Energy Loss Dynamics of Intense Heavy Ion Beams Interacting with Dense Matter (2003)

Intense heavy ion beams are an excellent tool to create large volumes of high energy density (HED) matter with very uniform physical conditions. Experimental study of matter under extreme conditions of density, temperature and pressure is of considerable interest to fundamental research in the fields of plasma physics, equation-of-state (EOS) of matter, astrophysics, geophysics and for the Inertial Fusion Energy applications as well as for designing basic nuclear physics experiments. One important problem in high-energy-density matter research is investigation of physical processes that occur during the slowing down of intense beams of energetic heavy ions in matter. High energy density induced by an intense heavy ion beam in an initially solid target leads to the creation of macroscopic volumes of dense, strongly coupled plasmas. Due to the fast hydrodynamic response of the heated target material, the line density of the target decreases and consequently the energy loss of the ion beam penetrating through the target is also reduced. Therefore measuring the energy loss of the ion beam during the interaction would provide important information about the physical processes in HED matter. At the GSI-Darmstadt, intense beams of energetic heavy ions have been used to generate HED states in matter by impact on solid targets. A novel diagnostic technique for the HED matter experiments, where the same intense beam of energetic heavy ions that heats the target material is used to provide information about the physical state of the interior of the target has been proposed. This is accomplished by measuring the energy loss dynamics (ELD) of the beam emerging from the back surface of the target. For this purpose, a new time-resolving energy loss spectrometer based on an original principle has been developed. This spectrometer, called scintillating Bragg-peak spectrometer allows for wide-range precision measurements of heavy-ion beam energy spectra with nanosecond time resolution. For the first time the energy loss dynamics of intense heavy ion beams interacting with dense matter has been observed experimentally. The ELD measurements of intense (108-1010 particles/pulse) focused beams of 238U, 86Kr, 40Ar and 18O ions with 150-350 MeV/nucleon initial energy interacting with rare-gas solid (RGS) targets, such as solid Ne and solid Xe have been carried out. A significant reduction in the ion beam energy loss during the interaction has been recorded which is due to the rapid hydrodynamic response of the ion-beam heated target matter. In order to interpret the experimentally observed physical phenomena, theoretical calculations of the energy loss dynamics have been performed. For these calculations a sophisticated two-dimensional hydrodynamic code BIG-2 has been employed as well as different EOS models for the RGS target materials, namely, the SESAME (Los Alamos, USA) and ChTEOS (Chernogolovka, Russia). A comparison of the simulation results and the measured ELD data has shown that the SESAME EOS tables for RGS materials have a limited accuracy in certain parameter regimes where a correct description of the phase transitions is essential. The simulations performed with the ChTEOS model are in better agreement with the experimental ELD data, in particular for solid Ne targets. We believe that the developed ELD diagnostic technique is an extremely useful tool for HED matter experiments, providing experimental data for verification of hydrodynamic computer codes and underlying theoretical models. The ELD measurements will be employed as a standard diagnostics in future experiments on investigation of the HED matter induced by intense heavy ion beams.