Electronic stopping power of hydrogen in KCl at the stopping maximum and at very low energies

The electronic energy loss of hydrogen ions in KCl was investigated in a wide energy range. Thin films of KCl were evaporated on an Au/Si substrate. Rutherford Backscattering Spectrometry (RBS) was performed with protons and deuterons at energies from 30 to 400 keV/nucleon. At lower energies experiments were performed by Time-Of-Flight Low energy ion scattering (TOF-LEIS) again with proton and deuteron projectiles. Experimental results are compared to calculated/tabulated values for the electronic energy loss. Whereas at energies beyond the stopping maximum very good agreement is found, at lower ion energies discrepancies between experiment and calculations increase. At very low ion velocities the extrapolated stopping cross section ε predicts vanishing electronic energy loss at energies below 100 eV/nucleon.     

Interactions of 5–30 keV deuterons with a carbon surface

Measurements have been made of the temperature dependence of methane formation during the bombardment of carbon with hydrogen ions of varying energies. It has been found that the value of the temperature at which maximum methane production occurs varies with incident ion energy, in agreement with the prediction of our earlier theoretical model. Measurements have also been made of the release of previously trapped hydrogen in carbon using hydrogen and deuterium ion beams. The cross sections measured for this release as a function of energy have been used in the model for methane production and confirm that ion-induced release plays an important role in determining the methane production rate.     

K-shell excitation dielectronic recombination resonance strengths of highly charged He-like to O-like Xe ions

Dielectronic recombination is an important process in high temperature plasmas.In the present work,the KLn (n =L,M,N and O) DR resonance strengths of He-like to O-like xenon ions are measured at the Shanghai electron beam ion trap using a fast electron beam energy scanning method.The experiment uncertainty reaches about 6％ with significant improvement of statistics.A relativistic configuration interaction calculation is also made.Theoretical results agree with the experiment results within 15％ in most cases.     

离子注入Cr、Y、Nb对γ-TiAl金属间化合物高温氧化性能的影响

采用MEVVA离子源将Cr、Y、Nb离子分别注入γ -TiAl金属间化合物 ,注入能量 50—6 0keV ,注入剂量为 1× 10 17cm- 2 ,研究γ -TiAl在 10 0 0℃空气中的循环氧化行为。结果表明 ,Cr离子和Y离子注入对γ -TiAl的高温氧化性能均没有明显影响 ;Nb离子注入γ -TiAl,在氧化初期 ,抗氧化性能得到显著提高 ,但随着氧化过程的继续 (超过 10 0h) ,这种改善作用逐渐降低。实验发现 ,通过离子注入和基体合金化向γ -TiAl中加入相同元素 ,由于工艺过程的差异 ,对其高温氧化性能的影响不同。在长时间高温氧化 (10 0 0℃ )条件下 ,离子注入表面改性无法达到提高γ -TiAl抗氧化性能的目的     

Sheath Characteristic in ECR Plasma Nitriding

1. IntroductionThe plasma sheath is an important and complexregion for nearly all plasma applications in materials processing. The theoretical and experimental research on the features of sheath is important for making the processing mechanism clear and for selectingthe best processing conditions.The main process Of plasma nitriding has been noal.widely accepted as being dominated b3' the excitednitrogen molecules, ions= and nitrogen atoms [l-41.As to their formation, Aloll [5] thought that i…     

Collision cascade temperature

Interaction of a projectile with a solid has been considered in detail. It has been found that any collision cascade generated by a projectile can be characterized by the average kinetic energy of cascade atoms that represents an “instantaneous temperature” of the cascade during its very short lifetime (10⁻¹² s). We refer to this value as the “dynamic temperature” in order to emphasize the fact that cascade atoms are in a dynamic equilibrium and have a definite energy distribution. The dynamic temperature defines the electron distribution in the cascade area and, hence, the ionization probability of sputtered atoms. The energy distribution of cascade atoms and, as a consequence, the dynamic temperature can be found experimentally by measuring the energy distribution of sputtered atoms. The calculated dynamic temperature has been found to be in good agreement with the experimental data on ion formation in the case of cesium and oxygen ion sputtering of silicon. Based on the developed model we suggest an experimental technique for a radical improvement of the existing cascade sputtering models.     

Experimental study on cold fusion using deuterium gas and deuterium ion beam with palladium

A series of experiments using deuterium gas and low energy deuteron beam with palladium has been designed at Mississippi State University to allow for the observation, if it exists, of cold fusion. Three experiments were performed. One involved the diffusion transient of deuterium gas into palladium. The gas was cooled by liquid nitrogen, and its temperature was permitted to rise to room temperature, changing from near –34°C to 19°C in 75 minutes. A spherical lithium neutron detector, 21 cm from the palladium, gave an audible indication of neutron levels approximately twice the background. A second experiment used a deuterium ion beam (1 kev) which bombarded a palladium target. An average counting rate of 36±6 counts for 2 minutes was measured by a BF₃ tube with a paraffin moderator, 50 cm from the target. The background varied from 1–7 counts for each 2 minutes of counting period and averaged 4±2 counts in 2 minutes. A nitrogen ion beam impinging on the same palladium target produced 6 counts for a 2-minute counting period. A third experiment used a hydrogen ion beam first, then a nitrogen ion beam, finally a deuterium ion beam to bombard the same palladium target. These ion beams had energy less than 1 kev, and created neutron counts in the range of background. The palladium specimens were a piece of foil and a tube which used to be the palladium leak in a neutron generator. These preliminary experiments will be repeated, improved, and extended later.     

磷酸二丁酯在2.0 mol/L HNO3介质中的水解动力学

通过红外光谱、气质联用和离子色谱等分析方法确定了磷酸二丁酯在后处理常见工况2.0 mol/L HNO₃下的反应产物主要为丁醇、丁酸、丙酸、磷酸一丁酯和磷酸根离子等。采用离子色谱定量分析测定了磷酸一丁酯和磷酸根离子的浓度与反应时间和温度的关系,计算了磷酸二丁酯水解反应的速率常数,并对测定数据进行了计算拟合。结果表明：在110~150 ℃范围内,磷酸二丁酯的水解速率随温度的升高呈指数增长,满足准一级反应动力学方程;110 ℃和150 ℃的一级水解速率常数分别为6.30×10^-3 s^-1和2.10×10^-1 s^-1,二级水解速率常数分别为3.10×10^-3 s^-1和1.98×10^-1 s^-1;一级水解反应的指前因子为9.38×10¹² s^-1,对应的活化能为111.0 kJ/mol,二级水解反应的指前因子为1.09×10¹⁶ s^-1,对应的活化能为135.2 kJ/mol。动力学计算值与实验值的误差在±9%以内。     

Trapping coefficients of energetic hydrogen (0.3–8 keV) in Ti at high doses

The trapping coefficient for hydrogen in Ti has been measured in the energy range from 300 eV to 8 keV and was compared with the trapping coefficient of Zr. In accordance with theory the trapping coefficient for Ti is higher than for Zr in the investigated energy range. The values for both materials fairly agree with computer calculations. Deviation has been found for Ti below 1 keV and for Zr below 1.5 keV. Room temperature irradiation produced swelling in the Ti target, most probably due to hydride formation.     

Controlling Energy Flow and Loss in p<Superscript>6</Superscript>Li Fusion Plasma

The proton-Lithium-6 (p⁶Li) fusion reaction is significant because it produces energy through charged particles. By selecting this reaction, the problems of tritium processes and 14 MeV neutron fluxes will be reduced. One of the main concerns for p⁶Li plasma is the control of energy flow and loss that occur in fusion reactor. The calculations of energy balance are essential for investigating the energy flow and loss in p⁶Li plasma. It has a fundamental role for describing the material conditions in this plasma. Energy production must compete with inevitable losses in plasma. The losses perform a principal role in determining the operating temperature of thermonuclear plasma. Some losses of energy can be minimized by the suitable selection of designing parameters while some are intrinsic in reactant system. Calculations of energy flow and loss suggest an operating point at 800 keV for p⁶Li plasma. The effect of electron temperature on ion–electron energy transfer and the bremsstrahlung losses is reviewed. It is indicated that the bremsstrahlung radiation losses resulting from large mean electron energies are a serious difficulty for p⁶Li fusion reactor. It would be highly desirable to reduce the electron temperature below their normal equilibrium values. If the ion–electron energy transfer be reduced from the classical value, the electron temperature and thus bremsstrahlung radiation losses would be reduced substantially and as a result the performance of a p⁶Li fusion reactor would be improved significantly. Meanwhile, the bremsstrahlung radiation losses can be minimized with suitable mixture for p⁶Li plasma in a fusion reactor.     

Software for automatization of IEA-analysis of plasma-laser spectra

A software has been developed in order to automatize the ion energy analyzer (IEA) spectra analysis of laser-generated plasmas.A Nd:Yag laser operating at an intensity of the order of 10¹⁰ W/cm², 9 ns pulse width and energy of the order of 600 mJ, has been employed to irradiate different metallic targets (Al, Ti, W) and to produce plasma pulses. The ion emission from the plasma is monitored through an IEA instrument permitting time-of-flight (TOF) measurements to determine the ion energy distributions as a function of the charge state.The software program consists in two sections. The first one permits to identify the IEA ion peaks corresponding to different charge states as a function of the theoretical TOF values. The second section permits to plot the ion velocity and energy distributions as a function of the charge state. The obtained distributions are fitted using the “Coulomb-Boltzamnn shifted” function approach through the “Peakfit” code. The fit of the experimental data permits to estimate the equivalent plasma temperature and the average energy shift of the distributions as a function of the ion charge state.     

Close encounter processes in Monte Carlo simulations of ion channeling

The backscattering yield is analyzed in terms of the depth-dependent distribution of ion trajectories, characterized by instantaneous values of such parameters as the ion energy, the scattering angle, the angle between the ion direction and the surface normal, and the impact parameter with respect to the equilibrium site of the nearest lattice atom. The normalized nuclear encounter probability (NEP) is reformulated as the expected value of the normalized NEP for a single trajectory, and the definition is extended for directions tilted by a large angle with respect to a major axis. It is shown that the normalized NEP cannot be defined to correspond to a physically measurable quantity if the energy and angular spreads of the beam in the crystal are taken into account. The scattering yield measured in the energy spectrum — to be used in comparisons of simulations with experiment — is also expressed as the expected value of the respective yield associated with a single trajectory. Examples of the distribution of trajectories are given for 1.5 MeV ⁴He ions traversing a Si(100) single crystal.     

Enhanced vacancy lifetimes in the Nimonic alloys: PE16 and 80A

The variation of resistance during isothermal ageing of the two Nimonic alloys PE16 and 80A has been analysed in terms of a simple model based on the nucleation and growth of γ' particles, which includes an exponential decay of the excess vacancy population, quenched-in during the pre-ageing heat-treatment of the alloys. Both the PE16 and the 80A results have been successfully described using this model and the values of vacancy lifetime derived have been compared with theoretical estimates, for diffusion to grain boundaries, dislocations and precipitates. We have shown that values of activation energy deduced from the variation of time to the resistance maximum as a function of inverse ageing temperature depend upon the vacancy lifetime. To obtain meaningful values for activation energy, this dependence must be included in the analysis.     

Determination of Average Ion Temperature of the TVD Tokamak by a Simple Charge Exchange Analyzer Detector

In this paper the average ion temperature of the TVD tokamak plasma is determined by a low cost charge exchange analyzer. When the neutral beam energy was equal to 3 keV, the stripping efficiency was 0.065. Estimated average ion temperatures for cold and hot regions of the plasma were 100 and 650 eV, respectively. Unlike the cold region of the plasma in which ion temperature was not related to the time, ion temperature in the hot region was maximum when the plasma current reached its maximum value.     

High Flux FRC Facility for Stability and Confinement Studies

To provide a path for advancing the FRC concept into a more fusion-like regime, the existing TCSU facility will be modified to take advantage of the new FRC formation method of dynamic formation and merging of FRCs. Results from recent experiments have shown that this methodology provides appreciable increases in the key parameters of ion temperature, poloidal flux and FRC lifetime. FRC stability has been found in numerical calculations where a subpopulation of high energy particles is present in sufficient numbers. A critical goal of the high flux FRC facility will be to form FRCs with poloidal fluxes sufficiently large to fully confine high energy ion orbits introduced from neutralized ion beams injected during FRC formation. A key aspect of the experiments will be to validate theoretical models and simulation codes, such as the 3D extended-MHD code NIMROD, in a in a high beta regime with large two-fluid effects, plasma flows, and an energetic minority species.     

一维Fokker-Planck方程的有限体积法求解及其在中性束注入加热中的应用

采用有限体积法数值求解一维Fokker-Planck方程,通过模拟电子自碰撞过程进行程序校验。研究表明,有限体积法能高效求解Fokker-Planck方程,能确保分布函数的非负性和粒子数密度守恒,同时计算程序能有效克服传统求解方法中出现的分布函数对麦克斯韦分布的过冲现象。模拟了HL-2A装置在中性束注入加热等离子体过程中,离子分布函数和温度随时间的演化情况。结果表明,随着中性束的注入,离子分布函数出现非麦克斯韦化,离子温度迅速增加后稳定;计算结果和实验结果符合较好。进一步讨论束能量和功率的影响,随束能量和功率的增加,等离子体离子温度均升高,离子温度随束能量的增加升高的幅值较大,而随束功率的增加升高的幅值较小。     

Combined Effect of Ion Temperature and Magnetic Field on Collisionless Sheath Structure

A steady state two-fluid model has been used to study the characteristics of the collisionless plasma sheath in the presence of an external magnetic field and by taking into account both the ion temperature and the ion drift velocity at the sheath edge. The number and momentum equations of ions, the Boltzmann distribution of electrons and Poisson equations are solved numerically. The dependence of the Bohm magnetized sheath criterion to ion temperature is examined. It is shown that the ion temperature has significant effects on the sheath characteristics such as ion velocity, charged particles densities and electric potential. In the specific orientations of the magnetic field, it is found that by increasing the ion temperature, the ions do not achieve energy and the kinetic energy of the ions in the depth direction reaches the specific value at bigger distance from the plasma-sheath boundary.     

Roughening of silicon (1 0 0) surface during low energy Cs ion bombardment

Nowadays, the use of low energy ion bombardment in secondary ion mass spectrometry (SIMS) is a mandatory step to obtain high depth resolution for the characterization of ultra shallow junctions. However, increment of roughness during ion bombardment leads to the degradation of depth resolution. The evolution of surface roughening and ripple formation on silicon at ambient temperature under 1 keV Cs⁺ ion bombardment with and without sample rotation has been studied by means of atomic force microscopy.Ripple formation with a perpendicular orientation with respect to the Cs⁺ beam direction has been detected, and their wavelength and correlation length have been monitored as a function of the experimental conditions. Roughness and wavelength increased with increasing ion fluence, while variations of ion flux showed little effect. The effect of sample rotation during ion bombardment led to a critical reduction of the surface roughness and disappearance of ripples.     

Method and experimental arrangement for Al thin film deposition from r.f. metal plasma with simultaneous self-ion bombardment

A method, experimental arrangement, and some particular details of the process for Al thin film deposition from r.f. metal plasma are described in this paper. In the plasma deposition system, Al is evaporated by an electron beam, partial ionization of the vapor is realized in r.f. inductive metal plasma, and film deposition is accompanied by simultaneous self-ion bombardment (SSIB) in a high-vacuum environment. Special attention is given to the accurate determination of such basic physical parameters of the process as plasma potential, ion energy, fraction of ions in the total arrival flux, added (normalized) energy, and power density of the ion bombardment. It is concluded that the fraction of secondary neutral energetic atoms in the total flux can be neglected in the calculations of the basic deposition parameters. At the power density in excess of about 0.5 W/cm², the substrate temperature can rise up to the Al melting point (660°C) during deposition. An analysis of the main heat sources in the plasma deposition system is presented in the paper. It is found that the results of the computer simulation of the substrate temperature increase caused by ion bombardment have a very good agreement with demonstrated experimental data.     

Effects of electronic and nuclear interactions in SiC

In this study, we performed irradiation experiments on nanostructured 3C-SiC samples, with 95 MeV Xe ions at room temperature. This energy permits the observation of the combined electronic and nuclear interactions with matter. The grazing incidence X-ray diffraction results do not reveal a complete amorphization, despite value of displacement per atom overcoming the total amorphization threshold. This may be attributed to competing effects between nuclear and electronic energy loss in this material since a total amorphization induced by nuclear interactions was found after low energy ion irradiation (4 MeV Au). Moreover, electronic interactions created by high energy ion irradiations induce no disorder in single crystalline 6H-SiC. But in samples previously disordered by low energy ion implantation (700 keV I), the electronic interactions generate a strong defects recovery.