On possibility of measurement of the electron beam energy using absorption of radiation by electrons in magnetic field

A possibility of precise measurement of the electron beam energy using absorption of radiation by electrons in a homogeneous magnetic field for electrons of high energy in the range up to a few hundred GeV, was considered earlier. In this paper, with the purpose of experimental checking of this method in the range of several tens MeV of electrons energies, a possibility of measurement of absolute energy of the electron beam with a relative accuracy up to 10^?4, is considered. We take into account influence of the laser beam diffraction, of the spread of electrons over energies, and of the length of formation of radiation absorption in the process of electron beam energy measurement. The laser wavelength and the length of the magnet are chosen depending on the length of photon absorption formation. It is found that the kinematical restrictions on the photon absorption process lead to the selection in angles of propagation of photons, which can be absorbed by the beam electrons. It is shown that parameters of the electron beam will noticeably not vary during the measurement of the energy.     

Angular and energy distribution of electrons produced by 200–500 keV protons in gases

The cross beam method was used to measure double differential ionization cross sections for electron production by 200–500 keV protons incident on a molecular beam. The ejected secondary electrons were detected by an electron multiplier and an electrostatic 90 °-spectrometer which was movable in the scattering chamber from 18 °–155 ° with respect to the incident proton direction. After the elimination of disturbing electric and magnetic fields, electrons were measured at energies down to 1 eV. The absorption of the very slow electrons along their path through the spectrometer could be minimized by using a relatively low gas pressure in the scattering chamber of a few 10^?5 Torr. The efficiency of the electron detector was determined with an electron source whose emission rate per solid angle was known. Absolute cross sections and their angular dependence were obtained by measuring the slow electrons—ejected with a relatively high rate—without the molecular beam; these data being used to normalize the electron spectra acquired with the molecular beam. Ionization cross sections with 300 keV protons incident on helium are discussed and except for the very slow electrons, a good agreement is found with results of Ruddet al.     

Ultrashort electron beam and volume high-current discharge in air under the atmospheric pressure

Conditions are studied under which an electron beam and a volume discharge with a subnanosecond rise time of a voltage pulse are produced in air under atmospheric pressure. It is shown that the electron beam appears in a gas-filled diode at the front of the voltage pulse in ∼0.5 ns, has a half-intensity duration of ≤0.4 ns and an average electron energy of ∼0.6 of the voltage across the gas-filled diode, and terminates when the voltage across the gap reaches its maximum value. The electron beam with an average electron energy of 60 to 80 keV and a current amplitude of ≥70 A is obtained. It is assumed that the electron beam is formed from electrons produced in the gap due to gas ionization by fast electrons when the intensity of the field between the front of the expanding plasma cloud and the anode reaches its critical value. A nanosecond volume discharge with a specific power input of ≥400 MW/cm³, a density of the discharge current at the anode of up to 3 kA/cm², and specific energy deposition of ∼1 J/cm³ over 3 to 5 ns is created.     

The Dynamics of Electron Orbits during the Acceleration of Electrons in a Betatron

This paper presents a system of equations that describe the motion of charged particles in the electromagnetic field of a betatron. This system of equation was successfully used to study the behavior of the electron orbits and to determine the principal parameters of the electron beam in the electromagnetic field of a betatron during the electron acceleration and deceleration. The results of this study may find application in developing systems designed to accelerate electron beams. It has been shown that in the course of acceleration there is no damping of the betatron oscillations by the law B _z ^–1/2 and, correspondingly, no decrease in beam cross section. In contrast to the existing belief, the initial departure of the kinetic energy (momentum) of the injected electrons from the energy (momentum) of the electrons following the equilibrium orbit is not preserved in the course of acceleration. In the betatron chamber, the electron beam, when accelerated, does not constrict to form a ring but occupies a broad zone, whose dimensions are determined by the initial double amplitudes of the vertical and horizontal oscillations. Despite the large double amplitude of the oscillations of the beam particles, the average energy of the electrons differs from the energy of the electrons following the equilibrium orbit only slightly, and the departure of the average energy from the energy of the equilibrium electrons varies proportionally to the (varying) field of the betatron.     

入射电子能量对低密度聚乙烯深层充电特性的影响

高能带电粒子与航天器介质材料相互作用引起的深层带电现象, 一直是威胁航天器安全运行的重要因素之一. 考虑入射电子在介质中的电荷沉积、能量沉积分布以及介质中的非线性暗电导和辐射诱导电导, 建立了介质深层充电的单极性电荷输运物理模型. 通过求解电荷连续性方程和泊松方程, 可以得出不同能量 (0.1–0.5 MeV) 电子辐射下, 低密度聚乙烯 (厚度为1 mm) 介质中的电荷输运特性. 计算结果表明, 不同能量的电子辐射下, 介质充电达到平衡时, 最大电场随入射能量的增加而减小; 同一能量辐射下, 最大电场随束流密度的增大而增加. 入射电子能量较低时 (≤ 0.3 MeV) , 最大电场随束流密度的变化趋势基本相同. 具体表现为: 当束流密度大于3× 10^-9 A/m²时, 最大场强超过击穿阈值2×10⁷ V/m, 发生静电放电 (ESD) 的可能性较大. 随着入射电子能量的增加, 发生静电放电 (ESD) 的临界束流密度增大, 在能量为0.4 MeV时, 临界束流密度为6×10^-8 A/m². 当能量大于等于0.5 MeV时, 在束流密度为10^-9–10^-6 A/m²的范围内, 均不会发生静电放电 (ESD) . 该物理模型对于深入研究深层充放电效应、评估航天器在空间环境下 深层带电程度及防护设计具有重要的意义. 关键词： 高能电子辐射 低密度聚乙烯(LDPE) 介质深层充电 电导特性     

Erzeugung polarisierter Elektronenstrahlen durch optisches Pumpen

The valence electrons in sodium vapour were aligned by optical pumping to a polarization between 5% and 15%. An electron beam of 10^?12 A current, 10^?2rad divergency and 1 mm diameter has been obtained by ionisation of the sodium vapour with uv-light. This electron beam was polarized up to 2% as measured by Mott scattering.     

The energy of thermal electrons in electron beam created helium discharges

We have measured the electron energy of the thermal group of electrons in both longitudinal and transverse electron beam created helium glow discharges. The measurement technique employs the ratio of intensities of spectral lines in the 2s³S?np³P He I series. Values of kT_e between 0.07 and 0.11 eV were obtained. These energies are typical of the beam-generated electric field free plasmas. The competitive loss of helium ions by recombination and by charge transfer in a He?Hg electron beam created plasma is calculated. The results are applied to the Hg⁺ laser pumping scheme using a electron beam created He?Hg plasma.     

Control over the space-time structure of electron beams by high-intensity femtosecond laser radiation

The space-velocity distribution of electrons propagating in vacuum can be deformed by the ponderomotive potential produced by high-intensity femtosecond laser pulses, which makes it possible to subsequently separate such electrons from the initial beam. It is shown that optical modification of electron beams with kinetic energies on the order of 100 eV by femtosecond laser radiation with an intensity from 10¹⁴ to 10¹⁸ W/cm² makes it possible to form electron beams with a duration on the order of 50–100 fs. Examples of optical control over the shape of electron beams, based on deflection, reflection, focusing, and splitting of electron beams, are considered.     

Application of a scanning electron microscope in simulating a beta-emission-induced current

The current induced by emission from a thin ⁶³Ni layer is simulated with allowance for the real spectrum of ejected electrons and their angular distribution in Si and GaN. The calculated results are compared with simulation data obtained for a monoenergetic electron beam perpendicular to the semiconductor detector. For both Si and GaN, the ratio between the currents induced by the SEM beam and β emission from ⁶³Ni is demonstrated to be almost completely independent of the diffusion length, if the electron-beam energy of a scanning electron microscope (SEM) is appropriately selected.     

Fast electron energy deposition in aluminium foils: Resistive vs. drag heating

The high current electron beam losses have been studied experimentally with 0.7 J, 40 fs, 6 10¹⁹ Wcm^-2 laser pulses interacting with Al foils of thicknesses 10-200 μm. The fast electron beam characteristics and the foil temperature were measured by recording the intensity of the electromagnetic emission from the foils rear side at two different wavelengths in the optical domain, ≈407 nm (the second harmonic of the laser light) and ≈500 nm. The experimentally observed fast electron distribution contains two components: one relativistic tail made of very energetic (T _h ^tail ≈ 10 MeV) and highly collimated (7° ± 3°) electrons, carrying a small amount of energy (less than 1% of the laser energy), and another, the bulk of the accelerated electrons, containing lower-energy (T _h ^bulk=500 ± 100 keV) more divergent electrons (35 ± 5°), which transports about 35% of the laser energy. The relativistic component manifests itself by the coherent 2ω₀ emission due to the modulation of the electron density in the interaction zone. The bulk component induces a strong target heating producing measurable yields of thermal emission from the foils rear side. Our data and modeling demonstrate two mechanisms of fast electron energy deposition: resistive heating due to the neutralizing return current and collisions of fast electrons with plasma electrons. The resistive mechanism is more important at shallow target depths, representing an heating rate of 100 eV per Joule of laser energy at 15 μm. Beyond that depth, because of the beam divergence, the incident current goes under 10¹² Acm^-2 and the collisional heating becomes more important than the resistive heating. The heating rate is of only 1.5 eV per Joule at 50 μm depth.     

Messung der Energie- und Winkelabhängigkeit der Asymmetrie der äußeren Bremsstrahlung

In order to obtain an azimuthal dependence of the external bremsstrahlung produced by electrons, the electron beam has to be transversely polarized. In first-order Born approximation the differential cross section does not depend on the azimuthal angle φ¹, but the second-order approximation includes the spin vector of the electrons^2,3 and yields, consequently, a φ-dependence. This paper deals with a measurement of the bremsstrahlung asymmetry as function of the photon energy and the emission angle Θ. The transversely polarized electron beam was produced by momentum deflection of longitudinally polarizedβ-decay electrons emitted from a⁹⁰Sr source. With a kinetic energy of 300±10 keV and a degree of transverse polarization of 74% the electrons hit a Pb target. Because of the high γ-background it was necessary to detect the emitted bremsstrahlung in coincidence with the incident electrons. We found effects of about 3% in contrast to considerably larger values (13%) published in an earlier paper. The asymmetry was numerically calculated according to Johnson and Rozics. Since at an electron energy of 300 keV the Born approximation gives not yet good results, theory and measurement agree only in order of magnitude, particularly at highγ-energies.     

Laser-induced recombination studies with the adiabatically expanded electron beam of the Heidelberg TSR

The enhancement of spontaneous radiative recombination of C⁶⁺ ions with free electrons in a resonant laser field has been investigated at the Heidelberg cooler ring TSR for different transverse electron temperatures realized by adiabatically expanding the magnetically guided electron beam. The recombination spectra close to the ionization threshold strongly deviate from calculations for free independent electrons, showing important contributions at energies below this threshold. Shape and relative size of these contributions change significantly as the transverse temperature is varied. These changes are not consistent with the expected behaviour of sub-threshold contributions due to electric stray fields.     

Simulation of the current induced by 63Ni beta radiation

The current generated by radiation from a ⁶³Ni layer of variable thickness is simulated with the actual spectrum of emitted electrons and with their distribution over the angles for Si and SiC taken into account. The dependences of the generation rate for nonequilibrium charge carriers on the depth are obtained for the cases of several Ni film thicknesses for both materials. The results are compared with the simulation results for a monoenergetic electron beam that is perpendicular to a semiconductor detector. It is shown that, for both Si and SiC, it is possible to choose an energy value of the electron beam in a SEM such that the ratio of the currents induced by the SEM beam and beta radiation from ⁶³Ni is essentially independent of the diffusion length.     

Electron scattering based on a novel internal target technique: SCRIT

A novel technique for forming internal targets, named SCRIT (Self-Confining RI Ion Target), has been developed, which can make electron scattering off short-lived radioactive nuclei possible in an electron storage ring. SCRIT confines the ions of interest by utilizing the “ion trapping” phenomenon in the electron storage ring. Approximately 10⁷ stable ¹³³Cs ions were trapped in a three-dimensional configuration along the electron beam axis at an electron beam current of 75mA. The angular distribution of the electrons scattered from the trapped ¹³³Cs ions was successfully measured, and a collision luminosity of 10²⁶/(cm² s) was achieved.     

Scattering of relativistic electrons by a focused laser pulse

The problem of the motion of a classical relativistic electron in a focused high-intensity laser pulse is solved. A new three-dimensional model of the electromagnetic field, which is an exact solution of Maxwell’s equations, is proposed to describe a stationary laser beam. An extension of the model is proposed. This extension describes a laser pulse of finite duration and is an approximate solution of Maxwell’s equations. The equations for the average motion of an electron in the field of a laser pulse, described by our model, are derived assuming weak spatial and temporal nonuniformities of the field. It is shown that, to a first approximation in the parameters of the nonuniformities, the average (ponderomotive) force acting on a particle is described by the gradient of the ponderomotive potential, but it loses its potential character even in second order. It is found that the three-dimensional ponderomotive potential is asymmetric. The trajectories of relativistic electrons moving in a laser field are obtained and the cross sections for scattering of electrons by a stationary laser beam are calculated. It is shown that reflection of electrons from the laser pulse and the surfing effect are present in the model studied. It is found that for certain impact parameters of the incident electrons the asymmetic ponderomotive potential can manifest itself effectively as an attractive potential. It is also shown that even in the case of a symmetric potential the scattering cross section contains singularities, known as rainbow scattering. The results are applicable for fields characterized by large (compared to 1) values of the dimensionless parameter η² = e ²〈E ²〉/m ²ω² and arbitrary electron energies.     

Hydrogen diffusion in steels under electron bombardment

We report on the results of measurement of the coefficients of hydrogen diffusion through metal membranes in the course of their simultaneous hydrogen saturation and bombardment with electrons (energy 30 keV, current density from 3 to 30 µA/cm²) both in a broad and in a narrow beam. It is found that the time of hydrogen discharge from the membrane is determined by the parameters of the electron beam, its periodicity and duration, and also depends on the structure of the phase state of the metal membrane. It is shown that the diffusion coefficient increases when a narrow electron beam in the scanning regime is used. Analysis of the hydrogen yield as a function of time is carried out on a mass spectrometer connected to a vacuum chamber containing an electron gun, a beam sweep oscillator, and an electrolytic cell. The hydrogen diffusion coefficients under the action of a scanning electron beam are 15 times larger than under the same conditions without irradiation.     

Li+低能(e,2e)反应角分布

利用修正的BBK理论，考虑入射道的库仑相互作用及出射电子的交换对称性，在共面-等能分享-垂直角度碰撞几何中，分别计算了能量为79.6，105.6，227.6和375.6eV的入射电子碰撞Li⁺(1s²)(e，2ｅ)反应三重微分截面(TDCS).结果表明：在接近阈能的碰撞中，两出射电子连线平行于入射电子方向时，TDCS最大；两出射电子连线垂直于入射电子方向时，TDCS最小；入射电子能量达5倍的电离阈能时，主要为单次双体碰撞，而且入射道库仑场对决定低能碰撞的TDCS起着重要作用. 关键词：     

Dynamics of an electron beam from a high-current picosecond accelerator

The dynamics of a high-current (10²–10⁴ A) electron beam with energies of 10⁵–10⁶ eV and picosecond duration (10⁻¹⁰ s) at the output of the accelerator tube is investigated. The slowing of electrons by the residual positive charge on the surface of the tube is found to have a significant influence in the case of short pulse durations. The distance of the electron beam from the surface of the tube in vacuum is estimated on the basis of a one-dimensional model. It is shown that the electron radiation can travel to a distance of several centimeters from the surface at current densities below 20 A/mm², whereas at high current densities the beam is trapped near the surface. Zh. Tekh. Fiz. 69, 111–115 (May 1999)     

An “instantaneous” distribution of the ionization-passive electrons and holes under irradiation of a dielectric by intense electron or laser beams

A method is worked out for calculation of an “instantaneous” energy distribution of the ionization-passive electrons and holes resulting from the electron-electron collisions before the onset of electron-phonon relaxation under 10⁻¹⁵–10⁻¹⁴ s irradiation of a dielectric by an intense electron or laser beam. The method is based on the solution of a system of integral-differential kinetic equations of general form. The Auger and impact ionization as well as hole recoil due to the momentum conservation law are taken into account in calculations. The “instantaneous” distribution is calculated in NaCl under irradiation of the sample by a high-density electron beam. The “instantaneous” distribution of ionization-passive electrons and holes is the initial one in solutions of all kinetic equations describing further relaxation of electron excitations in irradiated materials.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 15–22, November, 2004.     

Efficiency improvement of an electron collector intended for electron cooling systems using a Wien filter

An efficient collector for high-voltage systems of electron cooling is presented. Its efficiency (ratio of the reflected electron current to the current of the main beam) is greatly improved by suppressing the reflected particle flux in the Wien filter. Secondary electrons deflect in crossed transverse electric and magnetic fields and are absorbed by a special receiver plate (secondary collector). The filter is designed so that the whole backward flow of electrons deflects even if the trajectory and main beam profile are distorted insignificantly. Experiments carried out on a special-purpose test bench show that such a filter raises the efficiency of the collector hundredfold (up to 10^?6).