J N H Brunt

The charge-density method of solving electrostatic problems with and without the inclusion of space-charge

Discusses the singularities and approximations that occur in the charge-density method of solving electrostatic problems in which space-charge is absent (Laplaces equation) or present (Poissons equation). Describes the application of the method to electrostatic lenses in general and to the particular case of a high-current triode gun.

Resonance structure in elastic electron scattering from helium, neon and argon

High energy-resolution spectra of electrons scattered elastically from helium, neon and argon atoms have been obtained as functions of scattering angle and of incident electron energy. In addition to the well known levels of the lowest configurations of the temporary negative ions (resonances), the authors observe structures at energies close to those of the (core)np5(n+1)s levels of neon and argon. These structures are attributed to resonances having configurations (core)np5((n+1)s(n+1)p3P). By calibration against features occurring at known energies in the elastic scattering spectra and also metastable excitation spectra they determine accurately the energies of the observed resonances.

The optimization of electrostatic energy selection systems for low energy electrons

Abstract Design criteria are presented which allow electrostatic energy selection systems to be optimized to give the highest currents for electron beams having a low mean energy (≲ 500 eV) and a small energy spread (≲ 30 meV). Limitations in various parts of the system are discussed and a relationship between the current delivered by the system and the energy spread is presented. Different types and sizes for the energy selectors in these systems are considered and the best results are obtained with hemispherical deflectors. The advantage of using, within reasonable limits, a large selector with small image sizes is also demonstrated.

A study of resonance structure in helium using metastable excitation by electron impact with high energy resolution

The cross section for excitation of metastable states of helium by electron impact has been studied as a function of incident energy up to the ionization potential. The energy scale is established by determining accurately the position on the metastable spectra of the 23S and 21S levels, whose energies are precisely known from spectroscopic data. The positions of the numerous resonance structures observed in the cross section are determined and the values obtained compared with the results of previous electron transmission and metastable excitation experiments. The energy of the 22S resonance, observed in an elastic scattering experiment performed simultaneously, is found to be 19.367+or-0.007 eV. A modified Rydberg formula is used to predict energies of the n=3 and 4 resonance states, and the correspondences between the predicted and observed energies are used to suggest classifications for the observed resonances.

The realisation of high energy resolution using the hemispherical electrostatic energy selector in electron impact spectrometry

The design, construction and operation of a low-energy, high-resolution electron impact spectrometer are described. Emphasis is given to the means by which a practical hemispherical deflector can be made to approach its hypothetical optimum performance. Attention is also given to the design of the accompanying electron transport systems and to empirical methods of achieving good energy resolution in order to exploit the capabilities of the electrostatic energy selector. The authors have obtained elastic scattering spectra containing features whose measured full widths at half maxima are 12 meV, and these are presented.

Excitation of carbon monoxide and nitrogen molecules by electron impact at energies below 16 eV: studies of resonances in the excitation functions of metastable and ultraviolet-emitting levels

Measurements as functions of incident energy within the range 6 to 16 eV have been made of the yields of both metastables and ultraviolet photons following electron impact on carbon monoxide and nitrogen molecules. The energies of resonances in the excitation functions have been obtained from comparison with features of known energies in the noble-gas atoms. The configurations and binding energies of the resonances have been considered in terms of a model in which two Rydberg electrons couple together strongly in the field of the positive ion core.

A study of resonance structure in neon, argon, krypton and xenon using metastable excitation by electron impact with high energy resolution

Cross sections for the excitation of metastable states by electron impact have been studied as functions of incident energy up to 5 eV above the lowest metastable thresholds. The FWHM of the energy spread of the incident beam was typically 20 meV. A crossed-beam interaction region was used and the metastable atoms were detected by a channel electron multiplier placed in their direction of drift. Precautions were taken to avoid detection of scattered electrons and UV photons by the metastables detector. The incident energy scale could be calibrated from the onset positions of the metastable states, whose energies are accurately known from spectroscopic data. The energies of resonance structures in the cross sections could therefore be obtained, and are compared with the results of previous metastable-excitation and electron-transmission experiments.

The classification of resonances in electron impact on neon, argon, krypton and xenon

A jLS coupling scheme for the resonances which appear in electron impact on the noble-gas atoms neon, argon, krypton and xenon is discussed, and is used to classify the known lower-lying resonances.

Near-threshold electron impact excitation of ultraviolet-emitting levels of neon, argon, krypton and xenon atoms

The excitation by electron impact of levels of neon, argon, krypton and xenon atoms that decay by emission of ultraviolet light has been studied as a function of incident energy up to a few eV above the energies of the lowest excited levels. The width (FWHM) of the energy spread of the incident beam was typically less than 30 meV. A crossed-beam interaction region was used and UV photons emitted approximately normally to the electron and gas beam directions were detected by a channel electron multiplier. Precautions were taken to avoid detection of scattered electrons and metastable atoms by the photon detector. The onset positions of the lowest excited levels were used in calibrating the incident energy scales. The energies of resonance structures in the excitation functions could therefore be obtained, and are compared with the results of previous experiments.

Near-threshold electron impact excitation of ultraviolet-emitting levels of helium atoms

Abstract The excitation by electron impact of levels of helium atoms that decay by emission of ultraviolet light has been studied as a function of incident energy up to approximately the first ionization energy. The width (FWHM) of the energy spread of the incident beam was less than 30 meV. A crossed-beam interaction region was used and UV photons emitted approximately normally to the electron and gas beam directions were detected by a channel electron multiplier. Precautions were taken to avoid detection of scattered electrons and metastable atoms by the photon detector. The onset position of the lowest excited level was used in calibrating the incident energy scale. The energies of resonance structures in the cross-sections could therefore be obtained and are compared with the results of experiments detecting other products of the interaction.