Search Results (6 total)

High-energy heavy ions are an ideal tool to generate homogeneously excited, extended volumes of nonthermal plasmas. Here, the high-energy loss (dE/dx) and absolute power deposition of heavy ions interacting with matter has been used to pump an ultraviolet laser. A pulsed 70  MeV/u ²³⁸U beam with up to 2.5×10⁹ particles in ∼100  ns beam bunches was stopped in a 1.2 m long laser cell filled with a 1.6 bar Ar-Kr-F₂ mixture (typically 50%∶49.9%∶0.1%). Laser effect on the 248 nm KrF^* excimer transition is clearly demonstrated.

The subject of high-energy density (HED) in matter is of considerable interest to many branches of physics. Intense beams of energetic heavy ions are a promising tool for creating large samples of HED matter which can be used to study the equation-of-state properties of such exotic states of matter experimentally. The Gesellschaft für Schwerionenforschung (GSI), Darmstadt, is a unique laboratory worldwide which has a heavy ion synchrotron facility, SIS18 (with a magnetic rigidity of 18 Tm), that delivers intense heavy ion beams. Using the beams generated at this present facility, interesting experimental work has been carried out in the field of HED matter [D. H. H. Hoffmann , Nucl. Instrum. Methods Phys. Res., Sect. B 161–162, 9 (2000)]. The GSI is planning to significantly expand its accelerator capabilities with construction of a new synchrotron ring, SIS100, which will have a magnetic rigidity of 100 Tm. This new facility will deliver a uranium beam which will have orders of magnitude higher intensity than the existing facility and will also have the possibility of multibeam acceleration. This paper presents two-dimensional hydrodynamic simulations of different target geometries including solid as well as hollow cylinders that are irradiated with beams having different shapes of the focal spot which will be available at the SIS100 facility. These include a circular focal spot, an annular focal spot, and an elliptic focal spot, respectively. The purpose of this study is to determine the region of the physical parameters including density, temperature, and pressure that can be accessed using the SIS100 beam. This information, we hope, will be useful for designing experiments on the studies of thermophysical properties of matter including the designing of appropriate diagnostic tools.

A recombination laser scheme on the λ=164 nm n=3–2 transition in H-like He^+* ions is studied. Doubly ionized helium is produced in a 300-mbar He gastarget using a pulsed 110-MeV ³²S⁸⁺ heavy-ion beam. The cross section for this ionization process is 9.2×10^-17 cm². Since the flux of existing heavy-ion accelerators is limited, plasmas generated directly by heavy-ion beams reach only an electron density n_e on the order of 10¹² cm^-3. In order to study three body recombination of He²⁺ ions with free electrons, electron densities n_e of at least 10¹⁴ cm^-3 and electron temperatures T_e well below 0.1 eV are necessary. In this study the required electron density is produced by means of a special gas discharge. Time evolution of the plasma parameters n_e and T_e in the plasma target prior to the arrival of the heavy-ion beam pulse is described by a numerical model. Light intensity on the 164-nm n=3–2 transition following heavy-ion beam excitation is measured using time resolved optical spectroscopy. Light intensity on this spectral line and its dependence from electron density and temperature in the plasma is interpreted using a system of coupled rate equations modeling the He^+* system.

The time dependence of electron densities and temperatures in a heavy-ion-beam-excited gas target has been determined. A pulsed beam of 89-MeV ³²S ions, 2-ns pulse width, was used for the excitation of xenon at pressures of 500, 1000, and 1500 hPa. This type of excitation leads to the formation of a unique afterglow plasma. Electron densities and temperatures are of the order of those found in typical low-pressure gas discharges, but the electrons, ions, and excited atoms are embedded in a cold, dense gas. Molecule formation is therefore an important process. The dissociative recombination of Xe₂^+* molecules, which leads to the emission of the second excimer continuum of xenon at a wavelength of 172 nm, was used as a probe at times longer than 200 ns after termination of the beam pulses. The emission of light at shorter times was modeled by solving the coupled rate equations of the collisional and radiative processes involved.

An Ar target to which Cs vapor could be added, excited by a pulsed beam of 100-MeV ³²S ions, was studied as a prototype ion-atom charge-transfer system for pumping short-wavelength lasers. Low-velocity Ar²⁺ ions were efficiently produced; a huge increase in the intensity of the Ar ii 4d-4p spectral lines was observed when Cs vapor was added to the argon. This observation is explained by a selective charge transfer of the Cs 6s electron into the upper levels of the observed transitions. A rate constant of (1.4±0.2)×10^-9 cm³/s for the transfer process was determined.

The emission of the third excimer continuum of argon in the wavelength range between 175 and 250 nm has been studied by time-resolved optical spectroscopy. Argon gas at pressures between 5 and 100 kPa was excited with a pulsed beam of 100-MeV ³²S⁹⁺ ions from the Munich tandem van de Graaff accelerator. Wavelength spectra recorded in different time windows after the 2-ns beam pulses show that two different components contribute to the third continuum of argon. A radiative lifetime of 5.71±0.08 ns for the Ar₂²⁺ molecule and a rate coefficient k₃=(1.46±0.12)×10^-30 cm^-6/s for the reaction Ar²⁺+2Ar→Ar₂²⁺+Ar were determined from the pressure dependence of time spectra at a wavelength of 190 nm. Additional time spectra were measured at 210 and 230 nm.