A series of experiments has been conducted in order to investigate the azimuthal structures formed by the interactions of cylindrically converging plasma flows during the ablation phase of aluminium wire array Z pinch implosions. These experiments were carried out using the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. The main diagnostic used in this study was a two-colour, end-on, Mach-Zehnder imaging interferometer, sensitive to the axially integrated electron density of the plasma. The data collected in these experiments reveal the strongly collisional dynamics of the aluminium ablation streams. The structure of the flows is dominated by a dense network of oblique shock fronts, formed by supersonic collisions between adjacent ablation streams. An estimate for the range of the flow Mach number (M ¼ 6.2-9.2) has been made based on an analysis of the observed shock geometry. Combining this measurement with previously published Thomson Scattering measurements of the plasma flow velocity by Harvey-Thompson et al. [Physics of Plasmas 19, 056303 (2012)] allowed us to place limits on the range of the ZT e of the plasma. The detailed and quantitative nature of the dataset lends itself well as a source for model validation and code verification exercises, as the exact shock geometry is sensitive to many of the plasma parameters. Comparison of electron density data produced through numerical modelling with the Gorgon 3D MHD code demonstrates that the code is able to reproduce the collisional dynamics observed in aluminium arrays reasonably well. V C 2013 American Institute of Physics. [http://dx
Collimated outflows (jets) are ubiquitous in the universe appearing around sources as diverse as protostars and extragalactic supermassive blackholes. Jets are thought to be magnetically collimated, and launched from a magnetized accretion disk surrounding a compact gravitating object. We have developed the first laboratory experiments to address time-dependent, episodic phenomena relevant to the poorly understood jet acceleration and collimation region. The experimental results show the periodic ejections of magnetic bubbles naturally evolving into a heterogeneous jet propagating inside a channel made of self-collimated magnetic cavities. The results provide a unique view of the possible transition from a relatively steady-state jet launching to the observed highly structured outflows.
Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during DD fusion and can undergo secondary DT reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall DT to DD neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions are also shown to provide an upper bound for volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., to appear in PRL] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs. PACS numbers:Introduction.-Magneto-inertial fusion (MIF) offers some key advantages over traditional inertial confinement fusion (ICF). In MIF, fuel magnetization relaxes the extreme pressure requirements characteristic of traditional ICF and enhances thermal insulation of the hot fuel from the colder pusher [1-10]. We consider paradigmatically the radial compression of a long, thin cylinder of fuel magnetized with a uniform, axial field prior to compression [11][12][13][14][15][16][17]. At stagnation, the compressed magnetic flux redirects charged burn products axially, increasing the effective fuel areal density from ρR to ρZ, where ρ is the fuel mass density, R is the fuel radius, Z is the fuel length, and A ≡ Z/R ≫ 1 is the aspect ratio.Sandia National Laboratories has fielded the first integrated experiments investigating Magnetized Liner I nertial F usion (MagLIF) [14][15][16][17], which involves direct compression of magnetized, preheated deuterium fuel by a solid metal (beryllium) liner, imploded on the 26 MA, 100 ns Z Pulsed Power Facility [18]. The imploding cylindrical liner compresses a pre-seeded axial magnetic field, B 0 (≈ 10 T in the first experiments), to high amplitude at stagnation, B, where perfect flux conservation would imply B = B 0 (R 0 /R) 2 , and R 0 = 2.325 mm is the initial fuel radius. However, detailed simulations suggest that multiple effects (e.g., resistive losses, Nerst effect) can lead to leakage of magnetic flux out of the hot fuel [14,17]. Thus, diagnosing the efficacy of flux compression in experiments is critical for understanding target performance and the viability of the concept.
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