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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Planetary entry experiments

The final report summarizes the results from three research areas: (1) window design for the radiometric measurement of the forebody radiative heating experienced by atmospheric entry spaceraft; (2) survey of the current understanding of chemical species on selected solar system bodies and assess the importance of measurements with regard to vehicle environment and with regard to understanding of planetary atmospheres with emphasis on Venus, Mars, and Titan; and (3) measure and analyze the radiation (VUV to near-IR) from the shock heated gas cap of a blunt body in an Ames arc Jet wind-tunnel facility.

Craig, Roger A.↗
NASA NTRS2012

Electrospray Collection of Lunar Dust

A report describes ElectroSpray Ionization based Electrostatic Precipitation (ESIEP) for collecting lunar dust particles. While some HEPA filtration processes may remove a higher fraction (>99.9 percent) of the particles, the high efficiency may not be appropriate from an overall system standpoint, especially in light of the relatively large power requirement that such systems demand. The new electrospray particle capture technology is described as a variant of electrostatic precipitation that eliminates the current drawbacks of electrostatic precipitation. The new approach replaces corona prone field with a mist of highly charged micro-droplets generated by electrospray ionization (ESI) as the mechanism by which incoming particles are attracted and captured. In electrospray, a miniscule flow rate (microliters/minute) of liquid (typically water and a small amount of salt to enhance conductivity) is fed from the tip of a needle held at a high voltage potential relative to an opposite counter electrode. At sufficient field strength, a sharp liquid meniscus forms , which emits a jet of highly charged droplets that drift through the surrounding gas and are collected on the walls of a conductive tube. Particles in the gas have a high probability of contact with the droplets either by adhering to the droplets or otherwise acquiring a high level of charge, causing them to be captured on the collecting electrode as well. The spray acts as a filtration material that is continuously introduced and removed from the gas flow, and thus can never become clogged.

Dziekan, Michael↗
NASA NTRSDate not supplied

Absorption Laser Differential Interferometry for Simultaneous Colinear Flow Property and Fluctuation Measurements

An absorption laser differential interferometer (A-LDI) was constructed and tested in an effort to simultaneously and colinearly measure flow properties (pressure, temperature, concentration) and flow fluctuations (changes in optical path length). Whereas typical LDI and focused LDI (FLDI) systems use fixed wavelength lasers as the light source (often either green at approximately 532 nm or red at approximately 630 nm), a tunable 760 nm diode laser was used to probe the A-band absorption spectrum of molecular oxygen. The A-LDI system was used to measure O2 absorption and flow fluctuations in a sub-atmospheric pressure-controlled test cell, with absorption profiles from direct absorption and wavelength modulation absorption matching simulated results, while simultaneously being sensitive to high frequency fluctuations from jets of either compressed air or 100% O2 from a gas bottle. The A-LDI system was also installed at the NASA Langley Research Center Probe Calibration Tunnel to assess the freestream flow state in a Mach 3.5 flow. LDI measurements of the freestream indicated increasing amplitudes of flow fluctuations with increasing stagnation pressure at a fixed stagnation temperature, while absorption results demonstrated sensitivity to freestream pressure changes.

Joshua M. Weisberger↗
NASA NTRS1994

Narrowband HST images of M87: Evidence for a disk of ionized gas around a massive black hole

We present Hubble Space Telescope Wide Field/Planetary Camera-2 (HST WFPC2) narrowband H-alpha + (N II) images of M87 which show a small disk of ionized gas with apparent spiral structure surrounding the nucleus of M87. The jet projects approximately 19.5 deg from the minor axis of the disk, which suggests that the jet is approximately normal to the disk. In a companion Letter, Harms et al. measure the radial velocities at r = +/- 0.25 sec along a line perpendicular to the jet, showing that one side of the disk is approaching at 500 +/- 50 km/s and the other side of the disk is receding at 500 +/- 50 km/s. Absorption associated with the disk and the sense of rotation imply that the apparent spiral arms trail the rotation. The observed radial velocites corrected for a 42 deg inclination of the disk imply rotation at +/- 750 km/s. Analysis of velocity measurements at four positions near the nucleus gives a total mass of approximately 2.4 +/- 0.7 x 10(exp 9) solar mass within 18 pc of the nucleus, and a mass-to-light ratio (M/L)(sub I) = 170. We conclude that there is a disk of ionized gas feeding a massive black hole in the center of M87.

Ford, Holland C.↗
NASA NTRS2000

Mixing and NOx Emission Calculations of Confined Reacting Jet Flows in Cylindrical and Annular Ducts

Rapid mixing of cold lateral jets with hot cross-stream flows in confined configurations is of practical interest in gas turbine combustors as it strongly affects combustor exit temperature quality, and gaseous emissions in for example rich-lean combustion. It is therefore important to further improve our fundamental understanding of the important processes of dilution jet mixing especially when the injected jet mass flow rate exceeds that of the cross-stream. The results reported in this report describe some of the main flow characteristics which develop in the mixing process in a cylindrical duct. A three-dimensional computational fluid dynamics (CFD) code has been used to predict the mixing flow field characteristics and NOx emission in a quench section of a rich-burn/quick-mix/lean-burn (RQL) combustor. Sixty configurations have been analyzed in both circular and annular geometries in a fully reacting environment simulating the operating condition of an actual RQL gas turbine combustion liner. The evaluation matrix was constructed by varying the number of orifices per row and orifice shape. Other parameters such as J (momentum-flux ratio), MR (mass flowrate ratio), DR (density ratio), and mixer sector orifice ACd (effective orifice area) were maintained constant throughout the entire study. The results indicate that the mixing flow field can be correlated with the NOx production if they are referenced with the stoichiometric equivalence ratio value and not the equilibrium value. The mixing flowfields in both circular and annular mixers are different. The penetration of equal jets in both annular and circular geometries is vastly different which significantly affects the performance of the mixing section. In the computational results with the circular mixer, most of the NOx formation occurred behind the orifice starting at the orifice wake region. General trends have been observed in the NOx production as the number of orifices is changed and this appears to be common for all hole configurations and mixer types (circular or annular). The performance of any orifice shape (in producing minimum NOx) appears to be acceptable if the number of orifices can be freely varied in order to attain the optimum jet penetration.

Oechsle, Victor L.↗
NASA NTRS2008

Dynamic Measurement of Temperature, Velocity, and Density in Hot Jets Using Rayleigh Scattering

A molecular Rayleigh scattering technique was utilized to measure time-resolved gas temperature, velocity, and density in unseeded gas flows at sampling rates up to 10 kHz. A high power continuous-wave (cw) laser beam was focused at a point in an air flow field and Rayleigh scattered light was collected and fiber-optically transmitted to a Fabry-Perot interferometer for spectral analysis. Photomultipler tubes operated in the photon counting mode allowed high frequency sampling of the total signal level and the circular interference pattern to provide time-resolved density, temperature, and velocity measurements. Mean and rms velocity and temperature, as well as power spectral density calculations, are presented for measurements in a hydrogen-combustor heated jet facility with a 50.8-mm diameter nozzle at the NASA Glenn Research Center (GRC). The Rayleigh measurements are compared with particle image velocimetry data and CFD predictions. This technique is aimed at aeronautics research related to identifying noise sources in free jets, as well as applications in supersonic and hypersonic flows where measurement of flow properties, including mass flux, is required in the presence of shocks and ionization occurrence.

Mielke, Amy F.↗
DOE OSTI2024

Compressor Station Differential Risk Assessment for Hydrogen and Natural Gas Blends

Blending hydrogen into existing natural gas pipelines is a current initiative for large-scale hydrogen deployment in the United States. Understanding changes in hazards and risk for fuel blends can help inform regulations. A differential risk assessment was conducted to understand how the safety profile of fires and unignited flammable plumes of leaking fuel would change based on blend composition. The area affected by harmful heat fluxes from jet fires was found to be larger for blends with more natural gas in them, while the distance affected by unignited flammable fuel concentrations was found to be larger for blends with more hydrogen in them. Component leak frequencies and ignition probabilities greatly impact both heat flux risk and the flammable plume risk. The collection of additional blend-specific industry data could help understand which assumptions are most valid to make when calculating risk.

08 HYDROGEN↗
DOE OSTI2024

Biofuel production from palm oil deoxygenation using nickel-molybdenum on zirconia catalyst using glycerol as a hydrogen donor

The growing demand for renewable energy has generated interest in biofuels as alternatives to fossil fuels. Second-generation biofuels, derived from deoxygenating fats and oils, have garnered a higher level of interest from industry and academia due to their potential for direct replacement of diesel and jet fuels. Palm oil, mostly cultivated in Thailand and composed of C16 and C18 fatty acids, is a primary feedstock sought for biofuel production. Palm oil deoxygenation contains several pathways that may or may not require hydrogen gas. This study aimed to produce biofuels in different fuel ranges, such as gasoline, jet fuel, and diesel, through palm oil deoxygenation using glycerol as a hydrogen source. Glycerol, a low-value byproduct, was used as a hydrogen donor, whereas nickel-molybdenum-supported catalysts were chosen for their high efficiency in deoxygenation and cost-effectiveness. The study investigated the impact of reaction time, temperature, and catalyst activation method on palm oil deoxygenation. Catalyst characterization methods, including XRD, SEM, TEM, XPS, FTIR, TGA, and nitrogen-sorption, were employed to understand the role of catalysts’ activity during palm oil upgrading. Findings indicated that alkane hydrocarbons are the major components in liquid products. The presence of excess hydrogen in post reaction gaseous phase proves the hydrogen donation capability of glycerol. Increased reaction time and temperature facilitated the removal of oxygen from palm oil. Nickel-molybdenum on zirconia activated by sulfidation demonstrated higher stability than by reduction activation.

09 BIOMASS FUELS↗
DOE OSTI2023

Modeling of the spray-induced wall stress acting on the ignition assistance device

This research introduces a novel wall-stress model called the Spray-Induced Wall Stress (SIWS) model, which considers the effects of spray-wall impingement and the resulting formation of wall stress within the Lagrangian spray modeling framework. The primary objective of this paper is to provide a mathematical description of the fundamental physics underlying the model. Subsequently, the proposed model is validated using existing experimental data. Here, the remainder of the study focuses on the practical application of the model to an ignition assistance device. Specifically, this device is installed in a compression ignition engine and designed to enhance ignition in aviation-fueled high-altitude aircraft propulsion systems. The research sheds light on the mechanical impulse caused by the high-speed impact of the spray jet, leading to the accumulation of mechanical stress on the rigid body of the ignition assistance device. Previous studies on fluid-structure interaction have only considered the interaction between the gas phase and the solid wall. However, the SIWS model incorporates the additional impact of the impinging liquid spray jet. Consequently, the simulated stress distribution on the ignition assistance device can be estimated by considering both the gas-phase-induced term and the spray-induced term simultaneously.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2021

The Influence of Pressure on Flame-Flow Characteristics of a Reacting Jet in Crossflow

This work experimentally investigates the effects of elevated combustor pressures on the characteristics of a lean premixed reacting methane/air jet injected into a lean vitiated crossflow using a 12.7 mm axial jet. Experiments were conducted in an axially staged combustor, which implements a reacting jet in crossflow (RJIC) configuration and operates over a pressure range of 1–5 atmospheres. Simultaneous CH* chemiluminescence and particle image velocimetry (PIV) are used to study the flow field and flame behavior. The results show that the reacting jet trajectory exhibits greater penetration with elevated pressure, which is a novel finding compared to available data in the literature. However, the flame liftoff point and ignition delay time both decreased with elevated pressure, which was attributed to decreased vorticity along the flame boundary which corresponds to increased Damköhler numbers (Da). Emissions measurements confirm the NOx increase with pressure as reported in the literature for single-stage gas turbine combustors. Concurrently, emission measurements for the staged configuration show the strong NOx benefit of the RJIC system: the data prove a reduction of global outlet emission levels at elevated pressure with the axially staged configuration. Here, the axial emission reduction was attributed to the decreasing liftoff at elevated pressure levels. Hence, the research emphasizes that the flame and emission characteristics are coupled; they are not only dependent on the geometric parameters and momentum flux ratios but are also a function of pressure.

03 NATURAL GAS↗
DOE OSTI2024

High-resolution infrared spectroscopy of jet cooled cyclobutyl in the α-CH stretch region: large-amplitude puckering dynamics in a 4-membered ring radical

We report gas-phase cyclobutyl radical (c-C 4 H 7 ) is generated at a rotational temperature of T rot = 26(1) K in a slit-jet discharge mixture of 70% Ne/30% He and 0.5–0.6% cyclobromobutane (c-C 4 H 7 Br). A fully rovibrationally resolved absorption spectrum of the α-CH stretch fundamental band between 3062.9 cm −1 to 3075.7 cm −1 is obtained and analyzed, yielding first precision structural and dynamical information for this novel radical species. The α-CH stretch band origin is determined to be 3068.7887(4) cm −1 , which implies only a modest (≈0.8 cm −1 ) blue shift from rotationally unresolved infrared spectroscopic studies of cyclobutyl radicals in liquid He droplets [ A. R. Brown, P. R. Franke and G. E. Douberly, J. Phys. Chem. A , 2017, 121 , 7576–7587]. Of particular dynamical interest, a one-dimensional potential energy surface with respect to the ring puckering coordinate is computed at CCSD(T)/ANO2 level of theory and reveals a double minimum C s puckered geometry, separated by an exceedingly shallow planar C 2v transition state barrier (E barr ≈ 1 cm −1 ). Numerical solutions on this double minimum potential yield a zero-point energy for the ground state (E zero-point ≈ 27 cm −1 ) greatly in excess of the interconversion barrier. This is indicative of highly delocalized, large amplitude motion of the four-membered ring structure, for which proper vibrationally averaging of the moment of inertia tensor reproduces the experimentally determined inertial defect remarkably well. Finally, intensity alternation in the experimental spectrum due to nuclear spin statistics upon exchange of three indistinguishable H atom pairs (IH = ½) matches K a + K c = even : odd = 36 : 28 predictions, implying that the unpaired electron in the radical center lies in an out-of-plane p π orbital. Thus, high-resolution infrared spectroscopy provides first experimental confirmation of a shallow double minimum ring puckering potential with a highly delocalized ground state wave function peaked at a planar C 2v transition state geometry consistent with a cyclobutyl π radical.

Chemistry↗
NASA NTRS2011

DBD Plasma Actuators for Flow Control in Air Vehicles and Jet Engines - Simulation of Flight Conditions in Test Chambers by Density Matching

Dielectric Barrier Discharge (DBD) Plasma actuators for active flow control in aircraft and jet engines need to be tested in the laboratory to characterize their performance at flight operating conditions. DBD plasma actuators generate a wall-jet electronically by creating weakly ionized plasma, therefore their performance is affected by gas discharge properties, which, in turn, depend on the pressure and temperature at the actuator placement location. Characterization of actuators is initially performed in a laboratory chamber without external flow. The pressure and temperature at the actuator flight operation conditions need to be simultaneously set in the chamber. A simplified approach is desired. It is assumed that the plasma discharge depends only on the gas density, while other temperature effects are assumed to be negligible. Therefore, tests can be performed at room temperature with chamber pressure set to yield the same density as in operating flight conditions. The needed chamber pressures are shown for altitude flight of an air vehicle and for jet engines at sea-level takeoff and altitude cruise conditions. Atmospheric flight conditions are calculated from standard atmosphere with and without shock waves. The engine data was obtained from four generic engine models; 300-, 150-, and 50-passenger (PAX) aircraft engines, and a military jet-fighter engine. The static and total pressure, temperature, and density distributions along the engine were calculated for sea-level takeoff and for altitude cruise conditions. The corresponding chamber pressures needed to test the actuators were calculated. The results show that, to simulate engine component flows at in-flight conditions, plasma actuator should be tested over a wide range of pressures. For the four model engines the range is from 12.4 to 0.03 atm, depending on the placement of the actuator in the engine. For example, if a DBD plasma actuator is to be placed at the compressor exit of a 300 PAX engine, it has to be tested at 12.4 atm for takeoff, and 6 atm for cruise conditions. If it is to be placed at the low-pressure turbine, it has to be tested at 0.5 and 0.2 atm, respectively. These results have implications for the feasibility and design of DBD plasma actuators for jet engine flow control applications. In addition, the distributions of unit Reynolds number, Mach number, and velocity along the engine are provided. The engine models are non-proprietary and this information can be used for evaluation of other types of actuators and for other purposes.

Ashpis, David E.↗
NASA NTRS1956

Ram-jet Performance

The ram jet is basically one of the most dimple types of aircraft engine. It consists only of an inlet diffuser, a combustion system, and an exit nozzle. A typical ram-jet configuration is shown in figure 128. The engine operates on the Brayton cycle, and ideal cycle efficiency depends only on the ratio of engine to ambient pressure. The increased, engine pressures are obtained by ram action alone, and for this reason the ram jet has zero thrust at zero speed. Therefore, ram-jet-powered aircraft must be boosted to flight speeds close to a Mach number of 1.0 before appreciable thrust is generated by the engine. Since pressure increases are obtained by ram action alone, combustor-inlet pressures and temperatures are controlled by the flight speed, the ambient atmospheric condition, and by the efficiency of the inlet diffuser. These pressures and temperatures, as functions of flight speed and altitude, are shown in figure 129 for the NACA standard atmosphere and for practical values of diffuser efficiency. It can be seen that very wide ranges of combustor-inlet temperatures and pressures may be encountered over the ranges of flight velocity and altitude at which ram jets may be operated. Combustor-inlet temperatures from 500 degrees to 1500 degrees R and inlet pressures from 5 to 100 pounds per square inch absolute represent the approximate ranges of interest in current combustor development work. Since the ram jet has no moving parts in the combustor outlet, higher exhaust-gas temperatures than those used in current turbojets are permissible. Therefore, fuel-air ratios equivalent to maximum rates of air specific impulse or heat release can be used, and, for hydrocarbon fuels, this weight ratio is about 0.070. Lower fuel-air ratios down to about 0.015 may also be required to permit efficient cruise operation. This fuel-air-ratio range of 0.015 to 0.070 used in ram jets can be compared with the fuel-air ratios up to 0.025 encountered in current turbojets. Ram-jet combustor-inlet velocities range from 150 to 400 feet per second. These high linear velocities combined with the relatively low pressure ratios obtainable in ram jets require that the pressure drop through the combustor be kept low to avoid excessive losses in cycle efficiency. It has been estimated that, for a long-range ram-jet engine, an increase in pressure loss of one dynamic head would require a compensating 1-percent increase in combustion efficiency. Therefore, combustor pressure-loss coefficients (pressure drop/impact pressure) of the order of 1 to 4 are found in most current engines. The operating conditions described impose major problems in the design of stable and efficient ram-jet combustion systems. This chapter presents a survey of ram-jet combustor research and, where possible, points out criteria that may be useful in the design of ram-jet combustion systems.

Cervenko, A. J.↗
NASA NTRS1994

Implementation of and measurement with the LIPA technique in a subsonic jet

LIPA (Laser Induced Photochemical Anemometry) was used to measure velocity, vorticity, Reynolds stress, and turbulent intensity distributions in a subsonic jet. The jet region of interest was the area close to the jet-orifice. The LIPA-technique is a nonintrusive quantitative flow visualization technique, consisting of tracking a phosphorescing grid of fluid particles, which is impressed by laser-beams directed into the flow. The phosphorescence of biacetyl gas was used to enable tracking of the impressed light grid. In order to perform measurements in a jet, LIPA was developed and implemented for the specific flow requirements. Nitrogen was used as the carrier gas to avoid quenching of the phosphorescent radiation of the tracer gas biacetyl by ambient oxygen. The use of sulfur dioxide to sensitize phosphorescent emission of biacetyl was examined. Preliminary data was used in a discussion of the potential of the LIPA technique.

Falco, R. E.↗
NASA NTRS2001

Thermal Fault Tolerance Analysis of Carbon Fiber Rope Barrier Systems for Use in the Reusable Solid Rocket Motor ( RSRM) Nozzle Joints

Carbon Fiber Rope (CFR) thermal barrier systems are being considered for use in several RSRM (Reusable Solid Rocket Motor) nozzle joints as a replacement for the current assembly gap close-out process/design. This study provides for development and test verification of analysis methods used for flow-thermal modeling of a CFR thermal barrier subject to fault conditions such as rope combustion gas blow-by and CFR splice failure. Global model development is based on a 1-D (one dimensional) transient volume filling approach where the flow conditions are calculated as a function of internal 'pipe' and porous media 'Darcy' flow correlations. Combustion gas flow rates are calculated for the CFR on a per-linear inch basis and solved simultaneously with a detailed thermal-gas dynamic model of a local region of gas blow by (or splice fault). Effects of gas compressibility, friction and heat transfer are accounted for the model. Computational Fluid Dynamic (CFD) solutions of the fault regions are used to characterize the local flow field, quantify the amount of free jet spreading and assist in the determination of impingement film coefficients on the nozzle housings. Gas to wall heat transfer is simulated by a large thermal finite element grid of the local structure. The employed numerical technique loosely couples the FE (Finite Element) solution with the gas dynamics solution of the faulted region. All free constants that appear in the governing equations are calibrated by hot fire sub-scale test. The calibrated model is used to make flight predictions using motor aft end environments and timelines. Model results indicate that CFR barrier systems provide a near 'vented joint' style of pressurization. Hypothetical fault conditions considered in this study (blow by, splice defect) are relatively benign in terms of overall heating to nozzle metal housing structures.

Clayton, J. Louie↗
NASA NTRS2000

Lean direct wall fuel injection method and devices

A fuel combustion chamber, and a method of and a nozzle for mixing liquid fuel and air in the fuel combustion chamber in lean direct injection combustion for advanced gas turbine engines, including aircraft engines. Liquid fuel in a form of jet is injected directly into a cylindrical combustion chamber from the combustion chamber wall surface in a direction opposite to the direction of the swirling air at an angle of from about 50.degree. to about 60.degree. with respect to a tangential line of the cylindrical combustion chamber and at a fuel-lean condition, with a liquid droplet momentum to air momentum ratio in the range of from about 0.05 to about 0.12. Advanced gas turbines benefit from lean direct wall injection combustion. The lean direct wall injection technique of the present invention provides fast, uniform, well-stirred mixing of fuel and air. In addition, in order to further improve combustion, the fuel can be injected at a venturi located in the combustion chamber at a point adjacent the air swirler.

Choi, Kyung J.↗
DOE OSTI2021

Preheating and premixing effects on NO x emissions in a high-pressure axially staged combustor

NO x emissions remain a primary concern for modern and future gas turbines, particularly as we progress towards a net-zero carbon future. It is critical to identify novel strategies to mitigate environmental pollutants for both modern turbines operated on natural gas and future turbines projected to use carbon-free fuels (such as hydrogen). In the current study, NO x emissions of a reacting methane-air jet in a vitiated crossflow are experimentally investigated in a model axially staged combustor at 5 atm. The combustion products from the main stage combustor flow into the axial stage at temperatures ranging from 1580 to 1650 °C. The axial stage contains a reacting jet in crossflow, which provides an overall temperature rise ranging from 50 to 220 °C to generate exit temperatures similar to gas turbine engines. The focus of this paper is to explore the effects of flame liftoff and ignition timescales on the NO x contribution of this secondary jet. This is done by varying the premixed level and preheat temperature of the axial jet. The effects are explored at different momentum flux ratios (J), jet equivalence ratios (φ jet ), exit temperatures (T exit ), and main stage (headend) temperatures (T HE ). High-speed CH* chemiluminescence imaging is employed for each test case to determine the flame stabilization point. For a given temperature rise and combustor exit temperature, an increase in ignition delay was observed with a decrease in jet temperature. This provided a NO x benefit, particularly for jets that are injected at or close to an ignitable mixture fraction. Similarly, the coaxial injector caused a significant ignition delay compared to the fully premixed injector; this also led to a NO x benefit. Overall, the results show that a thermally driven delay in the axial stage provides a greater NO x reduction than a mixing delay.

03 NATURAL GAS↗
DOE OSTI2022

The role of ETG modes in JET–ILW pedestals with varying levels of power and fuelling

Abstract We present the results of GENE gyrokinetic calculations based on a series of JET–ITER-like-wall (ILW) type I ELMy H-mode discharges operating with similar experimental inputs but at different levels of power and gas fuelling. We show that turbulence due to electron-temperature-gradient (ETGs) modes produces a significant amount of heat flux in four JET–ILW discharges, and, when combined with neoclassical simulations, is able to reproduce the experimental heat flux for the two low gas pulses. The simulations plausibly reproduce the high-gas heat fluxes as well, although power balance analysis is complicated by short ELM cycles. By independently varying the normalised temperature gradients ( ω T e ) and normalised density gradients ( ω n e ) around their experimental values, we demonstrate that it is the ratio of these two quantities η e = ω T e / ω n e that determines the location of the peak in the ETG growth rate and heat flux spectra. The heat flux increases rapidly as η e increases above the experimental point, suggesting that ETGs limit the temperature gradient in these pulses. When quantities are normalised using the minor radius, only increases in ω T e produce appreciable increases in the ETG growth rates, as well as the largest increases in turbulent heat flux which follow scalings similar to that of critical balance theory. However, when the heat flux is normalised to the electron gyro-Bohm heat flux using the temperature gradient scale length L T e , it follows a linear trend in correspondence with previous work by different authors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗