28 research outputs found
Large-scale Kinetic Simulations of Colliding Plasmas within a Hohlraum of Indirect Drive Inertial Confinement Fusions
The National Ignition Facility has recently achieved successful burning
plasma and ignition using the inertial confinement fusion (ICF) approach.
However, there are still many fundamental physics phenomena that are not well
understood, including the kinetic processes in the hohlraum. Shan et al. [Phys.
Rev. Lett, 120, 195001, 2018] utilized the energy spectra of neutrons to
investigate the kinetic colliding plasma in a hohlraum of indirect drive ICF.
However, due to the typical large spatial-temporal scales, this experiment
could not be well simulated by using available codes at that time. Utilizing
our advanced high-order implicit PIC code, LAPINS, we were able to successfully
reproduce the experiment on a large scale of both spatial and temporal
dimensions, in which the original computational scale was increased by
approximately 7 to 8 orders of magnitude. When gold plasmas expand into
deuterium plasmas, a kinetic shock is generated and propagates within deuterium
plasmas. Simulations allow us to observe the entire progression of a strong
shock wave, including its initial formation and steady propagation. Although
both electrons and gold ions are collisional (on a small scale compared to the
shock wave), deuterium ions seem to be collisionless. This is because a
quasi-monoenergetic spectrum of deuterium ions can be generated by reflecting
ions from the shock front, which then leads to the production of neutrons with
unusual broadening due to beam-target nuclear reactions. This work displays an
unprecedented kinetic analysis of an existing experiment, shedding light on the
mechanisms behind shock wave formation. It also serves as a reference for
benchmark simulations of upcoming new simulation codes and may be relevant for
future research on mixtures and entropy increments at plasma interfaces
Transport of intense ion beams in plasmas: collimation and energy-loss reduction
We compare the transport properties of a well-characterized hydrogen plasma
for low and high current ion beams. The energy-loss of low current beams can be
well understood, within the framework of current stopping power models.
However, for high current proton beams, significant energy-loss reduction and
collimation is observed in the experiment. We have developed a new
particle-in-cell code, which includes both collective electromagnetic effects
and collisional interactions. Our simulations indicate that resistive magnetic
fields, induced by the transport of an intense proton beam, act to collimate
the proton beam and simultaneously deplete the local plasma density along the
beam path. This in turn causes the energy-loss reduction detected in the
experiment
Divergence gating towards far-field isolated attosecond pulses
Divergence gating, a novel method to generate far-field isolated attosecond pulses (IAPs) through controlling divergences of different pulses, is proposed and realized by relativistic chirped laser–plasma interactions. Utilizing various wavefronts for different cycles of incident chirped lasers, reflected harmonics with minimum divergences are obtained only at the peak cycle when plasma targets are adjusted to proper distances from foci of lasers. Therefore, the corresponding attosecond pulse is isolated in far field due to much slower decay during propagation than others. Confirmed by three-dimensional numerical simulations, millijoule-level sub-50 as IAPs with intensity approaching 10 ^16  W cm ^−2 (10 ^17 –10 ^18  W sr ^−1 ) are obtained by our scheme, where low-order harmonics can be preserved
Relativistic Vlasov code development for high energy density plasmas
A newly developed relativistic Vlasov code is introduced. The governing Vlasov-Maxwell equation system is solved numerically in one-dimensional space and three-dimensional momentum space. Spherical coordinate system is adopted to characterize the momentum variables for its potential advantage on reducing computational cost. The resulting Vlasov equation is split into two advection equations with respect to position and momentum, respectively. They are solved with a conservative finite volume scheme, together with techniques suppressing numerical oscillations at sharp interfaces. Relativistic longitudinal plasma oscillations are investigated for different plasma temperatures and wave numbers. Results from code simulations are in good agreement with the existing theories
Periodic and solitary waves of the cubic-quintic nonlinear Schrödinger equation
This paper presents the possible periodic solutions and the solitons of the cubic–quintic nonlinear Schrödinger equation. Corresponding to five types of different structures of the pseudo-potentials, five types of periodic solutions are given explicitly. Five types of solitons are also obtained explicitly from the limiting procedures of the periodic solutions. This will benefit the study of the generation of fast ions or electrons, which are produced from the soliton breaking when the plasma is irradiated a high-intensity laser pulse
Diagnosis of Fast Electron Transport by Coherent Transition Radiation
Transport of fast electron in overdense plasmas is of key importance in high
energy density physics. However, it is challenging to diagnose the fast
electron transport in experiments. In this article, we study coherent
transition radiation (CTR) generated by fast electrons on the back surface of
the target by using 2D and 3D first-principle particle-in-cell (PIC)
simulations. In our simulations, aluminium target of 2.7 g/cc is simulated in
two different situations by using a newly developed high order implicit PIC
code. Comparing realistic simulations containing collision and ionization
effects, artificial simulations without taking collision and ionization effects
into account significantly underestimate the energy loss of electron beam when
transporting in the target, which fail to describe the complete characteristics
of CTR produced by electron beam on the back surface of the target. Realistic
simulations indicate the diameter of CTR increases when the thickness of the
target is increased. This is attributed to synergetic energy losses of high
flux fast electrons due to Ohm heatings and colliding drags, which appear quite
significant even when the thickness of the solid target only differs by
micrometers. Especially, when the diagnosing position is fixed, we find that
the intensity distribution of the CTR is also a function of time, with the
diameter increased with time. As the diameter of CTR is related to the speed of
electrons passing through the back surface of the target, our finding may be
used as a new tool to diagnose the electron energy spectra near the surface of
solid density plasmas.Comment: accepted by New Journal of Physic
Diagnosis of fast electron transport by coherent transition radiation
Transport of fast electrons in overdense plasmas is of key importance in high energy density physics. However, it is challenging to diagnose the fast electron transport in experiments. In this article, we study coherent transition radiation (CTR) generated by fast electrons on the back surface of the target by using 2D and 3D first-principle particle-in-cell (PIC) simulations. In our simulations, aluminum targets of 2.7 g cc ^−1 are simulated in two different situations by using a newly developed high order implicit PIC code. Comparing realistic simulations containing collision and ionization effects, artificial simulations without taking collision and ionization effects into account significantly underestimate the energy loss of electron beams when transporting in the target, which fail to describe the complete characteristics of CTR produced by electron beams on the back surface of the target. Realistic simulations indicate the diameter of CTR increases when the thickness of the target is increased. This is attributed to synergetic energy losses of high flux fast electrons due to Ohm heating and colliding drags, which appear quite significant even when the thickness of the solid target only differs by micrometers. Especially, when the diagnosing position is fixed, we find that the intensity distribution of the CTR is also a function of time, with the diameter increased with time. As the diameter of CTR is related to the speed of electrons passing through the back surface of the target, our finding may be used as a new tool to diagnose the electron energy spectra near the surface of solid density plasmas