Peak Beam Intensity Research Articles

Controllable self-rotating array beam with an arc-shaped accelerating trajectory.

In this study, a modified interfering vortex phase mask (MIVPM) is proposed to generate a new type of self-rotating beam. The MIVPM is based on a conventional and stretched vortex phase for generating a self-rotating beam that rotates continuously with increasing propagation distances. A combined phase mask can produce multi-rotating array beams with controllable sub-region number. The combination method of this phase was analyzed in detail. This study proves that this self-rotating array beam has an effectively enhanced central lobe and reduced side lobe owing to adding a vortex phase mask compared with a conventional self-rotating beam. Furthermore, the propagation dynamics of this beam can be modulated by varying the topological charge and constant a. With an increase in the topological charge, the area crossed by the peak beam intensity along the propagation axis increases. Meanwhile, the novel self-rotating beam is used for optical manipulation under phase gradient force. The proposed self-rotating array beam has potential applications in optical manipulation and spatial localization.

Fine-tuning to minimize emittances of J-PARC RF-driven H⁻ ion source.

The Japan Proton Accelerator Research Complex (J-PARC) cesiated RF-driven H(-) ion source has been successfully operated for about one year. By the world's brightest level beam, the J-PARC design beam power of 1 MW was successfully demonstrated. In order to minimize the transverse emittances, the rod-filter-field (RFF) was optimized by changing the triple-gap-lengths of each of pairing five piece rod-filter-magnets. The larger emittance degradation seems to be caused by impurity-gases than the RFF. The smaller beam-hole-diameter of the extraction electrode caused the more than expected improvements on not only the emittances but also the peak beam intensity.

Effusive atomic oven nozzle design using an aligned microcapillary array.

We present a simple and inexpensive design for a multichannel effusive oven nozzle which provides improved atomic beam collimation and thus extended oven lifetimes. Using this design, we demonstrate an atomic lithium source suitable for trapped-atom experiments. At a nozzle temperature of 525 °C, the collimated atomic beam flux directly after the nozzle is 1.2 × 10(14) atoms/s with a peak beam intensity greater than 5.0 × 10(16) atoms/s/sr. This suggests an oven lifetime of several decades of continuous operation.

The Perspectives of the Boron Neutron Capture Therapy-Clinical Applications Research and Development in Saudi Arabia

Boron Neutron Capture Therapy (BNCT) is a binary form of experimental radiotherapy which is based on the administration of a drug able to concentrate the isotopes in a tumor cell that later are irradiated with a neutron beam. Even though the first evidence of the success of this treatment dates back many years ago, BNCT showed successful treatment results in malignant melanoma, and Glioblastoma. In order for BNCT to be successful, a sufficient amount of Boron (10B) must be selectively delivered to the tumor cell, and then irradiated by neutrons of sufficient enough. The CS-30 cyclotron at King Faisal Specialist Hospital & Research Center is a positive-ion machine capable of accelerating protons at 26MeV, and other isotopes as well. Although the peak beam intensity from the CS-30 is low, the key to success of using it for the BNCT is by using a high average beam current at low energy. This work is aimed at testing the capability of the CS-30 Cyclotron to produce a low-energy neutron beam to be used to activate the Boron atoms injected into the tumor cell, through simulation of a compatible moderator. We are also planning to measure the overall dosimetry of the energy dose as well as that for the boron in the tumor cell.

Optimal control of the ballistic motion of Airy beams

We demonstrate the projectile motion of two-dimensional truncated Airy beams in a general ballistic trajectory with controllable range and height. We show that the peak beam intensity can be delivered to any desired location along the trajectory as well as repositioned to a given target after displacement due to propagation through disordered or turbulent media.

Single neuron response to pulse-periodic laser microirradiation. Action spectra and two-photon effect

Cytoplasm regions of crayfish stretch receptor neurons were irradiated by the microbeam of a pulse-periodic dye laser (diameter 5 μm, pulse duration 15 nsec, pulse frequency 400 Hz). Irradiation wavelengths varied from 434 to 600 nm, and beam intensity (at 441.6 nm) from 0.25 to 5 × 10 3 W cm −2 (mean), or from 0.4 to 8 × 10 8 W cm −2 (peak). Under irradiation neuron firing typically accelerated and then inhibited. In some cases it accelerated again and then abruptly and irreversibly ceased. Action spectra of parameters describing different response phases had the flavin-like maximum at 460 nm. This suggests flavins as a primary intracellular photoreceptor for blue laser light. It was also found that firing acceleration rate quadratically depended on peak beam intensity. This finding indicates the participation of two-photon processes in neuronal membrane alteration leading to firing acceleration. Parameters describing inhibition phase depended on beam intensity linearly. That is characteristic for usual single-photon process.

A Model for Laser Hole Drilling in Metals

A direct computer simulation technique is developed to analyze quantitatively the influence of the fluid flow and heat transfer in the transient development of a laser drilled hole in a turbine airfoil material, where the material removal is effected by vaporization and melt ejection. The coupled conduction heat transfer in the solid and the advection-diffusion heat transfer in the liquid metal, the fluid dynamics of melt expulsion and the tracking of solid–liquid and liquid–vapor interfaces have been mathematically modeled for the 2D axisymmetric case. The donor–acceptor cell method using the volume of fluid approach is used to solve the complex problem and a versatile numerical code has been developed. It takes into account all thermophysical properties including latent heat of vaporization, gravity, and surface tension driving forces. The novelty of this model is to treat the melted pool surface as a deformable free surface. The impressed pressure and temperature on the melt surface is provided by an 1D gas dynamics model whose vaporization kinetics are also discussed. The model is used to simulate drilling for a number of spatially and temporally varying laser intensity profiles. It is found that resolidification of melt (recast formation) occurred throughout the pulse interval and had significant effect on the developing hole geometry, while the effect of vaporization material removal on the hole geometry is found to be small. Comparison of the simulated results indicates the material removed per joule of energy absorbed appears to be inversely proportional to the square root of the peak beam intensity and the drilling rate appears to be proportional to the square root of the surface pressure.

Li-beam-heated hohlraum experiments at Particle Beam Fusion Accelerator II.

Thermal radiation experiments with 9-MeV Li beams have been performed at Particle Beam Fusion Accelerator II with a peak beam intensity of $1--2\mathrm{TW}/{\mathrm{cm}}^{2}$. The peak brightness temperature of the target was $58\ifmmode\pm\else\textpm\fi{}4\mathrm{eV}$. We obtained specific depositions of 800--1600 TW/g in the foam. Important features of desired hohlraum performance have been demonstrated. These include a near-Planckian spectrum, increased heating due to the presence of a high-Z wall, x-ray mean free paths greater than the target size between 200 and 280 eV, thermal x-ray emission more uniform than the incident ion energy, and a high-Z wall velocity less than 3 cm/\ensuremath{\mu}s.

NUMERICAL STUDY OF RADIATIVE TRANSPORT HYDRODYNAMICS, AND CHEMICAL KINETICS IN A PHOTODISSOCIATION ATOMIC IODINE AMPLIFIER

Index-of-refraction changes induced by hydrodynamic activity have been blamed for poor beam quality in photodissociation lasers. Until recently, the pump field, hydrodynamics, chemical kinetics, and the losing field have been decoupled in theoretical models because of the wide range of time scales on which they act. Although these mechanisms occur at varying time scales ranging over seven orders of magnitude (subnanosecond to milliseconds), each mechanism strongly affects the others. In this paper we present a model that first couples the pump field, chemical kinetics, and hydrodynamics in the form of implicit and explicit finite-difference equations. We then couple in the laser field to show that index-of-refraction changes induced by radiative transfer degrade peak beam intensity

Operation Status of the Nevis Synchrocyclotron

The Nevis Synchrocyclotron (S.C.) has been running on a fairly regular basis since October, with peak beam intensity of 2.2 ..mu..A. It had also run from late January through mid-April 1976. The current operating status of the accelerator is reported, and new developments of the past year are outlined.

X-Ray Bremsstrahlung Measurements of an Intense Relativistic Electron Beam Propagating in a Plasma

Information on the peak electron energy, angular spread, and current density of a relativistic electron beam propagating in a plasma column is obtained from measurements of two-absorber transmission ratios, anistropy, and intensity, respectively, of x-ray bremsstrahlung from thin target foils in the plasma. Measurements indicate a 10% loss in peak electron energy and a factor of two loss in peak beam intensity over the distance of the plasma column, and show a large angular spread in the beam.

External Beam Cross Section Distribution Display

S>An intensity locus generator was developed for observing rapidly the position and focal properties of external beams at the Cosmotron. The generator uses a camera video, two amplitude discriminators, and a television monitor. The discriminator outputs are displayed on the monitor as a black dot marking the peak beam intensity and a black contour line marking the locus of 50% intensity. A horizontal sweep synchronized ramp is used to compensate the tilt of the video output. (D.L.C.)

Duty Cycle Improvement on the Harvard Synchrocyclotron

The frequency modulation of the Harvard synchrocyclotron was changed by redesigning the rotating condenser Frequency curves and tooth shapes are presented graphi cally. Peak beam intensity was reduced while keeping average intensity constant. Dead time losses and random coincidence events which depend on the square of the beam intensity were reduced; the average rate of nuclear events, which depends on the average beam intensity, was unchanged. (L.N.N.)

Zur Theorie der Molekularstrahlerzeugung mit langen Kan�len

According to a theory ofGiordmaine andWang concerning the formation of molecular beams by long parallel tubes, the peak beam intensity j should be proportional to N1/2 (N gas flow rate). This is in contradiction to the author's experimental results on NH3 molecular beams revealing j proportional to N2/3 in a wide range of gas flow rate. It is shown that this relation equally represents best the experimental results ofGiormaine andWang with CO2 molecular beams. The measured directivities are smaller than the theoretical values and the departures increase with decreasing flow rate and tube diameter. To improve the theoretical statements, the theory ofGiordmaine andWang is extended by consideration of the choking effects of the tube orifices. Furtheron another relatively simple theoretical procedure for the evaluation of the directivity of tubes is given using the concept of an “effective tubelength”. By this method the directivities of several differently formed tubes and of composed beam sources are calculated and compared with the experimental results. The evaluations confirm the experimental observation that sources which are composed of tubes are practically not superiour to those which consist of a few slits, the slit width being equal to the tube diameter. Then the remaining discrepancy between the theoretical and experimental results is partly overcome by using the total impact cross section in place of the gaskinetic one. At last the influence of surface diffusion on the tube walls and the effect of the gas cloud in front of the source on the beam formation are discussed.

Molecular Beam Formation by Long Parallel Tubes

The characteristics of molecular beams formed by sources consisting of long tube arrays are measured for several sources. The peak beam intensity and the beam width are calculated when collisions in the source are taken into account under the assumption that a limited region of Knudsen type flow occurs near the low-pressure end of the source. The peak beam intensity and the beam width are calculated to vary as the square root of the total flow rate for source pressures giving useful directivity, in good agreement with the observations. Considerations in the design of sources are discussed.