Abstract
We report on the successful use of a laser-driven few-MeV proton source to measure the differential cross section of a hadronic scattering reaction as well as on the measurement and simulation study of polarization observables of the laser-accelerated charged particle beams. These investigations were carried out with thin foil targets, illuminated by 100 TW laser pulses at the Arcturus laser facility; the polarization measurement is based on the spin dependence of hadronic proton scattering off nuclei in a Silicon target. We find proton beam polarizations consistent with zero magnitude which indicates that for these particular laser-target parameters the particle spins are not aligned by the strong magnetic fields inside the laser-generated plasmas.
Highlights
The field of laser-induced relativistic plasmas and, in particular, of laser-driven particle acceleration, has undergone impressive progress in recent years.1 Despite many advances in the understanding of fundamental physical phenomena, one unexplored issue is how the particle spins are influenced by the huge magnetic fields inherently present in the plasmas.2–5 There are two mechanisms which can potentially cause a polarization of the particle beam: either due to a spin alignment or by spatial separation of different spin states induced by gradients in the magnetic field of the plasma
We find proton beam polarizations consistent with zero magnitude which indicates that for these particular laser-target parameters the particle spins are not aligned by the strong magnetic fields inside the laser-generated plasmas
Garraway and Stenholm argued that it is not necessary to achieve a spatial splitting in the interaction region if the spin states can be separated in momentum space,8,9 They showed that it is in principle possible to achieve this separation even for charged particles by using a small diameter of the particle beam in a)Present address: European XFEL GmbH, WP-75, Albert-Einstein-Ring 19, 22761
Summary
The field of laser-induced relativistic plasmas and, in particular, of laser-driven particle acceleration, has undergone impressive progress in recent years. Despite many advances in the understanding of fundamental physical phenomena, one unexplored issue is how the particle spins are influenced by the huge magnetic fields inherently present in the plasmas. There are two mechanisms which can potentially cause a polarization of the particle beam: either due to a spin alignment or by spatial separation of different spin states induced by gradients in the magnetic field of the plasma. There are two mechanisms which can potentially cause a polarization of the particle beam: either due to a spin alignment or by spatial separation of different spin states induced by gradients in the magnetic field of the plasma. The field region and a sufficiently long propagation time in an interaction free region afterwards, during which the difference in the momentum direction can lead to spatial splitting of the beam These conditions may be fulfilled in laserplasma experiments, where the size of the field region relates to the focus size of the laser beam, i.e., is of the order of only 10 lm (cf inset of Fig. 7). A promising approach would be to use pre-polarized 3He gas as target material In this case it is crucial that the 3He atoms preserve their polarization during the laser-heating.
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