Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CLOSED PLASMA DEVICES”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Edge transport studies in the edge and scrape-off layer of the National Spherical Torus Experiment with Langmuir probes

Transport and turbulence profiles were directly evaluated using probes for the first time in the edge and scrape-off layer (SOL) of NSTX [Ono et al., Nucl. Fusion 40, 557 (2000)] in low (L) and high (H) confinement, low power (P{sub in}∼ 1.3 MW), beam-heated, lower single-null discharges. Radial turbulent particle fluxes peak near the last closed flux surface (LCFS) at ≈4×10{sup 21} s{sup −1} in L-mode and are suppressed to ≈0.2×10{sup 21} s{sup −1} in H mode (80%–90% lower) mostly due to a reduction in density fluctuation amplitude and of the phase between density and radial velocity fluctuations. The radial particle fluxes are consistent with particle inventory based on SOLPS fluid modeling. A strong intermittent component is identified. Hot, dense plasma filaments 4–10 cm in diameter, appear first ∼2 cm inside the LCFS at a rate of ∼1×10{sup 21} s{sup −1} and leave that region with radial speeds of ∼3–5 km/s, decaying as they travel through the SOL, while voids travel inward toward the core. Profiles of normalized fluctuations feature levels of 10% inside LCFS to ∼150% at the LCFS and SOL. Once properly normalized, the intermittency in NSTX falls in similar electrostatic instability regimes as seen in other devices. The L-H transition causes a drop in the intermittent filaments velocity, amplitude and number in the SOL, resulting in reduced outward transport away from the edge and a less dense SOL.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Laser radiation scattering from the wires and fibers of imploding arrays on the Angara-5-1 facility

A method is developed for measurements of laser radiation scattering by wires and fibers in different types of imploding arrays in the initial stage of plasma production at discharge currents per wire of up to 2 kA for aluminum arrays and up to 8 kA for tungsten arrays. The experiments were carried out on the Angara-5-1 facility at a current density in the wires of 10{sup 8} A/cm{sup 2} and current growth rate of {approx}10{sup 13} A/s. It is found that the indicatrix of laser radiation reflected from the wires (fibers) in cylindrical and conical arrays is modified at currents of 0.1-10 kA per wire (fiber). The experimental data on the reflection and scattering of laser radiation from wires and fibers are compared with the results of numerical simulations of their electric explosion in vacuum. It is proposed that the change in the reflection indicatrix of laser radiation is caused by the onset of thermal instabilities. The typical size of density and temperature inhomogeneities on the wire surface is in a range of 10-20 {mu}m, which probably results in a transition from specular to diffuse reflection of laser radiation. A simultaneous abrupt (over 2-3 ns) reduction in the reflection intensity from several wires of an array indicates a homogeneous distribution of the discharge current over the irradiated wires. This closes the issue of the quality of the contact between the wires and the electrodes. The obtained experimental information is of considerable importance for the development of numerical codes for simulations of the implosion of wire arrays and the refinement of the wire parameters in the initial stage of plasma production.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2011

Plasma Igniter for Reliable Ignition of Combustion in Rocket Engines

A plasma igniter has been developed for initiating combustion in liquid-propellant rocket engines. The device propels a hot, dense plasma jet, consisting of elemental fluorine and fluorine compounds, into the combustion chamber to ignite the cold propellant mixture. The igniter consists of two coaxial, cylindrical electrodes with a cylindrical bar of solid Teflon plastic in the region between them. The outer electrode is a metal (stainless steel) tube; the inner electrode is a metal pin (mild steel, stainless steel, tungsten, or thoriated-tungsten). The Teflon bar fits snugly between the two electrodes and provides electrical insulation between them. The Teflon bar may have either a flat surface, or a concave, conical surface at the open, down-stream end of the igniter (the igniter face). The igniter would be mounted on the combustion chamber of the rocket engine, either on the injector-plate at the upstream side of the engine, or on the sidewalls of the chamber. It also might sit behind a valve that would be opened just prior to ignition, and closed just after, in order to prevent the Teflon from melting due to heating from the combustion chamber.

Martin, Adam↗
DOE OSTI2013

Gyrokinetic simulation of global and local Alfvén eigenmodes driven by energetic particles in a DIII-D discharge

The unstable spectrum of Alfvén eigenmodes (AEs) driven by neutral beam-sourced energetic particles (EPs) in a benchmark DIII-D discharge (142111) is calculated in a fully gyrokinetic model using the GYRO code's massively parallel linear eigenvalue solver. One cycle of the slow (equilibrium scale) frequency sweep of the reverse shear Alfvén eigenmode (RSAE) at toroidal mode number n=3 is mapped. The RSAE second harmonic and an unstable beta-induced Alfvén eigenmode (BAE) are simultaneously tracked alongside the primary RSAE. An observed twist in the eigenmode pattern, caused mostly by shear in the driving EP profile, is shown through artificially varying the E×B rotational velocity shear to depend generally on shear in the local wave phase velocity. Coupling to the BAE and to the toroidal Alfvén eigenmode limit the RSAE frequency sweeps at the lower and upper end, respectively. While the present fully gyrokinetic model (including thermal ions and electrons) constitutes the best treatment of compressibility physics available, the BAE frequency is overpredicted by about 20% against experiment here and is found to be sensitive to energetic beam ion pressure. The RSAE frequency is more accurately matched except when it is limited by the BAE. Simulations suggest that the experiment is very close to marginal AE stability at points of RSAE-BAE coupling. A recipe for comparing the radial profile of quasilinear transport flux from local modes to that from global modes paves the way for the development of a stiff (critical gradient) local AE transport model based on local mode stability thresholds.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Short wavelength turbulence generated by shear in the quiescent H-mode edge on DIII–D

A region of turbulence with large radial wavenumber (k{sub r}ρ{sub s}>1) is found in the high-shear portion of the plasma edge in Quiescent H-mode (QH-mode) on DIII–D using the Phase Contrast Imaging (PCI) diagnostic. At its peak outside the minimum of the E{sub r} well, the turbulence exhibits large amplitude n{sup ~}/n∼40%, with large radial wavenumber |k{sup ¯}{sub r}/k{sup ¯}{sub θ}|∼11 and short radial correlation length L{sub r}/ρ{sub i}∼0.2. The turbulence inside the E{sub r} well minimum is characterized by the opposite sign in radial wavenumber from that of turbulence outside the minimum, consistent with the expected effects of velocity shear. The PCI diagnostic provides a line-integrated measurement of density fluctuations, so data are taken during a scan of plasma position at constant parameters to allow the PCI to sample a range in k{sub r}/k{sub θ}. Analysis of the Doppler shift and plasma geometry allows the turbulence to be localized to a narrow region 3 mm inside the last closed flux surface, outside the minimum of the E{sub r} well. The turbulence amplitude and radial wavenumber and correlation length are determined by fitting the PCI results with a simple non-isotropic turbulence model with two regions of turbulence. These PCI observations, made in QH-mode, are qualitatively similar to those made in standard edge localized modes (ELM)-free H-mode and between ELMs, suggesting a similar role for large k{sub r} turbulence there.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Unexpected magnetization enhancement in hydrogen plasma treated ferromagnetic (Zn,Cu)O film

The effects of H{sup +} incorporation on oxygen vacancies (H{sub O}{sup +}) on the giant ferromagnetic behavior (moment up to 3.26 μ{sub B}/Cu) in ZnO:Cu polycrystalline films have been closely examined using different microstructural and magnetic characterization tools. Fine thermal stability (up to 450 °C) and low resistivity demonstrate a significant correlation between Cu 3d-states and H{sub O}{sup +} donor defects in H plasma treated ZnO:Cu films, analogous to dual-donor (V{sub O} and Zn{sub i}) defects mediated case. These H{sub O}{sup +} donors can delocalize their electrons to the orbits of Cu atoms and contribute to a stronger spin-orbit coupling interaction. Suitable H{sub O}{sup +} defect concentration and matched proportion between Cu{sup 2+} and Cu{sup +} species ensure that orbital momentum shall not be quenched. Hence, unexpected moment enhancement, less than spin-orbit coupling upper limit (3.55 μ{sub B}/Cu), can be also expected in this scenario. The manipulation from spin-only to spin-orbit coupling mode, using a facile thermally-mediated H plasma exposure way, will allow achieving spin transport based diluted magnetic semiconductor device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Cryogenic Considerations for Superconducting Magnet Design for the Material Plasma Exposure eXperiment

In order to determine long term performance of plasma facing components such as diverters and first walls for fusion devices, next generation plasma generators are needed. A Material Plasma Exposure eXperiment (MPEX) has been proposed to address this need through the generation of plasmas in front of the target with electron temperatures of 1-15 eV and electron densities of 1020 to 1021 m-3. Heat fluxes on target diverters could reach 20 MW/m2. In order generate this plasma, a unique radio frequency helicon source and heating of electrons and ions through Electron Bernstein Wave (EBW) and Ion Cyclotron Resonance Heating (ICRH) has been proposed. MPEX requires a series of magnets with non-uniform central fields up to 2 T over a 5m length in the heating and transport region and 1 T uniform central field over a 1-m length on a diameter of 1.3 m. Given the field requirements, superconducting magnets are under consideration for MPEX. In order to determine the best construction method for the magnets, the cryogenic refrigeration has been analyzed with respect to cooldown and operational performance criteria for open-cycle and closed-cycle systems, capital and operating costs of these system, and maturity of supporting technology such as cryocoolers. These systems will be compared within the context of commercially available magnet constructions to determine the most economical method for MPEX operation. The current state of the MPEX magnet design including details on possible superconducting magnet configurations will be presented.

Duckworth, Robert C↗
DOE OSTI2015

Generalized Lawson Criteria for Inertial Confinement Fusion

The Lawson Criterion was proposed by John D. Lawson in 1955 as a general measure of the conditions necessary for a magnetic fusion device to reach thermonuclear ignition. Over the years, similar ignition criteria have been proposed which would be suitable for Inertial Confinement Fusion (ICF) designs. This paper will compare and contrast several ICF ignition criteria based on Lawson’s original ideas. Both analytical and numerical results will be presented which will demonstrate that although the various criteria differ in some details, they are closely related and perform similarly as ignition criteria. A simple approximation will also be presented which allows the inference of each ignition parameter directly from the measured data taken on most shots fired at the National Ignition Facility (NIF) with a minimum reliance on computer simulations. Evidence will be presented which indicates that the experimentally inferred ignition parameters on the best NIF shots are very close to the ignition threshold.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Study of the triton-burnup process in different JET scenarios using neutron monitor based on CVD diamond

We present the results of analysis of triton burn-up process using the data from diamond detector. Neutron monitor based on CVD diamond was installed in JET torus hall close to the plasma center. We measure the part of 14 MeV neutrons in scenarios where plasma current varies in a range of 1-3 MA. In this experiment diamond neutron monitor was also able to detect strong gamma bursts produced by runaway electrons arising during the disruptions. We can conclude that CVD diamond detector will contribute to the study of fast particles confinement and help predict the disruption events in future tokamaks.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Measurement of helicon waves with phase contrast imaging on DIII-D – A theoretical feasibility study

A DIII-D high-beta H-mode discharge, with I p = 850 kA, B t = 2.1 T n e = 4 10 19 m –3 , has been designed to validate full wave modeling of helicon waves by optimizing the expected response of the Phase Contrast Imaging diagnostic. Helicon waves have been predicted to have high current drive efficiency off-axis without facing the accessibility issues of lower-hybrid waves. To test these predictions experimentally, DIII-D has recently commissioned a high-power helicon antenna. To confidently predict the behavior of helicon waves in future devices, measurements of their fundamental properties and validation against models will be essential. Phase contrast imaging (PCI) is an absolutely calibrated internal reference interferometer able to measure density fluctuations with radial wavenumbers k R between 1.5 cm –1 and 20 cm –1 . For helicon waves 2 cm –1 < k R < 10 cm –1 is expected, allowing PCI to measure their envelope and wavenumber spectrum. This makes PCI a powerful tool for the validation of state-of-the-art models, like the AORSA full wave code. AORSA is used to compute the density perturbations measured by the PCI with 2D calculations corresponding to 11 different toroidal mode numbers combined to resolve the trajectory of the helicon wave in 3D. This is necessary because the waves travel 120 degrees toroidally from the antenna to the PCI. Here, a cold plasma finite element model (CPFEM) [4] is used to predict propagation through the scrape-off layer. The result of the CPFEM model is connected to AORSA by creating an artificial Gaussian antenna on the last closed flux surface. PCI shows best results for waves with small vertical wavenumbers k z . Modeling the helicon waves for several past DIII-D experiments shows that k z is minimized if the intersection of the helicon and the PCI laser beams occurs in the midplane. For such an optimized scenario the predicted signal level is two orders of magnitude larger than the background density fluctuations arising from broadband turbulence.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Computation of Alfvèn eigenmode stability and saturation through a reduced fast ion transport model in the TRANSP tokamak transport code

Alfvénic instabilities (AEs) are well known as a potential cause of enhanced fast ion transport in fusion devices. Given a specific plasma scenario, quantitative predictions of (i) expected unstable AE spectrum and (ii) resulting fast ion transport are required to prevent or mitigate the AE- induced degradation in fusion performance. Reduced models are becoming an attractive tool to analyze existing scenarios as well as for scenario prediction in time-dependent simulations. In this work, a neutral beam heated NSTX discharge is used as reference to illustrate the potential of a reduced fast ion transport model, known as kick model, that has been recently implemented for interpretive and predictive analysis within the framework of the time-dependent tokamak transport code TRANSP. Predictive capabilities for AE stability and saturation amplitude are first assessed, based on given thermal plasma profiles only. Predictions are then compared to experimental results, and the interpretive capabilities of the model further discussed. Overall, the reduced model captures the main properties of the instabilities and associated effects on the fast ion population. Additional information from the actual experiment enables further tuning of the model’s parameters to achieve a close match with measurements.

Alfven instabilities↗
DOE OSTI2014

The new TORPEX in-vessel toroidal conductor for the generation of a poloidal magnetic field

TORoidal Plasma EXperiment (TORPEX) is a Simple Magnetized Torus featuring open helical magnetic field lines obtained from the superposition of a small vertical component on the main toroidal field. This work introduces the experimental setup developed to include a poloidal magnetic field. The toroidal and poloidal fields generate a rotational transform, making the magnetic geometry of TORPEX closer to that of a tokamak. This upgrade opens the possibility to deal with closed and open flux surfaces, as well as with the transition region across the last closed flux surface. The main technical solutions are discussed together with the physical considerations at the basis of the system design. Selected examples of the magnetic configurations accessible with the set of magnetic field coils available on TORPEX are discussed, ranging from single-null X-points to magnetic snowflakes. The simplest magnetic configuration of quasi-circular concentric flux surfaces is tested experimentally. Measurements of the two-dimensional electron plasma density profiles and the particle confinement time are presented, together with the first steps towards the understanding of plasma production mechanisms.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Computation of Alfvèn eigenmode stability and saturation through a reduced fast ion transport model in the TRANSP tokamak transport code

Alfvénic instabilities (AEs) are well known as a potential cause of enhanced fast ion transport in fusion devices. Given a specific plasma scenario, quantitative predictions of (i) expected unstable AE spectrum and (ii) resulting fast ion transport are required to prevent or mitigate the AE-induced degradation in fusion performance. Reduced models are becoming an attractive tool to analyze existing scenarios as well as for scenario prediction in time-dependent simulations. Here, in this work, a neutral beam heated NSTX discharge is used as reference to illustrate the potential of a reduced fast ion transport model, known as kick model, that has been recently implemented for interpretive and predictive analysis within the framework of the time-dependent tokamak transport code TRANSP. Predictive capabilities for AE stability and saturation amplitude are first assessed, based on given thermal plasma profiles only. Predictions are then compared to experimental results, and the interpretive capabilities of the model further discussed. Overall, the reduced model captures the main properties of the instabilities and associated effects on the fast ion population. Finally, additional information from the actual experiment enables further tuning of the model's parameters to achieve a close match with measurements.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Three-dimensional simulation of H-mode plasmas with localized divertor impurity injection on Alcator C-Mod using the edge transport code EMC3-EIRENE

Experiments in Alcator C-Mod to assess the level of toroidal asymmetry in divertor conditions resulting from poloidally and toroidally localized extrinsic impurity gas seeding show a weak toroidal peaking (∼1.1) in divertor electron temperatures for high-power enhanced D-alpha H-mode plasmas. This is in contrast to similar experiments in Ohmically heated L-mode plasmas, which showed a clear toroidal modulation in the divertor electron temperature. Modeling of these experiments using the 3D edge transport code EMC3-EIRENE [Y. Feng et al., J. Nucl. Mater. 241, 930 (1997)] qualitatively reproduces these trends, and indicates that the different response in the simulations is due to the ionization location of the injected nitrogen. Low electron temperatures in the private flux region (PFR) in L-mode result in a PFR plasma that is nearly transparent to neutral nitrogen, while in H-mode the impurities are ionized in close proximity to the injection location, with this latter case yielding a largely axisymmetric radiation pattern in the scrape-off-layer. The consequences for the ITER gas injection system are discussed. Quantitative agreement with the experiment is lacking in some areas, suggesting potential areas for improving the physics model in EMC3-EIRENE.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Ballooning theory of the second kind-two dimensional tokamak modes

The 2-D ballooning transform, devised to study local high toroidal number (n) fluctuations in axisymmetric toroidal system (like tokamaks), yields a well-defined partial differential equation for the linear eigenmodes. In this paper, such a ballooning equation of the second kind is set up for ion temperature gradient driven modes pertinent to a 2-D non-dissipative fluid plasma; the resulting partial differential equation is numerically solved, to calculate the global eigenvalues, and the 2-D mode structure is presented graphically along with analytical companions. The radial localization of the mode results from translational symmetry breaking for growing modes and is a vivid manifestation of spontaneous symmetry breaking in tokamak physics. The eigenmode, poloidally ballooned at {theta}={+-}{pi}/2, is radially shifted from associated rational surface. The global eigenvalue is found to be very close to the value obtained in 1-D parameterized ({lambda}={+-}{pi}/2) case. The 2-D eigenmode theory is applied to estimate the toroidal seed Reynolds stress [Y. Z. Zhang, Nucl. Fusion Plasma Phys. 30, 193 (2010)]. The solution obtained from the relatively simplified ballooning theory is compared to the solution of the basic equation in original coordinate system (evaluated via FFTs); the agreement is rather good.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Comprehensive magnetohydrodynamic hybrid simulations of Alfvén eigenmode bursts and fast-ion losses in the Large Helical Device

Comprehensive magnetohydrodynamic (MHD) hybrid simulations with neutral beam injection and collisions were conducted to investigate the Alfvén eigenmode (AE) bursts and the fast-ion losses in the large helical device (LHD) for the realistic conditions close to the experiments. In this study, it is found in the simulation of the slowing-down time scale that the AE bursts take place repetitively accompanied by fast-ion redistribution and losses leading to lower saturation levels of stored fast-ion energy than those in a classical calculation where the MHD perturbations are neglected. The fast-ion loss rate caused by the AE burst has the quadratic dependence on AE amplitude, which was observed in the LHD experiment. The majority of the lost fast ions are counter-passing particles whose velocity and pitch-angle are close to those of the beam injection. The second component of the lost fast ions is transit particles whose velocity is close to thermal velocity. The loss of the counter-passing particles occurs mainly during the AE bursts, while the transit particles are lost both during the AE bursts and the quiescent periods with larger loss rate than that in the classical calculation. The initial location of the lost counter-injected particles spreads from the plasma edge to the plasma center, while only the particles initially located in the peripheral region are lost for the co-injected beam.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Omnigenity as generalized quasisymmetry

Any viable stellarator reactor will need to be nearly omnigenous, meaning the radial guiding-center drift velocity averages to zero over time for all particles. While omnigenity is easier to achieve than quasisymmetry, we show here that several properties of quasisymmetric plasmas also apply directly or with only minor modification to the larger class of omnigenous plasmas. For example, concise expressions exist for the flow and current, closely resembling those for a tokamak, and these expressions are explicit in that no magnetic differential equations remain. A helicity (M, N) can be defined for any omnigenous field, based on the topology by which B contours close on a flux surface, generalizing the helicity associated with quasisymmetric fields. For generalized quasi-poloidal symmetry (M = 0), the bootstrap current vanishes, which may yield desirable equilibrium and stability properties. A concise expression is derived for the radial electric field in any omnigenous plasma that is not quasisymmetric. The fact that the tokamak-like analytical calculations are possible in omnigenous plasmas despite their fully 3D magnetic spectrum makes these configurations useful for gaining insight and benchmarking codes. A construction is given to produce omnigenous B({theta},{zeta}) patterns with stellarator symmetry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Systematic analysis of magnetic equilibrium reconstruction with eddy currents on LTX- β

Magnetic equilibrium reconstruction in the Lithium Tokamak Experiment-Beta (LTX-β) is complicated by strong eddy currents and toroidal asymmetries arising from its segmented, close-fitting conducting shell. In the earlier experiment LTX, these three-dimensional (3D) conductor effects significantly distorted diagnostic signals and challenged conventional axisymmetric reconstruction methods. In this work, we demonstrate that accurate plasma equilibria can be recovered on LTX-β by incorporating a small number of dominant eddy current modes derived from realistic conductor models. Using the open-source $\tt{TokaMaker}$ Grad–Shafranov solver, we reconstruct equilibria across a systematically selected set of LTX-β discharges and validate them against the legacy $\tt{PSI-Tri}$ hybrid 2D-3D code. Our results show that fully 2D $\tt{TokaMaker}$ reconstructions achieve significantly improved agreement with flux loop and Mirnov probe measurements, reducing total chi-squared fitting errors, especially during startup. Finally, we develop new hybrid 2D-3D $\tt{TokaMaker}$ reconstructions by integrating the $\tt{ThinCurr}$ 3D eddy current model, which we optimize for significant further reduction of chi-squared in most scenarios. These findings underscore the importance of realistic wall-current modeling in short-pulse tokamaks, and establish a physics-based reconstruction framework that is extensible to devices with complex passive structures and 3D wall interactions.

Grad–Shafranov solver↗