Ion Jet Research Articles

Background fluctuations in heavy ion jet reconstruction

We present a new study by the STAR Collaboration of background fluctuations in jet reconstruction in heavy ion collisions.

Evidence for a flux transfer event generated by multiple X‐line reconnection at the magnetopause

Magnetic flux transfer events (FTEs) are signatures of unsteady magnetic reconnection, often observed at planetary magnetopauses. Their generation mechanism, a key ingredient determining how they regulate the transfer of solar wind energy into magnetospheres, is still largely unknown. We report THEMIS spacecraft observations on 2007‐06‐14 of an FTE generated by multiple X‐line reconnection at the dayside magnetopause. The evidence consists of (1) two oppositely‐directed ion jets converging toward the FTE that was slowly moving southward, (2) the cross‐section of the FTE core being elongated along the magnetopause normal, probably squeezed by the oppositely‐directed jets, and (3) bidirectional field‐aligned fluxes of energetic electrons in the magnetosheath, indicating reconnection on both sides of the FTE. The observations agree well with a global magnetohydrodynamic model of the FTE generation under large geomagnetic dipole tilt, which implies the efficiency of magnetic flux transport into the magnetotail being lower for larger dipole tilt.

Ion jet generation in the ultraintense laser interactions with rear-side concave target

AbstractIn this paper, the ion jet generation from the interaction of an ultraintense laser pulse and a rear-side concave target is investigated analytically using a simple fluid model. We find that the ion expanding surface at the rear-side is distorted due to a strong charge-separation field, and that this distortion becomes dramatic with a singular cusp shown on the central axis at a critical time. The variation of the transverse ion velocity and the relative ion density diverge on the cusp, signaling the emergence of an on-axis ion jet. We have obtained analytical expressions for the critical time and the maximum velocity of the ion jet, and suggested an optimum shape for generating a collimated energetic ion jet. The above theoretical analysis has been verified by particle-in-cell (PIC) numerical simulations.

Model for hypernucleus production in heavy ion collisions

We estimate the production cross sections of hypernuclei in projectile like fragment (PLF) in heavy ion collisions. The discussed scenario for the formation cross section of hypernucleus is: (a) Lambda particles are produced in the participant region but have a considerable rapidity spread and (b) Lambda with rapidity close to that of the PLF and total momentum (in the rest system of PLF) up to Fermi motion can then be trapped and produce hypernuclei. The process (a) is considered here within Heavy Ion Jet Interacting Generator HIJING-BBbar model and the process (b) in the canonical thermodynamic model (CTM). We estimate the production cross-sections for light hypernuclei for C + C at 3.7 GeV total nucleon-nucleon center of mass energy and for Ne+Ne and Ar+Ar collisions at 5.0 GeV. By taking into account explicitly the impact parameter dependence of the colliding systems, it is found that the cross section is different from that predicted by the coalescence model and large discrepancy is obtained for 6_He and 9_Be hypernuclei.

Composition of a plasma generated from N2–O2 by an Ar ion jet in a low pressure reactor

The expansion of a supersonic Ar+ ion jet in a low pressure (0.2 Torr) reactor filled with N2 and O2 has been investigated by means of hydrodynamic modelling. The gas velocity fields and the gas temperature distribution in the three-dimensional reactor have been determined. The formation of different species through the molecular kinetics triggered by the collision of Ar+ ions with N2 and O2 molecules has been studied. We have investigated the effect of the ions velocity and molecular gas flow rates on the gas temperature and species density distributions. We have shown that the main difference between this system and an N2–O2 post-discharge lies in the dissociation degrees of N2 and O2. While in an N2–O2 post-discharge the N2 dissociation degree is low and that of O2 is high, in the present system this can be varied through the gas flow rate of the molecular gases. We have also shown that the NO(X) molecules formation is governed by the surface processes, which is strongly influenced by the state of the surface.

Quantum and Quasiclassical Types of Superfluid Turbulence

By injecting negative ions in superfluid 4He in the zero-temperature limit (T<or=0.5 K), we have generated tangles of quantized vortex line with negligible large-scale flow. For this quantum regime of superfluid turbulence, the vortex line length L was found to decay at late time t as L proportional to t{-1}, the prefactor being independent of the initial value of L. The corresponding effective kinematic viscosity is 0.1 kappa, where kappa is the circulation quantum. At T>0.7 K, a jet of ions generates quasiclassical tangles identical to those produced by mechanical means.

Comment on “Jupiter: A fundamentally different magnetospheric interaction with the solar wind” by D. J. McComas and F. Bagenal

Comment on “Jupiter: A fundamentally different magnetospheric interaction with the solar wind” by D. J. McComas and F. Bagenal

Production of high-current heavy ion jets at the short-wavelength subnanosecond laser-solid interaction

Generation of ion fluxes at the interaction of 70J, 0.438μm subnanosecond laser pulse with a massive planar target has been investigated. It is shown that after proper optimization of high-Z (Cu or Ta) target irradiation, a highly collimated heavy ion jet of the ion current &amp;gt;100A and the ion current density &amp;gt;1A∕cm2 at 1m from the target can be produced with an energy conversion efficiency nearly 10%.

Propagating plasma patch and associated neutral stream flows

Plasma patches are regions of enhanced ionization that are created in the dayside cusp or equatorward of the cusp in the sunlit hemisphere during northward interplanetary magnetic field. After formation, and a change to a southward interplanetary magnetic field, they drift across the polar cap with the prevailing convection speed. As a plasma patch propagates, charge exchange reactions occur, which lead to the production of both ion and neutral particles throughout the patch. In the region directly above the patch, an upward jet of H + and O + forms. This ion jet, in turn, acts to produce an upward flux of neutral H and O stream particles because of charge exchange reactions between the ion jet and the background neutral atmosphere. A three-dimensional, time-dependent model of the ion and neutral polar winds was used in order to study the evolution of the neutral stream particles that are produced in a ‘representative’ propagating plasma patch, with the anticipation that the neutral stream particles produced by the ion jet would display a distinct signature. However, the outflow of neutral H atoms above a patch is only slightly visible in the simulation due to a continuous outflow flux of H (∼10 9 cm −2 s −1) across the entire polar cap. On the other hand, the upward flux of neutral O from the patch is more dependent on both the state of the ionosphere and the amount of heating, with increased upward fluxes over areas where the heating is high. Typically, the upward neutral O streams are predominantly located in the pre-midnight auroral oval.

Simulation of an electrohydrodynamic DC actuator

A semiempirical model of the electrohydrodynamic actuator operating on the basis of a dc corona discharge is proposed. The model is based on calculations of an electric field and a unipolar ion jet generated by a linear ion source on the surface of a dielectric plate and propagating along the plate in the laminar boundary layer. The ion source intensity and the potential difference on the actuator electrodes are determined experimentally. Estimates of the velocity induced by the electrohydrodynamic action in the flat-plate laminar boundary layer are obtained on the basis of the model. A comparison of the calculation results with the available experimental data confirms the adequacy of the model proposed. The effect of the adsorption properties of the dielectric surface on the distributions of the volume and surface electric discharge in the boundary layer is investigated within the framework of this model.

High Transverse Momentum Identified Particle Spectra in 200 GeV Collisions from STAR

Significant baryon over meson enhancement was measured at RHIC in the intermediate transverse momentum range of $p_T=2-4$ GeV/$c$ ("baryon-meson puzzle"). With STAR detector we were able to extend particle identification towards higher transverse momentum offering further insights into the particle production mechanisms at intermediate to high $p_T$. In this paper we present results on charged pion, proton and anti-proton spectra and ratios at intermediate to high $p_T$ exploiting the relativistic rise of the specific ionization energy loss measured in the STAR Time Projection Chamber. These measurements provide valuable information about the production mechanisms of particles at intermediate $p_T$ in relativistic heavy ion collisions, e.g. coalescence/recombination versus jet fragmentation.

Multiphase transport model for relativistic heavy ion collisions

We describe in detail how the different components of a multiphase transport (AMPT) model that uses the heavy ion jet interaction generator (HIJING) for generating the initial conditions, Zhang's parton cascade (ZPC) for modeling partonic scatterings, the Lund string fragmentation model or a quark coalescence model for hadronization, and a relativistic transport (ART) model for treating hadronic scatterings are improved and combined to give a coherent description of the dynamics of relativistic heavy ion collisions. We also explain the way parameters in the model are determined and discuss the sensitivity of predicted results to physical input in the model. Comparisons of these results to experimental data, mainly from heavy ion collisions at the BNL Relativistic Heavy Ion Collider, are then made in order to extract information on the properties of the hot dense matter formed in these collisions.

High energy heavy ion jets emerging from laser plasma generated by long pulse laser beams from the NHELIX laser system at GSI

High energy heavy ions were generated in laser produced plasma at moderate laser energy, with a large focal spot size of 0.5 mm diameter. The laser beam was provided by the 10 GW GSI-NHELIX laser systems, and the ions were observed spectroscopically in status nascendi with high spatial and spectral resolution. Due to the focal geometry, plasma jet was formed, containing high energy heavy ions. The velocity distribution was measured via an observation of Doppler shifted characteristic transition lines. The observed energy of up to 3 MeV of F-ions deviates by an order of magnitude from the well-known Gitomer (Gitomer et al., 1986) scaling, and agrees with the higher energies of relativistic self focusing.

Parameters of a fast ion jet generated by an intense ultrashort laser pulse on an inhomogeneous plasma foil

Analysis and simulations of fast particles produced by a high-intensity short laser pulse interacting with a foil target are performed. Initially, the plasma density distribution of the foil target has a smooth gradient with the scale length of plasma density varying across it. The absorbed laser energy is transferred to fast electrons, which penetrate in the foil and are partially ejected from the foil rear. These electrons produce an electric field that causes an ion beam to be emitted from the foil. We analyze the mechanism of ion acceleration in the foil plasma and the influence of the density gradient and other laser and plasma parameters on ion acceleration. The angular distributions of the ejected electrons and ions are calculated.

Net charge fluctuations inAu+Aucollisions atsNN=130GeV

We present the results of charged particle fluctuations measurements in Au+Au collisions at rootS(NN)=130 GeV using the STAR detector. Dynamical fluctuations measurements are presented for inclusive charged particle multiplicities as well as for identified charged pions, kaons, and protons. The net charge dynamical fluctuations are found to be large and negative providing clear evidence that positive and negative charged p article production is correlated within the pseudorapidity range investigated. Correlations are smaller than expected based on model-dependent predictions for a resonance gas or a quark-gluon gas which undergoes fast hadronization and freeze-out. Qualitative agreement is found with comparable scaled p+p measurements and a heavy ion jet interaction generation model calculation based on independent particle collisions, although a small deviation from the 1/N scaling dependence expected from this model is observed.

Plasma expansion into a vacuum.

The charge separation effects in the collisionless plasma expansion into a vacuum are studied in great detail. Accurate results are obtained concerning the structure of the ion front, the resultant ion energy spectrum, and more specifically the maximum ion energy. These are of crucial importance for the interpretation of recent experiments, where high-energy ion jets were produced from short pulse interaction with solid targets.

Shock front formation at vacuum arc anodes

A vacuum arc plasma jet between copper electrodes is considered as a supersonic hydrodynamic jet (the primary plasma jet) that bombards the anode and sputters and/or reflects ions (secondary plasma). An initial primary ion jet velocity of v0=1.5×104 m/s is assumed. The time-dependent interaction between primary and secondary ions is considered for primary ion concentrations of n0=1018 and 1019 m−3 and for a Cu-Cu self-sputtering yield coefficient of β=0.2. It is found by numerical calculation that the primary jet is decelerated by the collisions with the secondary ions. In the case where the mean free path in the primary plasma is much less than the interelectrode gap (l11≪L) and the mean free path for the primary-secondary ion collision is much more than the interelectrode gap (l12≫L), the primary jet decelerates, but initially remains supersonic, while at a later time the deceleration is to a subsonic value, and a shock front appears. For a primary ion concentration of n0=1018 m−3 and an initial secondary ion velocity ≈0.1×v0, a shock front appears at time t≈245×L/v0 while for n0=1019 m−3, at t≈135×L/v0.

MeV ion jets from short-pulse-laser interaction with thin foils.

Collimated jets of carbon and fluorine ions up to 5 MeV/nucleon ( approximately 100 MeV) are observed from the rear surface of thin foils irradiated with laser intensities of up to 5 x 10 (19)W/cm(2). The normally dominant proton acceleration could be surpressed by removing the hydrocarbon contaminants by resistive heating. This inhibits screening effects and permits effective energy transfer and acceleration of other ion species. The acceleration dynamics and the spatiotemporal distributions of the accelerating E fields at the rear surface of the target are inferred from the detailed spectra.

Multiphase transport model for relativistic nuclear collisions

To study heavy ion collisions at energies available from the Relativistic Heavy Ion Collider (RHIC), we have developed a multiphase transport model that includes both initial partonic and final hadronic interactions. Specifically, the Zhang's parton cascade (ZPC) model, which uses as input the parton distribution from the heavy ion jet interaction generator (HIJING) model, is extended to include the quark-gluon--to--hadronic-matter transition and also final-state hadronic interactions based on a relativistic transport (ART) model. Predictions of the model for central Au on Au collisions at RHIC are reported.

Experimental observation of correlated magnetic reconnection and Alfvénic ion jets

Correlations between magnetic reconnection and energetic ion flow events have been measured with merging force free spheromaks at the Swarthmore Spheromak Experiment. The reconnection layer is measured with a linear probe array and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The most energetic events occur in the reconnection plane immediately after formation as the spheromaks dynamically merge. The outflow velocity is nearly Alfv\'enic. As the spheromaks form equilibria and decay, the flow is substantially reduced.