpose experimental facility, the design of the USR has not only to cover in-ring experiments, but needs to include a highly flexible beam extraction for serving different external experiments as well.

A fast, low perturbation ionization beam profile monitor based on a gas-jet curtain for the ultra low energy storage ring

An ionization beam profile monitor relying on a supersonic gas-jet shaped into an extended, thin curtain is proposed for operation in an ultra high vacuum environment for very low perturbation on the accelerated beam, as requested for the in-ring profile monitoring at the Ultra low energy Storage Ring (USR) at the Facility for Low-energy Antiproton and Ion Research (FLAIR), in Darmstadt. In this paper, we describe the working principle of the monitor, as well as providing an analysis of sensitivity and resolution dependence on geometrical design and gas curtain thickness.

FLAIR – a facility for low-energy antiproton and ion research

In order to exploit the unique possibilities that will become available at the Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, a collaboration of about 50 institutes from 15 countries was formed to efficiently enable an innovative research program towards low-energy antimatter-physics. In the Facility for Low-energy Antiproton and Ion Research (FLAIR) antiprotons and heavy (radioactive) ions are slowed down from 30 MeV to energies as low as 20 keV by a magnetic low-energy storage ring (LSR) and an electrostatic ultra-low energy storage ring (USR) or are even brought to rest by a universal trap facility (HITRAP). In this paper, the facility and the research program covered are briefly described with some emphasis on the accelerator chain and the expected particle numbers.

Testing the ECPSSR theory and its modifications with ratios of antiproton-to-proton ionization cross sections

While fits to 90% of all ever measured K-shell ionization cross sections by protons are on the average within 10% of the ECPSSR [W. Brandt, G. Lapicki, Phys. Rev. A 23 (1981) 1717], this theory systematically overestimates the remaining 10% of all data (comprised mainly of the measurements on heavy target elements) in the slow collision regime of proton velocities less than 0.1 of the orbital velocity of the K-shell electron. For ionization of H and He, experimental ratios of antiproton-to-proton cross sections and benchmark theories thereof exist in the range around where the projectile and target electron velocities match and the cross sections peak. They confirm the excellent accuracy with which the antibinding/binding and antipolarization/polarization effects are accounted for in the perturbed-stationary state (PSS) treatment of the ECPSSR theory. It is shown that the K-shell ionization of heavy elements by MeV antiprotons, which were routinely extracted from the LEAR – or alternatively in ionization of light elements below 0.3MeV that will become available at the GSI’s future Facility for Low-Energy Antiproton and Ion Research (FLAIR) – would provide for a decisive and critical test between various modifications of the ECPSSR theory and any other theory of inner-shell ionization by protons and antiprotons.

An ultra-low-energy storage ring at FLAIR

The future accelerator Facility for Antiproton and Ion Research (FAIR) at GSI, Darmstadt will produce the highest flux of antiprotons in the world. So far it is foreseen to accelerate the antiprotons to high energies (3–15 GeV) for meson spectroscopy and other nuclear and particle physics experiments in the High-Energy Storage Ring (HESR). Within the planned complex of storage rings, it is possible to decelerate the antiprotons to about 30 MeV kinetic energy, opening up the possibility to create low-energy antiprotons. In the proposed Facility for Low-energy Antiproton and Ion Research (FLAIR) [ http://www.flair.eu.tt] the antiprotons shall be slowed down in a last step from 300 to 20 keV in an ultra-low-energy electrostatic storage ring (USR) for various in-ring experiments as well as for their efficient injection into traps. This paper presents the layout and design parameters of the USR.

Plans for a Next-Generation Low-Energy Antiproton Facility

Current antiproton physics as carried out at the Antiproton Decelerator (AD) of CERN is focussed on precision spectroscopy of antiprotonic atoms and antihydrogen for tests of CPT symmetry and QED. For efficient stopping of antiprotons, the energy of the AD is however still too high. A new facility called FLAIR (Facility for Low-energy Antiproton and Ion Research) has recently been proposed that includes cooled beams of antiprotons at energies below 100 keV. This will allow for a much higher rate of trapped antiprotons and therefore greatly advance the currently performed experiments. Furthermore, the availability of continuous beams will make many new experiments possible.