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In this community white paper, we describe an approach to achieving fusion which employs a hybrid of elements from the traditional magnetic and inertial fusion concepts, called magneto-inertial fusion (MIF). The status of MIF research in North America at multiple institutions is summarized including recent progress, research opportunities, and future plans.

A method is described for choosing experimental parameters in studies of high-energy-density (HED) physics relevant to fusion energy, as well as other applications. An important HED issue for magneto-inertial fusion (MIF) is the interaction of metal pusher materials with megagauss (MG) magnetic fields during liner compression of magnetic flux and fusion fuel. The experimental approach described here is to study a stationary conductor when a pulsed current generates MG fields at the surface, instead of studying the inner surface of a moving liner. This places less demand upon the pulsed power system, and significantly improves diagnostic access. Thus the deceptively simple geometry chosen for this work is that of a z pinch composed of a metal cylinder carrying large current. Consideration of well known stability issues for the z pinch shows that for given peak current and rise time from a particular power supply, there is a minimum radius and thus maximum B field that can be created without disruption of the conductor before peak current. The reasons are reviewed why MG levels of magnetic field, as required for MIF, result in high temperatures and plasma formation at the surface of the metal in response to Ohmic heating. The distinction is noted between the liner regime obtained with cylindrical rods, which have a skin depth small compared to the conductor radius, and the exploding thin-wire regime, which has skin depth larger than the wire radius. A means of diagnostic development is described using a small facility (DPM15) built at the University of Nevada, Reno. It is argued that surface plasma temperature measurements in the 10-eV range are feasible based on the intensity of visible light emission.

Simple transport-based scaling laws are derived to show that a density and time regime intermediate between conventional magnetic confinement and conventional inertial confinement offers attractive reductions in system size and energy when compared to magnetic confinement, and attractive reductions in heating power and intensity when compared to inertial confinement. This intermediate parameter space appears to be readily accessible by existing and near-term pulsed power technologies. Hence, the technology of the Megagauss conferences opens up an attractive path to controlled thermonuclear fusion.

Magnetized Target Fusion (MTF) target plasmas are being characterized at the Los Alamos National Laboratory Colt facility. The goal of this project is to demonstrate plasma conditions meeting the requirements for an MTF initial target plasma. In the experiments discussed, a z-directed current is driven through a polyethylene fiber that explodes, producing a plasma which is subsequently contained in a 2 cm radius by 2 cm high cylindrical metal wall. Technical limitations prevented the use of a cryogenically frozen deuterium fiber, as originally planned. Therefore, a polyethylene fiber was used to study plasma dynamics and to look for evidence that an exploding-fiber plasma would eventually become quiescent as the plasma expands and contacts the containing metal wall; i.e., becomes wall-confined and wall-stabilized.

At Los Alamos, we investigate solid density materials under extreme conditions of high pressure or strain. To further these studies, we develop pulsed power techniques for driving high energy imploding liners. We have developed the Ranchero explosive-driven magnetic flux compression generator (FCG) system to perform such experiments at very high energy, in remote locations. Our first charter is to support the development of the Atlas capacitor bank [1] which, when completed in 2001, will deliver up to 30 MA to hydrodynamic liners. The basic unit of the Ranchero system is a 1.4 m long coaxial FCG that is simultaneously initiated along its axis and has an armature expansion ratio of 2:1. We performed initial system tests using 43 cm long [2,3] coaxial modules and are finalizing the design and development of our 1.4 m detonation system. This development, which met with unexpected difficulties, is the subject of another paper in this conference [4]. The 43cm module combined with the 2.4 MJ capacitor bank at our high explosive pulsed power facility has the capability of delivering ~40 MA to a load of ~5 nH. Coupled with a fuse opening switch (FOS), the system will generate a good approximation of Atlas waveforms with 5 nH in the load and transmission lines. This allows us to begin preliminary Atlas related tests before the 1.4 m module is completed. Herein is described our efforts to develop the capability and the design of our first imploding liner experiment.

Ranchero is an explosively driven magnetic flux-compression generator that has been developed over the last four years as a versatile power source for high energy density physics experiments. It is coaxial and comprises a 15 cm diameter armature and a 30 cm diameter stator, each made of aluminum. The length may be varied to suit the demands of each experiment. Thus far, lengths of 0.43 m and 1.4 m have been used. The armature is filled and driven by a high-performance cast explosive, and the ultimate performance of the device is limited by the smoothness of the armature expansion. The armature explosive is initiated on axis by PETN hemispheres spaced at intervals of between 18 mm and 24.5 mm. Each is simultaneously detonated by a slapper detonator system. Armature expansion calculations predicted ripples less than 0.2 mm, which was confirmed in early experiments. Yet, ripples approaching tens of millimeters were observed in some more recent experiments. We will discuss the possible origins of these large ripples and the methods we have used to correct them.

This report discusses the analysis of a powerful disk electromagnetic generator on a condensed liner.

Experimental data which considerably complements earlier results [1] is given for the initial perturbation growth of liners made of high-purity soft aluminum (A995, 99.995% Al) and high-strength aluminum alloys with major magnesium (AMg6) or zinc (B95) additives. Preliminary data analysis and comparison with VNIIEF and LANL numerical simulation allows us to revise parameter estimations of dynamic strength and conductivity of the materials used for designing magnetically driven liners.

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane‐spanning lipids synthesized by bacteria in numerous substrates. The degree of methylation of the five methyl brGDGTs in both soils and lake sediments, described by the MBT′5Me index, is empirically related to surface atmospheric temperature. This relationship in lakes is generally assumed to reflect lake surface temperatures captured by brGDGT production in the water column and exported to lake sediments, and the MBT′5Me index has been applied to brGDGTs in lake sediment successions to reconstruct changes in temperature through time. We analyzed the relationship between MBT′5Me and the isomerization of brGDGTs (IR6Me) in globally distributed surficial lake sediments and demonstrated that the relationship, and calibrations, of MBT′5Me and temperature in middle and high latitude lakes are sensitive to incompletely understood factors related to IR6Me. IR6Me does not appear to track a non‐thermal influence of brGDGT methylation in tropical lakes, but this could change as the data set is expanded. We address ongoing challenges in the application of the MBT′5Me paleothermometer in middle and high latitude lakes with new MBT′5Me‐temperature calibrations based on grouping lakes by IR6Me. We demonstrate how IR6Me can distinguish samples with a significant non‐thermal influence on MBT′5Me by targeting anomalously warm temperatures during the Last Glacial Maximum from newly analyzed piston and gravity core samples from Lake Baikal, Russia. Plain Language Summary Branched glycerol dialkyl glycerol tetraethers are fats used by bacteria to build their cell walls. Bacteria build their cell walls with different kinds of brGDGTs in response to ambient temperature. BrGDGTs are often preserved in lake sediments, making them a useful tool for reconstructing past climate. While working on samples from Lake Baikal, Russia, we noticed unexpectedly warm temperatures during the last ice age estimated from brGDGTs. These warm temperatures coincided with unusually high relative amounts of 6‐methyl brGDGTs. This observation spurred the analysis of a large data set of published globally distributed lake brGDGT data. We found that samples from middle and high latitude lakes with relatively more 6‐methyl brGDGTs tended to have higher than expected brGDGT‐estimated temperatures. We use our findings to refine the equations that relate brGDGT distributions to surface air temperature in middle and high latitude lake sediments. Key Points A non‐thermal effect on brGDGT paleotemperature estimates in lakes is identified by the isomer ratio IR6Me The calibration of MBT′5Me to temperature in middle and high latitude lakes is strengthened if samples with IR6Me > 0.4 are excluded IR6Me does not appear to identify non‐thermal effects on tropical lake samples, but this could change as the data set is expanded