Characterisation of deuterium spectra from laser driven multi-species sources by employing differentially filtered image plate detectors in Thomson spectrometers

Abstract

A novel method for characterising the full spectrum of deuteron ions emitted by laser driven multi-species ion sources is discussed. The procedure is based on using differential filtering over the detector of a Thompson parabola ion spectrometer, which enables discrimination of deuterium ions from heavier ion species with the same charge-to-mass ratio (such as C 6+ , O 8+ , etc.). Commonly used Fuji Image plates were used as detectors in the spectrometer, whose absolute response to deuterium ions over a wide range of energies was calibrated by using slotted CR-39 nuclear track detectors. A typical deuterium ion spectrum diagnosed in a recent experimental campaign is presented, which was produced from a thin deuterated plastic foil target irradiated by a high power laser.

Beamed neutron emission driven by laser accelerated light ions

“…The ion beams were diagnosed in the earlier part of the experiment using a high resolution Thomson Parabola Spectrometer (TPS) [13] with image plate detectors along the target normal direction, as shown schematically in figure 1. Since traces for ions with the same charge to mass ratio overlap in the TPS, we implemented the differential filtering technique described by Alejo et al [14] in order to extract the deuteron spectra from the diagnostic. ∼2 mm thick solid blocks of CD and graphite were placed ∼3 mm behind the pitcher target (henceforth called catcher) in order to generate neutrons from nuclear reactions.…”

Selective deuterium ion acceleration using the Vulcan petawatt laser

“…Test particles are numerically propagated through this system and are spatially mapped onto the IP giving the energy dispersion for each TPS. The absolute response and decay properties of the IP are described in Alejo et al 29 In some cases, the deuterium signal was so strong that the scanner recorded regions of saturation. The PSL values for these pixels are calculated by rescanning the IP to generate a calibration function.…”

“…The details of the filtering are discussed thoroughly by Alejo et al 29 The thicknesses and materials of the IP filters are chosen to stop the higher-mass contaminant ions while allowing the deuterium ions and protons through to the IP. The entire IP is covered with a 6 lm thick Al foil so the 12 lm Al filter region is actually filtered by 18 lm thick Al, and so on.…”

Recent developments in the Thomson Parabola Spectrometer diagnostic for laser-driven multi-species ion sources

“…However, due to the broad energy spectrum of the laser-driven ions (ranging from sub-MeV up to tens of MeV), a single filter would either be too thin to stop the heavy ions of high energies, or too thick to let the light ions of low energy pass through. In order to overcome this limitation, one can use a stepped Differential Filtering (DF) technique [34], which consists of an array of foils of different materials and thickness along the energy dispersion (y) axis, ensuring the discrimination of the lightest ions from the rest of the overlapping species is achieved in the energy range covered by each filter. The choice for the thickness and material for each filter can vary depending on the materials available and the species to be discriminated.…”

“…Since the response of the detectors for different charged particles depends heavily on the ion species and energy, calibration functions for the most common types of TPS detectors and particles have been obtained experimentally by different groups. Some of the relevant works include calibration of Image Plates [30] for protons [31][32][33], deuterons [34,35], alpha particles [35,36] and carbon ions [37], and the calibration of MultiChannel Plates for protons [23,38] and carbon ions [39].…”