Tangential Injection Research Articles

Studies of beam ion confinement to enhance plasma performance on EAST

Abstract A key physics issue for achieving steady-state high-performance plasmas on EAST tokamak is to decrease beam-ion losses to improve plasma confinement during neutral beam injections (NBIs). To decrease the beam losses, previous counter-Ip NBI injections are upgraded to co-Ip injections. Analysis shows that due to the reversed direction of drift across the flux surfaces caused by the pitch angle, the beam prompt loss fraction decreases from about 49% to 3% after the upgrade. Moreover, because of the change of entire beam path, beam shine-through (ST) loss fraction for counter-Ip tangential and counter-Ip perpendicular injections is reversed to co-Ip tangential and co-Ip perpendicular injections, respectively. Due to change in the initial trapped-confined beam ion fraction caused by the peaked pitch profiles, the losses induced by toroidal ripple field are also reversed after the upgrade. To further improve the beam-ion confinement under the present NBI layout, the amplitudes of toroidal field are increased from 1.75 to 2.20 T. Result shows that, due to the smaller orbit width and peaked pitch angle profile, the beam prompt loss power is lower with higher toroidal field. Due to the synergy of higher initial trapped-confined beam ion fraction and narrower Goldston-White-Boozer (GWB) boundary, the loss induced by ripple diffusion is higher with higher toroidal field. The combined effect of beam ST loss, prompt loss, and ripple loss, contributes to the increase in beam ion density. The decrease in beam loss power enhances beam heating efficiency, especially the fraction of beam heating ions. Finally, comparison between simulation and measurement by 235U fission chamber (FC) indicates that the increase in neutron rate are mainly contributed by improvement of beam-ion confinement. This study can provide potential support for beam operation and high-Ti experiment on EAST tokamak.

Effects of vacuum magnetic field region on the compact torus trajectory in a tokamak plasma

The trajectory of the compact torus (CT) within a tokamak discharge is crucial to fueling. In this study, we developed a penetration model with a vacuum magnetic field region to accurately determine CT trajectories in tokamak discharges. This model was used to calculate the trajectory and penetration parameters of CT injections by applying both perpendicular and tangential injection schemes in both HL-2A and ITER tokamaks. For perpendicular injection along the tokamak’s major radius direction from the outboard, CTs with the same injection parameters exhibited a 0.08 reduction in relative penetration depth when injected into HL-2A and a 0.13 reduction when injected into ITER geometry when considering the vacuum magnetic field region compared with cases where this region was not considered. In addition, we proposed an optimization method for determining the CT’s initial injection velocity to accurately calculate the initial injection velocity of CTs for central fueling in tokamaks. Furthermore, this paper discusses schemes for the tangential injection of CT into tokamak discharges. The optimal injection angle and CT magnetic moment direction for injection into both HL-2A and ITER were determined through numerical simulations. Finally, the kinetic energy loss occurring when the CT penetrated the vacuum magnetic field region in ITER was reduced by by optimizing the injection angle for the CT injected into ITER. These results provide valuable insights for optimizing injection angles in fusion experiments. Our model closely represents actual experimental scenarios and can assist the design of CT parameters.

Numerical simulations on loss of ICRF-heated NBI ions in EAST

The loss of ion cyclotron resonance frequencies (ICRF)-heated neutral beam injection ions in experimental advanced superconducting tokamak was numerically investigated by ORBIT code simulations. The effects of collisions and ripples on particle losses were taken into account, and the distributions of fast ions generated by different beams in combination with ICRF heating were calculated using the TRANSP code. Results showed that ICRF waves altered the orbital distributions of beam ions, causing an increase in trapped ions and fast ion losses. Additionally, for co-current injected beams, perpendicular injection resulted in higher fast ion losses in synergistic heating than tangential injection. The study also found that the synergistic effect of collisions and ripples enhanced fast ion losses, which were highly localized and generated a maximum heat load of 0.165 MW m−2 on the first wall. However, conducting synergy heating experiments at high plasma currents and low effective ion charge numbers can significantly reduce the loss of fast ions.

An experimental study of dynamic flashing in a square tube using tap water

Flashing is a pressure driven phase change phenomenon. It is widely studied due to its richness in physics and applications such as in desalination, in nuclear industry to name a few. Dynamic flashing is a situation wherein the pressure drop for flashing is initiated through the flow of liquid. A recently developed novel desalination system [1] utilizes combined dynamic flashing and vapor separation through tangential injection for producing potable water. An understanding of dynamic flashing in a tube with reference to the novel desalination system could help with its optimization. In this work, dynamic flashing of tap water occurring in a clear quartz square tube was studied. The pressure and temperature measurements along the tube were made and analyzed for different inlet flowrates and initial liquid temperatures. The pressure and temperature values showed increasing gradients along the tube indicating increased vapor production or flashing for increasing flowrates and initial liquid temperatures. The vapor production from flashing and the resulting flow regimes along the tube were tracked and identified through high-speed imaging. Visual observations showed complex flow regimes with bubbles nucleating and growing throughout the tube due to flashing. Most of the bubble formation was observed in the bulk with little nucleation on the glass tube wall. Void fraction measurements along the tube based on capacitance impedance technique were performed to supplement the visual observations which showed increasing void fraction along the tube matching the observed flow regimes from vapor production.

Sustainability of flameless combustion mode with hydrogen addition to liquid kerosene fuel at high-intensity conditions

The application of hydrogen for fuel enrichment and blending has recently gained importance. The sustainability and performance enhancement through hydrogen addition in flameless combustion mode for liquid fuels needs further investigation to enhance our understanding. Therefore, the present study reports the effect of hydrogen addition on the flameless combustion of a kerosene-fired 30 kW swirl combustor with hydrogen addition. A divergence-shaped conical combustor with tangential air injection and asymmetric fuel injection scheme is adopted. The liquid fuel was injected using a solid-cone swirl nozzle with 34 μm Sauter Mean Diameter. The hydrogen addition was varied from 0 to 20% on a thermal input basis, and the thermal input of liquid fuel was maintained at a 30 kW level. Computational studies helped understand the flow physics behavior within the combustor volume. The hydrogen addition was observed to improve the reactant dilution ratio (Rdil). The maximum values of the Rdil increased from 4.47 to 5.44 with hydrogen addition. Hydrogen addition further helped extend the flameless combustion regime to φ = 0.3 without any air preheating. A uniformly distributed reaction with a reduced-temperature gradient is observed with extended combustion stability limits. A marginal increase in NOx emissions was observed with hydrogen addition, albeit within permissible limits, accompanied by ∼8–20 dB reduction in acoustic emissions.

Active generation and control of radial electric field by local neutral beamlets injection in tokamaks

The radial electric field plays an important role in plasma confinement in tokamaks and can be generated through neutral beam injection. In this study, we propose a model for calculating the radial electric field resulting from tangential local neutral beamlet injection, aiming to externally control and improve plasma confinement. The Neutral beamlet ion and Energetic particles Orbit mover and Electric field solver code has been developed to analyze this issue, and its simulation results have been validated against results from other codes as well as measurements from correlation reflectometers. The charge separation is primarily caused by the redistribution and loss of beam ions due to magnetic gradient and curvature drift as well as collision effects, and it is maintained through continuous beamlet injection. The electric field is calculated using Poisson’s equation, taking into account both classical and neoclassical polarization effects. The results demonstrate that despite the high losses and low heating efficiency associated with localized beamlets, they are capable of generating a significant radial electric field characterized by a steep gradient. This presents opportunities for external control of the electric field, potentially enhancing plasma confinement.

Effect of combined water-jet inlets on the hydrodynamic performances in square arc-corner aquaculture tanks

To enhance the energy utilization and waste collection efficiency in a recirculating aquaculture system (RAS), this study investigates the hydrodynamic performance of a square arc-corner aquaculture tank using various combined water-jet inlets. An experimental verification system was developed for the recirculating aquaculture tank (RAT) to validate the accuracy of the computational fluid dynamics (CFD) model. This was achieved by comparing flow velocities at various monitoring points. A comprehensive analysis of the tank's hydrodynamic performance was conducted, encompassing velocity distribution, vorticity strength, flow uniformity index, resistance coefficient, Froude number, energy utilization efficiency, and particle removal rate. The results clearly showed that incorporating combined water-jet inlets greatly improved the hydrodynamic performance of the tank compared to traditional one-way inflow patterns. The combined injection method ensured a more uniform flow velocity both longitudinally and radially throughout the RAT, effectively reducing the concentration of water flow in a single direction. Additionally, the tangential injection of water flow along the tank wall promoted a more even flow rate, enhancing water mixing and maintaining a homogeneous distribution of dissolved oxygen. By arranging and spacing the injection holes appropriately, the fluidity and mixing of water were enhanced, leading to increased energy utilization and improved efficiency in pollutant collection.

The effect of pressure anisotropy on 3-D MHD stability for low magnetic field LHD equilibria

The magnetohydrodynamic stability of plasmas with an anisotropic pressure component is analysed for a low magnetic field configuration of the large helical device. Magnetic equilibria are calculated by the anisotropic Neumann inverse moments equilibrium code, an extension of the three-dimensional variational moments equilibrium code. A modified version of the bi-Maxwellian is used to model the anisotropic particle velocity distribution. Magnetohydrodynamic stability calculations for the $n=1$ mode family are carried out by TERPSICHORE, which has been expanded by the Kruskal–Oberman energy principle. For on-axis particle deposition, the growth rate and plasma displacement show that the parallel dominant plasmas are significantly more stable than isotropic or perpendicular dominant plasmas. For off-axis particle deposition, the growth rate and the Mercier criterion in the peripheral region $\rho =0.9$ , show that low field (LF) deposition perpendicular dominant plasmas are most unstable. For the most realistic off-axis deposition profile, it is found that parallel dominant plasmas are most stable for LF deposition, while perpendicular dominant plasmas are most stable for high field deposition. We conclude that, under low magnetic field conditions in the large helical device, tangential neutral beam injection heating has a stabilising influence on the plasma.

Self-sustained azimuthal aeroacoustic modes. Part 2. Effect of a swirling mean flow on the modal dynamics

The whistling induced by a low-Mach turbulent flow through a deep axisymmetric cavity in a duct is investigated theoretically and experimentally. The experiments include acoustic measurements and stereoscopic particle image velocimetry (PIV). The paper focuses on the effect of a mean swirl on the dynamics of the azimuthal aeroacoustic modes. The mean swirl in the cavity has two origins: one component is imposed by a controlled tangential air injection upstream of the cavity, and the other component spontaneously arises under the action of the self-sustained azimuthal aeroacoustic mode, as explained in the companion paper, Part 1 (Faure-Beaulieu, Xiong, Pedergnana & Noiray, J. Fluid Mech., vol. 971, 2023, A21). Experiments show that the dynamics of the aeroacoustic wave is influenced by the imposed swirl. In particular, the spinning wave propagating against the swirl is promoted. To explain this, a linear perturbation analysis is performed around an incompressible mean swirling flow obtained from RANS simulations. It reveals that the dominant shear layer modes of azimuthal order 1 and −1 involved in the whistling phenomenon are helical modes winding respectively with and against the swirl, and spinning respectively in counterswirl and co-swirl directions. The counterswirl hydrodynamic mode is the least damped of the two, which is in agreement with the experimental observations. Finally, a low-order model based on the wave equation is derived. With only a few parameters, it fully reproduces the experimental observations for a wide range of imposed swirl intensity in the duct flow, and it allows us to disentangle the mechanisms responsible for this complex aeroacoustic instability.

Energetic passing particle-driven instabilities and their impact on discharge evolution in KSTAR

An experimental study is conducted on the onset and evolution characteristics of energetic particle-driven instabilities in Korea Superconducting Tokamak Advanced Research (KSTAR) with dominant tangential neutral beam injection (NBI). A scan of NBI beam energy shows the evanescence of the sawtooth crash and the concomitant onset of the strong passing particle-driven low-frequency fishbone instability. A quantitative analysis shows that the safety factor (q)-profile in the core region is clamped by a balance between the depletion of energetic passing particles by the fishbone instability and their external replenishment. Two synchronized chirping modes with distinct toroidal mode numbers (n = 1 and n = 5) supersede the fishbone instability after a self-organized q-profile is attained. An analysis shows that the n = 1 mode is likely to be a high-frequency beta-induced Alfvén eigenmode fishbone branch, while the n = 5 mode is an energetic particle mode (EPM). A dynamic system analysis of the synchronized EPM (S-EPM) shows that a stable S-EPM cycle can exist when the coupling between the two modes involved is insignificant. The potential impact of such EPMs on the establishment of a burning plasma scenario with a flat core q-profile is briefly discussed.

Characterizing Swirl Strength and Recirculation Zone Formation in Tangentially Injected Isothermal Flows

This paper presents a computational study characterizing the swirl intensity distribution and Internal Recirculation Zone (IRZ) formed in a cylindrical domain with tangential injections and isothermal flow. The range of inlet boundary conditions investigated is 5o to 25o for the injection angle and 7190 to 100711 for the bulk flow Reynolds number. The evolution of swirl intensity is presented with and without incorporating effects of the accompanying pressure variations. The Shear Stress Transport (SST) k-ω is used to model turbulence. Results show that the Swirl strength created by such tangential injections strongly depends on the injection angle but does not vary with bulk flow Reynolds number (Re), except for low Re values. The swirling flow is shown to result in IRZ formation at injection angles 6o and above or when asymptotic value of the maximum Swirl Number in the domain exceeds approximately 0.6, same as the transition value of inlet Swirl Number in swirling flows with axial injections. The IRZ length increases with injection angle and varies with Re for lower values of Re at a given injection angle but asymptotes for higher values above 40000. The conventional Swirl Number rises rapidly downstream of the injection plane followed by a slow decline. On the other hand, an alternative Swirl Number, which incorporates the gauge pressure variation, shows slow and consistent decay all the way downstream of the injection plane. The Swirl Number incorporated with gauge pressure term subsumes interconversions between the axial momentum and pressure in the regions of vortex breakdown and IRZ formation, thereby presenting an alternative picture of swirl intensity evolution in swirling flows.

First observations of confined fast ions in MAST Upgrade with an upgraded neutron camera

Spherical tokamaks are key to the successful design of operating scenarios of future fusion reactors in the areas of divertor physics, neutral beam current drive and fast ion physics. MAST Upgrade, which has successfully concluded its first experimental campaign, was specifically designed to address the role of the radial gradient of the fast ion distribution in driving the excitation of magneto-hydrodynamic (MHD) instabilities, such as toroidal Alfvén eigenmodes, fish-bones and long-lived mode, thanks to its two tangential neutral beam injection systems, one on the equatorial plane and one that is vertically shifted 65 cm above the equatorial plane. To study the fast ion dynamics in the presence of such instabilities, as well as of sawteeth and neo-classical tearing modes, several fast ion diagnostics were upgraded and new ones added. Among them, the MAST prototype neutron camera (NC) has been upgraded to six, equatorial sight-lines. The first observations of the confined fast ion behavior with the upgraded NC in a wide range of plasma scenarios characterized by on-axis and/or off-axis heating and different MHD instabilities are presented here. The observations presented in this study confirm previous results on MAST but with a higher level of detail and highlight new physics observations unique to the MAST Upgrade. The results presented here confirm the improved performance of the NC Upgrade, which thus becomes one of the key elements, in combination with the rich set of fast ion diagnostics available on the MAST Upgrade, for a more constrained modeling of the fast ion dynamics in fusion reactor relevant scenarios.

Main flow oriented vorticity noise experiments

Entropy inhomogeneities and vorticity spots induce so-called indirect combustion noise when passing through a choked nozzle; referred to as entropy noise and vorticity noise, respectively. We note that vorticity noise depends on the orientation of the vorticity; viz., oriented normal or parallel to the axial main flow. An experimental investigation of parallel component vorticity noise is presented. In the experiment a time- dependent swirling flow was induced by unsteady tangential injection in the pipe upstream of a choked convergent-divergent nozzle. As the resulting swirling flow passes through the nozzle, the axial stretching of the fluid caused an increase in rotation energy. The steady energy conservation in an isentropic flow implies a Mach number higher than unity at the throat and an associated reduction of density. Ergo, the critical mass-flow rate (for fixed reservoir pressure and temperature) decreases quadratically with increasing swirl intensity. The acoustic waves radiated downstream of the nozzle are a direct measure for this mass-flow modulation. Using a semi-empirical model, this sound production mechanism is demonstrated to indeed be quasi steady.

Experimental and numerical study on heat transfer characteristics of tangential effusion cooling for a combustor liner

A great number of studies have been conducted on effusion cooling, which is based on the flat plate. However, the differences in flow and heat transfer characteristics between a flat plate and a circular combustor restricted the immediate application of the previous studies to the design of combustor cooling. In this study, a new type of effusion cooling with tangential injection based on the cylinder, which was fabricated by electric discharging machining, is employed in the present investigation using infrared imaging technique. With the blowing ratio ranging from 2.2 to 17.9, the results of proposed structure were compared with that of effusion holes based on the flat plate. The compound angles (β) of tangential effusion are 45°, 60°,75°, 95° respectively. Results show that compared to the effusion cooling based on the flat plate, the cooling jets of the tangential effusion based on the cylinder have a large tangential velocity component, which keeps the cooling jets attached to the wall and flowing spiral forward. The overall cooling effectiveness of tangential effusion is about 50% higher than effusion holes based on the flat plate. This also indicates that the existing conclusions of effusion cooling based on the flat plate cannot be directly applied to the combustion chamber. The cooling performance of tangential effusion cooling is greatly influenced by the compound angle and the 75° is optimal among them. In the studied range of blowing ratio, the overall cooling effectiveness of tangential effusion is above 0.8, and there is a significant cooling enhanced with the increase of blowing ratio. This provides a reference and database for the cooling design for low-emission combustion chambers with low cooling consumption.

Stability and emission characteristics of ammonia-air flames in a lean-lean fuel staging tangential injection combustor

The present work suggests the stability and emission characteristics of an ammonia-air tubular flame in a fuel staging tangential injection combustor. Owing to the development of a large inner recirculation zone induced by a high swirling motion, the ammonia tubular flame exhibited wide operational flexibility at an ambient temperature condition. With ammonia fuel staging, we confirmed that the Thermal DeNOx process significantly mitigates NO emissions when the exit temperature of the primary region is close to the threshold for active NO reduction. In this study, fuel multi-stage technology was used for pure ammonia-air combustion, and the result effectively challenges the existing paradigm of the NO reduction strategy: Rich-Quench-Lean staging configuration. Thus, our results demonstrate the potential use of ammonia as a fuel in a dry low-NOx system.

Experimental and Computational Investigation upon Combustion Characteristics of Liquid Fuel in a Novel Combustor with Hybrid Swirl and Recirculation Bowl.

In the present study, a novel hybrid swirl combustor is designed to reduce the size and complexity of a conventional gas turbine combustor. In this combustor, a dual-swirl pattern is adopted by providing the central vane swirler (45° vane angle) and circumferential tangential injection scheme to achieve higher recirculation of heat and combustion products inside the combustor. Numerical and experimental studies are carried out to understand the flow patterns and combustion characteristics in this high mass-heat interacting environment. Initially, computational studies were carried out to find the optimum geometry for greater recirculation and interaction among the reacting species inside the combustor. Liquid fuel (kerosene) is sprayed into the combustor for two thermal inputs of 25 and 50 kW. Three cases were studied to analyze the effect of bowl recirculation and tangential air inputs in addition to the swirlers. The hybrid swirl, formed by the counter-flow pattern, helps in achieving low and uniform temperature throughout and assists in flame anchoring. The tangential air flow provides a push to the combustion products from the downstream to the central recirculation zone of the combustor. The combined effect of central and tangential swirlers helps in attaining a more distributed combustion. The CO and NO emissions reduced with the use of hybrid swirl.

Effects of external kink and fishbone-like modes on energetic particle transport in tokamak plasmas

Transport and loss of beam injected energetic particles (EPs) due to three-dimensional perturbations, associated with the external kink (XK) instability and fishbone-like mode (FLM), are numerically investigated utilizing the guiding center following code ORBIT for static toroidal plasmas in HL-2A. The perturbation structure for the XK is computed by the MARS-F code and then mapped to the Boozer coordinates as defined in ORBIT. The simulation shows that the EP profile experiences a significant change in the middle of the plasma column, when the XK-induced radial magnetic field perturbation amplitude, normalized by the equilibrium field, exceeds a threshold value of about . The EP transport is found to be dominated by a diffusion process instead of convection. Furthermore, by scanning the perturbation frequency as a free parameter while maintaining the XK mode structure (thus mimicking the FLM as observed in DIII-D and JT-60U tokamaks), redistribution and loss of EPs are found to be substantially enhanced due to strong resonances between the FLM and EPs, when the mode frequency exceeds a threshold value of ∼2 kHz for the case considered. For either XK or FLM, the response of passing EPs to the perturbation is dominant due to the assumed tangential neutral beam injection. Most lost EPs due to these instabilities are initially passing particles but are eventually lost through trapped orbits.

Experimental Results for a Novel Flash Evaporation and Phase Separation System for Desalination of Sea Water

Abstract A novel system combining dynamic flash evaporation and vapor separation for desalination has been investigated in this work. The feed water passes through injection tubes which are connected to injector passages installed tangentially onto a separator tube. Flashing in the injection tubes is initiated from pressure drop due to friction and acceleration resulting in a two-phase mixture. Centrifugal force from tangential injection separates the two-phase mixture. In this compact system, vapor production and phase separation occur on the order of several milliseconds. Tap water and seawater were used as inlet feed water for the system. Thermal conversion efficiency to analyze the vapor production efficacy and phase separation efficiency to evaluate the purity of the condensate were investigated to evaluate the system. Thermal conversion and phase separation efficiencies up to 98% were obtained with the single stage system. Further improvement in purity of condensate was achieved with a two-stage system. In the two-stage system, the vapor captured along with some entrained droplets from the first stage was directed to a second set of injector passages connected in series to the first stage retrieval tube. With a two-stage system and seawater with salt concentration by mass of 2.5%, collected condensate with salt concentrations lower than 0.02% by mass was achieved, which is comparable to that of potable water. Thus, the novel dynamic flash evaporation and vapor separation system have been demonstrated to be very effective in producing potable water.

Development and Performance of Hydrocyclone Separator for Biodiesel Production

Hydrocyclone is an equipment that uses a cyclone or tangential injection flow process with centrifugal forces to separate liquids of different densities. The denser liquid move downwards in a spiral path into an underflow chamber, while clean liquid which is less dense move upwards to the center of the spiral, towards the top outlet. Colman and Thew’s hydrocyclone geometry analysis approached was used in the design and the assumed inlet chamber diameter (D) used for this design was 150 mm and a reducing section length of 1500 mm at a reducing angle of 20°. The capacity of the designed hydrocyclone system in volume is 5.5 liters. The developed machine was tested with 15 liters of palm kernel oil (PKO) as raw material using two different pressures gauge (70 and 80 kPa) and also effect acid concentration (sulphuric acid) at 3 different experimental runs. After the experiments, it was deduced that at constant temperature level, as the pressure rate increases, there is a corresponding increase in the discharge rate at the underflow and overflow outlets where 2.04 minutes and 1.67 minutes were used to separate biodiesel and glycerin under 70 and 80 kPa respectively. Also, it was deduced experimentally that PKO with sulphuric acid gives a higher yield of biodiesel of 47.74% while the one without has 38.49% yield under same experimental and operational conditions.

Effect of Secondary Combustion on Thrust Regulation of Gas Generator Cycle Rocket Engine

Thrust regulation is applied to maintain the performance of the liquid propellant rocket engine. The thrust level of a rocket engine can be readily controlled by adjusting the number of propellants introduced into the combustion chamber. In this study, a gas generator design is proposed in which thrust regulation is maintained by performing secondary combustion in the divergent section of the nozzle of a gas generator. Tangential and normal injection techniques have also been studied for better combustion analyses. A normal injection technique is used for the experiment and CFD results are validated with the experimental data. Chemical equilibrium analyses are also performed by minimizing Gibbs free energy with the steepest descent method augmented by the Nelder–Mead algorithm. These equilibrium calculations give the combustion species as obtained through the CFD results. Performance evaluation of the rocket engine, with and without secondary combustion in the gas generator, led to an increase of 42% thrust and 46.15% of specific impulse with secondary combustion in the gas generator.