The application of laser-driven proton beams to the radiography of intense laser–hohlraum interactions

Experimental Observation of Thin-shell Instability in a Collisionless Plasma

“…Numerical simulations of similar scenarios demonstrated that the presence of background plasma restrains the generation of magnetic field (Sarri et al 2011), allowing one to assume that the proton deflections observed on the RCF are solely related to electrostatic fields. Under this assumption, the electric field responsible for the proton deflections can be analytically estimated (Sarri et al 2010) as long as protons are subject to small angular deflections. The extracted electric field profiles are shown in Figures 1(c)-(e), indicating that the electric field evolves from a bell-shaped profile to an asymmetric bipolar profile, while maintaining a peak amplitude of the order of 100 MV m −1 .…”

“…Moreover, the Coulomb logarithm for electron-electron and ion-ion collisions are of the order of 6 and 11, respectively, indicating a characteristic timescale for collisions of t~36 ns ee and t~600 ns ii , respectively. The PPI technique (Borghesi et al 2002;Sarri et al 2010) was employed to investigate the interaction of the ablated plasma with the background plasma. The probe proton beam was generated by focusing a second laser pulse of ∼1 ps duration and ∼50 J energy, to an intensity of~10 19 W cm −2 onto a thin gold foil (thickness ∼20 μm).…”

“…The error in defining the beginning of the interaction is mainly due to the systematic error in the synchronization of both laser beams. This does not affect the temporal resolution of the PPI technique, which is on the order of picoseconds (Sarri et al 2010). …”

Observation of plasma density dependence of electromagnetic soliton excitation by an intense laser pulse

“…The interaction was mainly diagnosed via the proton radiography technique, 16 which uses, as a particle probe, a laser accelerated proton beam, arising from the interaction of a secondary laser pulse (s L % 1 ps, E L % 30 J, and I L % 10 19 W cm 10 lm thick gold foil. The virtual point-like source 17 allowed imaging of the interaction area with a geometrical magnification M % (l þ L)=l % 11, where l % 3 mm and L % 3 cm (see Refs.…”

“…Thanks to the multi-frame capability of the proton radiography technique, 16 it has been possible to follow the temporal evolution of such structures in a temporal window ranging from 1 to 40 ps after the peak of the laser pulse. The bubbles are seen already at 1-2 ps, i.e., when the laser is still propagating inside the gas jet.…”