A Platform for Ultra-Fast Proton Probing of Matter in Extreme Conditions

Abstract

Recent developments in ultrashort and intense laser systems have enabled the generation of short and brilliant proton sources, which are valuable for studying plasmas under extreme conditions in high-energy-density physics. However, developing sensors for the energy selection, focusing, transport, and detection of these sources remains challenging. This work presents a novel and simple design for an isochronous magnetic selector capable of angular and energy selection of proton sources, significantly reducing temporal spread compared to the current state of the art. The isochronous selector separates the beam based on ion energy, making it a potential component in new energy spectrum sensors for ions. Analytical estimations and Monte Carlo simulations validate the proposed configuration. Due to its low temporal spread, this selector is also useful for studying extreme states of matter, such as proton stopping power in warm dense matter, where short plasma stagnation time (<100 ps) is a critical factor. The proposed selector can also be employed at higher proton energies, achieving final time spreads of a few picoseconds. This has important implications for sensing technologies in the study of coherent energy deposition in biology and medical physics.

Keywords: Warm Dense Matter; high repetition rate detection; ion acceleration; ion spectrometers; ions; magnetic transport; measurements with sensors; sensing technologies; sensors.

Figure 1

Diagram of the isochrone ion selector. (a) Scheme of magnetic transporter. Zoom of the final pinhole and (b) the slit system (c). Angles $\theta$ and $\phi$ are complementary.

Figure 2

Time dispersion as a function of the energy dispersion for different central energies.

Figure 3

Schematic of the Monte Carlo simulation of the entrance slit: (a) geometry of the slit, (b) characterization of the source placed 1 mm from the slit with a 20 degrees half-angle divergence and an initial spot diameter of 150 $\mathrm{\mu }$m.

Figure 4

Transmission coefficient of the whole system as a function of energy spread for different central energies. Higher central energy results in a longer path through the dipole and a larger final spatial band at the exit, implying greater particle losses. Higher energy spread increases the particle flux.

Figure 5

Example of particle tracking calculations with the following parameters: (i) distance between the source and the first slit of $d_{source}$ = 2 mm, (ii) distance between slits of 7.6 mm, (iii) slit width of 8 $\mathrm{\mu }$m, (iv) dipole magnetic field of B = 1 T, (v) angle between the dipole side and the proton beam $\theta$ = 60^∘ (30^∘ from the vertical axis), (vi) dipole length 15 cm. The exit pinhole is placed $p_{pinh}$ = 10.17 cm from the entrance of the proton beam, and has a radius of 2.3 mm.

Figure 6

Simulation of the ferromagnetic structure to minimize border effects for a magnetic dipole composed of Pure Iron and Neodymium magnets (N52 grade, $4\times {10}^3$ mm³), separated by 5 mm.

Figure 7

Line out of the simulated magnetic field in Figure 6 shows the field at Point A and Point B, where the magnet has a field of 0.5 T. The field outside the gap at 5 mm is 100 mT, and at 10 mm it is 50 mT. The field increases from 0.5 T to 1 T over approximately 6 mm and from 0.5 T to 1.25 T over 10 mm.

Figure 8

VisedX 3D view of the initial conditions for the MCNP6 simulation. The A zone is the output region of the proton beam, and the inset shows the proton energy distribution.

Figure 9

(a) MCNP6 proton trajectories as a function of energy. (b,c) Projection of the proton flux over the magnet surface with 0.2 degrees of divergence, and a detail of the magnet exit. (d) Normalized output proton profile at the magnet surface.

Figure 10

(a) Spot at the exit of the magnet. (b,c) are the vertical and horizontal profiles, respectively.