Measurements Of Ion Energy Distributions Research Articles

Comparative characteristics of atomic particle analyzers with solid and gaseous targets when used at large fusion facilities

The capabilities of atomic particle analyzers with solid and gaseous targets for measurements of plasma ion energy distribution functions at large fusion facilities are analyzed. It is shown that analyzers with a solid target have a number of advantages over the analyzers with a gaseous target and that their sensitivity at energies above 5 keV can be to 10–100 times higher. They are smaller in size. This makes it easier to shield them against X-ray and neutron irradiation and they are simpler in their design and maintenance.

Energy-mass spectrometer for low energy weak ion flux analysis

An instrument for energy- and mass-spectrum measurements of ion fluxes in the Earth magnetotail is described. The ion selection by energy and mass is provided by sequential analysis of the incident ion beam in the electrostatic field of a cylindrical detector and the field of a permanent magnet. The measurement of ion energy distribution is carried out through scanning the voltage supplied to the electrostatic deflector. At a fixed energy the intensities of the different ion fluxes are measured simultaneously. An electrostatic angular scanner allows for the variation of the direction of the polar view-angle (in a frame of reference with a polar axis coincident with the spin axis of the spacecraft). The scanning of the azimuth angle is obtained while the satellite is spinning. The operational principle and the design of the instrument are described and the results from the laboratory testing are presented.

Detailed measurements of anisotropic mirror plasma ion energy distributions during drift cyclotron loss-cone instability

Using improved computer filtering and a reconstruction analysis we have been able to extract additional details on a mirror plasma’s midplane ion energy distribution from the current–voltage (I–V) curve of a voltage-swept electrostatic end loss analyzer (ELA). For the University of Maryland’s MIX-1 plasma [Phys. Fluids 23, 3439 (1976)], the diagnostic technique has provided us with important information on the ‘‘loss-cone region’’ of an anisotropic ion distribution during drift cyclotron loss-cone (DCLC) instability experiments. Observations include convincing verification of ion distribution modification during DCLC evolution and an enhancement of the loss-region boundary over that predicted by simplified trapping theory. The reconstruction analysis involves matching the differentiated I–V curves (i.e., dI/dV vs V) to theoretically predicted curves based on model midplane ion distribution functions. The theoretical curves are obtained from the model midplane distributions by a mapping transformation based on conservation of magnetic moment and total energy of each ion along lines of magnetic flux.

Mass spectrometric and ion energy diagnostics in the study of plasma etching and polymerization

Mass spectrometric sampling of ions and neutrals from water, hydrogen, and styrene plasmas sustained by 13.56-MHz radio frequency excitation have been studied using a reactor equipped with a small (80–200 μm) sampling orifice leading to a quadrupole mass spectrometer. The apparatus is described, including a discussion of the use of retarding grids to measure ion energy distributions in the sheaths of these plasmas. For both etching and polymer deposition in the pressure regime of 1–50 mTorr, evidence is provided from the mass spectra and ion energy spectra suggesting that the sheath is not collisionless. The data indicate that collisionally activated dissociation and high-energy ion–molecule reactions occur in the sheath, while collisional stabilization occurs in the bulk of the discharge.

磁気中性点による散乱効果を用いたイオン源の基本特性

Two types of ion sources with a single magnetron injection gun-type-thermionic cathode were fabricated and tested. The cathode was positioned on the extended line of the cylindrical axis. These sources have magnetic multipole linecusps with different directions. One of them had azimuthally oriented magnetic field, and the other had axially oriented one. The measurement of ion current density and ion energy distribution revealed that the beam profile became a hollow-beam whose intensity increases in proportion to discharge current, and that the ion source with azially oriented magnetic field produces ion beams 450 times higher than those with azimuthally oriented magnetic field. Single extraction grid-ion source is also compared in extracted beam profile with the two grid-ion source.

Ion extraction from the cathode-fall region of Ar, N 2 and O 2 discharges

A relatively simple experimental apparatus has been developed to extract ions from several d.c. plasmas, involving a symmetrical three-element einzel lens and mass spectrometric detection. The measured ion energy distributions obtained for Ar d.c. plasmas are in good agreement with the classical results of Davis and Vanderslice and conform to their model except that there must be at least one other type of ion which contributes to the observed energy distributions in addition to those which experienced charge exchange during their last collision in the cathode-fall region. This additional group of ions has been tentatively identified. The distributions from N 2 d.c. plasmas show larger deviations from the Davis and Vanderslice model; two consecutive processes may be at work which also have been specified. The O 2 + and O + results obtained were non-reproducible, presumably because of changes of the internal surfaces which affected the electrical fields in the ion optics.

Interpretation of measurements of ion energy distributions in drift tubes

The interpretation of experimental measurements of the energy distributions of low-density, ion swarms drifting in an electric field is discussed. The ratio, R, of the mean energy of a measured energy distribution to that predicted by Wannier's equation is found to have an expected value greater than one at intermediate field strengths. Measurements of R for He + and Ar + ions in their respective parent gas are interpreted in terms of the analysis presented.

A high resolution mass-energy spectrometer for the study of liquid metal ion sources

A sector-magnet mass spectrometer has been modified to allow measurement of ion energy deficit and distributions as well as measurement of various mass species and their abundance to be made. The energy calibration and resolution measurement was achieved by using a simple, low cost, Cs surface ionization source which supplied monoenergetic Cs + and Cs 2 + ions of known energy, this energy analyzer has a resolution of < 2 eV and a mass energy product of 2 meV amu in the configuration in which it was used. Data are presented illustrating the versatility of the spectrometer in studying ion production mechanisms in liquid metal ion sources.

A combined retarding field analyser and E×B probe for measurement of ion and electron energy distribution in tokamak edge plasmas

A new probe has been designed to measure the electron and ion energy distributions in a tokamak edge plasma; it may be operated in both the retarding field analyser and E*B modes. In this type of probe aperture design is important and must include detailed consideration of Debye length, selective transmission, heat flux and space charge effects. Results obtained in the retarding analyser ion mode show that the ion parallel velocity distribution function as measured by the probe is a displaced Maxwellian in accordance with theoretical prediction. The electron parallel velocity distribution on the other hand is seen to be cut off by the wall sheath. Ion temperatures obtained under similar conditions in the E*B mode are in agreement with values obtained by fitting theoretical distributions to retarding field ion mode characteristics. The results which are presented were obtained in the edge region of discharges with line average densities of 1019 m-3. In this particular case approximately equal ion and electron temperatures of order 15 eV were measured. There is experimental evidence that at the current levels used space charge effects are negligible.

Mass resolving charge-exchange system on the poloidal divertor experiment

The charge-exchange system used on the Poloidal Divertor Experiment is comprised of four, ten-channel, mass-resolved, charge-exchange analyzers. Each analyzer is constructed with parallel electric and magnetic fields and is calibrated over an energy range of 0.5–40 keV. The mass rejection between hydrogen and deuterium has been measured as better than 1000 to 1. For Ohmic heated discharges the system can provide single shot radial ion temperature profiles (four point) with 1-ms time resolution. For neutral beam heated discharges, complete radial and temporal profiles can be obtained in two to four shots. The system is also equipped with a vertically aimed diagnostic neutral beam to allow local ion-energy distribution measurements. This report describes the analyzer system and its calibration, and presents results from Ohmic and neutral beam heated discharges.

Mobilities of O+, O+* and O22+in He and Ar from ion energy distribution measurements in an injected-ion drift tube

An injected-ion drift tube with axial exit orifice feeding a cylindrical electrostatic momentum analyser has enabled ion energy distributions in helium and argon buffer gases to be measured directly. The most probable energies have been used in conjunction with the Wannier relationship to yield mobilities of O+(4S), O+(2D) and O22+ in He over the range 20 to 150 Td and in Ar over the range 70 to 300 Td. Where comparison is possible, good agreement is obtained with recent flow-drift data and Monte Carlo calculations.

4993. Measurement of ion energy distribution in an orbitron device: M L Feidt and B Petit, J Vac Sci Technol, 18 (3), 1981, 987–993

4993. Measurement of ion energy distribution in an orbitron device: M L Feidt and B Petit, J Vac Sci Technol, 18 (3), 1981, 987–993

Adsorption of CO on W(110) as studied using electron-stimulated desorption and thermal desorption

The chemisorption of CO on the (110) face of W at room temperature is studied using a combined technique consisting of electron-stimulated desorption (ESD) and thermal desorption. Measurements of the ESD ion energy distribution as a function of CO exposure, crystal temperature, and incident electron energy are presented in conjunction with a comparison with the corresponding thermal-desorption spectra. The correlation between the presence of the binding states in the thermal-desorption spectra and the liberation of ions in ESD is discussed in detail. An interesting result is the observation that ${\mathrm{O}}^{+}$ and C${\mathrm{O}}^{+}$ are due to ${\ensuremath{\beta}}_{1}$ and virgin states of CO, respectively. In conjunction with data acquired from other surface techniques, the present results are used to discuss and propose the bonding geometry of the various binding states of CO on W(110).

Measurement of ion energy distribution in an orbitron device

The ion energy distribution in an orbitron device has been measured by means of a retarding field analyzer. The influence of the main geometric and electric parameters of the device on the ion spectra is reported here. The observed distributions show that, because of the electrostatic field configuration, the ionizing efficiency is much smaller near the reflector plates than in the central part of the device. In all cases the ion energy distribution is continuous and broad with a single maximum. Implications of the electron distribution in the orbitron are discussed. Particularly, it results from these investigations that the radial electron density distribution is a monotonically decreasing function of the radial position in the orbitron. These results are interpreted in terms of electron trajectories.

Pulsed-gas-valve measurements of impurity ion concentrations and energies in the 2XII mirror device

Measurements of impurity ion concentrations and energy distributions in the 2XII mirror device are desaibed. The measurements were made using a fast-pulsed gas valve and a charge-exchange analyser that employs both electrostatic and magnetic separation to obtain energy spectra of separate particle species. The predominant high-Z material detected wascarbon, having a concentration of ∼2% and a mean energy of 3-6 keV. Smaller amounts of oxygen were the only materialother than hydrogen detected. These energetic impurity levels are determined to be contained against self-scattering into themirror loss cones and to have only minor influences on plasma life-time and on mean ion and electron energy.

Measurement of the surface density of states by field ionization

It is shown that recent measurements of field ion energy distributions from clean tungsten surfaces probe the density of metal states in the vicinity of the surface. We find j( ω) = (2 π/ kh) Σ m | ∫ d 3 rψ m ( r) γ z | 2 δ( ω− ϵ m ), where j(ω) is the ion current a ω, ψ m and ϵ m are electronic metal eigenfunctions and eigenvalues in the presence of the external electric field used in field ionization and γ( z) is a function which is large near the noble gas atom. An explicit expression for γ( z) is given in the text. It is estimated that tungsten metal states with values of k ‖ at least as large as 0.5 Å −1 make an appreciable contribution to j(ω) where k ‖ is the electron momentum parallel to the surface.

Observation of clusters in a sputtering ion source

Abstract This paper reports previously unpublished results which were obtained in 1966. We systematically investigated the dependence of cluster ion intensities on the bombarding gases He+, Ar+ and Xe+ (energies: 4 to 12 keV, current densities: 100 mA/cm2). Frequently, the observed structures in the relative cluster intensities were quite puzzling, e.g. for A1 and Si. Attempts to correlate these structures to crystal configurations failed, nor did any pattern develop from simple valency considerations alone. Initial ion energy distribution measurements from 0 to 1200 eV showed significant differences for atomic ions and cluster ions. This effect is used to reduce interference problems caused by cluster ion peaks in SIMS applied to trace analysis of solids. The results are discussed and compared with those of other investigators, also including cluster formation by vaporization and sparking. Extending known theoretical considerations may possibly afford a general understanding of the intensity structure. T...