Intense heavy ion beams as a pumping source for short wavelength lasers

The high energy loss of heavy ions in matter as well as the small angular scattering makes heavy ion beams an excellent tool to produce almost cylindrical and homogeneously excited volumes in matter. This aspect can be used to pump short wavelength lasers. For the first time, a beam of heavy ions was used to pump a short wavelength gas laser in an experiment performed at the GSI ion accelerator facility in December 2005. In this experiment, the well-known KrF* excimer laser was pumped with an intense uranium beam. Pulses of an uranium beam compressed down to 110 ns (full width at half maximum) with initial particle energy of 250 MeV per nucleon were stopped inside a gas laser cell. A mixture of an excimer laser premix gas (95.5%Kr + 0.5%F2) and a buffer gas (Ar) in different proportions was used as the laser gas. The maximum beam intensity reached in the experiment was 2.5 × 109particles per pulse, which resulted in 34 J/g specific energy deposited in the laser gas. The laser effect on the transition at λ = 248 nm has been successfully demonstrated by various independent methods. There, the laser threshold was reached with a beam intensity of 1.2 × 109particles per pulse, and the energy of the laser pulse of about 2 mJ was measured for an ion beam intensity of 2 × 109particles per pulse. As a next step, it is planned to reduce the laser wavelength down to the vacuum ultraviolet spectral region, and to proceed to the excimer lasers of the pure rare gases. The perspectives for such experiments are discussed and the detailed estimations for Xe and Kr cases are given. We believe that the use of heavy ion beams as a pumping source may lead to new pumping schemes on the higher lying level transitions and considerably shorter wavelengths, which rely on the high cross sections for multiple ionization of the target species.

Three–dimensional simulations of a solid graphite target for high intensity fast extracted uranium beams for the Super–FRS

This paper presents three–dimensional numerical simulations of thermodynamic and hydrodynamic response of a wheel shaped solid graphite production target for the super conducting fragment separator (Super–FRS) that is irradiated with a fast extracted high intensity uranium beam. These fragment separator experiments will be carried out at the future Facility for Antiprotons and Ion Research (FAIR), at Darmstadt. Previously, we reported simulation results that were carried out using two–dimensional computer codes which showed that one can use a solid graphite target for the Super-FRS for the highest intensity (5 × 1011ions per spill) of the fast extracted uranium beam. Present results, however, have shown that due to three–dimensional effects the maximum intensity that can be used with such a target is 3 × 1011ions per spill. A detailed comparison between two–dimensional and three–dimensional results is presented in this paper.

Simulations of a solid graphite target for high intensity fast extracted uranium beams for the Super-FRS

Extensive numerical simulations have been carried out to design a viable solid graphite wheel shaped production target for the super conducting fragment separator experiments (Super-FRS) at the future Facility for Antiprotons and Ion Research (FAIR) using an intense uranium beam. In this study, generation, propagation and decay of deviatoric stress waves induced by the beam in the target, have been investigated. Maximum beam intensities that the target can tolerate using different focal spot sizes that are determined by requirements of good isotope resolution and transmission of the secondary beam through the fragment separator, have been calculated. It has been reported elsewhere that the tensile strength of graphite significantly increases with temperature. To take advantage of this effect, calculations have also been done in which the target is preheated to a higher temperature, that in practice can be achieved, for example, by irradiating the target with a defocused ion beam before the experiments are performed. We report results of a few examples using an initial temperature of 2000 K. This study has shown that employing such a configuration, one may use a solid graphite production target even for the maximum intensity of the uranium beam (5 × 1011ion per bunch) at the Super-FRS.

High energy density physics problems related to liquid jet lithium target for Super-FRS fast extraction scheme

The new international facility for antiproton and ion research (FAIR), at Darmstadt, Germany, will accelerate beams of all stable isotopes from protons up to uranium with unprecedented intensities (of the order of 1012 ions per spill). Planned future experiments include production of exotic nuclei by fragmentation/fission of projectile ions of different species with energies up to 1.5 GeV/u at the proposed super conducting fragment separator, Super-FRS. In such experiments, the production target must survive multiple irradiations over an extended period of time, which in case of such beam intensities is highly questionable. Previous work showed that with full intensity of the uranium beam, a solid graphite target will be destroyed after being irradiated once, unless the beam focal spot is made very large that will result in extremely poor transmission and resolution of the secondary isotopes. An alternative to a solid target could be a windowless liquid jet target. We have carried out three-dimensional numerical simulations to study the problem of target heating and propagation of pressure in a liquid Li target. These first calculations have shown that a liquid lithium target may survive the full uranium beam intensity for a reasonable size focal spot.

High-accuracy crystal spectroscopy of the n = 2 energy level of helium-like uranium

We present a new experiment for the accurate study of the intrashell transition 1s2p 3P2 → 1s2s 3S1 in helium-like uranium near 4.5 keV using a Johann-type Bragg spectrometer with a spherically bent crystal. The focusing property of the bent crystal enhances the spectrometer's efficiency compared to flat crystal spectrometers and it will enable us, for the first time, to evaluate, accurately, the Lamb shift for n = 2 states in highly charged helium-like ions. The data will be acquired at the storage ring ESR of GSI using a fast H-like uranium beam colliding with a gas target. This measurement will provide the most sensitive test for the relativistic electron–electron interaction in a strong Coulomb field.PACS Nos.: 07.85.Nc, 12.20.Fv, 29.30.Kv and 32.30.Rj

Compression of a cylindrical hydrogen sample driven by an intense co-axial heavy ion beam

The compression of a cryogenic hydrogen cylindrical sample contained in a hollow gold target driven by an intense co-axial uranium beam has been studied. The ion distribution is assumed to be Gaussian in space and parabolic in time. The hydrodynamics of the target is analyzed by means of one- and two-dimensional numerical simulations. A parametric study is performed to achieve the maximum average hydrogen density and temperature as a function of the sample radius, total number of ions and spread of the spatial ion distribution. A window in the beam-target parameters for which hydrogen compression is higher than a factor of 10 and temperature is below 0.2 eV has been found by considering a single bunch that contains 2 × 1011 uranium ions delivered in 100 ns. In this range of high densities and low temperatures, it is expected that hydrogen may become metallic.