Inference of the electron temperature in inertial confinement fusion implosions from the hard X‐ray spectral continuum

Using the free‐free continuum self‐emission spectrum at photon energies above 15 keV is one of the most promising concepts for assessing the electron temperature in inertial confinement fusion (ICF) experiments. However, these photons are due to suprathermal electrons whose mean free path is much larger than the thermal one, making their distribution deviate from Maxwellian in a finite‐size hotspot. The first study of the free‐free X‐ray emission from an ICF implosion is conducted, accounting for the kinetic modifications to the electron distribution. These modifications are found to result in qualitatively new features in the hard X‐ray spectral continuum. Inference of the electron temperature as if the emitting electrons are Maxwellian is shown to give a lower value than the actual one.     

黑腔靶中超热电子特性研究

近几年来,在“神光”装置上进行了1.053μm激光与平面靶及一系列柱形黑腔靶相互作用实验。用一台多道滤波—荧光X光能谱仪(FFS)测得各种靶发射的超热X射线谱,由谱推导超热电子温度T_h和超热电子总能量E_h当照射靶单束激光能量E_(tar)为400～670J、脉宽τ=650～1150ps时,发现黑腔内明显存在两群服从Maxwell分布高能电子(T_h=35～45keV;T_(hh)=150～350kev),而且E_(he)占E_(tar)的份额为10％～12％。实验还表明:腔内的E_(he)与非线性过程特征量(SRS)有较好的线性关系,因此推断出腔内超热电子产生的主要机制是受激Raman散射。在相同照射条件下,黑腔靶产生的超热电子比平面靶严重。     

超热电子与金黑腔靶作用产生硬X射线的蒙特卡罗模拟

激光打靶产生大量麦氏分布的超热电子,与金腔靶相互作用产生硬X射线.利用蒙特卡罗方法,对超热电子在金腔靶中的传输进行了研究,模拟了在不同超热电子温度、份额下硬X射线谱的变化及在不同腔体尺寸、腔壁厚度情况下,硬X射线谱的变化情况,给出硬X射线产生效率的决定因素.利用硬X射线谱反推得到的超热电子信息与蒙特卡罗程序模拟结果相结合的方法,获得金腔内部超热电子初始信息. 关键词： 热电子 超热电子 蒙特卡罗方法 硬X射线     

强流电子束轫致辐射复合薄靶设计

针对目前脉冲硬X射线源能谱硬、辐照面积小、辐射场电子份额高无法开展系统电磁脉冲效应实验研究的技术难题,提出了采用复合薄靶软化脉冲硬X射线能谱、降低电子份额的方法。采用MCNP程序数值模拟了电子和光子在不同材料中的输运规律,分析了复合靶结构和材料厚度对X射线能谱、电子份额的影响。以闪光二号加速器为电子束源,设计了复合薄靶、X射线窗。实验得到的X射线参数:平均能量121 keV;均匀性2∶1情况下,700 cm2平均剂量40 rad（Si）,500 cm2平均剂量170 rad（Si）;光子数与电子数的比值大于103,可以开展系统电磁脉冲效应初步实验研究。     

Excitation of X rays by electrons accelerated in air in the wake wave of a laser pulse

The characteristics of X rays of a laser plasma generated in the interaction of a femtosecond pulse with solid targets in an air atmosphere have been investigated. It has been shown that the mechanism for the generation of X rays in the interaction of short intense laser pulses with solid targets in a gas atmosphere is attributed to the generation of fast electrons in the region of the filamentation of a laser pulse. It has been proven experimentally that under such conditions, the solid target irradiated by laser radiation of even a low density of about 10¹⁵ W/cm² very efficiently emits ∼10-keV photons. It has been shown theoretically that the maximum energy of accelerated electrons can reach ɛ_max ∼ 100–200 keV under these conditions. This means that the proposed method can provide characteristic radiation with the energy of photons much higher than 10 keV.     

空腔靶超热电子实验研究

本文介绍了激光与空腔靶、平面靶相互作用时，利用多道高能X射线滤波-荧光谱仪(FF谱仪)、高能X射线角分布探测器以及激光功率能量计，对等离子体发射的超热X射线和受激喇曼散射光进行测量的情况；给出了不同实验条件下典型的超热X射线能谱、角分布、超热电子温度Th以及受激喇曼散射光能量ESRS，对实验结果作了分析和讨论。     

5~88keV能区硬X光能谱精密测量

利用滤波荧光(FF)法建立了5~88keV能区硬X光能谱测量系统,对闪烁探测器的灵敏度进行了精密标定,不确定度好于10%。通过研究干扰产生的原因,改善系统屏蔽,有效地排除了干扰,提高了系统的信噪比;通过更换大电流的光电倍增管,改变准直光阑的尺寸和滤片的厚度,将测量系统的线性动态范围从4提高到104。在神光Ⅲ原型物理实验中定量给出Au平面靶硬X光谱,实现硬X光能谱的精密测量。     

Compton Spectrum Due to L-Shell Electrons

Compton spectrum due to L-shell electrons of thorium has been measured by the coincidence technique, using 279 keV incident gamma photons. The influence of L-shell electron momenta on the distribution of the scattered photons has been studied with reference to the Compton profile due to free electrons and compared with the exact and impulse hydrogenic theoretical models. Significant deviations are found between experimental and theoretical Compton spectra.     

511 keV photons from color superconducting dark matter

We discuss the possibility that the recent detection of 511 keV gamma rays from the galactic bulge, as observed by the International Gamma-Ray Astrophysics Laboratory, can be naturally explained by the supermassive very dense droplets (strangelets) of dark matter. These droplets are assumed to be made of ordinary light quarks (or antiquarks) condensed in a nonhadronic color superconducting phase. The droplets can carry electrons (or positrons) in the bulk or/and on the surface. The e(+)e(-) annihilation events take place due to the collisions of electrons from the visible matter with positrons from dark matter droplets which may result in the bright 511 keV gamma-ray line from the bulge of the Galaxy.     

Compton scattering in ignited thermonuclear plasmas

Inertially confined, ignited thermonuclear D-T plasmas will produce intense blackbody radiation at temperatures T greater, similar20 keV; it is shown that the injection of GeV electrons into the burning core can efficiently generate high-energy Compton scattering photons. Moreover, the spectrum scattered in a small solid angle can be remarkably monochromatic, due to kinematic pileup; a peak brightness in excess of 10;{30} photons/(mm(2) mrad(2) s 0.1% bandwidth) is predicted. These results are discussed within the context of the Schwinger field and the Sunyaev-Zel'dovich effect.     

光子与相对论麦克斯韦分布电子散射截面的蒙特卡罗计算方法

高温全电离等离子体的辐射输运问题中,光子与电子的Compton散射与逆Compton散射是其中重要的特性,光子与相对论麦克斯韦电子散射的描述及截面的计算非常复杂且费时.本文提出了一种用于模拟计算光子与相对论麦克斯韦速度分布电子散射截面的蒙特卡罗计算方法.给出了各步骤的具体实现办法,推导了对应的计算公式,研究了相对论电子速率抽样方法,编写了光子与相对论电子散射的微观截面的蒙特卡罗计算程序.开展了高温全电离等离子体中,不同能量光子与不同温度电子散射的微观散射截面计算和分析.模拟计算结果显示,在电子温度低于25 keV情况下,本文方法与多重数值积分方法的计算结果非常接近;但随着电子温度继续升高,二者差异逐渐增大并较明显,经分析,可能是本文方法目前的电子速率抽样偏差所致,希望将来能够找到更好的相对论电子速率抽样方法以克服此缺陷.     

Koinzidenzexperimente zum Elementarprozeß der Bremsstrahlungserzeugung

By using a coincidence method, the angular distribution of bremsstrahlung has been measured for definite energy loss and definite angle of the outgoing electron. The incident electron energy was 300 keV. With a magnetic spectrometer, outgoing electrons with an energy of 170 keV and scattering angles of 0°, 5° and 10° were selected. The electrons and photons were both detected in scintillation counters. A gold foil of 250 Å thickness served as the target. The experimental results are compared with theoretical calculations.     

Primordial black holes and the observed Galactic 511 keV line

The observed 511 keV line from the Galactic Bulge is a real challenge for theoretical astrophysics: despite a lot of suggested mechanisms, there is still no convincing explanation and the origin of the annihilated positrons remains unknown. Here we discuss the possibility that a population of slowly evaporating primordial black holes with the mass around 10¹⁶–10¹⁷ g ejects (among other particles) low-energy positrons into the Galaxy. In addition to positrons, we have also calculated the spectrum and number density of photons and neutrinos produced by such black holes and found that the photons are potentially observable in the near future, while the neutrino flux is too weak and below the terrestrial and extra-terrestrial backgrounds. Depending on their mass distribution, such black holes could make a small fraction or the whole cosmological dark matter.     

电子-离子碰撞对超热电子影响的PIC模拟计算

超热电子-离子的产生和输运在传统的ICF方案和“快点火”方案中都是很重要的问题.讨论了电子-离子碰撞对参量不稳定性产生超热电子的过程和超热电子输运过程的影响.指出电子-离子弱碰撞项的加入增强了碰撞吸收,提高了热电子温度,降低了静电波破裂时的场能.这些改变了超热电子的总能量和分布,使之更集中于静电波的相速;电子-离子碰撞的存在还增强了自洽电场,阻碍了超热电子的输运,同样也是超热电子能量下降的原因之一.同时,为确保计算结果的可靠,讨论了初条件对PIC模拟计算的影响,指出空间位置随机热启动容易引入非物理因素,对 关键词：     

Improving Plasma Confinement by Controlling Hard X-Ray

Since runaway electrons and magnetohydrodynamics activity can contribute to serious damage and energy losses in tokamaks,the effect of an external electric field on runaway electrons and hard x-ray spectra is investigated.Parameters such as the plasma current,the hard x-ray photons count and the mean energy of runaway electrons are measured.Positive and negative voltages of 300 V are applied at 10 ms after the plasma initiation(while the plasma is forming),at 15ms(while the plasma is stable) and at 20ms(while the plasma is fading away) to attain the most effective time of applying the external electric held.The number of hard x-ray photons has the most changes in the range of 0-200 keV when the external electric fields are applied.Also in the duration of 20-30 ms of plasma the greatest number of hard x-ray spectra is detected.When the external electric fields are applied,the mean energy of runaway electrons reduces significantly,especially at 15ms(while the plasma is stable).     

Generation of suprathermal electrons during magnetic reconnection at the sawtooth crash and disruption instability in the T-10 tokamak

Evidence for excitation of suprathermal electrons ( E(gamma) approximately 20-100 keV) during magnetic reconnection in the T-10 tokamak is presented through analysis of the x-ray measurements with enhanced spatial and time resolution. A toroidally viewing x-ray imaging system and a fast hard x-ray detector placed inside the tokamak vessel allow identification of bursts of the nonthermal x-ray radiation around X points of the m = 1 and m = 2 magnetic islands during the sawtooth crash and prior to the energy quench at the density limit disruption.     

The role of Compton scattering in the low‐Z elements X‐ray fluorescence formation

The paper reviews the ionization of elements with low atomic numbers (boron, carbon, nitrogen, oxygen, and fluorine) by incoherent scattering of primary radiation and under the influence of Compton electrons. It is shown that at high energy of primary photons, the total contribution of these processes to X‐ray fluorescence formation becomes significant; at the energy of 80 keV, it becomes dominant. Copyright © 2013 John Wiley & Sons, Ltd.     

强激光束与空腔靶相互作用实验研究

1.06μm波长的强激光束辐照Au材料制作的空腔靶,采用目前国内最先进的诊断设备。对腔内高温等离子体现象演变规律进行了实验观察,获得了反射激光、能量吸收、X光转换、亚千X光能谱及时空特性、辐射温度、超热电子等重要物理信息,并就实验结果作了必要的分析和讨论     

Photon attenuation coefficients of different rock samples using MCNPX,Geant4 simulation codes and experimental results: a comparison study

ABSTRACT

The photon attenuation coefficients for the rocks (Feldspathic basalt, Compact basalt, Volcanic rock, Pink granite, Sandstone and Dolerite) have been investigated using MCNPX and Geant4 codes for photon energies 122, 356, 511, 662, 1170, 1275 and 1330 keV. Comparison of the simulation and experimental results of mass attenuation coefficients is presented. The exposure buildup factors also have been calculated with the help of the G-P fitting method. The comparison showed reasonable agreement between the simulated and experimental data for all rocks. The results show that sandstone has the highest mean free path as well as exposure buildup factor which signifies that sandstone requires a larger thickness for protection from photons.