I-BEAT 2: Ultrafast measurement of energy and angular distributions of single ion bunches

Powerful, ultrashort laser pulses can accelerate temporally very short ion bunches with high particle numbers in microscopic plasmas. This property is interesting for new approaches in studying matter with energetic ions, but challenges instrumentation and diagnostics. I-BEAT is a novel online diagnostic that can provide direct feedback on particle bunch properties. Ions deposit energy as they penetrate matter and due to their short duration this results in the emission of (ultra-)sound pulses. From these 'acoustic traces' the energy density distribution and thus e.g. the 'bunch energy' can be determined, which is not yet as well controllable in laser acceleration as it is in RF accelerators.

Previous I-BEAT generations have already provided important properties of mono-energetic ion bunches, both from RF-accelerator and laser-driven plasma sources. For example, the detection of heavy uranium ions with a minimum sensitivity of 200 ions per bunch or the three-dimensional dose reconstruction and position determination of energy-selected, laser-accelerated ion bunches.

This new project, I-BEAT 2, now focuses on increasing the detectable dynamic range in an improved model that will serve as primary ion monitor in close vicinity to the plasma. Laser-accelerated ion bunches are dominated by low-energy ions, the high-energy particles appear only in very small numbers. The acoustic traces are hence dominated by the signal of the slower particles, whereas the entire spectrum has remained inaccessible in reconstructions. By structuring the water reservoir of I-BEAT, we will now balance these signal heights and significantly increase the sensitivity at large particle energies, even in exponentially decaying energy distributions. I-BEAT can thus advance to an online tool with direct feedback, e.g. as primary monitor for laser-driven ion acceleration in plasmas.