Uniform Transverse Distribution Research Articles

One-dimensional longitudinal space charge calculation based on integrated green function approach

For fast longitudinal electron beam dynamics study or optimization in an x-ray free electron laser (FEL) linear accelerator, the one-dimensional longitudinal space charge (1D LSC) impedance, assuming a round cylinder beam with uniform transverse distribution is extensively used in both analytical analysis and numerical simulation. In this paper, instead of employing the impedance model in the frequency domain, we directly calculate the longitudinal electric field by convolving the longitudinal beam density with the slice green function, i.e., the longitudinal electric field generated by a slice beam. For high-energy electron beam, the slice green function rapidly diminishes to zero within a distance significantly smaller than the bunch length. In order to resolve the sharp variation, we report on a fast and high-precision method by applying the integrated green function (IGF) approach to compute the 1D LSC field numerically with few grid points, therefore, providing us with an alternative approach to the impedance model.

Characteristics of Laser Ablation Plasma in the Diverging Magnetic Field of a Solenoid

Laser ablation plasma(LAP) can be used as an ion source for particle accelerators and for ion implantation. Although the too intensive current intensity of laser ion sources give them advantages over other ion sources, yet the minute duration of laser produced ion pulses limits their applications in accelerators. By introducing a solenoid into the plasma expansion region, the modulation of the plasma temporal structure had been achieved[ 1 - 3 ]. In order to study the effect of solenoid magnetic field on LAP, we used different laser energies (1~8 J) to produce LAP at different initial conditions and applied various magnetic field strengths to confine the plasma. The transverse distribution of the laser produced ions were measured with a movable faraday cup (FC) at the edge of the fringe field of the solenoid. The main parameters of the ion pulses, the total charge, the peak current, and the pulse duration, enhanced at first and then got saturated with the increasing magnetic field, no matter what the initial plasma conditions were. Unlike the nearly uniform transverse distribution of the plasma without magnetic confinement, the plasma got concentrated when the magnetic field was applied. The experimental results presented and discussed in the present work are of great significance for further understanding the characteristics of magnetically confined LAP.

Performance Evaluation of a Boomless Oscillating Field Sprayer at Different Spraying Pressures and Oscillating Rates

The efficiency expected from any pesticide depends largely on the type of plant protection machine used in spraying and the operating parameters of the selected machine. Today, sprayers with different spraying wing width are widely used in field spraying. Especially with field sprayers with large working widths, it is difficult to work at high spraying speeds due to the wing width and wing weight. In this study, wingless field sprayer effectiveness was evaluated. Occasionally for spraying instead of sprayers with standard type field spraying booms, the field sprayers with commercial name Electropar, which are operated with high pressure and with oscillating nozzles are used. Since the sprayer has no wings, it can spray at high tractor speeds. optimum working width of this sprayer, pestisit distribution uniformity on a horizontal surface, etc. Its parameters are unknown. In this study, the optimum working width provided by the sprayer at different operating pressures and nozzle oscillation rates, and volumetric fluid distribution throughout the working width and optimum working parameters were determined. The three different working pressures (1, 2 and 3 MPa) and the transverse volumetric fluid distribution of the three jet nozzle units moving in opposite directions relative to each other on a horizontal ground at two oscillations (44 and 60 rpm) were determined by a portable patternator. Operation of the high-pressure cone jet nozzle unit at 1 MPa pressure and 60 rpm oscillating speeds provided a more uniform transverse distribution than other operating parameters. The increase in operating pressure caused an increase in the volume of fluid accumulated in the patternator's grooves at the same working height and sampling distance. The optimum working width, depending on the operating conditions specified by the boomless sprayer, varied between 11.20 and 12.80 m depending on the spray unit oscillating speed and spray pressure.

Electron beam dynamic study and Monte Carlo simulation of accelerator-based irradiation system for natural rubber vulcanization

This research focused on an electron beam accelerator system for natural rubber vulcanization. In this accelerator, electrons are generated from a 17-keV DC gun and accelerated in a 5-cell RF linac with a resonant frequency of 2996.39 MHz and an effective length of 22.15 cm. The RF macro-pulse has a length of 4 μs with a maximum repetition rate of 200 Hz. Electron beam dynamics in the linac were studied using software ASTRA. It was found that the electron beam can be accelerated to have average kinetic energy in a range of 1–3.86 MeV for accelerating gradients of 16.2 to 39.5 MV/m. This accelerating range corresponds to the RF peak powers of 0.32–1.49 MW. The beam dynamic simulation results were used as the inputs for GEANT4 Monte Carlo simulation of electrons in the irradiation system. The beams exit the linac and collide with a 50-μm titanium window. Then, they travel through 18 cm of air and penetrate in the rubber latex with optimal depths of 0.3–1.3 cm for electron beam energies of 1–3.85 MeV. At the rubber surface, rectangular apertures with well-defined effective area were considered to select the beams with more uniform transverse distribution. The effective volumes defined from the optimum depth and the effective irradiation area are 0.01–6.29 cm3 to obtain the required absorbed dose in a range of 50–150 kGy. The results from this study can be used to determine the parameters and conditions of the machine and the irradiation system for the practical operation.

Design of dual flattening filter for 4-MeV electron beam irradiation system

A 4-MeV electron radio-frequency linear accelerator (RF linac) at the Plasma and Beam Physics Research Facility is used to irradiate electron beam on the natural rubber latex for vulcanization process. The irradiation area and uniformity of electron dose have significant influence on the vulcanization quality and throughput. This research focuses on the design of electron beam flattening filter to enlarge the transverse beam size with more uniform energy and dose distribution. The flattening filter system consists of two different filters. The primary one is used to increases the transverse beam size while the secondary one is used to modify the beam for achieving more uniform transverse distribution. Optimization of the filter system was performed for 4 MeV electron beam by using the GEANT4 Monte Carlo simulation program. The initial electron beam has a pencil shape with transverse Gaussian distribution and an RMS radius of 2 mm. The optimized parameters of the filters are thickness, shape and position. The results of the optimization suggest that the primary filter should have high atomic number. The tantalum (Ta) sheet with a thickness of 30 micron was chosen. The material and shape of the secondary filter were also studied. It is found that the aluminium (Al) plate with a shape of the truncated cone can smear the beam to uniformly distribute over the irradiating area. The output of this work can be used to construct the flattening filter system in the electron beam irradiation system for increasing the vulcanization throughput.

Generation of uniform transverse beam distributions for high-energy electron radiography

AbstractHigh-energy electron radiography (HEER) has been proposed for time-resolved imaging of materials, high-energy density matter, and for inertial confinement fusion. The areal-density resolution, determined by the image intensity information is critical for these types of diagnostics. Preliminary experimental studies for different materials with the same thickness and the same areal-density target have been imaged and analyzed. Although there are some discrepancies between experimental and theory analysis, the results show that the density distribution can indeed be attained from HEER. The reason for the discrepancies has been investigated and indicates the importance of the uniformity in the transverse distribution beam illuminating the target. Furthermore, the method for generating a uniform transverse distribution beam using octupole magnets was studied and verified by simulations. The simulations also confirm that the octupole field does not affect the angle-position correlation in the center part beam, a critical requirement for the imaging lens. A more practical method for HEER using collimators and octupoles for generating more uniform beams is also described. Detailed experimental results and simulation studies are presented in this paper.

Hydrodynamics in a circulating fluidized bed with annular furnace and six parallel cyclones

Systematic measurements were conducted on a cold CFB with annular furnace and six parallel cyclones to study gas-solids flow in the annular furnace and flow non-uniformity among six cyclones. The results show that axial solids holdup in the annular furnace decreases exponentially with height, similar to the conventional rectangular furnace. The uniform transverse distribution of solids holdup suggests a good gas-solids mixing in the annular furnace. The annular furnace presents the core/double-annulus flow structure, and it results in enhanced gas-solids back-mixing than the conventional core/annulus flow structure. The gas-solids flow of the inner wall-layer and the outer wall-layer is very close at most part of the furnace height, and the wall-layer thickness decreases with height. Flow non-uniformity exists among six parallel cyclones in the annular furnace CFB. But non-uniform distribution of solids circulating rates and cyclone pressure drops show no regularity, and the flow non-uniformity is no larger than the CFBs with conventional furnace. Under typical operating conditions, the relative deviation of six solids circulating rates is 8.0%.

Numerical Simulation of Film Cooling with a Coolant Supplied Through Holes in a Trench

The results of numerical simulation and experimental investigation of the efficiency of film cooling behind a row of holes in a trench in the range of blowing ratio variation 0.5 ≤ m ≤ 2.0 are presented. This scheme is of practical interest for use in the systems of cooling the blades of high-temperature gas turbines. Comparative analysis has shown that the efficiency of the trench scheme substantially exceeds the efficiency of the traditional scheme. The commercial package ANSYS CFX 14 was used in the Calculation Fluid Dynamics (CFD) modeling of film cooling. It is shown that the best agreement between predicted and experimental data is provided by the use of the SST model of turbulence. Analysis of the physical picture of flow has shown that the higher efficiency of film cooling with secondary air supply to the trench is mainly due to the preliminary spreading of a coolant in the trench, decrease in the intensity and scale of the vortex pair structure, absence of the coolant film departure from the plate surface, and to the more uniform transverse distribution of the coolant film.

Approximate longitudinal space charge impedances of a round beam between parallel plates and inside a rectangular chamber

This paper presents the approximate analytical solutions to the longitudinal space charge (LSC) impedances of a round beam with uniform transverse distribution and sinusoidal line density modulations under two boundary conditions: (a) between parallel plates (b) inside a rectangular chamber, respectively. When the ratio of beam diameter to chamber height is small, the image charge fields of the round beam can be approximated by those of a line charge, the approximate analytical LSC impedances can be obtained by image method. The derived theoretical LSC impedances are valid at any perturbation wavelength and are consistent well with the numerical simulation results in a large range of ratios of beam diameters to chamber heights.

Transformation of the Transverse Beam Intensity Distribution by Sextupole Focusing in a Transport Line

We investigate the transformation of the transverse intensity distribution of a charged-particle beam focused by one or two sextupole magnets in a beam transport line. It is expected, from the equation of transverse motion, that the beam is deflected toward one direction and thus deformed due to the second-order force of the sextupole magnet. Such a sextupole-induced deformation of the beam distribution has been studied analytically in detail. The beam centroid displacement and the change of the beam size are determined using the first-order and second-order moments of the intensity distribution function. In order to verify the theoretical consideration, numerical simulations and experiments were performed at the cyclotron facility of Japan Atomic Energy Agency. We experimentally demonstrate that an ion beam with a uniform transverse distribution can be formed using two sextupole magnets.

Acceleration of microparticles in a gasdynamic facility with high expansion of flow

In addition to being used for achieving the traditional objective (developing a high-velocity steady flow with uniform transverse distribution of parameters), high-enthalpy aerodynamic facilities may be employed as devices which accelerate microparticles for implementing modern technological processes (for example, treating the surfaces of solids). The acceleration of particles to high velocities is accompanied by a decrease in the density of carrier gas and its deep cooling. In this paper, a physicomathematical model of two-phase flow is constructed, which takes into account the strong temperature dependence of the thermal properties of material of the dispersed phase (thermal conductivity coefficient and specific heat capacity in accordance with the Debye theory), as well as the possibility flow past particles at arbitrary values of Knudsen number (from continuous to free-molecule mode of flow). Numerical investigation results are given for the values of parameters, which are characteristic of a typical high-velocity aerogasdynamic facility and dielectric microparticles accelerated in this facility. Considered by way of example are the cases of two materials with particles of different sizes.

Off-axis channeling disorder analysis

A new method has been developed to obtain, by means of channeling measurements, the distribution of defects in a plane normal to a low-index axis direction. This method takes advantage of the response of nonsubstitutional atoms to the spatial distribution of the channeled ion flux. It represents then an extention of the flux-peaking effect used to locate foreign atoms in a single-crystal lattice. This method has been used to study the disorder introduced by 300-keV N+ implantations in Si with fluences ranging between 6×1014 and 1016 ions/cm2 and analyzed in situ with 2.0-MeV He+ backscattering. Flux distributions of channeled ions have been evaluated as a function of the impinging angle for the <111≳ and 〈110〉 crystal directions of a Si lattice. The dechanneling probability has been estimated as a function of the impinging angle and of the total number of scattering centers, on the basis of plural scattering treatment. The analysis of the experimental data indicates a departure from a uniform transverse distribution of scattering centers both along the 〈111〉 and the 〈110〉 directions for low damage levels. The analysis has been detailed together with the main assumptions, and the range of validity of the method has been defined.