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Development and calibration of a Thomson parabola with microchannel plate for the detection of laser-accelerated MeV ions
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) View into the TP as used in the experiment at the LULI 100 TW laser facility. The laser-accelerated ion beam enters the TP through a diameter pinhole on the right side of the image and propagates through the electric and magnetic fields produced by the two electrodes and the electromagnet. The ions are detected with a MCP detector, shown on the left side. (b): Simulated model of the TP with calculated proton trajectories from CST EM-STUDIO.22 This simulation was used to benchmark the measured data and to identify the ion traces in combination with a tracking routine.29

Image of FIG. 2.
FIG. 2.

Measured magnetic field distribution (a) of the electromagnet and electric field distribution (b) simulated by CST EM-STUDIO.22 The ions propagate in -direction through the fields. The maximum field strengths are 306 mT and . Both fields show a high homogeneity in the region of interest directly between the electrodes.

Image of FIG. 3.
FIG. 3.

RCF stack consisting of ten layers after the irradiation with laser-produced protons. The laser energy on target was 12.4 J. Only the lower half of the proton beam was observed to provide a simultaneous detection with RCFs and the TP in one laser shot. The energies written on each layer are the Bragg-peak energies of the protons stopped in the RCFs. The maximum proton energy is between 13 and 14 MeV and corresponds very well to the results from the TP in Fig. 6(a).

Image of FIG. 4.
FIG. 4.

Scaling factors calculated from the RCF proton spectrum to investigate the proton numbers of the MCP data. The curve shows a parabolic behavior with increasing scaling factors for higher energies. This is caused by the strong dependence on the energy loss of the protons at the MCP walls. The fit is given by with and .

Image of FIG. 5.
FIG. 5.

Comparison between the normalized CEs of protons into primary electrons at the MCP (open circles) and the normalized energy loss of protons in Inconel (dashed line). Both curves follow nearly the same slope. The efficiencies range from 9.1% for the 2 MeV protons to 0.7% for the maximum measured energy of 13 MeV.

Image of FIG. 6.
FIG. 6.

(a) Protons and carbon lines from an unheated thick Al target irradiated by the LULI laser with an energy of 12.4 J on target. The maximum proton energy is 13.6 MeV. The bright spot in the lower left corner originates from - and -radiations and neutral particles, all produced by the laser-plasma interaction propagating straight through the electromagnetic field. (b) Protons and carbon lines from a heated thick Au target. The proton line is reduced in energy (maximum energy ) and intensity [cf. Fig. 6(a)]. The carbon lines are getting stronger in intensity. (c) Oxygen, nitrogen, and palladium lines from a heated thick palladium target. The proton line is completely removed. ions are accelerated up to 5 MeV/u.

Image of FIG. 7.
FIG. 7.

Energy spectrum of the protons and carbon ions from a shot onto a heated Au target per 500 keV and per solid angle, see also Fig. 6(b). The target heating resulted in less contamination protons. Hence, much more carbon ions were accelerated. The laser energy on target was 13.1 J (the solid angle of the TP in the experiment was ). Preliminary calibration results were used to extract the number of carbons.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Development and calibration of a Thomson parabola with microchannel plate for the detection of laser-accelerated MeV ions