MHD Shock Waves Research Articles

Discontinuities in a Collisionless Plasma Flow Having a Strong Magnetic Field

Discontinuties in a collisionless anisotropic plasma flow having a strong magnetic field, their evolutionary condition, and the hose and mirror instability conditions for associated flow are considered on the basis of Chew, Goldberger and Low theory. Zero heat fluxes are assumed in both sides of the discontinuity, and the energy equation for transverse thermal motion is replaced by the adiabatic relation. Solutions are presented analytically and numerically for special angles of discontinuity and special upstream conditions. As a conclusion, it is found that remarkable differences exist between CGL discontinuity and MHD shock wave.

Plasma Radiation from Collisionless MHD Shock Waves. III. Type II Solar Radio Bursts

view Abstract Citations (15) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Plasma Radiation from Collisionless MHD Shock Waves. III. Type II Solar Radio Bursts Smith, D. F. Abstract The theory developed in Papers I and II of this series is applied to type II solar radio bursts. Observations are reviewed, and basic requirements for a theory are established. The case of a shock at the 80- MHz plasma level with a velocity of 1000 km s- , an Alfven Mach number of 2.5, and an angle between the plane of the shock and the ambient magnetic field of ' is examined in detail To explain a strong type II burst with a flux of tO-is at the Earth, a shock area of about 4 X lOis cm2 is required. If such a shock travelled 1 R0, about 1010 ergs would be expended. To explain the observed ratio of fundamental/harmonic intensities, the fundamental radiation must be amplified. This theory provides a method for determining the magnetic field in some parts of the corona since the Alfve'n Mach number of the shock must lie in the range 2.0 < JIlA < 2.9. A possible explanation for the difference in apparent positions of the sources of fundamental and second-harmonic radiation close to the limb is presented. Direct harmonic radiation is not seen because it is absorbed in the shock and in the region immediately behind the shock while fundamental radiation is only seen from a scatter image of the true source. The herringbone features of type II bursts are most likely the result of a shock wave impinging on a coronal streamer at almost right angles to the axis of the streamer. The connection between type II and type IV solar radio bursts is briefly discussed. Publication: The Astrophysical Journal Pub Date: June 1972 DOI: 10.1086/151526 Bibcode: 1972ApJ...174..643S full text sources ADS | Related Materials (2) Part 1: 1971ApJ...170..559S Part 2: 1972ApJ...174..121S

Plasma Radiation from Collisionless MHD Shock Waves. II. Plasmawave Generation and Transformation Processes

view Abstract Citations (11) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Plasma Radiation from Collisionless MHD Shock Waves. II. Plasmawave Generation and Transformation Processes Smith, D. F. Abstract The distribution of plasma waves which results when beams of electrons produced in a collisonless magnetohydrodynamic shock wave enter into the upstream plasma is examined. The upstream region is divided into two parts, a relaxation region in which the beams lose their directed energy and a forward region to which plasma waves with sufficiently high group velocity escape. Losses of plasma waves in the relaxation region due to escape to the forward region and into the shock are taken into account to establish a minimum beam density for self-consistency. Nonlinear processes are analyzed to determine the angular distribution of plasma waves. Processes for the transformation of plasma waves into radiation are considered. It is shown that interaction of plasma waves with the density inhomogeneity of the shock front will lead to negligible radiation. The process p + s t, where p is a plasma wave, S is an ion-acoustic wave, and t is a transverse wave, will not be important in the shock front due to the difficulty in satisfying the momentum conservation condition. The only significant transformation process for emission near the fundamental of the plasma frequency in the shock front and the upstream region is scattering on the polarization clouds of ions, p + i H t(wp) + i', where i is an ion. The absorption coefficient for this process can be negative, and hence a transfer problem must be solved to determine the total radiation. The only important transformation process for emission near the second harmonic of the plasma frequency is combination of two excited plasma waves, p + p H t( ). Since the cone of plasma waves is anisotropic and the two excited plasma waves must meet almost "head-on," spontaneous scattering of plasma waves must be taken into account in computing this combination process. Because the shock front is much narrower than the relaxation or forward regions, only the latter need to be considered in computing the radiation. Publication: The Astrophysical Journal Pub Date: May 1972 DOI: 10.1086/151474 Bibcode: 1972ApJ...174..121S full text sources ADS | Related Materials (2) Part 1: 1971ApJ...170..559S Part 3: 1972ApJ...174..643S

Oscillatory structure of a quasi-stationary MHD shock wave in a plasma

Oscillatory structure of a quasi-stationary MHD shock wave in a plasma

An experimental study of transverse ionizing MHD shock waves

The jump conditions across a transverse ionizing MHD shock wave, where the magnetic field is in the plane of the shock, are examined. The conservation laws, in conjunction with Maxwell's laws and the equation of state, yield three jump equations in four unknowns. To uniquely describe jumps across an ionizing wave requires an additional descriptive relationship. The theory of Kulikovskii &amp; Lyubimov and, later, Chu, in which the internal structure of the shock itself supplies the missing relationship, is examined. In particular, Kulikovskii &amp; Lyubimov show, for appropriate ratios of thermal to magnetic diffusivities, that for low-speed waves the magnetic field compression across the shock is unity and the jump equations reduce to the ordinary Rankine—Hugoniot relations. For high-speed shock waves, the magnetic field compression, B2/B1, equals the gas compression across the wave, p2/p1, and the jump equations become the magnetohydrodynamic shock jump relations. Furthermore, intermediate speed shocks induce magnetic field compressions between 1 and p2/p1. An experiment was performed in an inverse pinch where E behind the shock, the shock and piston velocities, and the magnetic field compression across the shock, were measured over a wide range of initial conditions and shock velocities in hydrogen. The jump relations were written with B2/B1 as a parameter and programmed into a digital computer. The program was written for real, equilibrium hydrogen. The program provided easy access to a unique solution of the jump equations for any B2/B1. The experiment tends to confirm the Kulikovskii—Lyubimov—Chu theory. Ordinary shock waves were observed at low speeds and near-MilD shocks were observed at high speeds. Further, the relation was verified for the plasma behind the shock for low-speed shock waves, and was verified to within experimental accuracy for the intermediate class of shock waves.

Bistatic-radar measurements of propagating interplanetary shock waves

Detection and measurement techniques for collisionless MHD shock wave propagation in interplanetary space, using bistatic-radar Earth- to-spacecraft transmissions

Magnetohydrodynamic shock waves

Starting from the fundamental equations of magnetohydrodynamics we derive the conservation laws for the case of an ideal plasma. Based on these laws the fundamental equations — that govern the behaviour of magnetohydrodynamic (mhd) shock waves along an arbitrary continuous surface of discontinuity — are obtained. It is shown that the mhd shock waves — similar to those of gas dynamics — are compression waves. Finally the properties of different kinds of mhd shock waves are discussed.