Design of an upgradeable 45–100 mA RFQ accelerator for FAIR

A 325 MHz, 35 mA, 3 MeV Radio-Frequency Quadrupole (RFQ) accelerator will be operated as the first accelerating structure of the proton linac injector for the newly planned international science center Facility for Antiproton and Ion Research (FAIR) at GSI, Germany. In previous design studies, two high beam intensities, 70 and 100 mA, were used. Most recently, the design intensity has been changed to 45 mA, which is closer to the operational value. Taking advantage of the so-called New Four-Section Procedure, a new design, which is upgradable from 45 to 100 mA, has been developed for the FAIR proton RFQ. Besides the upgradability analyses, robustness studies of the new design to spatial displacements of the input beam and field errors are presented as well.     

YO!—a time-of-arrival receiver for removal of helicity-correlated beam effects

A parity violation experiment, G⁰, at Jefferson Lab is sensitive to arrival time differences, at the target, of electron beams in the two helicity states. Instead of the Jefferson Lab standard 499 MHz beam structure, G⁰ uses a 31.1875 MHz structure where only 1 out of 16 microbunches contains electrons. Photon counters triggered by time-of-arrival at the target mandate that timing must be independent of delays associated with different orbits taken by the electrons in two helicity states. Corrections to the parity violating asymmetries due to any arrival time differences require the generation of a clean 31.1875 MHz trigger signal and phase matching this signal to the beam's arrival at the target. The time of arrival receiver, named the YO! receiver, has 10 kHz output bandwidth which is sufficiently larger than the settling time (500 μs) of the ≈30 Hz helicity flip. This enables the correction of each helicity bin for any orbit-induced timing inequalities. The device combines conventional receiver and DSP techniques for maximum sensitivity, bandwidth and flexibility and eliminates the 2π/n phase shifts associated with frequency dividers by means of a sampling phase detection scheme. This paper describes the performance of this device during bench testing, commissioning and in data taking phase of the experiment.     

Characterisation of a monolithic active pixel sensor for electron detection in the energy range 10–20 keV

As part of a feasibility study into the use of novel electron detectors for X-ray photoelectron emission microscopes (XPEEM), we have characterised the imaging performance of a back-illuminated monolithic active pixel sensor (MAPS) operating under both integrating and counting modes for electrons in the energy range 10–20 keV. For integrating mode, we present the detective quantum efficiency (DQE), which shows marked improvements over conventional indirect detectors based on microchannel plates. We also present the modulation transfer function (MTF) and noise power spectrum (NPS), again demonstrating significantly improved performance. For counting mode, we present the quantum efficiency (QE) as a function of incident electron energy. We have evaluated the charge collection efficiency (CCE) and we thereby demonstrate the presence of a ~200 nm thick dead layer that is linked with reduced CCE at low electron energies. Based on our findings, we believe that the MAPS technology is well matched to future XPEEM instruments using aberration correction.     

Optimization of a moderator-neutron guide system for diffractometers of beam line 7A of the IBR-2M reactor

Neutron guides are widely used to transport the neutrons from the moderator to the sample. Due to the constructive features of the ring corridor of the fast pulsed reactor IBR-2, the minimal distance between the moderator and the guide entrance is around 6 m. The main goal of the paper is to optimize the neutron optical system between the moderator and the entrance of the new neutron guides. Using Monte Carlo simulations we calculate the possible best gain of the neutron flux density at the guide exit. After the described optimization process, the optimal system is obtained. The recommendations for construction of the new beam line are provided too. Similar technique and the proposed system could be easily adapted for another similar beam line at the neutron sources.     

Molecular dynamics simulation of ion ranges in the 1–100 keV energy range

Binary collision approximation methods have been conventionally used to describe the slowing down of recoiling ions. In order to better understand the slowing-down process, molecular dynamics methods are more and more used in the literature. However, the computer capacity limits the usefulness of the methods in most practical cases where ion implantation in the 1–100 keV energy range is used. We present an efficient molecular dynamics method for calculating ion ranges and deposited energies in the recoil energy region 100 eV to 100 keV. By taking into account only the interactions that are involved in the slowing-down process, range and deposited energy distributions at higher energies can be simulated. The method is demonstrated by range calculations of 40 keV H atoms in Si, 40 keV He atoms in Ta and 100 eV to 10 keV Si atoms in Si.     

Mathematical modeling of the electron beam formatting systems on the basis of field emission cathodes with various shapes

In the present paper we solve some problems of field emission cathodes mathematical modeling and the electron guns for vacuum electronics. The supposed shape of the field emission cathode was either “sphere-on-cone” or “sphere-on-spindle” (as a cathode) on the sphere substrate and the spherical segment (as an anode).     

同步辐射光束线中柔性铰链的设计

为同步辐射光束线设计了一种新型的柔性铰链——直圆倒角复合柔性铰链。分析计算并通过实验验证了直圆倒角复合柔性铰链性能。与直圆柔性铰链相比,直圆倒角复合柔性铰链具有柔度大、转动精度高等优点,可在不损失精度的情况下大大提高微调机构的柔性;在要求最大转角一定的情况下,可大大降低对作动器驱动能力的需求,也使得机构内的应力大为减小。     

Unstable matrix equations and their relationship to measuring the emittance of an electron beam using beam position monitors

In general, the spatial distributions of electron beams from photoinjectors are unknown and are not well approximated by a Gaussian. Therefore, when measuring the emittance, it is important to make no assumptions about the beam's spatial distribution. An emittance diagnostic that fulfills this requirement uses beam position monitors to measure the second moment of the electron beam's image charge. This information, coupled with the beam line's transfer matrix, forms a set of linear equations. The least squares solution to these equations estimates the necessary beam parameters. More often than not, however, this solution is unstable and amplifies the errors in the second moment measurement. For this diagnostic to be viable, a stable implementation has to be found. Described here is an approach that accomplishes this task.     

Simulation of electron beam energy fluctuation in a linac: filtering of the utility parameter's information by ensemble average

Beam energy fluctuation in the linear accelerator (linac) is modeled for its stochastic factor and its determinate factor. Here, the stochastic factor means the noise in the RF component, and the determinate factor signifies only the utility parameters (the electric power supply, the temperature of the coolant water, and the room temperature). We demonstrate that the utility parameter's information buried in the stochastic factor appears in the N-units ensemble average. The results of the calculation using this model agree very well with the measurement data of the beam energy fluctuation.     

Embrittlement of a superduplex stainless steel in the range of 550–700 °C

Duplex stainless steels are very attractive materials, combining high mechanical properties with improved corrosion resistance. However, these steels present technical limitations because they can experience embrittlement as a consequence of thermal cycles. Moreover, the higher level of alloying elements (Cr and Mo) in the new duplex generation, called superduplex, accelerates the precipitation kinetics of harmful intermetallic phases, which are the responsible of embrittlement. This fact raises the question of the influence of these cycles on the actual performance of duplex components and structures and on its possible failure during service.

In order to investigate this question, heat treatments in the range of 550–700 °C, with different exposure times and cooling rates, have been made on a superduplex stainless steel type EN 1.4507. The evolution of mechanical properties has been followed by means of hardness measurements, impact and fracture toughness tests, whereas microstructural changes have been identified by using optical and transmission electron microscopy analysis. A correlation between the degree of embrittlement and the different types of precipitates has been established.     

Transverse beam instability in a 50 GeV×50 GeV muon-collider ring

The transverse beam instability due to a broad-band impedance in a 50 GeV×50 GeV muon-collider ring is numerically investigated. It is shown that the transverse beam size is increased by a factor of five when the impedance, Z_||/n, is 1.7 Ω. The transverse instability is shown to be cured by introducing tune spreads, such as BNS damping, chromaticity, amplitude-dependent tune shift, and beam–beam interaction. It is shown that any one of these tune spreads limits the growth of the beam size to less than 20%.     

Charging kinetics in virgin and 1 MeV-electron irradiated yttria-stabilized zirconia in the 300–1000 K range

A study performed with a dedicated scanning electron microscope (SEM) on the surface electrical properties of (1 0 0)-oriented yttria-stabilized zirconia (YSZ) single crystals irradiated with 1 MeV electrons is presented. When compared with virgin YSZ, the 1 MeV-irradiated YSZ shows a decrease of the intrinsic total electron emission coefficient σ₀ and an increase of the time constant τ associated with the charging kinetics of the material at room temperature. These measurements performed with the SEM beam at 10 keV indicate that the defects induced by the 1 MeV-electron irradiation generate a positive electric field of the order of 0.5 × 10⁶ V/m at a depth of about 1 μm that prevents electrons to escape. When the SEM beam with a 1.1 keV energy is used, a smaller field (0.5 × 10³ V/m) is detected closer to the surface (20 nm). The fading of these fields during the thermal annealing in the 400–1000 K temperature range provides information on the nature of defects induced by the 1 MeV-electron irradiation.     

Stability of industrial-grade platinum resistance thermometers in the range 77 – 273 K

The paper pays attention to stability of 10 two-lead industrial-grade 100 Ω platinum resistance thermometers used in the temperature range from 77 to 273 K. The static stability was checked by the method of storing the thermometers for about two years, the dynamic stability was tested by the method of cycling the thermometers in 25 cycles from room temperature to the temperature of liquid nitrogen. it has been found that the static instability of the thermometers ranged within + 2.5 to + 7.7 mK only one thermometer showed –2.5 K The dynamic instability ranged within –5 mK to –80 mK only one thermometer showed +35 mK.     

Properties of Ti–6Al–4V non-stochastic lattice structures fabricated via electron beam melting

This paper addresses foams which are known as non-stochastic foams, lattice structures, or repeating open cell structure foams. The paper reports on preliminary research involving the design and fabrication of non-stochastic Ti–6Al–4V alloy structures using the electron beam melting (EBM) process. Non-stochastic structures of different cell sizes and densities were investigated. The structures were tested in compression and bending, and the results were compared to results from finite element analysis simulations. It was shown that the build angle and the build orientation affect the properties of the lattice structures. The average compressive strength of the lattice structures with a 10% relative density was 10 MPa, the flexural modulus was 200 MPa and the strength to density ration was 17. All the specimens were fabricated on the EBM A2 machine using a melt speed of 180 mm/s and a beam current of 2 mA. Future applications and FEA modeling were discussed in the paper.     

Hot carrier degradation in MOSFETs in the temperature range of 77–300 K

In this paper the DC hot carrier degradation of n-channel and p-channel MOSFETs is treated in the temperature range of 77–300 K. A thorough analysis of the degradation mechanisms is made possible by an extensive use of the charge pumping technique for the determination of the interface properties of the MOS devices prior to and after degradation in this temperature range, in addition to the more conventional techniques based on shifts and/or distortions of the current–voltage characteristics. The physical processes responsible for the transistor degradation are identified in each voltage regime for the two types of transistor.     

Design and performance of a Tesla transformer type relativistic electron beam generator

A relativistic electron beam generator driven by an air core Tesla transformer is described. The Tesla transformer circuit analysis is outlined and computational results are presented for the case when the coaxial water line has finite resistance. The transformer has a coupling coefficient of 0·56 and a step-up ratio of 25. The Tesla transformer can provide 800 kV at the peak of the second half cycle of the secondary output voltage and has been tested up to 600 kV. A 100–200 keV, 15–20 kA electron beam having 150 ns pulse width has been obtained. The beam generator described is being used for the beam injection into a toroidal devicebeta.     

Vibrations of the beam due to a load moving with stochastic velocity

The aim of this work is to give an approach for obtaining the probabilistic characteristics of the beam response due to a load moving with stochastic velocity. It is assumed that the load is modelled by a set of point forces of random amplitudes, the inter-arrival times are random variables that constitute the Poisson stochastic process and the forces are moving along the beam with velocities that are also stochastic. The effective solution in such a case can be obtained by applying the Ito integral and the Ito differentiation rule. In this paper, the theoretical basis for such an approach is given. Analytical expressions for calculating the probabilistic characteristics of the beam response and numerical results are shown.     

EB固化油墨的研制及发展前景

首先列举了当前应用比较广泛的几种油墨,如溶剂型油墨、水性油墨和能量固化型油墨.然后主要针对能量固化油墨中的电子束固化油墨进行了分析.从电子束固化油墨的组成出发,对其固化机理进行了详细的分析,接着对线性加速器和扫描式加速器进行了介绍,最后对电子束油墨的广阔前景做出了分析.     

Piezoresistive response of thin film manganin gauges in the 50–100-GPa range

To extend the measurement range to 100 GPa, a new type of manganin gauge was prepared by thin film techniques. The manganin sensing elements were deposited by magnetron sputtering, and then encapsulated in an alumina matrix by electron beam evaporation. Shock loading in the 50–107-GPa range by a light gas gun resulted in flat-topped stress–time profiles with approximately 1-μs record history. The initial calibration presented a linear curve having a piezoresistance coefficient of 0.0198±0.0002 GPa⁻¹.