Effects Of Plasma Beta Research Articles

Plasma beta effects on the edge magnetic field structure and divertor heat loads in Wendelstein 7-X high-performance scenarios

To support the scenario design for the upcoming long-pulse high-performance campaign of Wendelstein 7-X, this work presents a study of high-beta full-field 3D equilibria obtained with the HINT code. For three magnetic configurations of different edge-ι, the effects of both overall pressure and pressure profile changes on the magnetic topology are analyzed. Anisotropic diffusion modeling is used to obtain estimates of the conductive heat load distribution both on the divertor and other plasma-facing components in finite-beta magnetic configurations. For the magnetic standard configuration, limitations of the model are outlined by comparing measured and predicted heatloads by performing a linear regression of the main strike-line position against various plasma parameters in both the experimental and the simulated device.

Higher‐order inertial Alfvén wave dressed solitons, quasiperiodic structures, and chaos in plasmas

AbstractThe higher‐order, low‐amplitude inertial Alfvén wave (IAW) dressed soliton and chaos are investigated in a magnetized plasma. In the linear limit, the dispersion relation for propagation of IAWs in plasmas is also obtained in the presence of electron thermal effects and illustrated numerically. It is found that the electron inertial length plays an important role for wave dispersion effects and its phase speed is increased on including the electron temperature in the model. The reductive perturbation method is employed to obtain the first‐order IAW Korteweg–de Vries (KdV) soliton and second‐order dressed soliton solutions analytically, which gives electron density dip (or rarefactive) structure and moves with super Alfvénic speed in plasmas. The numerical illustrations of the KdV and dressed IAW solitons are also presented by using the laboratory and space plasma parameters given in the literature. Furthermore, a numerical study of quasi‐periodicity and chaotic behaviour of IAWs in the presence of external periodic force is also discussed in detail. The effects of plasma beta (which depends on plasma density, electron temperature, and magnetic field intensity) and obliqueness of the wave propagation on the formation of nonlinear Alfvénic wave structures have also been presented.

Interaction of magnetoacoustic solitons in plasmas with dispersion effects through electron inertia

The head‐on collision between two magnetoacoustic solitons is investigated in a magnetized plasma containing inertial cold ions and warm electrons. A two‐fluid magnetohydrodynamic (MHD) model is used to study the magnetoacoustic solitons interaction in plasmas. The magnetoacoustic wave dispersion effects appearing through electron inertial length (skin depth) are also included in the model. By using the extended Poincaré–Lighthill–Kuo (PLK) method, the Korteweg–de Vries (KdV) equations are derived for the low amplitude left and right moving magnetoacoustic solitons, their trajectories, and corresponding phase shifts after their elastic collisions are obtained analytically and examined numerically as well. It is found that only positive polarity (compressive) soliton structures of magnetoacoustic waves are formed. The profiles of head‐on collision and the time evolution of two compressive interacting magnetoacoustic solitons are also presented for illustration. The effect of plasma beta, which depends on plasma density, electron temperature, and magnetic field intensity, on the phase shift of the interacting magnetoacoustic solitons is also examined.

Measurement of local, internal magnetic fluctuations via cross-polarization scattering in the DIII-D tokamak (invited).

We present new measurements of internal magnetic fluctuations obtained with a novel eight channel cross polarization scattering (CPS) system installed on the DIII-D tokamak. Measurements of internal, localized magnetic fluctuations provide a window on an important physics quantity that we heretofore have had little information on. Importantly, these measurements provide a new ability to challenge and test linear and nonlinear simulations and basic theory. The CPS method, based upon the scattering of an incident microwave beam into the opposite polarization by magnetic fluctuations, has been significantly extended and improved over the method as originally developed on the Tore Supra tokamak. A new scattering geometry, provided by a unique probe beam, is utilized to improve the spatial localization and wavenumber range. Remotely controllable polarizer and mirror angles allow polarization matching and wavenumber selection for a range of plasma conditions. The quasi-optical system design, its advantages and challenges, as well as important physics validation tests are presented and discussed. Effect of plasma beta (ratio of kinetic to magnetic pressure) on both density and magnetic fluctuations is studied and it is observed that internal magnetic fluctuations increase with beta. During certain quiescent high confinement operational regimes, coherent low frequency modes not detected by magnetic probes are detected locally by CPS diagnostics.

The effect of plasma beta on high-n ballooning stability at low magnetic shear

An explanation of the observed improvement in H-mode pedestal characteristics with increasing core plasma pressure or poloidal beta, , as observed in MAST and JET, is sought in terms of the impact of the Shafranov shift, , on ideal ballooning MHD stability. To illustrate this succinctly, a self-consistent treatment of the low magnetic shear region of the ‘’ stability diagram is presented using the large aspect ratio Shafranov equilibrium, but enhancing both and so that they compete with each other. The method of averaging, valid at low s, is used to simplify the calculation and demonstrates how , , plasma shaping and ‘average favourable curvature’ all contribute to stability.

Solar wind double ion beams and the heliospheric current sheet

Double ion beams are often observed in the solar wind, but little work has been done in relating these beams to structures within the solar wind. Double ion beams are observed as beams of a given ion species and charge state occurring at two different energies. We use the three‐dimensional ion plasma instrument on board the Ulysses spacecraft to look for evidence of such beams associated with the heliospheric current sheet. In a subset chosen independently of plasma parameters consisting of 8 of over 47 crossings of the current sheet made during the in‐ecliptic phase of the Ulysses mission we find that these double ion beams are always present on either side of the current sheet. The double beams are present in both the proton and helium species. The secondary beam typically has a higher helium abundance, which suggests that these beams are formed in the helium‐rich corona rather than in interplanetary space. The double beams are not present in the interior of the current sheet. Neither collisions nor effects of plasma beta can account for the disappearance of the double beams inside the current sheet in all eight cases. We postulate that these beams are formed by reconnection occurring near the Sun in the boundary region between the open field lines of the coronal holes and the closed field line region of the heliospheric current sheet. Such a scenario would be consistent with previous X ray measurements which suggest that reconnection is occurring in this region.