Analysis of X-ray spectra emitted from a laser-produced lead plasma

X-ray spectra emitted by a laser produced plasma are analyzed using calculated X-ray energies for Co-, Ni-, Cu-, Zn-, Ga-, Ge-, As-, Se-, Br-, Kr-, Rb-, Sr-, Y-, and Zr-like lead ions. The charge state distribution in the plasma is studied and a functional dependence of this distribution as a function of the ionic charge, atomic number, free electron density and temperature in the plasma is proposed.     

金激光等离子体的空间分辨X射线发射谱及其应用

在星光II激光装置上,采用PET平面晶体谱仪与宽20μm的狭缝构成一维空间分辨光谱测量系统,对金平面靶激光等离子体进行观测,获得了沿靶面法向一维空间分辨的金M带发射谱。在实验谱中观察到了Au元素类Ni离子的电四极跃迁线3p63d10(1S0) 3p53d104d(3/2,5/2)J=1。利用电四极跃迁线对电子密度的敏感特性,开展了金激光等离子体电子密度诊断的尝试,确定出利用该谱线进行电子密度诊断的有效范围大致在1019～4.5×1021cm-3之间。     

Properties of the Kα X-ray transitions in highly ionized cobalt

Multi-Configuration Dirac–Fock and relativistic configuration interaction calculations with the inclusion of the Breit interaction, quantum electrodynamics and finite nuclear mass corrections have been carried out in the extended optimal level (EOL) scheme on the transition wavelengths, transition probabilities, absorption oscillator strengths and line strengths of the Kα X-ray from Co XIIX to Co XXVI. The calculated values are compared with the other available data on He-like to Be-like cobalt and are found to be in very good agreement with them. This confirms the present calculations. These data provide reference values for level lifetimes, charge state distribution and average charge of cobalt plasmas.     

高电荷态离子Arq+与不同金属靶作用产生的X射线

研究了高电荷态离子Arq+(q=16,17,18)入射金属Be,Al,Ni,Mo,Au靶表面产生的X射线谱.实验结果表明,Ar的Kα-X射线是离子在与固体表面相互作用过程中固体表面之下形成空心原子发射的.电子组态1s2的高电荷态Ar16+离子在金属表面中性化过程中,存在的多电子激发过程使Ar16+的K壳层电子激发产生空穴,级联退激发射Ar的Kα特征X射线.Ar17+离子在金属表面作用过程中产生的X射线谱形与靶材料没有明显的关联,入射离子的Kα-X射线产额与其最初的电子组态有关,靶原子的X射线产额与入射离子的动能有关.     

Detection of low-energy hydrogen atoms from a tokamak plasma by means of H-formation on tungsten surfaces

Formation of negative hydrogen ions by scattering of protons from a cesiated tungsten (110) surface has been studied in the incident energy range from 15 to 500 eV. From the results a new type of diagnostic for studying the plasma boundry is proposed.     

Temperature independence of the angle-resolved X-ray photoemission spectra of gold and platinum valence bands

Angle-resolved valence-band X-ray photoemission spectra were taken along the [111] and [100] directions of gold single crystals and along the [100] direction of a platinum single crystal at room temperature (293 K) and on a probe cooled nearly to liquid nitrogen temperature (77 K). No change was detected on cooling the samples, in contrast to expectations based on a simple direct-transition model. A simple “matrix-element” model appears to predict spectra well even at low temperatures, perhaps because the complexity of the high-energy final-state bands permits sampling effectively throughout the zone.     

Soft picosecond X-ray laser nanomodification of gold and aluminum surfaces

Experimental and theoretical investigations of aluminum (Al) and gold (Au) surface modification by soft X-ray laser pulse are presented. Well-polished samples of Al and Au are irradiated by ps-duration pulse with wavelength of 13.9 nm at the energy range of 24–72 nJ. Differences in the melting and the ablation processes for those materials are observed. It is shown that at low laser pulse energy, the nanoscale ripples on the surface may be induced by melting without following ablation. In that case, the nanoscale changes in the surface are caused by splash of molten metal under gradient of fluence. At higher laser pulse energy, the ablation process occurs and craters are formed on the surface. However, the melting determines the size of the modified surface at all ranges of the laser energies. For interpretation of experimental results, the atomistic simulations of melting and ablation processes in Al and Au are provided. The calculated threshold fluencies for melting and ablation are well consistent with measured ones.     

Determination of the charge state distribution of a highly ionized coronal Au plasma

We present the first definitive measurement of the charge state distribution of a highly ionized gold plasma in coronal equilibrium. The experiment utilized the Livermore electron beam ion trap EBIT-II in a novel configuration to create a plasma with a Maxwellian temperature of 2.5 keV. The charge balance in the plasma was inferred from spectral line emission measurements which accounted for charge exchange effects. The measured average ionization state was 46.8+/-0.75. This differs from the predictions of two modeling codes by up to four charge states.     

Guiding of intense laser beams in highly ionized plasma columns generated by a fast capillary discharge

We have demonstrated the guiding of laser pulses with peak intensities up to 2.2 x 10(17) W/cm(2) in a 5.5 cm long plasma column containing highly charged Ar ions generated by a fast capillary discharge. A rapid discharge-driven hydrodynamic compression guides progressively lower order modes through a plasma with increasing density and degree of ionization, until the guide collapses on axis. The lowest order mode (FWHM approximately 50 microm) is guided with 75% transmission efficiency shortly before the plasma reaches the conditions for lasing in Ne-like Ar. The subsequent rapid plasma expansion forms a significantly leakier and more absorbent guide.     

A study of the VUV emission from highly ionized krypton in a theta pinch plasma

The ionization rates of Kr(IX), (X), (XI), and (XII) have been measured using a fast 60-kV-60kJ theta pinch as a plasma source. The line emission from each ion stage has been identified and the time evolution observed. A coupled set of rate equations was used along with time- and space-resolved measurements of the electron density and temperature to model the plasma light emission. The ionization rates of Kunze were adjusted by multiplying the rate for each ion stage with a constant until the peak intensity of the calculated emission agreed with the time of the observed peak intensity. The constants required for best fit were 2.5, 0.15, 3.0, and 2.0 for Kr(IX), (X), (XI), and (XII), respectively. Two successive ionization stages, Kr(X) and Kr(XI), have shown the same time dependence and possible reasons for this observation are discussed. During the course of modeling the light emission, we have also found that the rate for the excitation from the 3dⁿ to the 3p⁵3dⁿ⁺¹ level in Kr(X) (n=9) and Kr(XI) (n=8) is a factor of 5 lower than predicted by the van Regemorter excitation rate equation.     

高电荷态离子Arq+与不同金属靶作用产生的X射线

研究了高电荷态离子Ar^q+(q=16，17，18)入射金属Be，Al，Ni，Mo，Au靶表面产生的X射线谱.实验结果表明，Ar的Kα-X射线是离子在与固体表面相互作用过程中固体表面之下形成空心原子发射的.电子组态1s²的高电荷态Ar¹⁶⁺离子在金属表面中性化过程中，存在的多电子激发过程使Ar¹⁶⁺的K壳层电子激发产生空穴，级联退激发射Ar的Kα 特征X射线.Ar¹⁷⁺离子在金属表面作用过程中产生的X射线谱形与靶材料没有明显的关联,入射离子的Kα-X射线产额与其最初的电子组态有关，靶原子的X射线产额与入射离子的动能有关. 关键词： 高电荷态离子 空心原子 多电子激发 X射线     

Mobilization of tungsten dust by electric forces and its bearing on tritiated particles in the ITER tokamak

Experimental investigations on the electric field strength required to overcome the adhesion forces of micron size tungsten metallic dust as well as silver and aluminum oxide in powdery form deposited on a conductive surface are presented. The results reveal a strong influence of particulate surface properties on the detachment threshold, especially for tungsten particles which exhibit a thin surface oxide layer that screens their electrical conductivity. Such tungsten particles makes possible that electrostatic self-charging occurs when tritiated because of their dielectric properties even if there are deposited on a conductive grounded surface.     

Effects of the Chodura sheath on tungsten ionization and emission in tokamak divertors

The decay of the electric potential in the sheath region in tokamak divertors occurs on a scale length on the order of the main ion gyroradius (Chodura sheath) due to magnetic fields lines intersecting the divertor plates at grazing incidence. As a consequence, high-Z impurities like tungsten ionize within the sheath region in attached plasma conditions. The modification of the electron distribution in the sheath region must thus be taken into account to accurately model ionization and emission of impurities within the sheath region. To that end, an analytical expression of the distribution of the vertical ionization path for impurities sputtered from divertor plasma-facing components is derived. This expression is then used to estimate the fraction of neutral impurities ionizing within the sheath and the average vertical ionization path, and to derive an effective SXB (the number of ionizations per emitted photon) coefficient which includes the effects of the variation of the electron distribution in the sheath region. These results are applied to tungsten impurities sputtered from divertor plates. It is shown that the SXB coefficient for neutral tungsten is significantly reduced in high-density attached divertor plasma conditions (n_e ≳ 5 × 10¹³ cm⁻³) because of the ionization of neutral tungsten well within the sheath region.     

~(129)Xe~(q+)激发Mo表面产生的X射线谱

研究了高电荷态离子129Xeq+(q=25,26,27)入射金属Mo表面产生的特征X射线谱.实验结果表明,在束流强度小于120nA条件下,高电荷态离子129Xeq+可以激发Mo的L壳层特征X射线谱.单离子X射线相对产额可达10-8量级,特征X射线的相对产额随入射离子的动能和电荷态(势能)的增加而增加.通过Mo原子的Lα1特征X射线谱,利用Heisenberg不确定关系对Mo原子的第M能级寿命进行了估算.     

Valence bands of silver halides determined by X-ray and UV photoemission

Photoemission from AgCl, AgBr, and AgI has been studied at photon energies hω = 16.8, 21.2, 26.9, 40.8, 48.4 and 1486.6 eV. By exploiting the strong     

Calculation of X-ray and Auger transition rates, lifetimes, X-ray wavelengths, and fluorescence yields of variously ionized silicon atoms

X-ray and Auger transition rates, X-ray wavelengths, and fluorescence yields are calculated for variously ionized silicon atoms with configurations 1s2s^m2pⁿ, m=0-2, n=1-6. The calculation has been performed using the Hartree-Fock atomic model. Intermediate coupling and configuration interaction have been taken into account. The energies and widths are found to be strongly affected by configuration mixing. The results from the present calculation have been compared with those available in the literature. The theoretical K_α hypersatellite and satellite spectra fall into several well-separated regions, corresponding to each of the possible number of spectator electrons in the 2s and 2p shells. The dependence of radiative rates and fluorescence yields on the number of spectator electrons is also investigated.     

Soft X-ray enhancement from porous target irradiated by high power sub-nanosecond laser beam and the effect of plasma opacity

In this paper, we investigate numerically the enhancement of the soft continuum X-ray yield emitted from porous aluminum targets irradiated by sub-nanosecond high power pulsed laser beam. The calculations were conducted for two different conditions: (i) ignoring plasma opacity, and (ii) including it in the calculations; and finally the results were compared. In the calculations, the main emission mechanisms were assumed to be the free–bound and free–free (bremsstrahlung) transitions at water windows wavelengths ranges 2.3–4.4 nm and also 12.6–14.6 nm, which is useful for lithography applications. The free–free and bound–free transitions were also considered for calculating the opacity. The results show that for both conditions, the X-ray yield rises with increasing the porosity and the increase rate is almost equal in both cases; however, the calculations are not appropriate for estimating the absolute values of the X-ray yield when the plasma opacity is ignored.     

Analysis of the M-shell spectra emitted by a short-pulse laser-created tantalum plasma

The spectrum of tantalum emitted by a subpicosecond laser-created plasma, was recorded in the regions of the 3d-5f, 3d-4f, and 3d-4p transitions. The main difference with a nanosecond laser-created plasma spectrum is a broad understructure appearing under the 3d-5f transitions. An interpretation of this feature as a density effect is proposed. The supertransition array model is used for interpreting the spectrum, assuming local thermodynamic equilibrium (LTE) at some effective temperature. An interpretation of the 3d-4f spectrum using the more detailed unresolved transition array formalism, which does not assume LTE, is also proposed. Fitted contributions of the different ionic species differ slightly from the LTE-predicted values.