No abstract

Muons produced by the Bethe–Heitler process from laser wakefield accelerated electrons interacting with high $Z$ materials have velocities close to the laser wakefield. It is possible to accelerate those muons with laser wakefield directly. Therefore for the first time we propose an all-optical ‘Generator and Booster’ scheme to accelerate the produced muons by another laser wakefield to supply a prompt, compact, low cost and controllable muon source in laser laboratories. The trapping and acceleration of muons are analyzed by one-dimensional analytic model and verified by two-dimensional particle-in-cell (PIC) simulation. It is shown that muons can be trapped in a broad energy range and accelerated to higher energy than that of electrons for longer dephasing length. We further extrapolate the dependence of the maximum acceleration energy of muons with the laser wakefield relativistic factor $\unicode[STIX]{x1D6FE}$ and the relevant initial energy $E_{0}$. It is shown that a maximum energy up to 15.2 GeV is promising with $\unicode[STIX]{x1D6FE}=46$ and $E_{0}=1.45~\text{GeV}$ on the existing short pulse laser facilities.

Relativistic collisionless shock charged particle acceleration is considered as a possible origin of high-energy cosmic rays. However, it is hard to explore the nature of relativistic collisionless shock due to its low occurring frequency and remote detecting distance. Recently, there are some works attempt to solve this problem by generating relativistic collisionless shock in laboratory conditions. In laboratory, the scheme of generation of relativistic collisionless shock is that two electron–positron pair plasmas knock each other. However, in laboratory, the appropriate pair plasmas have been not generated. The 10 PW laser pulse maybe generates the pair plasmas that satisfy the formation condition of relativistic collisionless shock due to its ultrahigh intensity and energy. In this paper, we study the positron production by ultraintense laser high Z target interaction using numerical simulations, which consider quantum electrodynamics effect. The simulation results show that the forward positron beam up to 1013/kJ can be generated by 10 PW laser pulse interacting with lead target. The estimation of relativistic collisionless shock formation shows that the positron yield satisfies formation condition and the positron divergence needs to be controlled. Our results indicate that the generation of relativistic collisionless shock by 10 PW laser facilities in laboratory is possible.

Electrons can be efficiently injected into a plasma wave by colliding two counterpropagating laser pulses in a laser wakefield acceleration. However, the generation of a high-quality electron beam with a large charge is difficult in the traditional on-axis colliding scheme due to the growth of the electron beam duration coming from the increase of the beam charge. To solve this problem, we propose an off-axis colliding scheme, in which the collision point is away from the axis of the driver pulse. We show that the electrons injected from the off-axis region are highly concentered on the tail of the bubble even for a large trapped charge, thus feeling almost the same accelerating field. As a result, quasimonoenergetic electron beams with a large charge can be produced. The validity of this scheme is confirmed by both the particle-in-cell simulations and the Hamiltonian model. Furthermore, it is shown that a Laguerre-Gauss (LG) laser can be adopted as the injection pulse to realize the off-axis colliding injection in three dimensions symmetrically, which may be useful in simplifying the technical layout of the real experiment setup.

We report experimental evidence of ion–ion acoustic instability in laser-produced astrophysically relevant plasma. Irradiation of a copper foil with a short (2 ps) intense (1017 W cm−2) laser pulse generates dense hot plasma, whose expansion into the rarefied preplasma generates the electrostatic collisionless shock. A shock-reflected ion beam penetrates through the shock upstream excites the ion–ion acoustic instability. The shock oscillation electric field and the instability filamentary modulation are monitored by proton radiography. Particle-in-cell and particle-tracing simulations reproduce the experimental observation.