Steering of Sub-GeV electrons by ultrashort Si and Ge bent crystals

We report the observation of the steering of 855 MeV electrons by bent silicon and germanium crystals at the MAinzer MIkrotron. Crystals with 15 \(\upmu \)m of length, bent along (111) planes, were exploited to investigate orientational coherent effects. By using a piezo-actuated mechanical holder, which allowed to remotely change the crystal curvature, it was possible to study the steering capability of planar channeling and volume reflection vs. the curvature radius and the atomic number, Z. For silicon, the channeling efficiency exceeds 35%, a record for negatively charged particles. This was possible due to the realization of a crystal with a thickness of the order of the dechanneling length. On the other hand, for germanium the efficiency is slightly below 10% due to the stronger contribution of multiple scattering for a higher-Z material. Nevertheless this is the first evidence of negative beam steering by planar channeling in a Ge crystal. Having determined for the first time the dechanneling length, one may design a Ge crystal based on such knowledge providing nearly the same channeling efficiency of silicon. The presented results are relevant for crystal-based beam manipulation as well as for the generation of e.m. radiation in bent and periodically bent crystals.     

Emission of Photons at the Interaction of a High-Energy Electron Beam with a Sequence of Bent Single Crystals

A radiation source based on the emission of electrons and positrons moving in a short bent crystal has been recently discovered. The emission of particles is due to oscillations of their trajectories near the point of reflections, where trajectories approach a tangent to bent atomic planes. In the experiment performed with the secondary electron beam of the U70 accelerator, it has been shown that the emission intensity can be increased by using a sequence of oriented bent crystals. Passing through six 2.5-mm-long silicon crystals, 7-GeV electrons lose on average 2.0 GeV on emission. This value is several times larger than that in an amorphous medium. Thus, an intense source of radiation has been demonstrated with prospects of application at accelerators.     

Deflection of MeV protons by an unbent half-wavelength silicon crystal

The interaction of a 2?MeV proton beam with an ultrathin unbent Si crystal was studied through simulation and experiment. Crystal thickness along the beam was set at 92?nm, i.e., at half the oscillation wavelength of the protons in the crystal under planar channeling condition. As the nominal beam direction is inclined by less than the critical angle for planar channeling with respect to the crystal planes, under-barrier particles undergo half an oscillation and exit the crystal with the reversal of the transverse momenta; i.e., the protons are "mirrored" by the crystal planes. Over-barrier particles suffer deflection, too, to a direction opposite that of mirroring with a dynamics similar to that of volume reflection in a bent crystal. On the strength of such coherent interactions, charged particle beams can be efficiently steered through an ultrathin unbent crystal by the same physical processes as for thicker bent crystals.     

Coherent effect in the radiation of relativistic electrons in the field of bent atomic crystallographic planes

The effect of the intense monochromatic radiation arising when relativistic electrons intersect periodically bent atomic crystallographic planes in a crystal is predicted. This effect is independent of the channeling of the particles in the crystal and is possible for relativistic positrons and electrons.     

Radiation from 39 and 45 MeV electrons channeled in Lithium Niobate

Abstract

Channeling radiation from 39 and 45 MeV electrons channeled along the <0001> axis, the (0110) plane and the (1210) plane of a 30 μm thick LiNbO ₃ crystal has been measured. Calculations of the planar crystal potentials were performed by means of the many-beam formalism. Good agreement between theory and experiment is obtained for the planar channeling radiation. Associated with channeling additional radiation lines have been observed, which may be explained by a periodic perturbation of the continuum potential.     

变曲率弯晶的粒子退道行为

利用正弦平方势和变曲率的抛物线近似描写了弯曲硅单晶的粒子退道效应,进一步证实利用弯晶来偏转(或控制)带电粒子运动方向的可能性。导出弯晶的退道系数并讨论了它的可能应用。 关键词：     

Deflection of a 100-MeV positron beam by repeated reflections in thin crystals

The phenomenon of the deflection of a charged particle beam due to channeling in a bent crystal is thoroughly investigated and successfully applied for the extraction of the beam in high-energy accelerators, at the energies of about 10 GeV and higher. However, a big practical interest lies in the task of bending and extracting charged particles with energies below 1 GeV, for example, for the production of ultrastable beams of low emittance for medical and biological applications. That is why a novel crystal technique, namely thin straight crystal targets, is investigated in this article, using crystals as elements for extraction and collimation of the circulating beam in a ring accelerator. The advantages of reflection in straight crystals in comparison with bent crystal channeling consist in the small length of straight crystals along the beam that reduces the amount of nuclear interactions and improves the background. Experimental results were obtained for the bending of a 100 MeV positron beam with using five sequential straight crystals.     

Simulation of radiation energy losses by channeled relativistic electrons in a crystal

A computer code is developed to calculate the radiation energy losses (RELs) of electrons during both 〈100〉 axis and (100) plane channeling in a thin Si crystal. A computer simulation of these losses is carried out by taking the initial angular divergence of the beam into account, and the REL dependences on the angle of electron entry into the crystal are obtained for both axial and planar channeling (orientational dependences). The calculations are carried out in connection with experiments on the interaction of 20–255 MeV electrons with crystals conducted at the SAGA Light Source linear accelerator (Tosu, Saga, Japan). The simulation results show the possibility of using the orientational dependence of the RELs of channeled electrons in thin crystals to diagnose the initial angular divergence of the electron beam and to orient crystals.     

Measurements of energetic proton transport through magnetized plasma from intense laser interactions with solids

Protons with energies up to 18 MeV have been measured from high density laser-plasma interactions at incident laser intensities of 5x10(19) W/cm(2). Up to 10(12) protons with energies greater than 2 MeV were observed to propagate through a 125 &mgr;m thick aluminum target and measurements of their angular deflection were made. It is likely that the protons originate from the front surface of the target and are bent by large magnetic fields which exist in the target interior. To agree with our measurements these fields would be in excess of 30 MG and would be generated by the beam of fast electrons which is also observed.     

Neutralization of specularly reflecting ions on a clean (001) surface of SnTe

Neutral fractions of specularly reflected beams have been measured for the glancing-angle incidence of (0.2-0.5) MeV ions on a clean (001) surface of SnTe. The measured fractions have been compared with the results calculated by a classical model for charge exchanges and by a model based on the first-order perturbation theory. The experimental and calculated results have differed greatly. The disagreements are attributed to collisions with valence electrons on the surface. The electron capture cross-sections of (0.2-0.5) MeV ions for valence electrons have been derived, based on the measured neutral fraction and distribution of valence electrons for jellium background positive charges, and are found to be about ten times larger than those for the outermost electrons of Sn and Te atoms calculated by the classical model. Received: 23 October 1998     

The dependence of angular width ψ1/2 the axial dip on the depth of particle penetration into crystal

The depth dependence of angular width ψ_1/2 of the axial dip in the yield of backscattering of protons (E ₀ = 6.3 MeV) from a tungsten single crystal has been investigated experimentally. The interpretation of the results was based on a two-dimensional kinetic equation which accounts for the multiple scattering of channelled particles by electrons and thermal vibrations of the lattice.     

Transitions between bound states for axially channeled MeV electrons

Photon lines emitted in the forward direction from 2.0–4.5 MeV electrons channeled along a 〈110〉 axis in a 3400 Å Si crystal have been measured and compared with calculations and with previous results from a 12 000 Å Si 〈111〉 crystal. Nearly all features agree with predictions based on an isolated string.     

Influence of incoherent scattering on stochastic deflection of high-energy negative particle beams in bent crystals

An investigation on stochastic deflection of high-energy negatively charged particles in a bent crystal was carried out. On the basis of analytical calculation and numerical simulation it was shown that there is a maximum angle at which most of the beam is deflected. The existence of a maximum, which is taken in the correspondence of the optimal radius of curvature, is a novelty with respect to the case of positively charged particles, for which the deflection angle can be freely increased by increasing the crystal length. This difference has to be ascribed to the stronger contribution of incoherent scattering affecting the dynamics of negative particles that move closer to atomic nuclei and electrons. We therefore identified the ideal parameters for the exploitation of axial confinement for negatively charged particle beam manipulation in future high-energy accelerators, e.g., ILC or muon colliders.     

Spectral method in axial channeling theory

The energy quantization of transverse particle motion in continuous potentials of atomic chains and planes can occur when fast charged particles travel in crystals. In the proposed paper, the energy levels of electrons moving in the mode of axial channeling in a system of parallel atomic chains have been found (Si crystal [110] chains have been used as an example). The energy eigenvalues were determined numerically using the so-called spectral method, which shows itself to good advantage in the problem of the plane channeling of charged particles in crystals.     

Comparison of the efficiency of the deflection of proton beams with various energies by a bent crystal with the use of planar channeling and the stochastic deflection mechanism

The efficiency of the deflection of 50-, 15-, and 1.3-GeV proton beams by means of planar channeling in a bent silicon crystal has been compared to that by means of the stochastic mechanism of the deflection of charged particles by the bent crystal. The deflection of protons at single passage through the crystal has been simulated. The results of the experiment on the deflection of a circulating beam at the U-70 accelerator (Institute for High Energy Physics, Protvino, Moscow region) are presented. It has been shown that the efficiency of the stochastic deflection mechanism increases with a decrease in the energy, whereas the efficiency of the planar channeling for deflection decreases.     

On the mechanism of the volume reflection of relativistic particles

The mechanisms of the volume reflection of positively and negatively charged relativistic particles in a bent crystal have been analyzed. It has been shown that the empty core effect is significant for the reflection of the negatively charged particles. The average reflection angle of the negatively charged particles has been determined and the conditions for the observation of the reflection and refraction are discussed.     

不同粒子辐射条件下CC4013器件辐射损伤研究

本文采用60 MeV Br离子、5 MeV质子和1 MeV电子等三种辐射源, 针对CC4013型互补金属氧化物半导体器件(complementary metal oxide semiconductor, CMOS)进行辐射损伤研究. 通过Geant4程序计算了该器件电离辐射吸收剂量与芯片厚度的关系, 经过计算, 在相同注量下, 60 MeV Br离子的电离吸收剂量最大, 1 MeV电子产生的电离吸收剂量最小. 应用Keithley4200-SCS半导体特性分析仪在原位条件下研究了CC4013器件电性能参数随辐射吸收剂量的变化关系. 测试结果表明, 相同电离辐射吸收剂量下, 1 MeV电子对CC4013器件的阈值电压参数影响最大, 5 MeV质子其次, 60 MeV Br离子的影响最弱. 关键词： CMOS器件 高能带电粒子 电离辐射 辐射损伤     

正弦平方势与环形加速器的弯晶束流引出

在经典力学框架内和偶极近似下, 引入正弦平方势, 把粒子在弯晶中的运动方程化为具有固定力矩的摆方程。 利用Jacobian椭圆函数和椭圆积分分析了系统的相平面特征。 导出了弯晶的最大偏转能量、 退道系数和退道长度。 计算结果表明, 对于曲率半径为1 m, 能量为1.0 GeV的质子, Si(110)面沟道的引出效率为70%; 对于MeV范围的粒子, 退道长度大约是μm量级; 对于TeV范围的粒子, 退道长度可达1 m以上。 In the classical mechanics frame and the dipole approximation the particle motion equation in bent crystal is reduced to the pendulum equation with a constant momentum by using the sine squared potential.The phase planar properties are analysed by means of Jacobian elliptic function and the elliptic integral. The maximum deflected energy, the dechanneling factor and the dechanneled length are derived. The results show that the extrated efficiency is 70% for a proton beam with energy E=1.0 GeV moved in the channel on Si(110) if a radius of curvature R=1 m; and dechanneled length is of the order of μm for the particles with MeV energy; the dechanneled length is above 1 meter for the particle with TeV energy.     

Features of the scattering of protons and relativistic electrons intersecting a thin planar target at a small angle to its surface

The processes of scattering of protons and relativistic electrons incident on a planar target at a small angle to its surface have been simulated by the Monte Carlo method. The spatial and energy distributions of the beams of particles both passed through the target and reflected from it have been calculated. The dependence of the characteristics of beams on the initial energy and direction of injection of particles, as well as on the material and thickness of the target, has been considered. The transmission, reflection, and absorption coefficients for electrons in the target have been calculated. The initial energy in the calculations is varied in the range of 7–100 MeV and the angle between the trajectory of particles and the surface of the target is in the range of 1°–45°. The thickness of the target varies from 0.2 to 3 mm. Aluminum, iron, and copper targets have been considered. It has been shown that the intersection of targets at small angles not only increases the transverse dimensions of a beam, but also changes the direction of its motion. The results of the reported calculations of the scattering of relativistic electrons intersecting a foil at small angles to its surface are in qualitative agreement with experimental data.     

Radiation defect clusters in electron-irradiated silicon

Radiation defect formation in Czochralski-grown (pulled) and vacuum float-zone n-Si (ρ=15 to 150 ωcm) irradiated by electrons with energy E_e=2.5 to 1200 MeV has been studied. The results have been obtained from an analysis of the dose, energy and temperature dependences of the concentration n, Hall mobility μ _n , and charge-carrier lifetime τ. The experimentally observed peculiarities in the variation of n, μ _n , and τ irradiation by electrons with E10 MeV have been explained taking into account the formation of radiation defect clusters in the bulk of the crystal induced by such electrons. The correlation coefficients K_i have bsen obtained which take into consideration the “evolution” of primary displacement cascades in the location of which clusters are formed. The parameters of radiation defect clusters produced by electrons of different energies have been calculated using these coefficients.