Ricerc@Sapienza

Next-generation plasma-based accelerators can push electron bunches to gigaelectronvolt energies within centimetre distances1,2. The plasma, excited by a driver pulse, generates large electric fields that can efficiently accelerate a trailing witness bunch3–5, enabling the realization of laboratory-scale applications ranging from high-energy colliders6 to ultrabright light sources7. So far, several experiments have demonstrated large accelerations8–10 but the resulting beam quality, particularly the energy spread, is still far from state-of-the-art conventional accelerators.

Next-generation plasma-based accelerators can push elec-tron bunches to gigaelectronvolt energies within centimetre distances. The plasma, excited by a driver pulse, generates large electric fields that can efficiently accelerate a trailing witness bunch, enabling the realization of laboratory-scale applications ranging from high-energy colliders to ultrabright light sources.

Shock-ignition (SI) is a direct-drive laser fusion scheme, in which the fuel is imploded at velocity somewhat smaller than in conventional schemes. The hot spot required for ignition is attained thanks to a converging shock-wave generated by an intense final spike of the laser pulse. Earlier studies show potentials of SI for high gain at driver energy of the order of 1 MJ, provided that laser-plasma instabilities do not degrade laser absorption and do not preheat the fuel. However, also hydrodynamic aspects need investigation.

Our understanding of the dynamics of ion collisional energy loss in a plasma is still not complete, in part due to the difficulty and lack of high-quality experimental measurements. These measurements are crucial to benchmark existing models. Here, we show that such a measurement is possible using high-flux proton beams accelerated by high intensity short pulse lasers, where there is a high number of particles in a picosecond pulse, which is ideal for measurements in quickly expanding plasmas.

Collisionless shocks are ubiquitous in the Universe as a consequence of supersonic plasma flows sweeping through interstellar and intergalactic media. These shocks are the cause of many observed astrophysical phenomena, but details of shock structure and behavior remain controversial because of the lack of ways to study them experimentally. Laboratory experiments reported here, with astrophysically relevant plasma parameters, demonstrate for the first time the formation of a quasiperpendicular magnetized collisionless shock.

Simultaneously measured DD, DT, and (DHe)-He-3 reaction histories are used to probe the impacts of multi-ion physics during the shock phase of inertial confinement fusion implosions. In these relatively hydrodynamiclike (burn-averaged Knudsen number NK similar to 0.3) shock-driven implosions, average-ion hydrodynamic DUED simulations are able to reasonably match burnwidths, nuclear yields, and ion temperatures. However, kinetic-ion FPION simulations are able to better simulate the timing differences and time-resolved reaction rate ratios between DD, DT, and (DHe)-He-3 reactions.

The impact of fuel-ion diffusion in inertial confinement fusion implosions is assessed using nuclear reaction yield ratios and reaction histories. In T3He-gas-filled (with trace D) shock-driven implosions, the observed TT/T3He yield ratio is ∼23lower than expected from temperature scaling. InD3He-gas-filled (with trace T) shock-driven implosions, the timing of theD3He reaction history is ∼50 ps earlier than those of the DT reaction histories, and average-ion hydrodynamic simulations cannot reconcile this timing difference.

Fuel-ion species dynamics in hydrodynamiclike shock-driven DT3He-filled inertial confinement fusion
implosion is quantitatively assessed for the first time using simultaneously measured D3He and DT reaction
histories. These reaction histories are measured with the particle x-ray temporal diagnostic, which captures
the relative timing between different nuclear burns with unprecedented precision (∼10 ps). The observed
50 +- 10 ps earlier D3He reaction history timing (relative to DT) cannot be explained by average-ion

Exploding pusher targets, i.e. gas-filled large aspect-ratio glass or plastic shells, driven by a strong laser- generated shock, are widely used as pulsed sources of neutrons and fast charged particles. Recent experiments on exploding pushers provided evidence for the transition from a purely fluid behavior to a kinetic one [1]. Indeed, fluid models largely overpredict yield and temperature as the Knudsen number Kn (ratio of ion mean-free path to compressed gas radius) is comparable or larger than one.