Energy spectra measurements of X-ray emission from electron interaction in a dense plasma focus device

Electrons generated during a pinch implosion in a hollow anode Mather-like plasma focus device (PF) are considered as a possible X-ray source via the impinging of those particles on medium and high-Z targets. A usual PF device has been slightly modified to optimise the X-ray production and their measurements by means of a suitable and non-invasive spectrometer. This ensemble allows measurements of X-rays generated booth by electrons turning back to the anode and by target collision of the so-called relativistic electron beam. The spectrum of the emitted photons is evaluated by using a differential absorption based technique. The X-ray spectrometer consists of a stack of LiF dosimeters which act both as detectors and filters to give curves of attenuated intensities. Finally, the energy distribution is calculated from such attenuation curves using an iterative procedure based on spectral algebra formalism.     

The interaction of high-current pulse beams with plasma in a magnetic field

We have studied the interaction of an electron beam with currents up to 8.5 A and energies up to 15 keV with a plasma in a magnetic field, the intensity of which varied between 36O and 1320 Oe. We studied the energy distribution of electrons after passage of the electron beam through the plasma as a function of the beam current, residual gas pressure (air), and the intensity of the longitudinal magnetic field. We measured the intensities of the transverse and longitudinal highfrequency fields excited by the beam in the plasma; these reach about 100 V/cm and 1–2 kV/cm respectively. This proves that the high energy losses of the beam due to its passage through the plasma are caused by excitation of high-frequency vibrations.Translated from Atomnaya Énergiya, Vol. 14, No. 3, pp. 249–256, March, 1963     

Effects of the Hot Electron Interchange Instability on Plasma Confined in a Dipolar Magnetic Field

The Levitated Dipole Experiment (LDX) explores confinement and stability of plasma created within the dipole field of a strong superconducting magnet. During initial experiments, long-pulse, quasi-steady state discharges that last more than 10 s and have peak beta of more than 20% are studied. The plasma is created by multi-frequency electron cyclotron resonance heating (ECRH) at 2.45 and 6.4 GHz. A population of energetic electrons, with mean energies above 50 keV, dominates the plasma pressure. Creation of high pressure, high beta plasma is possible only when intense hot electron interchange (HEI) instabilities are stabilized by sufficient neutral gas fueling. The instabilities resonate with the magnetic drift motion of the energetic electrons and can cause rapid radial transport. Measurements of the electrostatic and magnetic fluctuations of the HEI instability are described along with observations of the instability’s spectral characteristics. Fluctuations of the outer poloidal field induced by the HEI show a rapid evolution of the perturbed pressure profile.      

Forward and Backward Photoemission Yields from Metals at Various X-Ray Angles of Incidence

X-ray generated photoemission from thin metal foils backed by graphite was measured with radiation incident from the front and back sides at several angles. Irradiation was provided by a 100-kV x-ray tube with three different filters to harden the spectrum. The total 2? photoelectron emission current from a surface was measured; a biased grid retarded the low-energy secondary electrons, which added only 10-30% to the current at zero grid bias. Investigated metals were: Mg, Al, Ti, Fe, Cu, Ag, Ta, Au, and Pb; also the total emission from just the graphite support was measured. The front-to-back ratio of emission currents at normal incidence ranged from about 1.9 for Al and Mg down to about 1.1 for Ta. The photoelectron yield was found to be Ge ?a Se electrons/photon, where ?a and Se are the energy-dependent photon absorption cross section and computed electron mean path length in the emitter, and Ge is a constant assumed independent of photon energy in the range studied (but does depend on radiation angle of incidence). For the photon energy range of 20-70 keV, the measured emission current densities corresponded to the following average values for ?e: 0.37 ± 0.06 for C, 0.30 ± 0.03 for Al, 0.21 ± 0.02 for Cu and Ag, and 0.18 ± 0.02 for Ta.     

A Simple Technique to Record X-Ray Fluence Anisotropy of a Source

A simple technique to record the fluence anisotropy of x-rays emitted from a source is presented. The simplicity of the technique and response curves of the photographic film, along with corresponding filters, enables one to readily use the same for diagnostic purposes in different sources such as plasma focus, vacuum spark, z-pinch, and laser-produced plasmas. As an application example, the technique is employed to measure fluence anisotropy of x-ray emission in a low-energy plasma focus operated with hydrogen. With increase in filling pressure, the anisotropy is found to increase, although the total x-ray emission is lowered. It is therefore concluded that at a lower filling pressure of 0.75 mbar, the x-ray emission is dominantly due to interaction of energetic electrons in the current sheath, whereas at a higher filling pressure of 2.5 mbar, the contribution of energetic electron beam is much higher.     

Channel Multiplier Instrumentation for the Measurement of Low-Energy Auroral Particles

Channel multiplier instruments have been developed and used to measure the low-energy electron and proton auroral fluxes from a polar-orbiting satellite. Seven channel multipliers preceded by individual 90° magnetic analyzers were used to measure the differential electron energy spectrum. The central energies of the analyzers were 1.1, 2.1, 5.3, 14, 31, and 76 keV; the seventh channel was designed to be a background monitor. The integral proton number spectrum was measured using four channel multiplier threshold counters. Proton thresholds, determined by nickel foils, were chosen to be 21, 38, 56, and 1000 keV. A broom magnet was used to sweep out low-energy electrons. The saturated output pulses from each channel multiplier were amplified and fed into a logarithmic ratemeter. The in-flight operation of the instruments was monitored with low-level radioactive sources. The ratemeter calibration was independently monitored using a programmed pulser which was activated by ground command. Data obtained from these instruments during a three-day period in November, 1965, will be presented. Improved versions of these instruments, described herein, have been designed and tested for future flights.     

半导体器件在辐射作用下的电学输出性能研究

半导体结型器件是决定辐射伏特效应同位素电池能量转换效率的核心部件。采用加速器产生的不同能量电子束和63Ni源的β射线对硅基PIN结型器件进行辐照,在线测量了其电学输出性能。当电子束能量为18 keV,可得到大于4%的能量转换效率;电子束能量为6 keV,能量转换效率在0.16%～0.33%之间; 活度2.96×108 Bq的63Ni源片辐照的能量转换效率为0.1%左右。     

Electron Multiplication in Cavities

A computer program which simulates the multiplications of electrons in cavities using Monte Carlo techniques has been developed. This electron multiplication program has provided an understanding of the x-ray energy spectrum produced by cavities and of x-ray photographs taken of cavities at high fields. Also, this simulation has predicted two new effects: (1) an electron avalanche multiplication effect which is non-resonant in nature (as opposed to the well known resonant electron multi-pactoring), and (2) electrons produced in this way tend to form a low energy (on the order of 10 eV) electron cloud near the cavity major diameter.     

基于电子直线加速器的空间电子环境地面模拟用电子源设计与实现

空间电子环境地面模拟装置由1台电子直线加速器提供能量1~5 MeV范围内的电子,后续束流传输系统将电子束进行扩束处理。较大的能量范围对加速器的设计与运行条件提出了较高要求。本文主要阐述了该加速器的设计与实现过程,综合考虑了能量开关技术和束流负载效应,通过研究不同条件下的耦合度参数特性确定了加速管耦合度,分析提出了磁控管输出参数并进行了实验研究。加速器实验测试结果表明,电子束能量参数达到指标要求,为模拟装置提供了有效可靠的电子源。     

Assessment of Neutron Cross Sections for Titanium with Neutron Spectrum in Titanium Pile

The measurement of angular neutron spectrum in a quasi-spherical pile of Ti was carried out by the linac time-of-flight method for the assessment of neutron cross sections for Ti in the energy range from a few keV to a few MeV. The measured spectrum in the pile is generally in good agreement with the calculated one from ENDF/B-IV (MAT = 1,286 for Ti) except in the energy range from about 60 keV to a few 100 keV, where the calculation gives considerably lower neutron flux than the measurement.

In order to investigate the cause of this discrepancy between the measured and calculated spectra, the total cross sections for Ti were measured by the transmission method. The results give larger values of total cross sections for Ti by about 30% than ENDF/B-IV below 200 keV, and smaller values by about 10% above 200 keV. These results were ensured at 55 and 147 keV by the measurement using a Si-filtered neutron beam. The calculation based on the measured cross sections shows better agreement with the measured spectrum than that based on ENDF/B-IV. The discrepancy is still observed around 100 keV.

The sensitivity analysis shows the importance of cross sections above 1 MeV and elastic cross sections in the resonance energy region to solve the disagreement between the measured spectrum and the calculated one.     

Electron population properties with different energies in a helicon plasma source

The characteristics of electrons play a dominant role in determining the ionization and acceleration processes of plasmas. Compared with electrostatic diagnostics, the optical method is independent of the radio frequency(RF) noise, magnetic field, and electric field. In this paper, an optical emission spectroscope was used to determine the plasma emission spectra, electron excitation energy population distributions(EEEPDs), growth rates of low-energy and highenergy electrons, and their intensity jumps with input powers. The 56 emission lines with the highest signal-to-noise ratio and their corresponding electron excitation energy were used for the translation of the spectrum into EEEPD. One discrete EEEPD has two clear different regions,namely the low-energy electron excitation region(neutral lines with threshold energy of13–15 eV) and the high-energy electron excitation region(ionic lines with threshold energy?19 e V). The EEEPD variations with different diameters of discharge tubes(20 mm, 40 mm,and 60 mm) and different input RF powers(200–1800 W) were investigated. By normalized intensity comparison of the ionic and neutral lines, the growth rate of the ionic population was higher than the neutral one, especially when the tube diameter was less than 40 mm and the input power was higher than 1000 W. Moreover, we found that the intensities of low-energy electrons and high-energy electrons jump at different input powers from inductively coupled(H) mode to helicon(W) mode; therefore, the determination of W mode needs to be carefully considered.     

Use of the Hot-Electron Mirror Machine Interem as a High-Z Ion Source

Production of the high-Z charge states in helium, nitrogen, and argon has been measured in the INTEREM device at the Oak Ridge National Laboratory. The INTEREM device contains a hot electron (~500 keV) plasma trapped in a minimum B geometry. The device is of interest because its parameters, electron density and energy, and ion lifetime are consistent with those required for the production of highly charged ions. Ion charge and ion energy spectra were measured independently using an einzel lens type energy analyzer combined with a quadrupole mass filter. For helium, most of the ions were doubly charged under proper operating conditions. For nitrogen, we found the ion yield to be peaked at Q = 4, and under these conditions the yield at Q = 6 was down by a factor of about 20. Energy distribution curves for different charge states show interesting features, from which important information may be inferred about the plasma in INTEREM. Although discrepancies exist in the ion yields we conclude that an INTEREM-like device employing a minimum B geometry and electron cyclotron resonance heating may be expected to be a good high-Z ion source.     

The possible role of anisotropy in kinetic electronic excitation of solids by particle bombardment

The kinetic excitation of a solid surface by impact of energetic particles is investigated by means of internal electron emission across a buried metal-insulator-metal (MIM) tunnel junction. By bombarding the top metal surface of such a device with keV noble gas ions, internal emission yields were determined as a function of projectile impact energy and angle of incidence with respect to the surface normal. In order to understand the observed impact angle dependence, we apply a modified formalism originally published to describe external electron emission. As a result, we find that the measured data can be explained by assuming the spatial distribution of excited electrons propagating towards the buried oxide interface to be strongly influenced by the projectile impact angle. A simple ballistic model assuming excited electrons generated by direct collisions with the projectile to preferably propagate along the direction of the original projectile motion, while electrons excited by scattering from moving recoils propagate isotropically, appears to describe the observed experimental data quite well.     

T(d,n)4He强流中子发生器的中子能谱和角分布模拟计算

采用将厚靶分割成薄靶的方法对厚氚钛靶、260keV氘束流能量条件下T(d,n)⁴He反应中子源的能谱和角分布进行计算。以分割法计算得到的能谱和角分布数据为基础,建立了D-T中子源Monte-Carlo模拟抽样模型,在考虑中子发生器各元件材料及实验大厅墙壁对快中子的慢化、散射和吸收的条件下,采用MCNP程序对兰州大学3×10¹²s^-1强流中子发生器260keV氘束流能量下的中子能谱和角分布进行了模拟,给出了模拟结果。为检验模拟结果的可靠性,与实验测量能谱进行了比较,Monte-Carlo模拟谱和实验测量谱基本符合。     

Post-collision interaction after electron impact measured by (e,2e) coincidence technique

Auger electron line-shapes after electron impact inner-shell ionization of Argon at 350 eV primary electron energy have been studied by coincidence spectrometry. Emitted Auger electrons are detected in coincidence with the scattered electrons and the energy of the very slow PCI inducer ejected electron was calculated from energy conservation. The background, caused by outer-shell electrons was measured and then removed from the coincident spectrum. The effect of PCI is studied on the background-free diagram Auger spectrum. A systematic deviation was found from the line-shape given by the semi-classical approach.     

低能Xe离子辐照在Al表面上的光辐射研究

本文测量了200~550 keV的Xe10+离子轰击高纯度（9999%）Al表面诱发的溅射Al原子的光发射,研究了Al Ⅰ 30810、30914、39452、39628 nm光谱线强度比值和光子产额随入射离子能量的变化趋势。在本实验能量范围内,辐射光谱线强度比值随入射离子能量增加几乎不变,而发射谱线的光子产额随入射离子能量的增加呈现出不同趋势：入射离子能量为450 keV时,光子产额出现极大值,入射离子能量超过450 keV时,光子产额随能量的增加而减少,其变化趋势与核阻止本领随能量增加的变化没有出现类同的变化特征。结合核阻止和电子阻止效应对实验结果进行了讨论,结果表明：入射离子能量低于450 keV时,核阻止在碰撞中起主导作用,入射离子能量高于450 keV时,电子阻止在碰撞中起主导作用。     

High energy electron beam generation during interaction of a laser accelerated proton beam with a gas-discharge plasma

The study of the interaction between ion beam and plasma is very important to the areas of inertial fusion energy and high energy density physics. With detailed one-dimensional electromagnetic particle-in-cell simulations, we investigate here the interaction of a laser-accelerated proton beam assuming an ideal monoenergetic beam with a gas-discharge plasma. After the saturation stage of the two-stream instability excited by the proton beam, significant high energy electrons are observed, with maximum energy approaching 2 MeV, and a new two-stream instability occurs between the high energy electrons and background electrons. The trajectories of plasma electrons are studied, showing the process of electron trapping and de-trapping from the wakefield.     

Electron emission in 10–100 keV H and He grazing ion-surface collisions

We have measured energy distributions of electrons ejected during grazing 10–100 keV H⁺ and He⁺ ions scattering from Si surfaces for a broad range of electron observation angles. The distributions have contributions strongly dependent on the directions of incidence and observation. For observation regions around the specular reflection of the ions we have studied the angular dependence of the electron structure resulting from electron transfer to the continuum of the effective ion potential. Far from the ion scattering plane we have observed the Si Auger electron spectrum. We discuss the differences between the Auger peaks obtained by electron and grazing proton bombardment of Si surfaces partially covered with O₂ and Al.     

Development of a Double Layered Scintillator for Separating and Detecting Low Energy Protons and Electrons

A scintillator system consisting of a thin (5,000 ? - 15,000 ?) CsI(Tl) layer evaporated onto a plastic scintillator (NE-102) has been developed for the purpose of distinguishing low energy protons from electrons and measuring the energy of each species. Evaporations in a high vacuum (10-8 Torr) produced layers of CsI(Tl) that scintillate with an efficiency comparable to optimally doped bulk material, If the CsI(Tl) layer thickness is 15,000 ?, it stops protons with energies below 170 keV and electrons with energies below 18 keV. Thus, protons with energies between about 25 and 250 keV can be distinguished from electrons with energies above 18 keV by examining the shape of the light pulse generated in the dual scintillator. Results obtained with protons and electron beams will be presented.     

Schottky junctions on semi-insulating LEC gallium arsenide for X and γ-ray spectrometers operated at and below roomtemperature

This work deals with the study of a Schottky junction used as an X- and γ-ray detector in a spectrometer operated in the temperature range from -30°C to +22°C. The device (7 mm² active area and 100 μm thickness), fabricated on liquid encapsulated Czochralski (LEG) semi-insulating Gallium Arsenide, is designed with a noninjecting ohmic contact which allows biasing voltages up to 550 V. At room temperature (22°C) the energy resolution is found to be relatively poor (15.5-keV full-width at half-maximum (FWHM) at 59.5 keV) due to the large junction reverse current, whose density (7-37 nA/mm² at V_bias=100-500 V) is within the typical values for Schottky junctions on SI LEC GaAs. By cooling of the detector to -30°C, the noise of the reverse current is drastically lowered, thus achieving electronic noise levels around 160-180 rms electrons (1.6-1.8 keV FWHM), At 500-V bias, the ²⁴¹Am spectrum has been resolved down to an energy of 4 keV with charge collection efficiency of cce=97% and a resolution of about 2-keV FWHM for the Np L lines and 2.4-keV FWHM for the 59.5-keV γ photons. The linearity of the detector has been measured to be better than ±0.6% within the explored energy range (14-59 keV). From the experimental spectra, it has been analyzed how either the electronic noise or the trapping of the signal charge contribute to the energy resolution of the spectrometer. The result is that despite the high measured cce. The trapping gives a contribution higher than 1.5 keV FWHM for the 59.5-keV spectral line. A comparison between the experimental results and Monte Carlo simulations, based on the Hecht model of charge trapping in detectors, is shown to give a satisfactory justification of the observed phenomena. A total mean drift length of carriers has been experimentally derived, finding an exponential dependence upon the bias voltage applied to the detector