Speaker
Description
At FAIR, pulsed beams of a wide range of heavy ions with energies up to 1.5 GeV/nucleon are anticipated to be used for the projectile fragmentation/fission. Rare isotopes of all the elements up to uranium will be produced and spatially separated at the superconducting fragment separator (Super-FRS) within a few hundred nanoseconds to enable the study of very short-lived nuclei. The beam stoppers are the energy intercepting and dissipating equipment used in the Super-FRS to safely stop the unwanted fragments and the primary beam and dissipate the resulting heat.
Each of the three beam stopper units consists of two shielding plugs each containing a copper absorber and a graphite absorber for the slow and fast extraction modes of operation, respectively. The primary beam specification for fast extraction is ∼ 5× 10^11 particles per spill of 238U of 0.4-1.5 GeV/nucleon which deposits up to 29 kJ energy in the absorbing medium (graphite) in 50-100 ns pulse (spill) duration with the interval between two consecutive pulses being 1.67s. The energy (particle flux) distribution across the beam cross-section is considered to be two dimensional Gaussian. The localized Bragg’s peak in the axial deposition rate curve causes a highly concentrated energy deposition in the absorber medium with the peak energy density reaching as high as ~ 330 J/g for 740 MeV/u. It is expected to induce high magnitude pressure waves in graphite. Simulation of the propagation behaviour of these waves is one of the major design challenges along with the high average thermal power of 17.1 kW at 1500 MeV/u and material degradation due to irradiation of graphite.
The transient coupled thermo-mechanical analysis of the pulsed form deposition of the beam energy is carried out using explicit finite element code LS-DYNA® to study the propagation of pressure waves within the absorber. The simulation results show the generation and propagation pressure wave from the core to the boundary and subsequent reflection at the boundary. The failure of graphite is usually in the form of cracking and spalling and is determined by the maximum and minimum principal stresses generated and the ultimate tensile and compressive strengths of graphite using Coulomb-Mohr failure criterion.
The heat removal performance is studied through the quasi-static thermo-mechanical study. The absorber, which is in the form of a segmented graphite block, is water cooled through copper heat sinks. The entry shape of the absorber is optimized to enable maximum distribution of energy along beam direction, reducing steady state temperature reached from 2200K to ~1500K.
| Themes for the contribution | 4 Target design, analysis, and validation of concepts: |
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