A. Schempp

Accelerated radioactive beams from REX-ISOLDE

In 2001 the linear accelerator of the Radioactive beam EXperiment (REX-ISOLDE) delivered for the first time accelerated radioactive ion beams, at a beam energy of 2 MeV/u. REX-ISOLDE uses the method of charge-state breeding, in order to enhance the charge state of the ions before injection into the LINAC. Radioactive singly-charged ions from the on-line mass separator ISOLDE are first accumulated in a Penning trap, then charge bred to an A/q < 4.5 in an electron beam ion source (EBIS) and finally accelerated in a LINAC from 5 keV/u to energies between 0.8 and 2.2 MeV/u. Dedicated measurements with REXTRAP, the transfer line and the EBIS have been carried out in conjunction with the first commissioning of the accelerator. Thus the properties of the different elements could be determined for further optimization of the system. In two test beam times in 2001 stable and radioactive Na isotopes (Na-23-Na-26) have been accelerated and transmitted to a preliminary target station. There Ni-58- and Be-9- and H-2-targets have been used to study exited states via Coulomb excitation and neutron transfer reactions. One MINIBALL triple cluster detector was used together with a double sided silicon strip detector to detect scattered particles in coincidence with gamma-rays. The aim was to study the operation of the detector under realistic conditions with gamma-background from the beta-decay of the radioactive ions and from the cavities. Recently for efficient detection eight tripple Ge-detectors of MINIBALL and a double sided silicon strip detector have been installed. We will present the first results obtained in the commissioning experiments and will give an overview of realistic beam parameters for future experiments to be started in the spring 2002.

Four-rod-λ/2-RFQ for light ion acceleration☆

Abstract A simple type of RFQ structure with circular rods as electrodes has been developed in Frankfurt. The improved design uses a linear arrangement of supporting stems on a massive common bar. This linear rf structure consists of a chain of λ/2-line pairs and leads to an advantageously simple but nonetheless effective RFQ structure. With this stable cheap type of RFQ resonator preaccelerator prototypes have been built for light ions. New results of electrode and structure optimization and beam measurements are presented.

RFQ ion accelerators with variable energy

Abstract RFQs are low-energy rf accelerator structures which can efficiently transport and accelerate high-current ion beams. Whilst usually RFQs, like all rf accelerators, have a fixed velocity profile and output energy per amu, attempts have been made to vary the ion beam energy by changing the resonator frequency. The 4-rod λ/2-RFQ resonator developed in Frankfurt for heavy-ion acceleration is well suited for such an application. Results of the work on variable-energy VE-RFQs are presented and the status of the variable-energy cluster accelerator project is discussed.

Matching of a cylindrical ion beam to a periodic quadrupole channel

Abstract A procedure to match a cylindrically symmetric ion beam to a periodic electrostatic quadrupole channel is described. He + beams are extracted from a plasma source with a voltage of 40 kV. Behind the ion source the beam current and emittance are measured. The extracted beam current is variable from 1 to 20 mA, while the measured emittance is 10–20 π mm mrad. For a chosen zero-current phase advance per cell μ 0 in the focusing channel the so-called periodic solution is calculated for the measured current and emittance. μ 0 is varied between 43° and 114°. The model, which is used for the calculations, is based on the Kapchinsky-Vladimir-sky equations. The quadrupole lens forces are calculated separately by solving the Laplace equation in 2 dimensions. Furthermore, the voltages on the first five quadrupole singlet lenses, which adapt the extracted beam to the periodic solution, are determined. The beam current and emittance are again measured after the sixth quadrupole singlet lens, which is the first lens of the periodic channel. These measured values are compared with the calculated beam parameters. A reasonable agreement is found.

Multichannel acceleration of intense, low-energy ion beams

We present measurements on multichannel acceleration of intense, low‐energy ion beams with a multiple electrostatic quadrupole array linear accelerator. The beam properties are investigated for different transverse and longitudinal focusing strengths, which can be adjusted independently in the accelerator. A maximum He+ ion current of four times 2 mA has been accelerated from 40 to 115 keV with an acceleration efficiency of 50%. Measurements and computer simulations suggest that the current is limited by transverse fields and by mismatch and misalignment of the beams, whereas longitudinal fields are of minor importance. The energy spread in the bunches is roughly three times the gap voltage.

Opportunities for Nuclear Astrophysics at FRANZ

The ‘Frankfurter Neutronenquelle am Stern–Gerlach–Zentrum’ (FRANZ), which is currently under development, will be the strongest neutron source in the astrophysically interesting energy region in the world. It will be about three orders of magnitude more intense than the well-established neutron source at the Research Center Karlsruhe (FZK).

Funnelling study with a low energy proton beam

Funneling is a method used to increase the brightness of ion beams by filling all RF buckets in order to use the full current transport capability of an RF accelerator by frequency jumps at higher energies. This has been proposed for HIIF (heavy ion inertial fusion) type drivers and neutron sources. A simple funneling experiment was prepared using modest fields in a setup with a 50 keV proton beam and an rf deflector to study especially emittance growth effects in such funneling lines. First results are reported.<<ETX>>

Fission fragment accelerators for the Grenoble and Munich high flux reactors

Abstract Accelerators for the Munich and Grenoble high flux reactors are under design 1 , 2 . These accelerators will be able to deliver intense beams of very neutron rich fission fragments out of a target ion source inside the reactor tube for the production of super heavy elements [3] . In order to obtain an efficient acceleration in a LINAC, charge breeding of the 1+ ion beam from the reactor to a q/A⩾0.16 is required. Depending on the scheme of charge breeding the LINAC can work with 10% duty cycle with a final energy between 3.7 and 5.9 MeV/u. Two sources which can deliver highly charged ions are to be considered as possible charge breeders: the Electron Beam Ion Source (EBIS) and the Electron Cyclotron Resonance Ion Source (ECRIS). The LINAC will consist of an Radio Frequency Quadrupole (RFQ) accelerator, three interdigital H-type (IH) structures and two seven-gap resonators to vary the final energy of the ions. The whole concept, the charge breeding and the LINAC parameters will be discussed carefully in this paper.

A resonant Schottky pickup for the study of highly charged ions in storage rings

A resonant Schottky pickup was built into the experimental storage ring at GSI Darmstadt in 2010 and a similar one in the CSRe storage ring at IMP Lanzhou in 2011. Single-ion sensitivity was achieved at 400 MeV u−1. The pickup has also been used in many storage ring experiments ever since. A brief description of the pickup and its application in single-ion lifetime spectroscopy is provided in this work.

Properties of RFQ accelerators for ion implantation

Abstract While electrostatic accelerators are commonly used for ion implantation in research and industry, the progress in the development of efficient low energy rf accelerators has led to proposals for the application of radiofrequency quadrupoles (RFQ) structures in ion implanters. RFQs are rf structures which can efficiently accelerate ion beams to energies between 100 keV and several MeV. Features are a strong electrical rf-focusing which allows ion beam currents up to 10 mA and a compact and reliable system with the ion source only on a low 10–30 kV potential. Critical issues are the beam quality and the energy variation. The status of work on RFQ implanters in Frankfurt will be discussed.