Steady Beam Research Articles

Accumulative dose response of CdZnTe detectors to 14.1 MeV neutrons

The accumulative dose response of CdZnTe (CZT) detectors to 14.1MeV neutrons is discussed experimentally in this paper. The Cockcroft–Walton Accelerator is used to obtain a steady neutron beam of 14.1MeV neutrons. A pulsed X-ray source is used to test the response parameters of the neutron-exposed CZT detectors under the pulse mode. The irradiation time (hours) is shorter relative to the time scales (years) where annealing effects occur. Time and linearity response is analyzed to evaluate the maximum dose rate of the CZT detectors and the pulse shape. The result shows that the experimental CZT detectors maintain stable response behaviors, while the maximum dose rate and the total accumulative dose are less than 106neutrons/(cm2·s) and 1010neutrons/cm2, respectively.

Development of High Intensity D-T fusion NEutron Generator (HINEG)

A high intensity D-T fusion neutron generator (HINEG) is keenly needed for the research and development (R&D) of nuclear technology and safety of the advanced nuclear energy system, especially for the radiation protection and shielding. The R&D of HINEG includes two phases: HINEG-I and HINEG-II. HINEG-I is designed to have both the steady beam and pulsed beam. The neutron yield of the steady beam is up to 1012 n/s. The width of pulse neutron beam is less than 1.5 ns. HINEG-I is used for the basic neutronics study, such as measurement of nuclear data, validation of neutronics methods and software, validation of radiation protection and so on. HINEG-II aims to generate a high neutron yield of 1013 n/s neutrons by adopting high speed rotating tritium target system integrated with jet/spray array enhanced cooling techniques, and can further upgrade to obtain neutron yield of 1014~1015n/s by using of accelerators-array in a later stage. HINEG-II can be used for fundamentals research of nuclear technology including mechanism of materials radiation damage and neutronics performance of components, radiation shielding as well as other nuclear technology applications.

Compensation for booster leakage field in the Duke storage ring**Supported by National Natural Science Foundation of China (11175180, 11475167) and US DOE (DE-FG02-97ER41033)

The High Intensity Gamma-ray Source (HIGS) at Duke University is an accelerator-driven Compton gamma-ray source, providing high flux gamma-ray beam from 1 MeV to 100 MeV for photo-nuclear physics research. The HIGS facility operates three accelerators, a linac pre-injector (0.16 GeV), a booster injector (0.16—1.2 GeV), and an electron storage ring (0.24—1.2 GeV). Because of the proximity of the booster injector to the storage ring, the magnetic field of the booster dipoles close to the ring can significantly alter the closed orbit in the storage ring being operated in the low energy region. This type of orbit distortion can be a problem for certain precision experiments which demand a high degree of energy consistency of the gamma-ray beam. This energy consistency can be achieved by maintaining consistent aiming of the gamma-ray beam, and therefore a steady electron beam orbit and angle at the Compton collision point. To overcome the booster leakage field problem, we have developed an orbit compensation scheme. This scheme is developed using two fast orbit correctors and implemented as a feedforward which is operated transparently together with the slow orbit feedback system. In this paper, we will describe the development of this leakage field compensation scheme, and report the measurement results, which demonstrate the effectiveness of the scheme.

Optimal control of supersonic pre-twisted rotating functionally graded thin-walled blades

In this paper, the optimal vibration control of a rotating, pre-twisted, single-celled box thin-walled beam made of functionally graded material is discussed. This beam is under aerothermoelastic loading and warping restraint. A first-order shear deformation theory enabling satisfaction of traction-free boundary conditions is employed to achieve governing dynamical model. These equations include the effects of the presetting angle, the secondary warping, temperature gradient through the wall thickness of the beam, and also the rotational speed. Moreover, quasi-steady aerodynamic pressure loadings are determined using first-order piston theory, and steady beam surface temperature is obtained from gas dynamics theory. The extended Galerkin method is then used to transform the blade partial differential equations into a set of ordinary differential equations. Transversely isotropic sensor-actuator piezoelectric pairs that are surface embedded along the blade are also considered for the purpose of closed-loop control. An optimal observer-based output feedback control scheme is used to stabilize the closed-loop system. Simulation studies demonstrate the effectiveness of the proposed method.

A 10 MeV RF linac for industrial applications

This paper discusses the studies on a standing wave, biperiodic, on-axis coupled cavity RF linac operated at 2856 MHZ used for various industrial applications. Results of beam transmission experiments conducted in this accelerator have been presented. Analytical study and experimental verification of steady state beam loading in this facility have been explained. Finally some of the irradiation experiments performed in this system have been described.

Ultrawideband Coalesced-Mode Operation for a Sheet-Beam Traveling-Wave Tube

Wider bandwidth property of traveling-wave tubes (TWTs) is continuously pursued to satisfy the increased data rates and multiple channels in modern communications. In this paper, the coalesced-mode operation instead of the general single-mode operation for the double staggered grating waveguide (DSGW) slow-wave structure (SWS) is proposed to achieve an ultrawideband property of the TWTs driven by sheet electron beam. Analytical results of the high-frequency properties for the SWS, including the dispersion characteristics, interaction impedance, and transmission property, demonstrate that the coalesced-mode operation for the DSGW is possible. A novel loading approach of the attenuator with good performance, and meanwhile, a compact configuration is proposed to suppress the potential oscillations, thus leading to a steady beam–wave interaction for the coalesced-mode operation. To verify the concept of coalesced-mode operation, particle-in-cell simulation is performed. Simulation results demonstrate that the optimized RF circuit indeed can steadily operate in coalesced mode and produce over 5-kW saturated output power ( $\sim 10$ % efficiency) in a very broad frequency ranging from 37 to 52 GHz, corresponding to a relative bandwidth of 33.7%.

Underlying conservation and stability laws in nonlinear propagation of axicon-generated Bessel beams

In light filamentation induced by axicon-generated, powerful Bessel beams, the spatial propagation dynamics in the nonlinear medium determines the geometry of the filament channel and hence its potential applications. We show that the observed steady and unsteady Bessel beam propagation regimes can be understood in a unified way from the existence of an attractor and its stability properties. The attractor is identified as the nonlinear unbalanced Bessel beam (NL-UBB) whose inward H\"ankel beam amplitude equals the amplitude of the linear Bessel beam that the axicon would generate in linear propagation. A simple analytical formula that determines de NL-UBB attractor is given. Steady or unsteady propagation depends on whether the attracting NL-UBB has a small, exponentially growing, unstable mode. In case of unsteady propagation, periodic, quasi-periodic or chaotic dynamics after the axicon reproduces similar dynamics after the development of the small unstable mode into the large perturbation regime.

Development of superconducting magnets for RAON 28 GHz ECR ion source.

RAON, a 28 GHz electron cyclotron resonance ion source (ECR IS), was designed and tested as a Rare Isotope Science Project. It is expected that RAON would provide not only rare-isotope beams but also stable heavy ions ranging from protons to uranium. In order to obtain the steady heavy-ion beam required for ECR IS, we must use a 28 GHz microwave source as well as a high magnetic field. A superconducting magnet using a NbTi wire was designed and manufactured for producing the ECR IS and a test was conducted. In this paper, the design and fabrication of the superconducting magnet for the ECR IS are presented. Experimental results show that the quench current increases whenever quenching occurs, but it has not yet reached the designed current. The experiment is expected to reveal the ideal conditions required to reach the designed current.

Research of transportation efficiency of low-energy high- current electron beam in plasma channel in external magnetic field

Effective high current (5-20 kA) and low energy (tens of keV) electrons beam transportation is possible only with almost complete charging neutralization. It is also necessary to use quite high current neutralization for elimination beam self-pinching effect. The research is based on the self-consistent mathematical model that takes into account beam and plasma particles dynamic, current and charge neutralization of electron beam and examines the transportation of electron beam into a chamber with low-pressure plasma in magnetic field. A numerical study was conducted using particle in cell (PIC) method. The study was performed with various system parameters: rise time and magnitude of the beam current, gas pressure and plasma density and geometry of the system. Regularities of local virtual cathode field generated by the beam in the plasma channel, as well as ranges of parameters that let transportation beam with minimal losses, depending on the external magnetic field were determined through a series of numerical studies. In addition, the assessment of the impact of the plasma ion mobility during the transition period and during steady beam was performed.

A microfluidic flow-cell for the study of the ultrafast dynamics of biological systems.

The study of biochemical dynamics by ultrafast spectroscopic methods is often restricted by the limited amount of liquid sample available, while the high repetition rate of light sources can induce photodamage. In order to overcome these limitations, we designed a high flux, sub-ml, capillary flow-cell. While the 0.1 mm thin window of the 0.5 mm cross-section capillary ensures an optimal temporal resolution and a steady beam deviation, the cell-pump generates flows up to ∼0.35 ml/s that are suitable to pump laser repetition rates up to ∼14 kHz, assuming a focal spot-diameter of 100 μm. In addition, a decantation chamber efficiently removes bubbles and allows, via septum, for the addition of chemicals while preserving the closed atmosphere. The minimal useable amount of sample is ∼250 μl.

Role of graphite in isotopic analysis of boron in metal boron alloys by Positive-Thermal Ionization Mass Spectrometry (P-TIMS)

Isotopic composition of boron in alloy samples was determined by Positive-Thermal Ionization Mass Spectrometry (P-TIMS) using Rb2BO2+. The titanium based boron alloy sample was treated with nitric acid to bring it to slurry form which was fused with rubidium carbonate on the high purity Rhenium filament for the formation of borate. Control of pH was found necessary to be necessary for both the formation of alkali borate compound as well as for obtaining good yield Rb2BO2+. Alkaline conditions were required for the formation of rubidium borate during fusion though neutral pH favored formation of Rb2BO2+ ions in the ion source. The sample loading procedure was suitably modified to obtain good ion intensities for Rb2BO2+ for high precision analysis. Steady ion beam was obtained when graphite was loaded on the filament after fusion of alloy carbonate mixture contrary to the reverse procedure that is normally followed. Sequence of graphite addition on the filament plays an important role in the formation of Rb2BO2+ ions. The paper gives the details of the investigations carried out.

Theoretical research on electron beam modulation in a field-emission cold cathode electron gun

In order to develop miniaturized and integrated electron vacuum devices, the electron beam modulation in a field-emission (FE) electron gun based on carbon nanotubes is researched. By feeding a high-frequency field between the cathode and the anode, the steady FE electron beam can be modulated in the electron gun. The optimal structure of the electron gun is discovered using 3D electromagnetism simulation software, and the FE electron gun is simulated by PIC simulation software. The results show that a broadband (74–114 GHz) modulation can be achieved by the electron gun with a rhombus channel, and the modulation amplitude of the beam current increases with the increases in the input power and the electrostatic field.

Loss of wave-packet coherence in stationary scattering experiments

We consider the cross section for a scattering reaction averaged over a statistical ensemble of incident beam wave packets. We generalize a result known from neutron diffraction that static experiments involving stationary scattering via conservative interactions and steady beam currents cannot distinguish the wave-packet nature of the incident beam. Thus we interpret the results of recent experiments on the loss of interference effects in proton scattering from molecular hydrogen as due to the weak collimation of the incident beam rather than alterations to beam wave packets.

A particle-in-cell Monte Carlo code for electron beam ion source simulation

FAR-TECH, Inc., has developed a particle-in-cell Monte Carlo code (EBIS-PIC) to model ion motions in an electron beam ion source (EBIS). First, a steady state electron beam is simulated by the PBGUNS code (see http://far-tech.com/pbguns/index.html). Then, the injected primary ions and the ions from the background neutral gas are tracked in the trapping region using Monte Carlo method. Atomic collisions and Coulomb collisions are included in the EBIS-PIC model. The space charge potential is updated by solving the Poisson equation each time step. The preliminary simulation results are presented and compared with BNL electron beam test stand (EBTS) fast trapping experiments.

The Lent Boy

Winter dusk is particularly conducive to melancholy. At twelve, Aaron was perhaps young to know such things, to feel them as deeply as he did, but temperament and experience had created in him a specific type of preco ciousness. Thus, as he made his way to the Bergstroms' house, the normally pleasant sound of snow crunching beneath his sneakers nearly brought him to tears. In truth, it was not just the crunching or the day's steady retreat but so many things, all piling up inside of him like the mounds of snow that flanked the recently plowed streets, mounds that other children, not he, liked to climb upon as they walked home from school, pummeling one another to preserve their spots on top. There were no street lamps in this part of Morton, but all around him the houses were aglow, predictably, with Christmas lights and kitchen lights and the steady yellow beam from the porch, each anticipating a specific event: a holiday, a warm meal, a father's return. And so the lights discouraged him as well. He could tell, almost to a house, who was having chicken that night and who, roast, the odors wafting from these well-lit kitchens into the street where he walked. His mother was back at the cafe, creating her own good smells as she cooked, but this thought only added to his mood, surrounded as he was by mothers making meals for their families, families whom they solely considered as they cooked, taking into account a child's dislike of onions or preparing to settle a dispute over the much-coveted drumsticks. Aaron could not remember the last time his mother had prepared something just for him, something that was not a leftover from the day's special or a kitchen mistake, an overcooked hamburger that became his supper. He trudged along, dreading his visit to the Bergstroms, whom he had never met, for they rarely visited the cafe. Of course, he knew that Mrs. Bergstrom had taught fifth grade for many years, but he knew nothing of her, of her reputation among students that is, for she had taught all those years not in Morton but in a nearby town. Parents generally liked to keep their teachers close—in town, where they could keep an eye on them—which made her residence in Morton somewhat of an aberration. The Bergstroms had established themselves here, in Morton, because Mr. Bergstrom's liveli hood had demanded it: he owned a tire shop, long closed because they were

The splitted laser beam filamentation in interaction of laser and an exponential decay inhomogeneous underdense plasma

The splitted beam filamentation in interaction of laser and an exponential decay inhomogeneous underdense plasma is investigated. Based on Wentzel-Kramers-Brillouin (WKB) approximation and paraxial/nonparaxial ray theory, simulation results show that the steady beam width and single beam filamentation along the propagation distance in paraxial case is due to the influence of ponderomotive nonlinearity. In nonparaxial case, the influence of the off-axial of α00 and α02 (the departure of the beam from the Gaussian nature) and S02 (the departure from the spherical nature) results in more complicated ponderomotive nonlinearity and changing of the channel density and refractive index, which led to the formation of two/three splitted beam filamentation and the self-distortion of beam width. In addition, influence of several parameters on two/three splitted beam filamentation is discussed.

Analytical solutions for transient and steady state beam loading in arbitrary traveling wave accelerating structures

Analytical solutions are derived for both transient and steady state gradient distributions in the traveling wave (TW) accelerating structures with arbitrary variation of parameters over the structure length. The results of the unloaded and beam loaded cases are presented. Finally, the exact analytical shape of the rf pulse waveform was found in order to apply the transient beam loading compensation scheme during the structure filling time. The obtained theoretical formulas were cross-checked by direct numerical simulations on the CLIC main linac accelerating structure and demonstrated a good agreement. The proposed methods provide a fast and reliable tool for the initial stage of the TW structure analysis.

A wide-beam continuous solar simulator for simulating the solar flux at the orbit of Mercury

We report on the design, construction and testing of a wide-beam continuous solar simulator which can be used to simulate air mass zero (AM0) solar irradiance at fluxes of up to 6.5 solar constants. The instrument has been designed to produce a steady collimated beam with a homogeneous flux distribution across an aperture area of diameter 290 mm. The instrument is being used to test hardware designed to fly on the ESA/JAXA space mission to Mercury, BepiColombo. It has applications for other spacecraft missions which envisage passing inside the orbit of Venus (e.g. Solar Orbiter).

Single-cell isolation using a DVD optical pickup

A low-cost single-cell isolation system incorporating a digital versatile disc burner (DVD RW) optical pickup has been developed. We show that these readily available modules have the required laser power and focusing optics to provide a steady Gaussian beam capable of optically trapping micron-sized colloids and red blood cells. Utility of the pickup is demonstrated through the non-destructive isolation of such particles in a laminar-flow based microfluidic device that captures and translates single microscale objects across streamlines into designated channel exits. In this, the integrated objective lens focusing coils are used to steer the optical trap across the channel, resulting in the isolation of colloids and red blood cells using a very inexpensive off-the-shelf optical component.

Aiming for the theoretical limit of sensitivity of Bonse-Hart USANS instruments

The basis of the Double-Crystal Diffractometer (DCD), used for ultra-small angle neutron scattering (USANS), is that the reflectivity function is very near 1.0 for |y| < 1, where y = (θ - θB)/ δΘD, falls off rapidly for |y| >1, eventually decreasing as y −2. In the Bonse-Hart multi-bounce crystal the reflectivity function R(y) transforms into Rm(y) and in the wings, for large |y|, theoretically decreases as y−2m after m consecutive Bragg reflections inside the channel-cut crystal. Here θ and θB are respectively the diffraction angle and the Bragg angle (for given wavelength) and δΘD is the width of the Darwin plateau. However, the experimental reflectivity Rmexp(y) obtained for m = 3 exceeds the theoretical prediction by over two orders of magnitude in the range of the far wings, which creates limitations for USANS studies of weakly scattering objects.We used the pulsed-source neutron time-of-flight (TOF) technique to study this discrepancy in more detail. Two identical Si(111) crystals, a slab-shaped single-bounce and a channel-cut triple-bounce, were measured at the nominal Bragg angle θB = 24.4o in the TOF powder diffractometer GPPD at IPNS, in the range 0.2 < λ < 4.0 Å of the first seven Bragg reflections from Si(111) family. Cadmium shielding protected the detectors from view of the first-bounce crystal. The experimental data obtained from the single-bounce crystal shows thermal diffuse (phonon) scattering (TDS) filling the region between the Bragg reflections, and exhibiting the symmetry of the reciprocal lattice. With appropriate shielding installed, the triple-bounce Bragg reflections, in contrast, are TDS-free in the range 0.6 < λ < 3.0 Å; however, the intensity of TDS grows in the range λ < 0.5 Å, reaching the level of TDS registered for the single-bounce reflections (777) and (888). The growth of TDS correlates with the increase of the Cd transmission T(λ) in the range 0.2 < λ < 0.5 Å, which in the vicinity of (888) reflection is T(λ) ≈ 0.9. Therefore, the Cd shielding of the triple-bounce crystal becomes ineffective and the parasitic single-bounce back-face reflection and TDS, blocked for 0.5 < λ < 3.0 Å, reappear for λ< 0.5 Å.It is practically impossible to separate this parasitic scattering from the triple-bounce reflection at steady state neutron beam lines except by the use of highly curved neutron guides. However, the TOF-USANS instrument, which is currently under construction at SNS, allows separation of the orders of Bragg reflections and the residual TDS in time-of-flight and thus the discovered parasitic effect cannot compromise its sensitivity. Thus, we expect to approach the theoretical limit of sensitivity for the SNS TOF-USANS instrument.