Ultra-low Energy Storage Ring 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 diagnostics for low energy beams

Low-energetic ion and antimatter beams are very attractive for a number of fundamental studies. The diagnostics of such beams, however, is a challenge due to low currents down to only a few thousands of particles per second and significant fraction of energy loss in matter at keV beam energies. A modular set of particle detectors has been developed to suit the particular beam diagnostic needs of the ultralow-energy storage ring (USR) at the future facility for low-energy antiproton and ion research, accommodating very low beam intensities at energies down to 20 keV. The detectors include beam-profile monitors based on scintillating screens and secondary electron emission, sensitive Faraday cups for absolute intensity measurements, and capacitive pickups for beam position monitoring. In this paper, the design of all detectors is presented in detail and results from beam measurements are shown. The resolution limits of all detectors are described and options for further improvement summarized. Whilst initially developed for the USR, the instrumentation described in this paper is also well suited for use in other low-intensity, low-energy accelerators, storage rings, and beam lines.

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.

Study of slow and fast extraction for the ultralow energy storage ring (USR)

The Facility for Antiproton and Ion Research (FAIR, GSI) will not only provide future users with high fluxes of antiprotons in the high-energy range, but it is also intended to include a dedicated program for low-energy antiproton research in the keV regime, realized with the FLAIR project. The deceleration of antiprotons with an initial energy of 30 MeV down to ultralow energies of 20 keV will be realized in two steps. First, the beam is cooled and slowed down to an energy of 300 keV in a conventional magnetic ring, the Low energy Storage Ring (LSR) before being transferred into the electrostatic Ultralow energy Storage Ring (USR). In this synchrotron the deceleration to a final energy of 20 keV will be realized. This paper describes the ion-beam optical and mechanical layout of the beam extraction from the USR and summarizes the expected beam qualities of extracted beams.

Realization of nanosecond antiproton pulses in the ultra-low energy storage ring

The international Facility for Antiproton and Ion Research (FAIR) at the GSI Helmholtz Centre for Heavy Ion Research in Germany is composed of a chain of accelerators and storage rings that will, amongst others, produce, store and slow down antiprotons with unprecedented beam characteristics. One of these rings, the Ultra-low energy electrostatic Storage Ring (USR), will provide cooled beams of antiprotons at energies as low as 20 keV with a small momentum spread of ∼10 −4 and an emittance in the order of 1 π mm mrad. Crossed-beam atomic physics experiment that will allow, for the first time, to investigate into the collision dynamics of antiprotons with different target gases on the level of differential cross sections, require very short antiproton pulses of 1–2 ns duration. An “ultra-short pulse” operation mode was developed to enable these novel experiments. This paper describes two alternative schemes that were developed in the QUASAR Group and summarizes the changes required to enable the USR to operate in this mode.

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.

Beam instrumentation for the future ultra-low energy electrostatic storage ring at FLAIR

To enable the efficient investigation of some fundamental questions concerning the physics with low-energy antiprotons, a novel Ultra-low energy Storage Ring (USR) will be developed. Aiming to be a multipurpose machine, it puts challenging demands on the necessary beam instrumentation and requires new diagnostic methods as most of the standard techniques will no longer work. In this paper, beam diagnostics devices proposed for the USR are presented and their further development is discussed.

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.