Speaker
Description
For many applications especially in combination with storage rings pulsed high energy beams of heavy ions are needed.
The energy deposition of heavy ions is dominated by their high electronic stopping power (dE/dx), leading to high energy densities even for lower numbers per pulse. We will give examples of energy deposition profiles.
The FAIR facility under construction is planned to operate with 5x1011 Uranium ions per pulse of less than 100ns. With millimeter spots energy densities of 40 kJ/g can be reached, which is beyond any limit for solid materials. The HIAF facility (China) is based on similar beams. Not only targets but also beam dumps and collimators are affected.
Only with a careful choice of beam parameters an operation close to material limits will be possible. The best material choice is given by low thermal expansion, low mass number of material (resulting in low dE/dx), good yield strength and high temperature before phase transition. Here polycrystalline graphite is a favored choice. Examples of dynamic stress calculations for a FAIR beam catcher will be shown.
Simulations of the resulting pressure waves are possible and several criteria for stability exist. But tests with similar beam conditions on the actual materials remain most import. They must be done at a dedicated facility to also provide the proper diagnostics in beam. While the first choice is to avoid plastic deformation, this regime must be investigated for failure tolerance and as some creep will occur.
Few tests have been done in last years with the existing GSI beam of up to 1010 U/pulse reaching up to 2 kJ/g. But downscaling is not easily possible because the pulse structure cannot be reduced enough correspondingly and critical stresses by pressure waves are washed out and not peak pressures are important but tensile forces at critical boundaries.
HiRadMat also with proton beams offers energy densities in this range. The more complicated pulse structure requires improved simulation. In a facility like HiRadMat no long term irradiation is possible, but pre-irradiated samples can be used. Damage creation and material modifications are much stronger for same dose at lower projectile velocities and can be done at other facilities for high dose.