Validation of low-Z impurity transport theory using boron perturbation experiments at ASDEX Upgrade

An experimental technique has been developed at ASDEX Upgrade (AUG) to separately identify the diffusive and convective components of the boron particle flux. Using this technique a database of B transport coefficients has been assembled that shows that the normalized ion temperature gradient (R/LTi) is the strongest organizing parameter for both the B diffusion and convection and large R/LTi is a necessary ingredient to obtain hollow B density profiles in AUG. This database also shows that large changes in the applied neutral beam injection (NBI) have a relatively small impact on impurity transport compared to similar changes in electron cyclotron resonance heating (ECRH). Even low levels of ECRH power dramatically increase both the diffusive and convective fluxes and lead to peaking of the impurity density profile. Comparisons to a combination of neoclassical and quasi-linear gyrokinetic simulations show good agreement in the measured and predicted diffusion coefficients. The outward convection measured in NBI dominated plasmas, however, is not well captured by the simulations, despite the inclusion of fast ions. In contrast, the convection is reasonably well reproduced for plasmas with flat or peaked boron density profiles. This dataset provides an excellent experimental validation of the non-monotonic, predicted, convective-particle-flux created by the combination of pure-pinch, thermo-diffusion, and roto-diffusion. In addition, this dataset demonstrates a non-monotonic dependence of the experimental particle diffusivity to ion heat conductivity (D/χi) in qualitative agreement with theoretical predictions.

IGNITION CONDITIONS OF A SINGLE BORON PARTICLE IN HOT GAS FLOW

The basic experimental studies on boron combustion are done with the same general scheme of the experiment. Boron particles are injected into flat-flame burner products with the help of the transporting jet of cold nitrogen. Boron particle combustion process is registered with a number of optical methods. It is proposed that boron particle is injected into the main hot gas flow instantly, combustion takes place at the flame temperature and predefined oxygen concentration, and the influence of the transporting cold nitrogen jet is ignored. Recent combustion models are based mostly on this type of experiments and characterized with high complexity and low prediction level. In our study, we reconstruct the particle injection conditions for several basic experimental papers. It is shown that in all experimental setups, ignition, combustion, and even total particle burnout take place in the wake of the cold nitrogen jet. This zone is characterized with a much lower gas temperature and oxygen concentration than the main flat burner flow. The total temperature decrease can be about several hundred degrees, oxygen concentration can be 30%-50% lower than that used in the previous analysis of the experimental results. The temperatures of ignition and transition to the second stage of combustion are found with the help of the test particle trajectory and temperature tracking. It is shown that analysis of the influence of boron particles injection on gas temperature and oxygen concentration is mandatory for the development of future combustion models.

Influences of Boron Concentration on Mechanical Properties of Ni-W-B Composite Coatings

Ni-W-B alloy coating containing amorphous boron particle were fabricated by direct current electrodeposition on low carbon steel substrates. The effect of boron concentration in the plating bath on the surface morphology, the overall boron content in the deposited layers and the hardness of the resulting coating layer were investigated. Scanning electron microscopy (SEM) revealed that the surface morphology of the Ni-W-B coating layer was largely modified by the boron particle loading in the electroplating suspension. Distinct nodular structures were observed in these samples. Energy dispersive X-ray spectroscopy (EDS) spectra suggested that the overall boron content in the coating layer increased with increasing boron particle loading from 1 to 3 g/L. Too high boron particle loading of 10 g/L resulted in lower overall boron content. The highest hardness of 680.86 ± 17.67 Hv was obtained from Ni-W-B/B coating layer fabricated using the boron particle loading of 5 g/L.

Atomization of Gel Fuels with Solid Particle Addition Utilizing an Air Atomizing Nozzle

Microscopic high-speed imaging is used to experimentally measure the velocity and size of droplets of gelled RP-1 based fuels with a solid particle additive. The gels are atomized using an air atomizing nozzle. The droplet diameter and velocity at a fixed position 20 cm from the nozzle on the centerline of the spray are measured at air mass flow rates of 1.5, 3 and 5 g/s. A parametric study is conducted to study the effect of gas mass flow rate, boron particle content, and species of the solid particle on the droplet characteristics. The results indicate that the droplet size decreases with the increasing of gas mass flow rate and boron particle content. Gel fuels with an aluminum particle are observed to produce smaller droplets at a low gas mass flow rate than that with a boron particle. The implication of these observations is that the atomization processes for gelled fuels with an additive of solid particles is controlled by the velocity difference between the gas and the droplets.