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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Current distribution monitoring enables quench and damage detection in superconducting fusion magnets

Abstract Fusion magnets made from high temperature superconducting ReBCO CORC ® cables are typically protected with quench detection systems that use voltage or temperature measurements to trigger current extraction processes. Although small coils with low inductances have been demonstrated, magnet protection remains a challenge and magnets are typically operated with little knowledge of the intrinsic performance parameters. We propose a protection framework based on current distribution monitoring in fusion cables with limited inter-cable current sharing. By employing inverse Biot-Savart techniques to distributed Hall probe arrays around CORC ® Cable-In-Conduit-Conductor (CICC) terminations, individual cable currents are recreated and used to extract the parameters of a predictive model. These parameters are shown to be of value for detecting conductor damage and defining safe magnet operating limits. The trained model is then used to predict cable current distributions in real-time, and departures between predictions and inverse Biot-Savart recreated current distributions are used to generate quench triggers. The methodology shows promise for quality control, operational planning and real-time quench detection in bundled CORC ® cables for compact fusion reactors.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Tritium Aspects of Fueling and Exhaust Pumping in Magnetic Fusion Energy

Magnetically confined fusion plasmas generate energy from deuterium-tritium (DT) fusion reactions that produce energetic 3.5 MeV alpha particles and 14 MeV neutrons. Since the DT fusion reaction rate is a strong function of plasma density, an efficient fueling source is needed to maintain high plasma density in such systems. Energetic ions in fusion plasmas are able to escape the confining magnetic fields at a much higher rate than the fusion reactions occur, thus dictating the fueling rate needed. These lost ions become neutralized and need to be pumped away as exhaust gas to be reinjected into the plasma as fuel atoms.The technology to fuel and pump fusion plasmas has to be inherently compatible with the tritium fuel. An ideal holistic solution would couple the pumping and fueling such that the pump exhaust is directly fed back into pellet formation without including impurity gases. This would greatly reduce the processing needs for the exhaust. Concepts to accomplish this are discussed along with the fueling and pumping needs for a DT fusion reactor.

Baylor, Larry↗
DOE OSTI2014

Ablation of high-Z material dust grains in edge plasmas of magnetic fusion devices

The model, including shielding effects of high-Z dust grain ablation in tokamak edge plasma, is presented. In a contrast to shielding models developed for pellets ablation in a hot plasma core, this model deals with the dust grain ablation in relatively cold edge plasma. Using some simplifications, a closed set of equations determining the grain ablation rate Γ is derived and analyzed both analytically and numerically. The scaling law for Γ versus grain radius and ambient plasma parameters is obtained and confirmed by the results of numerical solutions. The results obtained are compared with both dust grain models containing no shielding effects and the pellet ablation models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

LiWall Fusion - The New Concept of Magnetic Fusion

Utilization of the outstanding abilities of a liquid lithium layer in pumping hydrogen isotopes leads to a new approach to magnetic fusion, called the LiWall Fusion. It relies on innovative plasma regimes with low edge density and high temperature. The approach combines fueling the plasma by neutral injection beams with the best possible elimination of outside neutral gas sources, which cools down the plasma edge. Prevention of cooling the plasma edge suppresses the dominant, temperature gradient related turbulence in the core. Such an approach is much more suitable for controlled fusion than the present practice, relying on high heating power for compensating essentially unlimited turbulent energy losses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

REBCO coated conductor cables for fusion magnets - Final Report

The feasibility for fusion as a practical energy source needs to be enhanced significantly by removing some of the restrictions that low -- temperature superconductors (LTS) put on the fusion magnet systems. One method to simplify the magnet system is by using high -- temperature superconductors (HTS) that allow for much larger temperature margins, a higher magnet performance and much less mechanical degradation in the superconductor during operation. For use in fusion magnets, HTS need to be bundled into high -- current cables that can be operated at high magnetic fields and at high current ramp rates, while experiencing a homogenous current distribution.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Performance of low-loss demountable joints between CORC ® cable-in-conduit-conductors at magnetic fields up to 8 T developed for fusion magnets

Abstract High-temperature superconductors (HTS) are promising candidates for use in the high-field magnets needed in particle accelerators and fusion reactors. HTS conductor on round core (CORC ® ) cables and wires wound from ReBa 2 Cu 3 O 7- x (REBCO) coated tapes are being developed for use in high-field magnet applications including fusion magnets operating at currents beyond 80 kA, requiring them to be bundled into cable-in-conduit conductor (CICC) configurations. The use of HTS cables enable demountable superconducting fusion magnets that would allow easier access to the fusion machine for maintenance and parts replacement. Such demountable magnets require practical, low-resistance joints, capable of injecting current uniformly into the many REBCO tapes that make up different cable designs. Optimization steps on CORC ® cables have resulted in high-current terminations and joints with a joint resistance measured between a pair of 30-tape CORC ® cables of 51 nΩ at 76 K and 1.9 nΩ at 4 K. Demountable joints between CICCs consisting of six CORC ® cables arranged in flat and round configurations were also tested and compared to joints between low-temperature superconducting (LTS) CICCs consisting of NbTi Rutherford cables. Samples were paired into two configurations (LTS-to-LTS and HTS-to-HTS) with a demountable joint between them that were each tested in series with currents up to 10 000 A in an applied background magnetic field of up to 8 T. The total loop resistance of the HTS-to-HTS sample, including their terminations and joint, was about 4 nΩ at 4 K in self-field with the resistance of the copper pressed joint being less than 1 nΩ. At 8 T, the total loop resistance increased to 6.9 nΩ with the pressed joint contributing 1.4 nΩ. These initial tests prove the feasibility of producing remountable (dry) joints with low resistance between superconducting magnet windings in future compact fusion machines.

Physics↗
DOE OSTI2013

An in situ accelerator-based diagnostic for plasma-material interactions science on magnetic fusion devices

This paper presents a novel particle accelerator-based diagnostic that nondestructively measures the evolution of material surface compositions inside magnetic fusion devices. The diagnostic's purpose is to contribute to an integrated understanding of plasma-material interactions in magnetic fusion, which is severely hindered by a dearth of in situ material surface diagnosis. The diagnostic aims to remotely generate isotopic concentration maps on a plasma shot-to-shot timescale that cover a large fraction of the plasma-facing surface inside of a magnetic fusion device without the need for vacuum breaks or physical access to the material surfaces. Our instrument uses a compact (∼1 m), high-current (∼1 milliamp) radio-frequency quadrupole accelerator to inject 0.9 MeV deuterons into the Alcator C-Mod tokamak at MIT. We control the tokamak magnetic fields – in between plasma shots – to steer the deuterons to material surfaces where the deuterons cause high-Q nuclear reactions with low-Z isotopes ∼5 μm into the material. The induced neutrons and gamma rays are measured with scintillation detectors; energy spectra analysis provides quantitative reconstruction of surface compositions. An overview of the diagnostic technique, known as accelerator-based in situ materials surveillance (AIMS), and the first AIMS diagnostic on the Alcator C-Mod tokamak is given. Experimental validation is shown to demonstrate that an optimized deuteron beam is injected into the tokamak, that low-Z isotopes such as deuterium and boron can be quantified on the material surfaces, and that magnetic steering provides access to different measurement locations. The first AIMS analysis, which measures the relative change in deuterium at a single surface location at the end of the Alcator C-Mod FY2012 plasma campaign, is also presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Efficient high-order singular quadrature schemes in magnetic fusion

Several problems in magnetically confined fusion, such as the computation of exterior vacuum fields or the decomposition of the total magnetic field into separate contributions from the plasma and the external sources, are best formulated in terms of integral equation expressions. Based on Biot–Savart-like formulae, these integrals contain singular integrands. The regularization method commonly used to address the computation of various singular surface integrals along general toroidal surfaces is low-order accurate, and therefore requires a dense computational mesh in order to obtain sufficient accuracy. In this work, we present a fast, high-order quadrature scheme for the efficient computation of these integrals. Several numerical examples are provided demonstrating the computational efficiency and the high-order accurate convergence. A corresponding code for use in the community has been publicly released.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Applications of high-speed dust injection to magnetic fusion [Slides]

It is now an established fact that a significant amount of dust is produced in magnetic fusion devices due to plasma-wall interactions. Dust inventory must be controlled, in particular for the next-generation steady-state fusion machines like ITER, as it can pose significant safety hazards and degrade performance. Safety concerns are due to tritium retention, dust radioactivity, toxicity, and flammability. Performance concerns include high-Z impurities carried by dust to the fusion core that can reduce plasma temperature and may even induce sudden termination of the plasma. We have recognized that dust transport, dust-plasma interactions in magnetic fusion devices can be effectively studied experimentally by injection of dust with known properties into fusion plasmas. Other applications of injected dust include diagnosis of fusion plasmas and edge localized mode (ELM)'s pacing. In diagnostic applications, dust can be regarded as a source of transient neutrals before complete ionization. ELM's pacing is a promising scheme to prevent disruptions and type I ELM's that can cause catastrophic damage to fusion machines. Different implementation schemes are available depending on applications of dust injection. One of the simplest dust injection schemes is through gravitational acceleration of dust in vacuum. Experiments at Los Alamos and Princeton will be described, both of which use piezoelectric shakers to deliver dust to plasma. In Princeton experiments, spherical particles (40 micron) have been dropped in a systematic and reproducible manner using a computer-controlled piezoelectric bending actuator operating at an acoustic (0,2) resonance. The circular actuator was constructed with a 2.5 mm diameter central hole. At resonance ({approx} 2 kHz) an applied sinusoidal voltage has been used to control the flux of particles exiting the hole. A simple screw throttle located {approx}1mm above the hole has been used to set the magnitude of the flux achieved for a given voltage. Particle fluxes ranging from a few tens of particle per second up to thousands of particles per second have been achieved using this simple device. To achieve higher dust injection speed, another key consideration is how to accelerate dust at controlled amount. In addition to gravity, other possible acceleration mechanisms include electrostatic, electromagnetic, gas-dragged, plasma-dragged, and laser-ablation-based acceleration. Features and limitations of the different acceleration methods will be discussed. We will also describe laboratory experiments on dust acceleration.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Need for development of higher strength cryogenic structural materials for fusion magnet

A prototype fusion reactor is targeted as a beyond ITER project which is so called DEMO. Several conceptual designs have been carried out. Recently, in order to recognize practical aspects on maintenance of the prototype reactor, the replacement procedure of in-vessel components was focused and “sector process” was proposed. The process is that the reactor consists of sectors and all sectors will be drowned and replaced in a short time. The slim coil which generated higher magnetic field is required to realize the sector process. From the point of coil design, the occupancy of the structural material on the cross section of the coil increases with an increase of magnetic field. To realize the slim coil, the cryogenic structural material with higher yield strength and the proper toughness is desired.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Favorable Collisional Demixing of Ash and Fuel in Magnetized Inertial Fusion

Magnetized inertial fusion experiments are approaching regimes where the radial transport is dominated by collisions between magnetized ions, providing an opportunity to exploit effects usually associated with steady-state magnetic fusion. Here, the low-density hotspot characteristic of magnetized liner inertial fusion results in diamagnetic and thermal frictions, which can demix thermalized ash from fuel, accelerating the fusion reaction. For reactor regimes in which there is a substantial burnup of the fuel, increases in the fusion energy yield on the order of 5% are possible.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

SIMS and HR-XPS characterization of lithiated graphite from the magnetic fusion device RFX-mod

Lithium wall conditioning has improved the performance of many magnetic fusion devices. Li conditioning in the RFX-mod device was performed by: (1) a single Li pellet injector and (2) a multi-Li pellet injector during He plasma discharges; (3) a Li evaporator after He glow discharge cleaning and He plasma discharge exposure. This report compares the spatial and depth distributions of Li deposited on polycrystalline graphite witness samples at different locations in RFX-mod and the elemental and chemical compositions of the resulting surfaces. The sample surfaces were analyzed ex situ using secondary ion mass spectrometry (SIMS) and high-resolution X-ray photoelectron spectroscopy (HR-XPS). The results showed that Li pellet injection provided a relatively uniform toroidal coverage while Li evaporation produced highly localized Li deposition. A Li 1s HR-XPS peak at 56.5 eV binding energy (BE) characteristic of lithium-intercalated graphite was only observed with the sample exposed to Li evaporation. All of the samples exhibited a HR-XPS C 1s peak at 285.1–285.2 eV BE that is largely attributed to hydrogenated graphite. This finding suggests that hydrogenation of fresh graphite occurs during He plasma discharge exposures. Finally, our results have implications for density control and the selection of Li conditioning techniques in magnetic fusion devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗