ION BEAM PROPAGATION STABILITY IN A LINAC ACCELERATING CHANNEL BASED ON COMBINED RF-FOCUSING

The issue of simultaneous longitudinal and transverse particle propagation stability in a linear ion accelerator channel based on combined RF-focusing is investigated. Values for RFQ field gradient to provide transverse propagation stability for all the particles in an acceleration mode are calculated. It is also shown that electrical strength of the electrodes influences the gradient value. Much attention is given to modeling of an accelerating-focusing channel which provides the minimal growth in beam emittance.

Mechanism Understanding of the Role of Rare Earth Inclusions in the Initial Marine Corrosion Process of Microalloyed Steels

In this study, the corrosion behavior of rare earth (RE) microalloyed steels was first evaluated through potentiodynamic polarization tests and corrosion weight loss experiments, and then the corrosion morphologies were observed by scanning electron microscope (SEM). After immersion in a NaCl solution, the sulfides (or oxygen sulfides) dissolved preferentially, followed by corrosion at the boundary between the Fe matrix and oxides. Afterwards, the inclusions fell off as a whole, which promoted pitting nucleation. The first principle modeling demonstrated that the work functions of various kinds of inclusions descended in the following order: La2Zr2O7 > LaAlO3 > (La2O3 ≈ Fe ≈ La2O2S) > La2S3, which provided a theoretical explanation to the dissolution behaviors of inclusions. That is, inclusions containing sulfur tend to dissolve preferentially, whereas the oxides do not dissolve easily. Subsequently, the surface current distributions were detected by the scanning vibrating electrode technique (SVET), which provided more microscopic insight into the role of inclusions in the corrosion propagation. Results showed that the active sites of pitting nucleation accelerated the transverse propagation of corrosion. Finally, local corrosion spread to the whole surface as uniform corrosion.

Development of a Metamodel for Predicting Near-Field Propagation of Hazardous and Noxious Substances Spilled From a Ship

This study aims to numerically analyze the near-field propagation behavior of hazardous and noxious substances (HNSs) and to develop a new metamodel for HNS propagation. Extensive computational fluid dynamics (CFD) simulations were conducted using the ANSYS FLUENT (V. 17.2) code for various HNS spill scenarios. We newly introduced several key parameters, including the streamwise propagation velocity, transverse propagation velocity, and averaged HNS mass fraction. From the results, the advection effect is more dominant with an increase in the current velocity and streamwise propagation velocity, and with a decrease in the transverse propagation velocity. Also, the HNS mass fraction decreases as the current velocity increases with the change of concentration and propagation area. Particularly, a new metamodel of HNS propagation based on the current CFD results was validated by the hidden point test, showing very good fit. We believe this model would make useful predictions under various scenarios without CFD simulations.

Dispersive and effective properties of two-dimensional periodic media

We consider transverse propagation of electromagnetic waves through a two-dimensional composite material containing a periodic rectangular array of circular cylinders. Propagation of waves is described by the Helmholtz equation with the continuity conditions for the tangential components of the electric and magnetic fields on the boundaries of the cylinders. We assume that the cell size is small compared with the wavelength, but large compared with the radius a of the inclusions. Explicit formulae are obtained for asymptotic expansion of the solution of the problem in terms of the dimensionless magnitude q of the wavevector and radius a . This leads to explicit formulae for the effective dielectric tensor and the dispersion relation with the rigorously justified error of order O (( q 2 + a 2 ) 5/2 ).

Gravitational instability of rotating magnetized quantum anisotropic plasma

The present problem deals with the study of gravitational (Jeans) instability of magnetized, rotating, anisotropic plasmas considering quantum effects. The basic equations of the considered system are constructed using combined Chew–Goldberger–Low (CGL) fluid model and quantum magnetohydrodynamic (QMHD) fluid model. A dispersion relation is obtained using the normal mode technique which is discussed for transverse and longitudinal modes of propagation. It is found that a rotating quantum plasma influences the gravitational mode in transverse propagation but not in longitudinal propagation. The presence of rotation decreases the critical wavenumber and it has a stabilizing effect on the Jeans instability criterion of magnetized quantum plasma in transverse propagation. The firehose instability is unaffected due to the presence of uniform rotation and quantum corrections. We observe from the numerical analysis that region of instability and critical Jeans wavenumber are both decreased due to the presence of uniform rotation. The stabilizing influence of uniform rotation is observed for magnetized, rotating, anisotropic plasmas in the presence of quantum correction. In the case of a longitudinal mode of propagation we found the Jeans instability criterion is not affected by rotation. The quantum diffraction term has a stabilizing effect on the growth rate of the Jeans instability when the wave propagates along the direction of the magnetic field.