RESUMEN
Multi-MeV high-purity proton acceleration by using a hydrogen cluster target irradiated with repetitive, relativistic intensity laser pulses has been demonstrated. Statistical analysis of hundreds of data sets highlights the existence of markedly high energy protons produced from the laser-irradiated clusters with micron-scale diameters. The spatial distribution of the accelerated protons is found to be anisotropic, where the higher energy protons are preferentially accelerated along the laser propagation direction due to the relativistic effect. These features are supported by three-dimensional (3D) particle-in-cell (PIC) simulations, which show that directional, higher energy protons are generated via the anisotropic ambipolar expansion of the micron-scale clusters. The number of protons accelerating along the laser propagation direction is found to be as high as 1.6 [Formula: see text] [Formula: see text] 10[Formula: see text]/MeV/sr/shot with an energy of 2.8 [Formula: see text] MeV, indicating that laser-driven proton acceleration using the micron-scale hydrogen clusters is promising as a compact, repetitive, multi-MeV high-purity proton source for various applications.
RESUMEN
The dynamics of the boundary layer in between two distinct collisionless plasmas created by the interaction between a dense object modeling a cluster and a short laser pulse in the presence of an ambient gas is studied with two dimensional relativistic particle-in-cell simulations, which are found to be described by three successive processes. In the first phase, a collisionless electrostatic shock wave, launched near the cluster expansion front, reflects the ambient gas ions at a contact surface as a moving wall, which allows a particle acceleration with a narrower energy spread. In the second phase, the contact surface disappears and the compressed surface of the ambient gas ions passes over the shock potential, forming an overlapping region between the cluster expansion front and the compressed surface of the ambient gas. Here, another type of nonlinear wave is found to be evolved, leading to a relaxation of the shock structure, while continuing to reflect the ambient gas ions. The nonlinear wave exhibits a bipolar electric field structure that is sustained for a long timescale coupled with slowly evolving ion dynamics, suggesting that a quasistationary kinetic equilibrium dominated by electron vortices in the phase space is established. In the third phase, a rarefaction wave is triggered and evolves at the compressed surface of ambient gas. This is because some of the ambient gas ions tend to pass over the potential of the bipolar electric field. Simultaneously, a staircase structure, i.e., a kind of internal shock, is formed in the cluster due to the deceleration of cluster ions. Such structure formations and successive dynamics accompanied by the transitions from the shock wave phase through the overlapping phase to the rarefaction wave phase are considered to be a unique nature at the boundary layer created by an explosion of a dense plasma object in an ambient dilute plasma.
RESUMEN
An approach for accelerating a quasimonoenergetic proton bunch via a hemispherically converging collisionless shock created in laser-cluster interactions at the relativistically induced transparency (RIT) regime is studied using three-dimensional particle-in-cell simulations. By the action of focusing a petawatt class laser pulse onto a micron-size spherical hydrogen cluster, a crescent-shaped collisionless shock is launched at the laser-irradiated hemisphere and propagates inward. The shock converges at the sphere center in concurrence with the onset of the RIT, thereby allowing the proton bunch to be pushed out from the shock surface in the laser propagation direction. The proton bunch experiences further acceleration both inside and outside of the cluster to finally exhibit a quasimonoenergetic spectral peak around 300 MeV while maintaining a narrow energy spread (â¼10%) and a small half-divergence angle (â¼5°) via the effect of the RIT. This mechanism works for finite ranges of parameters with threshold values concerning the laser peak intensity and the cluster radius, resulting from the synchronization of the multiple processes in a self-consistent manner. The present scheme utilizing the internal and external degrees of freedom ascribed to the spherical cluster leads to the proton bunch alternative to the plain target, which allows the operation with a high repetition rate and impurity free.
RESUMEN
We have recently found an H+/quinidine (a lipophilic cation, QND) antiport system in Madin-Darby canine kidney (MDCK) cells. The primary aim of the present study was to evaluate whether the H+/lipophilic cation antiport system is expressed in porcine LLC-PK1 cells. That is, we investigated uptake and/or efflux of QND and another cation, bisoprolol, in LLC-PK1 cells. In addition, we studied the renal clearance of bisoprolol in rats. Uptake of QND into LLC-PK1 cells was decreased by acidification of the extracellular pH or alkalization of the intracellular pH. Cellular uptake of QND from the apical side was much greater than from the basolateral side. In addition, apical efflux of QND from LLC-PK1 cells was increased by acidification of the extracellular pH. Furthermore, lipophilic cationic drugs significantly reduced uptake of bisoprolol in LLC-PK1 cells. Renal clearance of bisoprolol in rats was approximately 7-fold higher than that of creatinine, and was markedly decreased by alkalization of the urine pH. The present study suggests that the H+/lipophilic cation antiport system is expressed in the apical membrane of LLC-PK1 cells. Moreover, the H+/lipophilic cation antiport system may be responsible for renal tubular secretion of bisoprolol in rats.