Mach Cone Structure Research Articles

Interaction of a supersonic particle with a three-dimensional complex plasma

The influence of a supersonic projectile on a three-dimensional complex plasma is studied. Micron sized particles in a low-temperature plasma formed a large undisturbed system in the new “Zyflex” chamber during microgravity conditions. A supersonic probe particle excited a Mach cone with Mach number M ≈ 1.5–2 and double Mach cone structure in the large weakly damped particle cloud. The speed of sound is measured with different methods and particle charge estimations are compared to the calculations from standard theories. The high image resolution enables the study of Mach cones in microgravity on the single particle level of a three-dimensional complex plasma and gives insight to the dynamics. A heating of the microparticles is discovered behind the supersonic projectile but not in the flanks of the Mach cone.

Fore-wake excitations from moving charged objects in a complex plasma

A charged object moving at a supersonic speed in a plasma creates the familiar Mach cone structure in its wake but can also give rise to nonlinear wave excitations ahead of it. Using molecular dynamic simulations, we explore such fore-wake excitations in a strongly coupled dusty plasma and demonstrate the existence of precursor solitonic pulses and dispersive shock waves in that region. The excitation conditions as well as the propagation characteristics of such pulses are delineated as a function of the projectile velocity, the plasma density, the Coulomb coupling parameter, and the amount of charge on the projectile. Our simulation results provide a kinetic basis for earlier fluid model calculations and also give insights into the dynamical processes responsible for such excitations that can aid in future experimental and application oriented studies.

Towards numerical simulations of supersonic liquid jets using ghost fluid method

A computational tool based on the ghost fluid method (GFM) is developed to study supersonic liquid jets involving strong shocks and contact discontinuities with high density ratios. The solver utilizes constrained reinitialization method and is capable of switching between the exact and approximate Riemann solvers to increase the robustness. The numerical methodology is validated through several benchmark test problems; these include one-dimensional multiphase shock tube problem, shock–bubble interaction, air cavity collapse in water, and underwater-explosion. A comparison between our results and numerical and experimental observations indicate that the developed solver performs well investigating these problems. The code is then used to simulate the emergence of a supersonic liquid jet into a quiescent gaseous medium, which is the very first time to be studied by a ghost fluid method. The results of simulations are in good agreement with the experimental investigations. Also some of the famous flow characteristics, like the propagation of pressure-waves from the liquid jet interface and dependence of the Mach cone structure on the inlet Mach number, are reproduced numerically. The numerical simulations conducted here suggest that the ghost fluid method is an affordable and reliable scheme to study complicated interfacial evolutions in complex multiphase systems such as supersonic liquid jets.

Emission of Low Momentum Particles at Large Angles from Jet

We study dynamics of a QGP fluid induced by energetic partons propagating through it. We construct a (3+1)-dimensional QGP-fluid+Jet model. When a jet traverses a uniform fluid, it induces a Mach cone structure of energy density distribution and a vortex ring surrounding a path of the jet. When a pair of jets travels through a radially expanding fluid, low momentum particles are dominantly induced at large angles from the quenched jet. This result is qualitatively consistent with observation of the CMS Collaboration at LHC.

Cavity dynamics and particle alignment in the wake of a supersonic projectile penetrating a dusty plasma

The penetration of a projectile into a strongly coupled dusty plasma was studied in a radio-frequency discharge under microgravity conditions. A supersonic projectile produces an elongated dust-free cavity in its wake. The dynamics of the cavity is analyzed and compared with Langevin dynamics simulations. Besides a three-dimensional Mach cone structure, the simulation shows that the cavity dynamics can be subdivided into three phases: An opening phase with fixed time scale, a closing phase, whose duration is affected by the projectile speed and, finally, a phase of particle realignment in the target cloud, which persists for a long time after the closure of the cavity.

Thermal field theory derivation of the source term induced by a fast parton from the quark energy-momentum tensor

I derive the distribution of energy and momentum transmitted from a fast parton to a medium of thermalized quarks, or the source term, in perturbative thermal field theory directly from the quark energy-momentum tensor. The fast parton is coupled to the medium by adding an interaction term to the Lagrangian. The thermal expectation value of the energy-momentum tensor source term is then evaluated using standard Feynman rules at finite temperature. It is found that local excitations, which are important for exciting an observable Mach cone structure, fall sharply as a function of the energy of the fast parton. This may have implications for the trigger $p_T$ dependence of measurements of azimuthal dihadron particle correlations in heavy-ion collisions. In particular, a conical emission pattern would be less likely to be observed for increasing trigger $p_T$. I show that the results presented in this paper can be generalized to more realistic modeling of fast parton propagation, such as through a time dependent interaction term, in future studies.

Mach Cones in Viscous Matter

Employing a microscopic transport model we investigate the evolution of high energetic jets moving through a viscous medium. For the scenario of an unstoppable jet we observe a clearly strong collective behavior for a low dissipative system η/s ≈ 0.005, leading to the observation of cone-like structures. Increasing the dissipation of the system to η/s ≈ 0.32 the Mach Cone structure vanishes. Furthermore, we investigate jet-associated particle correlations. A double-peak structure, as observed in experimental data, is even for low-dissipative systems not supported, because of the large influence of the head shock.

Relativistic shock waves and Mach cones in viscous gluon matter

To investigate the formation and the propagation of relativistic shock waves in viscous gluon matter we solve the relativistic Riemann problem using a microscopic parton cascade. We demonstrate the transition from ideal to viscous shock waves by varying the shear viscosity to entropy density ratio η/s. Furthermore we compare our results with those obtained by solving the relativistic causal dissipative fluid equations of Israel and Stewart (IS), in order to show the validity of the IS hydrodynamics. Employing the parton cascade we also investigate the formation of Mach shocks induced by a high-energy gluon traversing viscous gluon matter. For η/s = 0.08 a Mach cone structure is observed, whereas the signal smears out for η/s ≥ 0.32.

Wakes in the quark-gluon plasma

Using the high temperature approximation we study, within the linear response theory, the wake in the quark-gluon plasma by a fast parton owing to dynamical screening in the spacelike region. When the parton moves with a speed less than the average speed of the plasmon, we find that the wake structure corresponds to a screening charge cloud traveling with the parton with one sign flip in the induced charge density resulting in a Lennard-Jones type potential in the outward flow with a short range repulsive and a long range attractive part. On the other hand if the parton moves with a speed higher than that of plasmon, the wake structure in the induced charge density is found to have alternate sign flips and the wake potential in the outward flow oscillates analogous to Cerenkov-like wave generation with a Mach cone structure trailing the moving parton. The potential normal to the motion of the parton indicates a transverse flow in the system. We also calculate the potential due to a color dipole and discuss consequences of possible new bound states and $J/\ensuremath{\psi}$ suppression in the quark-gluon plasma.

Probing color response—wakes in a color plasma

The wake induced in a hot QCD medium by a high momentum parton (jet precursor) is calculated in the framework of linear response theory. Two different scenarios are discussed: a weakly coupled quark gluon plasma (pQGP) as described by hard-thermal loop (HTL) perturbation theory and a strongly cupled QGP (sQGP) with the properties of a quantum liquid. In the latter case the wake could exhibit a pronounced Mach cone structure. This physical mechanism could be important for the understanding of preliminary data from the PHENIX and STAR experiments at RHIC on the angular distribution of low-pt secondaries stemming from the away-side jet which indicate maxima at ∇ϕ = π ± 1.1.

Laser-excited mach cones in a dusty plasma crystal

Experimental studies of the formation and structure of Mach cones in a plasma crystal are presented. Plasma crystals are ordered structures of charged microspheres trapped in the sheath of an rf discharge plasma. Using a monolayer crystal with a hexagonal lattice, Mach cones were excited by the radiation pressure of a focused laser beam. The beam was swept at a supersonic speed through the crystal, in a controlled and repeatable manner. A multiple Mach cone structure was observed, with at least three distinct Mach cones. The Mach angle relation was verified over a wide range of Mach numbers, for both the first and second cones. The sound speed, measured from the first Mach angle, was found to increase with the particle number density. Two methods of determining the particle charge and screening distance are developed, making use of the sound speed and an assumption of a Yukawa interparticle potential. Molecular-dynamics simulations of the experiment were carried out, using a monolayer of particles interacting through a Yukawa potential, and these show close agreement with the experiment.

Mach cone structure generation by the interaction of a short microwave pulse with a plasma

When a non-uniform unmagnetized plasma is irradiated by a short microwave pulse with length of the order of an ion-wave period, the travelling wavepacket of the electron plasma wave, and nonlinear large-amplitude waves in an ion-wave regime have been observed. The observed large-amplitude waves typically have two frequencies. The higher-frequency wave is an ion wakefield excited by the travelling wavepacket of the electron plasma wave, while the lower-frequency mode, also called a density cavity streamer, can be interpreted as a pseudowave induced by the supersonic ion bunch with a typical energy of 25 eV produced at the resonance layer. The experimental results are in reasonable agreement with a theoretical model based on the Mach cone structure.

VLF emission produced by a rarefied electron beam during active experiments in the Earth ionosphere: Conditions of observation of the emission

The peculiarities of whistler waves spontaneously radiated by an electron beam artificially injected into the Earth ionosphere are discussed. The conditions of registration of the whistler wave packets by a remote on board VLF receiver have been analyzed; they depend on mutual disposition of the electron gun and the VLF receiver as well as on the pitch angle of the injected electrons. It is shown that the internal frequency width of the whistler signal, connected with ray representation of a wave field, depends on the distance between the emitting region of the beam and the receiver and determines the lowest bandwidth of the VLF receiver in use. In the case of a dense plasma (when the plasma frequency ωp is much greater than the electron gyrofrequency ωc) the main results are obtained analytically. The effective value of the electron collision frequency for the background plasma can be estimated through measurements of the maximum value of the injection pitch angle of the beam's electrons, which leads to a steep drop in the level of the whistler signal. It is shown that double‐pole singularity in the single electron Cherenkov energy loss near the Gendrin's velocity appears only at a single frequency depending on the beam and the background plasma parameters. Thus the total growth of the energy loss in this case reveals an increase by a factor of the order of ωp/ωc compared to the usual single‐pole contribution. The Cherenkov radiation from the sharp leading front of the beam does not reveal any Mach cone structure. The peculiarities of the spectral parameters of the whistler emission at the Doppler‐shifted resonances are also discussed; the Mach cone exists in these cases. Thus this feature can be responsible for the crucial difference between the registration pattern of high‐frequency and whistler frequency emission in active experiments similar to ARAKS.