High resolution Thomson Parabola Spectrometer for full spectral capture of multi-species ion beams

Abstract

We report on the experimental characterisation of laser-driven ion beams using a Thomson Parabola Spectrometer (TPS) equipped with trapezoidally shaped electric plates, proposed by Gwynne et al. [Rev. Sci. Instrum. 85, 033304 (2014)]. While a pair of extended (30 cm long) electric plates was able to produce a significant increase in the separation between neighbouring ion species at high energies, deploying a trapezoidal design circumvented the spectral clipping at the low energy end of the ion spectra. The shape of the electric plate was chosen carefully considering, for the given spectrometer configuration, the range of detectable ion energies and species. Analytical tracing of the ion parabolas matches closely with the experimental data, which suggests a minimal effect of fringe fields on the escaping ions close to the wedged edge of the electrode. The analytical formulae were derived considering the relativistic correction required for the high energy ions to be characterised using such spectrometer.

Dispersion calibration for the National Ignition Facility electron–positron–proton spectrometers for intense laser matter interactions

“…Particles can be recorded with image plates 13 , or through imaging of scintillating screens 14 . The spatial distribution of particles and photons can be directly recorded [15][16][17] or particle spectrometers can be employed to separate charged particles by mass and energy with magnetic, or also with electric fields 18 . By using image plates and permanent magnets [19][20][21] , imaging can be done hours later in an external scanner and the magnetic spectrometers can be ruggedized against electromagnetic pulses of laser-matter interactions.…”

TOF diagnosis of laser accelerated, high-energy protons

“…The TPS [25], consisting of a 1 T dipole magnet, electric field plates and a 400 µm pinhole faced the front side of the target at a pinhole-target distance of 125 cm and at an angle of about 10 • from the target normal. An image plate (IP) wrapped with a 5 um Al foil, was used as detector of the particle traces deflected by the TPS.…”

“…In this experiment, the ion beam emitted in the laser forward direction was not diagnosed using a TPS, thus speculations about the species, charge states and maximum energies of heavier ions accelerated from the target rear-side cannot be confirmed by TPS ion spectra. Nevertheless, on the basis of Thomson spectra obtained in other experimental run on the VULCAN PW system with similar targets and laser conditions, we can assume that the maximum energy per nucleon of Carbon/Oxygen ions accelerated in the forward direction will be below 10 MeV/u [25]. On this basis, with reasonable confidence, the TOF signal acquired for proton energies higher than about 10 MeV, which corresponds to TOF shorter than about 60 ns, can be uniquely attributed to H + .…”

A new energy spectrum reconstruction method for time-of-flight diagnostics of high-energy laser-driven protons

“…A laser pulse of wavelength 1.054 µm, duration of ∼ 700 fs and energy up to ∼ 400 J on target, was focused onto a 25 µm-thick Al target leading to the acceleration (from surface contaminants) of protons and light ions, such as carbon and oxygen. A Thomson Parabola Spectrometer (TPS) coupled with Image Plates was placed in the backward direction at about 1.2 m from target, separating the ion species according to charge-to-mass ratio and providing the ion energy cut-off and spectra measurements using the analysis method and the calibration reported in 27,28 . A 100 µm thick polychrystalline diamond detector was placed at the target front side at about 2.35 m (P1) from the target location, with an applied voltage of 200 V. The experimental setup is shown in FIG.…”