Efective Parameters on Energy Losses of Fast Electron in Fusion Mediums

The stopping and scattering of fast electrons in a dense plasma relevant to inertial confinement fusion(ICF)are investigated numerically with the latest improved cross section equations.Binary and collective efects are considered to determine beam transport parameters such as range,penetration depth,spreading processes as straggling and blooming versus electron energy and plasma parameters.Blooming and straggling efects,which act as consequences of scattering with statistical assumption in collisions,lead to a non-uniform,extended region of energy deposition.Finally the mean angle of deflections is calculated for diferent plasma energies.     

Energy loss straggling measurements for helium ions in Mylar and polypropylene polymeric foils

In the present contribution, we report results on energy straggling of He ions penetrating Mylar and polypropylene thin polymeric foils. The measurements were performed in the 900–3000 keV incident particle energy range by using the indirect transmission technique developed previously. The experimental straggling data are corrected to consider the roughness effects due to target thickness inhomogeneity. As expected, the roughness contribution to straggling is more important for helium than for proton ions and decreases as the ion energy increases. At low velocities, (<500 keV/amu), the variation of the experimental energy straggling results differs strongly from predictions based on Bohr’s formalism, and with increasing energies, the experimental results approach gradually the Bohr values.     

热电子与聚变等离子体相互作用模拟计算的误差分析

对惯性约束聚变(ICF)实验条件下热电子辐照聚变等离子体（DD,DT）的射程岐离和散射进行了分析。结果表明,射程岐离和散射随射程增加近似呈直线增加;射程岐离和散射大小与等离子质量有一定关系。在单能热电子入射下,散射是计算结果误差的主要来源,误差在5%以下,绝对数在数十MA。入射束流的电子完全沉积在热斑中的聚焦角度,在边沿点火方式中,氘等离子体中为20.64,氘氚等离子体中为21.8;在中心加热方式中,氘等离子体中为16.36,氘氚等离子体中为17.6,在技术上相对易于实现。     

MeV能量离子在生物样品中的能量损失与能量离散

为了研究 MeV能量离子在生物样品中的能量损失与能量离散, 分别使用1.0, 1.8和2.8 MeV质子和4.5 MeV氦离子分别辐照不同质量厚度的洋葱内表皮膜。 当质子穿过该生物样品后, 可以利用透射能谱测量透射离子的能量损失和能量离散。 实验结果显示, 在以上的生物样品中, MeV能量离子的能量损失值和TRIM程序模拟的结果相吻合, 但是透射离子的能量离散值却与TRIM程序模拟结果有很大的不同。 结合生物样品的结构不均匀的特性, 对Bohr能量离散理论进行了修正, 并发现修正后的Bohr能量离散理论计算结果与实验值符合得很好。     

Antiproton and proton energy loss straggling at keV energies

The slowing-down process of point-like charged particles in matter has been investigated by measuring the energy straggling for antiprotons and protons in Al, Ni and Au. A comparison with binary theory shows good agreement for Al and Au. For Ni, experimental data are not as convincing. In particular for the aluminum target, the Barkas-like effect of reduced energy straggling for antiprotons compared to protons is visible in the experimental data and a nearly velocity-proportional straggling is found, in good agreement with binary theory.     

Energy loss and online directional track visualization of fast electrons with the pixel detector Timepix

The spectral-, position- and tracking-response of Timepix to energetic electrons has been tested and characterized with well-defined low-intensity parallel beams of monoenergetic electrons in the 7–21 MeV range. The per-pixel energy sensitivity of Timepix serves as a position-sensitive dE/dx detector to determine the energy loss over along the particle track. The sampling path pitch can be set to 55 μm (pixel-size) and arbitrary values between 300 μm (sensor thickness) and nearly 2 mm. Timepix can register and visualize not only the position and trajectories but also the direction of trajectories and the rate of directional scattering of single fast electrons across the semiconductor sensor. The technique serves to measure the spatial distribution of a parallel beam, the beam size spread, transversal beam flux homogeneity and lateral straggling at the pixel-size scale. The mean scattering path along the beam axis and the mean path for lateral beam straggling in silicon can be determined. Measured energy loss distributions were compared with model and previous data as well as with dedicated Monte Carlo MCNPX simulations performed for this work. Tracking distributions were also simulated.     

Transition from the Fluctuation Mode of Stimulated Resonant Coherent Raman Scattering to the Energy–Stabilized Mode

The equations of the semiclassical theory for the stimulated resonant coherent Raman scattering (SRS) in an extended medium have been solved numerically. The distribution function of the energy of Stokes pulses at different detunings and energies of a laser has been determined. Just as for the nonresonant coherent SRS, in the situation considered there occurs transition from the large–scale fluctuation mode to the mode of relatively small straggling of the energies of Stokes pulses with increase in the pumping energy. With approach to the resonance, the energy required to stabilize the Stokes radiation decreases.     

Nonthermal effects on the entanglement fidelity for elastic scatterings in Lorentzian plasmas

The nonthermal effects on the entanglement fidelity for the elastic electron-ion scattering are investigated in generalized Lorentzian plasmas. The dynamically screened effective potential and partial wave analysis are employed to obtain the entanglement fidelity in Lorentzian plasmas as a function of the spectral index, collision energy, and plasma parameters. It is shown that the entanglement fidelity increases with decreasing the collision energy, especially, for small Debye radii. It is also shown that the nonthermal effect enhances the entanglement fidelity in Lorentzian plasmas. In addition, it is found that the entanglement fidelity increases with an increase of the plasma temperature.     

Energy loss straggling in collisions of fast finite-size ions with atoms

The influence of ion size on straggling of energy losses by fast partially stripped ions is studied using the nonperturbative approach based on the eikonal approximation. It is shown that such a consideration of collisions of ions with complex atoms can lead to considerable corrections in calculating root-mean-square straggling of energy losses by fast ions compared to the results obtained for point ions. The root-mean-square straggling of energy losses are calculated for bromide and iodine ions in collisions with copper, silver, and aluminum atoms. It is shown that allowance for the size of the electron “coat” of an ion noticeably improves the agreement with experimental data.     

The Bragg-peak studies in CR-39 SSNTD on the basis of many-hit model for track etch rates

Etching rates along tracks of protons and lithium ions with energies in the Bragg peak region were explored. The energy losses in this region, especially for protons of low energies, are of particular interest from the physical as well as biological points of view. The microscopic track etch rate, V_T, is studied using the many-hit model in its first approximation assuming that V_T is a function of the restricted energy loss (REL_ω). The ions multiple scattering and straggling effects on the average experimental V_T values are corrected by shifting the calculated REL_ω values along the track, until its maximum coincides with that of the V_T. The fitting of least square differences between calculated and experimental V_T values is used in order to determine the many-hit model registration parameters for the detector under investigation.     

Ranges of implanted atoms under polyatomic cluster bombardment of the Cu (111) surface

A computer simulation of the bombardment of the Cu (111) surface with Cu_N and Au_N polyatomic clusters differing in size (N = 1, 6, and 13) with energies of 0.5 and 5 keV/atom has been performed in the framework of classical molecular dynamics. The spatial distribution of the implanted atoms, their ranges, and range fluctuations (straggling) depending on the size N and energy E/N of the incident cluster has been investigated. It has been shown that an increase in the mean range and range straggling is observed at a fixed energy per incident atom as the cluster size N increases. At the same time, the effect of an increase in the range (at a specified value of E/N) gradually disappears with increasing cluster energy, whereas the effect of an increase in straggling is retained. These tendencies qualitatively agree with the available experimental observations. It has been shown that the dominating contribution to the increase in the atom range of the implanted cluster is made by the so-called clearing-the-way effect, which is weakened with increasing the incident cluster energy. The effect of the range straggling increasing is significantly due to the presence of nonlinear “spike” effects at the bombarded target.     

DEVELOPMENT OF A NEUTRAL PARTICLE ANALYZER FOR THE HL-1M TOKAMAK

1　IntroductionConfinementandheatingofplasmasareele mentarytopicsinfusionresearch .Tocharacterizethefusionplasmasinauxiliaryheatingexperimentsaswellasinohmicheatingexperiments,measure mentofionenergyinplasmasbecomesnecessary .Neutralparticleanalyzersaresuchdevicesthatareaimedatdirectanalysisofneutralparticlesemittedfromfusionplasmasandareusedinmanyfusionresearchlaboratories[1～ 4] .Detailsofparticledi agnosticprincipleforfusionplasmacanbefoundinReference [5].Emissionofneutralparticlesisintrin…     

Drastic enhancement of energy-loss straggling of relativistic heavy ions due to charge-state fluctuations

Stopping power and energy-loss straggling of 197Au, 208Pb, and 209Bi projectiles have been measured in different solids (4相似文献   

Spectroscopy and scattering matrices with nitrogen atom: Rydberg states and optical oscillator strengths

The scattering matrices of ${\rm e}+ {\rm N}^{+}$ with $J^\pi=1.5^{+}$ in discrete energy regions are calculated using the eigenchannel R-matrix method. We obtain good parameters of multichannel quantum defect theory (MQDT) that vary smoothly as the function of the energy resulting from the analytical continuation property of the scattering matrices. By employing the MQDT, all discrete energy levels for N could be calculated accurately without missing anyone. The MQDT parameters (i.e., scattering matrices) can be calibrated with the available precise spectroscopy values. In this work, the optical oscillator strengths for the transition between the ground state and Rydberg series are obtained, which provide rich data for the diagnostic analysis of plasma.     

Energy losses of muons, pions, protons, and deuterons channeled in Si

The energy loss of positive muons, pions, protons, and deuterons channeled in Si crystals has been investigated by computer simulation. The model considers the individual trajectories of particles inside the target and calculates the electronic energy loss for each particle history. The results show important differences in the energy loss distributions, stopping powers, and straggling values for low and intermediate energies, as a consequence of channeling effects.     

Analysis of scattering by conducting objects covered with arbitrarily magnetised plasma using finite element-boundary integral-fast multipole algorithm

The electromagnetic (EM) scattering by conducting objects covered with arbitrarily magnetised plasma is computed using the hybrid vector finite element-boundary integral-fast multipole method (FE-BI-FMM). The relative permittivity tensor of arbitrarily magnetised plasma is described. The FE-BI-FMM formulation for scattering by three-dimensional (3D) conducting objects covered with arbitrarily magnetised plasma is derived in detail. The validity of FE-BI-FMM is verified by comparing numerical results with analytical values. The radar cross-sections (RCS) of conducting objects covered with magnetised plasmas are simulated and the effects of plasma parameters on RCS are analysed. Numerical results indicate that magnetised plasma cover layer is effective on reducing the back scattering if appropriate parameters of plasma are chosen.     

Barkas effect,shell correction,screening and correlation in collisional energy-loss straggling of an ion beam

Collisional electronic energy-loss straggling has been treated theoretically on the basis of the binary theory of electronic stopping. In view of the absence of a Bloch correction in straggling the range of validity of the theory includes both the classical and the Born regime. The theory incorporates Barkas effect and projectile screening. Shell correction and electron bunching are added on. In the absence of shell corrections the Barkas effect has a dominating influence on straggling, but much of this is wiped out when the shell correction is included. Weak projectile screening tends to noticeably reduce collisional straggling. Sizable bunching effects are found in particular for heavy ions. Comparisons are made with selected results of the experimental and theoretical literature. Received 24 September 2002 / Received in final form 1st December 2002 Published online 4 February 2003     

Stopping power and straggling of energetic light ion beams in yttrium

Energy loss and straggling for protons, deuterons and α-particles in yttrium were measured in the energy region between 0.15 MeV and 2.5 MeV. The measured stopping powers of the hydrogen ions agree reasonably well with the semi-empirical values of Andersen and Ziegler, although better agreement was found with the values of Janni. For helium ions there are a marked difference with the values of Ziegler. Below 200 keV/amu the stopping ratios of the helium and hydrogen ions are lower than Ziegler's master curve. The straggling values of the hydrogen ions are about 15% lower than the Bohr estimate, while the straggling of the helium ions reach the Bohr value at about 0.2 MeV/amu.