Neutron Stars 1: Equation of State and Structure

There has recently been growing evidence for the existence of neutron stars possessing magnetic fields with strengths that exceed the quantum critical field strength of 4.4 × 1013 G, at which the cyclotron energy equals the electron rest mass. Such evidence has been provided by new discoveries of radio pulsars having very high spin-down rates and by observations of bursting gamma-ray sources termed magnetars. This paper will discuss the exotic physics of this high-field regime, where a new array of processes becomes possible and even dominant and where familiar processes acquire unusual properties. We review the physical processes that are important in neutron star interiors and magnetospheres, including the behaviour of free particles, atoms, molecules, plasma and condensed matter in strong magnetic fields, photon propagation in magnetized plasmas, free-particle radiative processes, the physics of neutron star interiors and field evolution and decay mechanisms. Application of such processes in astrophysical source models, including rotation-powered pulsars, soft gamma-ray repeaters, anomalous x-ray pulsars and accreting x-ray pulsars will also be discussed. Throughout this review, we will highlight the observational signatures of high magnetic field processes, as well as the theoretical issues that remain to be understood.

Physics of strongly magnetized neutron stars

Plasmas consisting exclusively of particles with a single sign of charge (e.g., pure electron plasmas and pure ion plasmas) can be confined by static electric and magnetic fields (in a Penning trap) and also be in a state of global thermal equilibrium. This important property distinguishes these totally unneutralized plasmas from neutral and quasineutral plasmas. This paper reviews the conditions for, and the structure of, the thermal equilibrium states. Both theory and experiment are discussed, but the emphasis is decidedly on theory. It is a huge advantage to be able to use thermal equilibrium statistical mechanics to describe the plasma state. Such a description is easily obtained and complete, including for example the details of the plasma shape and microscopic order. Pure electron and pure ion plasmas are routinely confined for hours and even days, and thermal equilibrium states are observed. These plasmas can be cooled to the cryogenic temperature range, where liquid and crystal-like states are realized. The authors discuss the structure of the correlated states separately for three plasma sizes: large plasmas, in which the free energy is dominated by the bulk plasma; mesoscale plasmas, in which the free energy is strongly influenced by the surface; and Coulomb clusters, in which the number of particles is so small that the canonical ensemble is not a good approximation for the microcanonical ensemble. All three cases have been studied through numerical simulations, analytic theory, and experiment. In addition to describing the structure of the thermal equilibrium states, the authors develop a thermodynamic theory of the trapped plasma system. Thermodynamic inequalities and Maxwell relations provide useful bounds on and general relationships between partial derivatives of the various thermodynamic variables.

/pdf/trapped-nonneutral-plasmas-liquids-and-crystals-the-thermal-2ubwc98t2q.pdf

Trapped nonneutral plasmas, liquids, and crystals (the thermal equilibrium states)

In the 2015 review paper 'Petawatt Class Lasers Worldwide' a comprehensive overview of the current status of highpower facilities of >200 TW was presented. This was largely based on facility specifications, with some description of their uses, for instance in fundamental ultra-high-intensity interactions, secondary source generation, and inertial confinement fusion (ICF). With the 2018 Nobel Prize in Physics being awarded to Professors Donna Strickland and Gerard Mourou for the development of the technique of chirped pulse amplification (CPA), which made these lasers possible, we celebrate by providing a comprehensive update of the current status of ultra-high-power lasers and demonstrate how the technology has developed. We are now in the era of multi-petawatt facilities coming online, with 100 PW lasers being proposed and even under construction. In addition to this there is a pull towards development of industrial and multidisciplinary applications, which demands much higher repetition rates, delivering high-average powers with higher efficiencies and the use of alternative wavelengths: mid-IR facilities. So apart from a comprehensive update of the current global status, we want to look at what technologies are to be deployed to get to these new regimes, and some of the critical issues facing their development.

/pdf/petawatt-and-exawatt-class-lasers-worldwide-10zgtun6jp.pdf

Petawatt and exawatt class lasers worldwide

During the past five years, major progress has been made in the experimental study of solid hydrogen at ultrahigh pressures as a result of developments in diamond-cell technology. Pressures at which metallization has been predicted to occur have been reached (250-300 Gigapascals). Detailed studies of the dynamic, structural, and electronic properties of dense hydrogen reveal a system unexpectedly rich in physical phenomena, exhibiting a variety of transitions at ultrahigh pressures. This colloquium explores the study of dense hydrogen as an archetypal problem in condensed-matter physics.

Ultrahigh-pressure transitions in solid hydrogen

We report an observation of surface acceleration of fast electrons in intense laser-plasma interactions. When a preformed plasma is presented in front of a solid target with a higher laser intensity, the emission direction of fast electrons is changed to the target surface direction from the laser and specular directions. This feature could be caused by the formation of a strong static magnetic field along the target surface which traps and holds fast electrons on the surface. In our experiment, the increase in the laser intensity due to relativistic self-focusing in plasma plays an important role for the formation. The strength of the magnetic field is calculated from the bent angle of the electrons, resulting in tens of percent of laser magnetic field, which agrees well with a two-dimensional particle-in-cell calculation. The strong surface current explains the high conversion efficiency on the cone-guided fast ignitor experiments.

/pdf/surface-acceleration-of-fast-electrons-with-relativistic-4rahhumw80.pdf

Surface acceleration of fast electrons with relativistic self-focusing in preformed plasma

Since the approval of the first phase of the Fast-Ignition Realization Experiment (FIREX-I), we have devoted our efforts to designing advanced targets and constructing a petawatt laser, which will be the most energetic petawatt laser in the world. Scientific and technological improvements are required to efficiently heat the core plasma. There are two methods that can be used to enhance the coupling efficiency of the heating laser to the thermal energy of the compressed core plasma: adding a low-Z foam layer to the inner surface of the cone and employing a double cone. The implosion performance can be improved in three ways: adding a low-Z plastic layer to the outer surface of the cone, using a Br-doped plastic ablator and evacuating the target centre. An advanced target for FIREX-I was introduced to suit these requirements. A new heating laser (LFEX) has been constructed that is capable of delivering an energy of 10 kJ in 10 ps with a 1 ps rise time. A fully integrated fast-ignition experiment is scheduled for 2009.

Plasma physics and laser development for the Fast-Ignition Realization Experiment (FIREX) Project

We report on the discovery of superconductivity in the noncentrosymmetric antiferromagnet ${\text{CeIrGe}}_{3}$ below 15 K at a pressure of 20 GPa We performed electrical resistivity measurements in single crystals of ${\text{CeIrGe}}_{3}$ in the temperature range 004--300 K at pressures up to 24 GPa From these measurements we deduced the $P\text{\ensuremath{-}}T$ phase diagram The data imply a crossover from localized to itinerant $4f$ electrons of the type caused by a Kondo-lattice phenomenon as pressure increases The antiferromagnetic phase weakens with pressure and eventually vanishes above 22 GPa, indicative of the occurrence of a quantum critical point Superconductivity appears inside the antiferromagnetic phase near this critical point After the disappearance of the magnetic ordering a non-Fermi-liquid behavior is observed Resistivity measurements taken at 24 GPa in magnetic fields up to 8 T strongly suggest that ${\text{CeIrGe}}_{3}$ has a very large upper critical field for $H\ensuremath{\parallel}[001]$

Pressure-induced superconductivity and large upper critical field in the noncentrosymmetric antiferromagnet CeIrGe 3

We have explored the stable phases of solid hydrogen by calculating band-theoretical energies in the local density approximation, for the system of oriented molecules at Mbar pressures and at zero temperature. It is shown that the hexagonal-close-packed lattice persists up to \ensuremath{\sim}300 GPa with a structure of space group Pca${2}_{1}$, which has wide band gaps. The subsequent phase is still molecular with a rutile structure with c/a\ensuremath{\sim}0.9 which must be conducting. The molecular phase terminates at \ensuremath{\sim}600 GPa, where the atomic phase with a planar structure appears.

Stable phases of solid hydrogen at megabar pressures and at zero temperature.

/pdf/ground-state-energy-difference-of-hcp-and-fcc-ortho-2k7kgtfklk.pdf

Tuto Nakamura

Papers

Surface acceleration of fast electrons with relativistic self-focusing in preformed plasma

Plasma physics and laser development for the Fast-Ignition Realization Experiment (FIREX) Project

Pressure-induced superconductivity and large upper critical field in the noncentrosymmetric antiferromagnet CeIrGe 3

Stable phases of solid hydrogen at megabar pressures and at zero temperature.

Ground State Energy Difference of Hcp and Fcc Ortho-Hydrogens