Publications
349 results found
Crilly AJ, Schlossberg DJ, Appelbe BD, et al., 2024, Measurements of dense fuel hydrodynamics in the NIF burning plasma experiments using backscattered neutron spectroscopy, Physics of Plasmas, Vol: 31, ISSN: 1070-664X
The hydrodynamics of the dense confining fuel shell is of great importance in defining the behavior of the burning plasma and burn propagation regimes of inertial confinement fusion experiments. However, it is difficult to probe due to its low emissivity in comparison with the central fusion core. In this work, we utilize the backscattered neutron spectroscopy technique to directly measure the hydrodynamic conditions of the dense fuel during fusion burn. Experimental data are fit to obtain dense fuel velocities and apparent ion temperatures. Trends of these inferred parameters with yield and velocity of the burning plasma are used to investigate their dependence on alpha heating and low mode drive asymmetry. It is shown that the dense fuel layer has an increased outward radial velocity as yield increases, showing that burn has continued into re-expansion, a key signature of hotspot ignition. A comparison with analytic and simulation models shows that the observed dense fuel parameters are displaying signatures of burn propagation into the dense fuel layer, including a rapid increase in dense fuel apparent ion temperature with neutron yield.
Abu-Shawareb H, Acree R, Adams P, et al., 2024, Achievement of target gain larger than unity in an inertial fusion experiment, Physical Review Letters, Vol: 132, Pages: 1-16, ISSN: 0031-9007
On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.
Merlini S, Hare JD, Burdiak GC, et al., 2023, Radiative cooling effects on reverse shocks formed by magnetized supersonic plasma flows, Physics of Plasmas, Vol: 30, ISSN: 1070-664X
We study the structure of reverse shocks formed by the collision of supersonic, magnetized plasma flows driven by an inverse (or exploding) wire array with a planar conducting obstacle. We observe that the structure of these reverse shocks varies dramatically with wire material, despite the similar upstream flow velocities and mass densities. For aluminum wire arrays, the shock is sharp and well-defined, consistent with magneto-hydrodynamic theory. In contrast, we do not observe a well-defined shock using tungsten wires, and instead we see a broad region dominated by density fluctuations on a wide range of spatial scales. We diagnose these two very different interactions using interferometry, Thomson scattering, shadowgraphy, and a newly developed imaging refractometer that is sensitive to small deflections of the probing laser corresponding to small-scale density perturbations. We conclude that the differences in shock structure are most likely due to radiative cooling instabilities, which create small-scale density perturbations elongated along magnetic field lines in the tungsten plasma. These instabilities grow more slowly and are smoothed by thermal conduction in the aluminum plasma.
Mannion OM, Taitano WT, Appelbe BD, et al., 2023, Evidence of non-Maxwellian ion velocity distributions in spherical shock-driven implosions., Phys Rev E, Vol: 108
The ion velocity distribution functions of thermonuclear plasmas generated by spherical laser direct drive implosions are studied using deuterium-tritium (DT) and deuterium-deuterium (DD) fusion neutron energy spectrum measurements. A hydrodynamic Maxwellian plasma model accurately describes measurements made from lower temperature (<10 keV), hydrodynamiclike plasmas, but is insufficient to describe measurements made from higher temperature more kineticlike plasmas. The high temperature measurements are more consistent with Vlasov-Fokker-Planck (VFP) simulation results which predict the presence of a bimodal plasma ion velocity distribution near peak neutron production. These measurements provide direct experimental evidence of non-Maxwellian ion velocity distributions in spherical shock driven implosions and provide useful data for benchmarking kinetic VFP simulations.
Datta R, Angel J, Greenly JB, et al., 2023, Plasma flows during the ablation stage of an over-massed pulsed-power-driven exploding planar wire array, PHYSICS OF PLASMAS, Vol: 30, ISSN: 1070-664X
Russell DR, Burdiak GC, Carroll-Nellenback JJ, et al., 2023, Observation of subcritical shocks in a collisional laboratory plasma: scale dependence near the resistive length, Journal of Plasma Physics, Vol: 89, ISSN: 0022-3778
We present a study of subcritical shocks in a highly collisional laboratory plasma with a dynamically significant magnetic field. Shocks were produced by placing cylindrical obstacles into the supermagnetosonic ( MMS∼1.9 ) outflow from an inverse wire array z-pinch at the MAGPIE pulsed power facility ( ne∼8.5×1017cm−3 , v∼45kms−1 ). We demonstrate the existence of subcritical shocks in this regime and find that secondary stagnation shocks form in the downstream which we infer from interferometry and optical Thomson scattering measurements are hydrodynamic in nature. The subcritical shock width is found to be approximately equal to the resistive diffusion length and we demonstrate the absence of a jump in hydrodynamic parameters. Temperature measurements by collective optical Thomson scattering showed little temperature change across the subcritical shock ( <10% of the ion kinetic energy) which is consistent with a balance between adiabatic and Ohmic heating and radiative cooling. We demonstrate the absence of subcritical shocks when the obstacle diameter is less than the resistive diffusion length due to decoupling of the magnetic field from the plasma. These findings are supported by magnetohydrodynamic simulations using the Gorgon and AstroBEAR codes and discrepancies between the simulations and experiment are discussed.
Sio H, Moody JD, Pollock BB, et al., 2023, Performance scaling with an applied magnetic field in indirect-drive inertial confinement fusion implosions, PHYSICS OF PLASMAS, Vol: 30, ISSN: 1070-664X
Crilly AJ, Niasse NPL, Fraser AR, et al., 2023, SpK: A fast atomic and microphysics code for the high-energy-density regime, High Energy Density Physics, Vol: 48, Pages: 1-12, ISSN: 1574-1818
SpK is part of the numerical codebase at Imperial College London used to model high energy density physics (HEDP) experiments. SpK is an efficient atomic and microphysics code used to perform detailed configuration accounting calculations of electronic and ionic stage populations, opacities and emissivities for use in post-processing and radiation hydrodynamics simulations. This is done using screened hydrogenic atomic data supplemented by the NIST energy level database. An extended Saha model solves for chemical equilibrium with extensions for non-ideal physics, such as ionisation potential depression, and non thermal equilibrium corrections. A tree-heap (treap) data structure is used to store spectral data, such as opacity, which is dynamic thus allowing easy insertion of points around spectral lines without a-priori knowledge of the ion stage populations. Results from SpK are compared to other codes and descriptions of radiation transport solutions which use SpK data are given. The treap data structure and SpK’s computational efficiency allows inline post-processing of 3D hydrodynamics simulations with a dynamically evolving spectrum stored in a treap.
Valenzuela-Villaseca V, Suttle LG, Suzuki-Vidal F, et al., 2023, Characterization of quasi-Keplerian, differentially rotating, free-boundary laboratory plasmas, Physical Review Letters, Vol: 130, ISSN: 0031-9007
We present results from pulsed-power driven differentially rotating plasma experiments designed tosimulate physics relevant to astrophysical disks and jets. In these experiments, angular momentum is injectedby the ram pressure of the ablation flows from a wire array Z pinch. In contrast to previous liquid metal andplasma experiments, rotation is not driven by boundary forces. Axial pressure gradients launch a rotatingplasma jet upward, which is confined by a combination of ram, thermal, and magnetic pressure of asurrounding plasma halo. The jet has subsonic rotation, with a maximum rotation velocity 23 3 km=s. Therotational velocity profile is quasi-Keplerian with a positive Rayleigh discriminant κ2 ∝ r−2.8 0.8 rad2=s2.The plasma completes 0.5–2 full rotations in the experimental time frame (∼150 ns).
Strucka J, Lukic B, Koerner M, et al., 2023, Synchrotron radiography of Richtmyer–Meshkov instability driven by exploding wire arrays, Physics of Fluids, Vol: 35, Pages: 1-11, ISSN: 1070-6631
We present a new technique for the investigation of shock-driven hydrodynamic phenomena in gases, liquids, and solids in arbitrary geometries. The technique consists of a pulsed power-driven resistive wire array explosion in combination with multi-MHz synchrotron radiography. Compared to commonly used techniques, it offers multiple advantages: (1) the shockwave geometry can be shaped to the requirements of the experiment, (2) the pressure (P > 300 MPa) generated by the exploding wires enables the use of liquid and solid hydrodynamic targets with well-characterized initial conditions (ICs), (3) the multi-MHz radiography enables data acquisition to occur within a single experiment, eliminating uncertainties regarding repeatability of the ICs and subsequent dynamics, and (4) the radiographic measurements enable estimation of compression ratios from the x-ray attenuation. In addition, the use of a synchrotron x-ray source allows the hydrodynamic samples to be volumetrically characterized at a high spatial resolution with synchrotron-based microtomography. This experimental technique is demonstrated by performing a planar Richtmyer–Meshkov instability (RMI) experiment on an aerogel–water interface characterized by Atwood number A 0 ∼ − 0.8 and Mach number M ∼ 1.5. The qualitative and quantitative features of the experiment are discussed, including the energy deposition into the exploding wires, shockwave generation, compression of the interface, startup phase of the instability, and asymptotic growth consistent with Richtmyer's impulsive theory. Additional effects unique to liquids and solids—such as cavitation bubbles caused by rarefaction flows or initial jetting due to small perturbations—are observed. It is also demonstrated that the technique is not shape dependent by driving a cylindrically convergent RMI experiment.
Mundy T, Bland S, Lebedev S, et al., 2023, Novel Experiment for Scaled Power Flow Studies Towards Next-Generation Pulsed Power, ISSN: 2158-4915
In order to develop a better understanding of current losses in the magnetically insulated region of high-power pulsed power machines, it is crucial to be able to conduct experiments at scale in smaller facilities. Here, we present a novel experiment that has been tested on the MAGPIE driver at Imperial College. The targets are inexpensive and easy to customize for experiments ranging from power flow to warm dense matter. Simulations in COMSOL indicated electric fields of up to 600 MV/m and magnetic fields of up to 300 T could be produced on MAGPIE. In initial testing, Electric fields exceeding 100 MV/m and magnetic fields exceeding 50 T were generated, and both magnetically insulated transmission and plasma-shorted transmission were demonstrated.
Crilly AJ, Appelbe BD, Mannion OM, et al., 2022, Constraints on ion velocity distributions from fusion product spectroscopy, NUCLEAR FUSION, Vol: 62, ISSN: 0029-5515
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- Citations: 4
Datta R, Russell DR, Tang I, et al., 2022, The structure of 3-D collisional magnetized bow shocks in pulsed-power-driven plasma flows, Journal of Plasma Physics, Vol: 88, ISSN: 0022-3778
We investigate three-dimensional (3-D) bow shocks in a highly collisional magnetized aluminium plasma, generated during the ablation phase of an exploding wire array on the MAGPIE facility (1.4 MA, 240 ns). Ablation of plasma from the wire array generates radially diverging, supersonic ( MS∼7 ), super-Alfvénic ( MA>1 ) magnetized flows with frozen-in magnetic flux ( RM≫1 ). These flows collide with an inductive probe placed in the flow, which serves both as the obstacle that generates the magnetized bow shock, and as a diagnostic of the advected magnetic field. Laser interferometry along two orthogonal lines of sight is used to measure the line-integrated electron density. A detached bow shock forms ahead of the probe, with a larger opening angle in the plane parallel to the magnetic field than in the plane normal to it. Since the resistive diffusion length of the plasma is comparable to the probe size, the magnetic field decouples from the ion fluid at the shock front and generates a hydrodynamic shock, whose structure is determined by the sonic Mach number, rather than the magnetosonic Mach number of the flow. The 3-D simulations performed using the resistive magnetohydrodynamic (MHD) code Gorgon confirm this picture, but under-predict the anisotropy observed in the shape of the experimental bow shock, suggesting that non-MHD mechanisms may be important for modifying the shock structure.
Russell D, Burdiak G, Carroll-Nellenback JJ, et al., 2022, Perpendicular subcritical shock structure in a collisional plasma experiment, Physical Review Letters, Vol: 129, ISSN: 0031-9007
We present a study of perpendicular subcritical shocks in a collisional laboratory plasma. Shocks areproduced by placing obstacles into the supermagnetosonic outflow from an inverse wire array z pinch. Wedemonstrate the existence of subcritical shocks in this regime and find that secondary shocks form in thedownstream. Detailed measurements of the subcritical shock structure confirm the absence of ahydrodynamic jump. We calculate the classical (Spitzer) resistive diffusion length and show that it isapproximately equal to the shock width. We measure little heating across the shock (< 10% of the ionkinetic energy) which is consistent with an absence of viscous dissipation.
Moody JD, Pollock BB, Sio H, et al., 2022, Increased ion temperature and neutron yield observed in magnetized indirectly driven D_{2}-filled capsule implosions on the national ignition facility, Physical Review Letters, Vol: 129, ISSN: 0031-9007
The application of an external 26 Tesla axial magnetic field to a D_{2} gas-filled capsule indirectly driven on the National Ignition Facility is observed to increase the ion temperature by 40% and the neutron yield by a factor of 3.2 in a hot spot with areal density and temperature approaching what is required for fusion ignition [1]. The improvements are determined from energy spectral measurements of the 2.45 MeV neutrons from the D(d,n)^{3}He reaction, and the compressed central core B field is estimated to be ∼4.9 kT using the 14.1 MeV secondary neutrons from the D(T,n)^{4}He reactions. The experiments use a 30 kV pulsed-power system to deliver a ∼3 μs current pulse to a solenoidal coil wrapped around a novel high-electrical-resistivity AuTa_{4} hohlraum. Radiation magnetohydrodynamic simulations are consistent with the experiment.
Datta R, Russell DR, Tang I, et al., 2022, Time-resolved velocity and ion sound speed measurements from simultaneous bow shock imaging and inductive probe measurements, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 93, ISSN: 0034-6748
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- Citations: 3
Crilly A, Garin-Fernandez I, Appelbe B, et al., 2022, Efficacy of ICF experiments in light ion fusion cross section measurement at nucleosynthesis relevant energies, Frontiers in Physics, Vol: 10, Pages: 1-11, ISSN: 2296-424X
Inertial confinement fusion (ICF) experiments create a unique laboratory environment in which thermonuclear fusion reactionsoccur within a plasma, with conditions comparable to stellar cores and the early universe. In contrast, accelerator-basedmeasurements must compete with bound electron screening effects and beam stopping when measuring fusion cross sections atnucleosynthesis-relevant energies. Therefore, ICF experiments are a natural place to study nuclear reactions relevant to nuclearastrophysics. However, analysis of ICF-based measurements must address its own set of complicating factors. These include: theinherent range of reaction energies, spatial and temporal thermal temperature variation, and kinetic effects such as speciesseparation. In this work we examine these phenomena and develop an analysis to quantify and, when possible, compensate fortheir effects on our inference. Error propagation in the analyses are studied using synthetic data combined with Markov ChainMonte Carlo (MCMC) machine learning. The novel inference techniques will aid in the extraction of valuable and accurate data fromICF-based nuclear astrophysics experiments.
Eggington J, Coxon J, Shore R, et al., 2022, Response timescales of the magnetotail current sheet during a geomagnetic storm: global MHD simulations, Frontiers in Astronomy and Space Sciences, Vol: 9, Pages: 1-17, ISSN: 2296-987X
The response of the Earth’s magnetotail current sheet to the external solar wind driver is highly time-dependent and asymmetric. For example, the current sheet twists in response to variations in the By component of the interplanetary magnetic field (IMF), and is hinged by the dipole tilt. Understanding the timescales over which these asymmetries manifest is of particular importance during geomagnetic storms when the dynamics of the tail control substorm activity. To investigate this, we use the Gorgon MHD model to simulate a geomagnetic storm which commenced on 3 May 2014, and was host to multiple By and Bz reversals and a prolonged period of southward IMF driving. We find that the twisting of the current sheet is well-correlated to IMF By throughout the event, with the angle of rotation increasing linearly with downtail distance and being morepronounced when the tail contains less open flux. During periods of southward IMF the twisting of the central current sheet responds most strongly at a timelag of ∼ 100 min for distances beyond 20 RE, consistent with the 1-2 hr convection timescale identified in the open flux content. Under predominantly northward IMF the response of the twisting is bimodal, with the strongest correlations between 15-40 RE downtail being at a shorter timescale of ∼ 30 min consistent with that estimated for induced By due to wave propagation, compared to a longer timescale of ∼ 3 hr further downtail again attributed to convection. This indicates that asymmetries in the magnetotail communicated by IMF By are influenced mostly by global convection during strong solar wind driving, but that more prompt induced By effects can dominate in the near-Earth tail and during periods of weaker driving. These results provide new insight into the characteristic timescales of solar wind-magnetosphere-ionosphere coupling.
Abu-Shawareb H, Acree R, Adams P, et al., 2022, Lawson criterion for ignition exceeded in an inertial fusion experiment, Physical Review Letters, Vol: 129, ISSN: 0031-9007
For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.
Moody JD, Pollock BB, Sio H, et al., 2022, The Magnetized Indirect Drive Project on the National Ignition Facility, JOURNAL OF FUSION ENERGY, Vol: 41, ISSN: 0164-0313
Crilly AJ, Appelbe BD, Mannion OM, et al., 2022, Neutron backscatter edges as a diagnostic of burn propagation, PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X
Mannion OM, Crilly AJ, Forrest CJ, et al., 2022, Measurements of the temperature and velocity of the dense fuel layer in inertial confinement fusion experiments, PHYSICAL REVIEW E, Vol: 105, ISSN: 2470-0045
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- Citations: 5
Bose A, Peebles J, Walsh CA, et al., 2022, Effect of strongly magnetized electrons and Ions on heat flow and symmetry of inertial fusion implosions, Physical Review Letters, Vol: 128, ISSN: 0031-9007
This Letter presents the first observation on how a strong, 500 kG, externally applied B field increases the mode-two asymmetry in shock-heated inertial fusion implosions. Using a direct-drive implosion with polar illumination and imposed field, we observed that magnetization produces a significant increase in the implosion oblateness (a 2.5× larger P2 amplitude in x-ray self-emission images) compared with reference experiments with identical drive but with no field applied. The implosions produce strongly magnetized electrons (ωeτe≫1) and ions (ωiτi>1) that, as shown using simulations, restrict the cross field heat flow necessary for lateral distribution of the laser and shock heating from the implosion pole to the waist, causing the enhanced mode-two shape.
Halliday JWD, Crilly A, Chittenden J, et al., 2022, Investigating radiatively driven, magnetized plasmas with a university scale pulsed-power generator, Physics of Plasmas, Vol: 29, Pages: 1-13, ISSN: 1070-664X
We present first results from a novel experimental platform which is able toaccess physics relevant to topics including indirect-drive magnetised ICF;laser energy deposition; various topics in atomic physics; and laboratoryastrophysics (for example the penetration of B-fields into HED plasmas). Thisplatform uses the X-Rays from a wire array Z-Pinch to irradiate a silicontarget, producing an outflow of ablated plasma. The ablated plasma expands intoambient, dynamically significant B-fields (~5 T) which are supported by thecurrent flowing through the Z-Pinch. The outflows have a well-defined(quasi-1D) morphology, enabling the study of fundamental processes typicallyonly available in more complex, integrated schemes. Experiments were fielded onthe MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time). On this machine awire array Z-Pinch produces an X-Ray pulse carrying a total energy of ~15 kJover ~30 ns. This equates to an average brightness temperature of around 10 eVon-target.
Eggington J, Desai R, Mejnertsen L, et al., 2022, Time-varying magnetopause reconnection during sudden commencement: global MHD simulations, Journal of Geophysical Research: Space Physics, Vol: 127, ISSN: 2169-9380
In response to a solar wind dynamic pressure enhancement, the compression of the magnetosphere generates strong ionospheric signatures and a sharp variation in the ground magnetic field, termed sudden commencement (SC). Whilst such compressions have also been associated with a contraction of the ionospheric polar cap due to the triggering of reconnection in the magnetotail, the effect of any changes in dayside reconnection is less clear and is a key component in fully understanding the system response. In this study we explore the time-dependent nature of dayside coupling during SC by performing global simulations using the Gorgon MHD code, and impact the magnetosphere with a series of interplanetary shocks with different parameters. We identify the location and evolu tion of the reconnection region in each case as the shock propagates through the magnetosphere, finding strong enhancement in the dayside reconnection rate and prompt expansion of the dayside polar cap prior to the eventual triggering of tail reconnection. This effect pervades for a variety of IMF orientations, and the reconnection rate is most enhanced for events with higher dynamic pressure. We explain this by repeating the simulations with a large explicit resistivity, showing that compression of the magnetosheath plasma near the propagating shock front allows for reconnection of much greater intensity and at different locations on the dayside magnetopause than during typical solar wind conditions. The results indicate that the dynamic behaviour of dayside coupling may render steady models of reconnection inaccurate during the onset of a severe space weather event.
Walsh CA, O'Neill S, Chittenden JP, et al., 2022, Magnetized ICF implosions: Scaling of temperature and yield enhancement, PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X
Farrow G, Chittenden JP, Kagan G, 2022, Self-similar solutions for resistive diffusion, Ohmic heating, and Ettingshausen effects in plasmas of arbitrary beta, Physics of Plasmas, Vol: 29, ISSN: 1070-664X
ABSTRACTMagneto-inertial fusion (MIF) approaches, such as the MagLIF experiment, use magnetic fields in dense plasma to suppress cross-field thermal conduction, attempting to reduce heat loss and trap alpha particles to achieve ignition. However, the magnetic field can introduce other transport effects, some of which are deleterious. An understanding of these processes is thus crucial for accurate modeling of MIF. We generalize past work exploiting self-similar solutions to describe transport processes in planar geometry and compare the model to the radiation-magnetohydrodynamics (MHDs) code Chimera. We solve the 1D extended MHD equations under pressure balance, making no assumptions about the ratio of magnetic and thermal pressures in the plasma. The resulting ordinary differential equation (ODE) boundary value problem is solved using a shooting method, combining an implicit ODE solver and a Newton–Raphson root finder. We show that the Nernst effect dominates over resistive diffusion in high β plasma, but its significance is reduced as the β decreases. On the other hand, we find that Ettingshausen and Ohmic heating effects are dominant in low β plasma and can be observable in even order unity β plasma, though in the presence of a strong temperature gradient heat conduction remains dominant. We then present a test problem for the Ohmic heating and Ettingshausen effects which will be useful to validate codes modeling these effects. We also observe that the Ettingshausen effect plays a role in preventing temperature separation when Ohmic heating is strong. Neglecting this term may lead to overestimates for the electron temperature at a vacuum–plasma interface, such as at the edge of a z-pinch. The model developed can be used to provide test problems with arbitrary boundary conditions for magnetohydrodynamics codes with the ability to freely switch on terms to compare their individual implementations.
Walsh CA, Florido R, Bailly-Grandvaux M, et al., 2022, Exploring extreme magnetization phenomena in directly driven imploding cylindrical targets, Plasma Physics and Controlled Fusion, Vol: 64, Pages: 1-19, ISSN: 0741-3335
This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realizable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10 kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally driven or current-driven transport is dominating.
Strucka J, Yanuka D, Theocharous S, et al., 2022, Direct Observation of Multimode Richtmyer-Meshkov Instability Seeded by Electrothermal Instability in Dielectrically Tamped Exploding Wires, ISSN: 0730-9244
We report on results from an experiment conducted at the European Synchrotron Radiation Facility Microtomography Beamline investigating the use of conductors submerged underwater and vaporised by high current densities ∼1012 A/m2 to seed plasma instabilities.
Bland SN, Theocharous S, Chittenden J, et al., 2022, Target Compression from Shock Waves Driven in Insulators by Wire Explosion, ISSN: 0730-9244
We explore the production of highly uniform, initially planar shockwaves in water and other insulators by the pulsed power driven explosion of wire arrays. The shockwaves are then either directly interacted with small, low density spherical targets or focused via shaped reflectors onto these targets to increase the drive pressures.
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