Electromagnetic Thomson parabola spectrometer for detection of fs laser-driven keV ions

Unconfined high-energy-density laser plasmas are known to emit broadband ion spectra in terms of species and their kinetic energy. The diagnostic of choice is often the Thomson parabola method, which is well-studied for the particle energies in the MeV range. In this work, a spectrometer is presented that is specifically designed to function down to energies of a few keV. Advancing into this regime requires an accurate knowledge of the spectrometer fields, which were precisely determined by simulations and measurements The dynamic range was substantially increased by adopting a compact electromagnet instead of a permanent one. We demonstrate how the field parameters can be chosen for obtaining exceptionally broad spectra while keeping the energy uncertainty minimal. Finally, the performance of the device is demonstrated for the ion emission of a carbon plasma ignited by sub-10-fs laser pulses.