On plasma-neutral gas interaction

The paper emphasises the importance of plasma-neutral boundary layer in a wide variety of physical phenomena occurring in laboratory and cosmic plasmas. The interaction of a magnetised plasma stream penetrating a neutral gas cloud is discussed in the light of Alfvén’s critical velocity and Varma’s threshold velocity on the ionising interaction. Interaction of a moving magnetised plasma with a stationary neutral gas has been studied and described. The device comprises of a plasma gun and an interaction region where neutral gas cloud is injected. The interaction region is provided with a transverse magnetic field of upto 1000 G. Several diagnostics deployed at the interaction region to make measurements on the macroscopic parameters of plasma and neutral gas are described. The parameters of discharge circuits are measured with high current and voltage probes. An interaction between a magnetised plasma stream and a neutral gas cloud is demonstrated. It is shown that this interaction does not have Varma’s threshold on their relative velocity. The Alfvén’s critical velocity phenomenon is shown to depend on the integrated column neutral gas density that a plasma stream encounters while penetrating through it and not on the neutral gas density in the range of 10¹⁷–10²¹ m^?2.     

Experiments on the sputtering of neutral Cu2 dimers from Cu by Ar+ ions (60–300 eV)

A planar polycrystalline copper target was bombarded normally by Ar⁺ ions with energies ranging from 60 to 300 eV. in the source of a mass spectrometer. The neutral particles sputtered normally from the target were post-ionized and analyzed in the mass spectrometer. A thermionically sustained, magnetically confined low pressure arc plasma was used to supply the bombarding ions, and for post-ionization of the neutral sputtered species. It was found that the relative yields of the sputtered neutral post-ionized Cu₂ dimers are linearly proportional to S², where S is the total sputtering yield for Ar⁺ -Cu. The results support the recombination model for the formation of neutral dimers in sputtering.     

A measurement of deuterium neutrals by the balmer-series in the STP-2 high beta screw pinch tokamak

The neutral particle density of a deuterium plasma in the STP-2 screw pinch tokamak has been determined spectroscopically. The particle density for the ground state of deuterium is calculated from the rate equations for population density of the excited levels with principal quantum numbers 3 and 4; both of the population densities were obtained from intensities of the Balmer alpha and beta lines, and the rate coefficients for electronic collision were estimated from the electron density (10¹⁴/cm³) and temperature (10 eV) measured by laser scattering. We find that the neutral density is approx. 2 × 10¹²/cm³ at the center of the plasma and 2 × 10¹⁴/cm³ on the periphery. The time history of the neutral deuterium density is consistent with the observed increase in plasma density.     

Microwave diagnostics of ultracold neutral plasma

The microwave method is suggested to diagnose the ultracold neutral plasma. Based on the calculations of the dipole radiation, we derive the microwave scattering cross section of the ultracold neutral plasma, and microwave power scattered by the ultracold plasma is calculated as a function of time. The scattering cross section is nearly ¹⁰−11 m².     

Herstellung eines neutralen Wasserstoffatomstrahls im MeV-Bereich

An arrangement is described to produce a neutral hydrogen beam by splitting an accelerated H ₂ ⁺ -Ion in a gas target. At 500 keV energy of the neutral H-atom, the ratio of H ₂ ⁺ -ions to neutral H-atoms is measured to be about 12%. In the energy domain of 300 to 650 keV this ratio decreases only very little with increasing energy. The cross sections σ₁, σ₂ and σ₃ for splitting inH ⁺+H°, 2H ⁺+e ^? and for electronloss of the neutral atom are given.     

Fluctuations and correlations in pion system with fixed isospin

The statistical system of π⁰, π⁺ and π⁻ mesons with zero total isospin is studied. For neutral pions there is the enhancement of the fluctuations, whereas for charged pions the isospin conservation suppresses fluctuations. The correlations between the numbers of charged and neutral pions are observed for finite systems.     

The electron-nucleon weak neutral current and 0− -0+ nuclear isomerism

Since one photon exchange is completely forbidden in processes of the type ?0^? → ?0⁺ (? is a charged lepton) or any crossed version of such a process, weak neutral current effects are considerably enhanced. It is shown that 0̄?0⁺ nuclear isomers, if they exist, will accordingly exhibit strikingly large neutral current effects. In particular, the monoenergetic conversion electrons will have helicities h of the order of 25% which should be easily measurable. In certain favourable cases, the nuclear weak current matrix elements may be measured experimentally via the analogue β decay or electron capture so that measuring h will constitute a measurement of the electron's neutral vector current coupling constant. In any event, detection of h would prove the existence of an as yet unseen class of neutral currents.     

Acoustic perturbations in a pulsedRF-plasma

The response of a stationary weakly ionized plasma to a density perturbation in the neutral gas component was studied in a neon plasma with the following typical properties: electron density ¯N _e≈8×10¹² cm^?3, electron temperature on the axis of the vesselT _e0≈3.0 eV; neutral gas densityN _n≈1×10¹⁷cm^?3 and neutral gas temperatureT _n0≈600 °K. A neutral density perturbation, generated 50 cm apart from the plasma, produces a fluctuation in the ion density and a sharp spike in the differential voltage of a floating double probe. The experimental observations demonstrate the propagation of an ion sheath and of an electric field perturbation together with the neutral density perturbation. An interpretation of the plasma response to acoustic wave pulses has been proposed by Ingard and Schulz in a theory on acoustic wave modes in a weakly ionized gas. The experimental results are in good agreement with the theoretical expectations.     

HL-2A托卡马克中性束辐射光谱的数值模拟

采用数值模拟的方法研究中性束辐射光谱(BES)对开展与中性束相关的光谱诊断与实验有重要的指导意义.本文在HL-2A托卡马克装置上利用ADAS数据库（Atomic Data and Analysis Structure,1998）计算有效束辐射系数和有效束衰减系数,分析了束辐射光谱强度与等离子体运行参数和中性束参数的关系,并在不同的中性束注入能量、等离子体密度分布和等离子体温度分布的情况下,获得了束辐射光谱强度的空间分布.在n_e=2×10¹³ cm< 关键词： 中性束 束辐射光谱 束衰减     

Trap-free lifetime in hopping systems: Neutral traps in PVK

The concentration of deep hole traps in layers of PVK is found to be ≈-10¹⁵cm^?3. The traps are believed to be neutral. An expression of general validity in hopping transport is derived for the free carrier lifetime before capture by neutral traps. In PVK the lifetime depends on field, but the Schubweg ≈-10^?4/T cm²V^?1, does not.     

Bose-Einstein correlations of neutral gauge bosons in pp collisions

The theory for Bose-Einstein correlations in case of neutral gauge bosons in pp collisions at high energies is presented. Based on quantum field theory at finite temperature, the two-particle Bose-Einstein correlations of neutral gauge bosons are carried out for the first time. As a result, the important parameters of the correlation functions can be obtained for the Z ⁰ Z ⁰ pairs. The article is published in the original.     

On the Stability of Ballooning Modes in the Boundary Layers of a Gas Insulated Plasma

In order to fulfill power density requirements in future steady-state fusion reactors the ion density in central parts must be of the order 10²⁰–10²¹–m^?3. In such systems high density neutral gas may surround the hot plasma, whether introduced on purpose or not, provided the neutral gas flux from the plasma is not continuously removed by external means. In gas insulated plasmas large density and pressure gradients will arise close to the boundaries on account of plasma neutral gas interaction effects. In this paper the stability of gravity driven ballooning modes in the boundary region is investigated. In particular, the coupling between plasma and neutral gas investigated in previous stability analysis is reconsidered. Also effects previously neglected for example the Nernst effect is taken into account.     

乙腈-水和乙二醇-水均相溶液中光诱导杜醌激发三重态与色氨酸、酪氨酸的氢原子转移反应

本文用激光闪光光解技术研究了光诱导生物醌杜醌激发三重态(³DQ^*)和色氨酸(Trp)与酪氨酸(Tyr)在乙腈-水(MeCN-H₂O)及乙二醇-水(EG-H₂O)均相溶液中的光化学反应,分析了反应的机理,并基于Stern-Volmer方法测量了反应速率常数. 光解DQ体系可以生成³DQ^*,³DQ^*与Trp、Tyr发生的氢原子转移反应占主导地位. 对于DQ/Trp/MeCN-H₂O和DQ/Trp/EG-H₂O溶液,³DQ^*与Trp反应生成杜醌中性自由基DQH^·、以碳为中心的色氨酸中性自由基Trp^·/NH和以氮为中心的色氨酸中性自由基Trp/N^·. 对于DQ/Tyr/MeCN-H₂O和DQ/Tyr/EG-H₂O溶液,³DQ^*与Tyr反应生成DQH^·和酪氨酸中性自由基Tyr/O^·. ³DQ^*与Trp、Tyr的氢原子转移反应速率常数都在10⁹ L·mol^-1·s^-1量级,反应近似受扩散控制. MeCN/H₂O均相溶液中³DQ^*与Trp、Tyr的反应速率常数要明显高于EG/H₂O均相溶液中的反应速率常数,这与Stokes-Einstein方程定性一致.     

The decay h0 → A0 → A0A0: a complete one-loop calculation in the MSSM

In the minimal supersymmetric standard model the decay h⁰ → A⁰A⁰ of the light neutral scalar h⁰ is kinematically allowed for low values of tan β when radiative corrections to the neutral Higgs masses are taken into account. The width of this decay mode is revisited on the basis of a complete one-loop diagrammatic calculation. We give the analytical expressions and numerical results and compare them with the corresponding ones from the simpler and compact approximations of the effective potential method and the renormalization group approach.     

The measurement of energy spectra of neutral particles in low energy ion scattering

An apparatus is described for low energy (0.1–10 keV) ion scattering (LEIS) experiments. A time of flight (TOF) spectrometer is incorporated in the system to be able to measure the energy of particles in the neutral state after scattering. The energy resolution ΔE/E of the TOF spectrometer is discussed and found to be 0.5% (FWHM). This is sufficient for our scattering experiments. An electrostatic analyzer (ESA) is used to measure the energy of scattered ions [ΔE/E=0.5% (FWHM)]. Experiments show that in general the ion dose needed to obtain a TOF spectrum (2×10¹⁰ ions/cm²) is much smaller than the dose needed for an ESA-spectrum (6×10¹³ ions/cm²). The ion spectra measured with the TOF spectrometer, by subtracting the neutral yield from the total yield, as well as with the ESA are found to agree quite well. This provides a way to calibrate the TOF spectrometer. The determination of the ion fraction of scattered particles is discussed [10 keV⁴⁰Ar⁺ on Cu(100), scattering angle 30°]. It is shown that the TOF spectrometer is able to measure light recoil particles (e.g. hydrogen) from a heavy substrate. In the analysing system is, in addition to the TOF spectrometer, also incorporated a stripping cell to measure the energy of neutral scattered particles. An energy spectrum of neutral scattered particles measured with both methods is shown.     

Sputtered neutral mass spectrometry (SNMS) as a tool for chemical surface analysis and depth profiling

An experimental system for mass spectrometry of supttered neutral particles involving a hf plasma operated in Ar at several 10⁻⁴ Torr is described. The potentialities of the method for quantitative surface analysis are reasoned. Depth profiling by sputtered neutral mass spectrometry is demonstrated for anodic oxide layers on Nb and Ta.     

An analysis of the gargamelle freon data concerning pion production by the weak neutral current

Semi-inclusive pion production of all three charge states by the weak neutral current has been analysed in the Gargamelle Freon neutrino and antineutrino experiments. Using the complete neutral current sample a κ² fit of the measured charge ratios to the hypothesis of a purely isoscalar current has a confidence level of less than 10^?4. Using a restricted pion sample, corresponding to current fragment pions, a κ² fit of the π⁺/π^- ratios in νv and $\text{ν}$ to the predictions of an isovector current has confidence level 0.017. The sign of the isovector-isoscalar interference term is found to be consistent with that predicted by the Weinberg-Salam model.     

Die Diffusionskoeffizienten und mittleren freien Weglängen der geladenen und neutralen Radon-Folgeprodukte in Luft

The knowledge of the diffusion coefficients of radioactive atoms and ions in air is very important in a number of investigations on and computations of the attachment of radon decay products to aerosol particles. In this work measurements of the diffusion coefficients of neutral and charged²¹²Pb atoms are reported. The values found areD ₀=(7.6±0.4)·10^?2cm²s^?1 for neutral atomsD=(5.0±0.3)·10^?2cm²s^?1 for charged atoms The used method of measurement allowed to determine these constants 1–5 seconds after the formation aged²¹²Pb atoms, so that a “cluster” formation was improbable. The mean free path for neutral (λ₀=(4.9±0.3)·10^?6cm) and charged (λ=(3.2±0.2)· 10^?6cm) lead 212 atoms in air were computed from the measured diffusion coefficients. All obtained results were compared with values, calculated from theory.