Magnetic Sector Field Research Articles

Bombardon: an apparatus for investigating the influence of 5–20 keV ions on metal targets

An apparatus for ion bombardment in the energy range of 5–20 keV is described. The ion beam, produced by a duoplasmatron ion source, is purified by a magnetic sector field and directed into a target chamber 60 cm in diameter. The chamber is evacuated by sputter ion and titanium sublimation pumps with a total pumping speed of 20000 ls −1 for H 2. The energy and angular distributions of particles backscattered from metal targets can be measured with an electrostatic spherical condenser which can be pivoted around the target. The whole apparatus is bakeable up to 250°C. With a 100 μA proton beam a pressure of 10 −9 torr is maintained in the target chamber. The black off pressure is a few 10 −11 torr.

A versatile sector-focusing magnetic β-ray spectrometer

A K = 0.82 single gap β-ray spectrometer with broad range and high transmission was constructed using a magnetic sector-field H = H φ∼ 1 r . Rectangular-like plates, nearly 640 × 380 mm 2, were used and form a gap width angle Δφ = 28°. The maximum entrance angle along the gap amounts to 90°, resulting in a maximum usable solid angle of 4.3%. The geometrical solid angle available amounts to 5.3%. The distance between source and focal point is L = 300 mm. Shaping of the pole plates for a wide range was achieved. Fringing-field effects and the focusing properties are discussed. The focal line for an electron spectrum was investigated. Dispersion, resolution and transmission for differential parts of the gap were determined. A resolution of 1.2% and 2.4% corresponds to the transmission values of 1.1% and 3.0% respectively. The sector-focusing properties for a broad range electron spectrum were investigated. Transmission and dispersion values along the spectrometer axis are presented. An empirical relation between transmission and the usable spectrum range was found. The influence of transmission and dispersion on the upper and lower spectrum range limit is discussed. Absolute transmission functions are presented. The spectrometer is designed for the investigation of β-γ correlations in forbidden β-decay.

New Directional and Energy Focusing Time of Flight Mass Spectrometers for Special Tasks in Vacuum and Surface Physics

This paper describes a variety of new directionally focusing TOFMS with equal momentum or equal energy acceleration and with no first order dependence on ion velocity in time of flight. This is achieved by combining linear drift spaces with magnetic or electrostatic sector fields. Mathematical expressions for velocity focusing are presented together with the requirements for directional focusing, and the characteristic values of a number of geometries which afford stigmatic imaging are given. With special configurations it is further possible to avoid any first order dependence of resolution on slit width. Finally, the resolution is also strongly influenced by the different means of ion production and acceleration. TOFMS with magnetic sector fields and equal momentum acceleration seem well suited for gas analysis together with the coincidence method, while the combination of a sputtering ion source with an electrostatic instrument is particularly promising for the analysis of solids and surfaces.

The study of rearrangement reactions by field ionization mass spectrometry: I. Theoretical aspects

The peak shapes of fragment ions caused by rearrangement reactions in a field ionization ( fi) mass spectrometer are derived theoretically. The quasi-equilibrium theory ( qet) is used and different distributions of rate constants are assumed. The peak shapes agree qualitatively with those observed in the fi mass spectra. The shift of the rearrangement peak maxima from the normal fragment peak position is discussed for the case of a single-focusing magnetic sector field mass spectrometer. The peak shifts are studied as a function of the emitter geometry and radius of curvature, surface structure, ion retardation, emitter to cathode distance and emitter temperature. The rate constants as a function of energy are compared for the case of electron impact and fi.

The use of magnetic sector fields with cylindrical symmetry as one-gap broad-range spectrographs

The suitability of cylinder-symmetric magnetic sector fields for one-gap broad-range heavy particle spectrographs is investigated. If the desired energy range is not large ( E max E min ≤2 ) the focusing properties are good. The biggest advantages compared to homogeneous field analysers are a wider opening angle (≈2 msr) and a larger dispersion. The usable energy range E max E min ) can be increased by curving the entrance and exit edges of the analyser, which partly eliminates the aberration.

Stigmatische fokussierung mit homogenen magnetischen sektorfeldern

For a long time it has been known that the axial focusing strength of the fringing field of a homogenenous magnetic sector field can be used to achieve stigmatic focusing. This stigmatic focusing is in general only valid for ions of one specific mass, as the radial and axial focusing curves in general do not coincide. In this paper arrangements with coinciding radial and axial focusing curves are discussed. In addition, the correction of second order image aberrations by curved field boundaries is treated. Besides stigmatic focusing, some properties of the so-called linear focusing are reported

Die trennschärfe von homogenen und inhomogenen magnetischen sektorfeldern bei optimaler stromtransmission

The general aspects of the ion optics of single focusing magnetic mass spectrometers are treated. It is shown that magnetic sector fields transmit maximum ion current if the beam is convergent at the entrance and divergent at the exit of the field. Compared to the classical arrangement of a divergent beam at the entrance the arrangement of maximum acceptance needs only a fraction of the field volume to obtain comparable resolution and transmission. The product acceptance × resolution is defined as “figure of merit of the field”. It increases with increasing logarithmic field index n.

Third order calculation of the ion trajectories in an inhomogenenous magnetic sector field

The ion trajectories in an inhomogeneous magnetic field are calculated in a third order approximation. The field distribution on the median plane is assumed to be B z = B 0(1+ n 1ϱ+ n 2ϱ 2+ n 3ϱ 3). The radial transfer matrix which transforms the third order vector: k (3) = u, tan x, τ, u 2, uα, uτ, α 2, ατ, τ 2, ν 2, νβ, β 2, u 3, u 2α, u 2τ, uα 2, uατ, uτ 2, uν 2, uνβ, uβ 2, α 3, α 2τ, ατ 2, αν 2, ανβ, αβ 2, τ 3, τν 2, τνβ, τβ 2, is derived. The matrix elements are expressed as functions of the deflection angle φ.

Ion optical design and field-shaping calculations for the 180° Oak Ridge sector isotope separator

An analysis of the optical properties of sector magnetic fields and of the field-shaping techniques used to produce them is presented in connection with their applications to high-purity, medium-current, isotopes separators. Particular emphasis is placed on the use of axially symmetric, inhomogeneous, magnetic sector fields. The Oak Ridge Sector Isotope Separator (ORSIS), which resulted from this study, has been constructed and has successfully operated at strontium beam currents of 6.4 mA for 65 h with a beam resolution of ≈ 3000 fwhm. This separation used natural strontium metal charge having 0.56% 84Sr and produced a purified sample of 99.40% 84Sr weighing 3.7 mg. The ORSIS operates with a beam-deflecting radius of 24-in., 180° of beam deflection, field inhomogeneity of n=0.8, object and image distances of 100-in., acceleration voltage of 40 kV, and uses an electron-bombardment ion source which employs a side-extraction slit geometry. The optical techniques, which are being used to improve the resolution and throughput of this separator, are reported along with the projected improvement in machine performance expected from these changes. The first test model of this separator presently averages 1–7 mA of total collected beam current with isotopic enrichments ranging from 1000 to 60 000. These figures vary with the element being separated and the program emphasis.

Focusing properties of magnetic sectors of the wedge type. Part I

The focusing properties of inhomogeneous magnetic sector fields with cylindrical symmetry are investigated. For the case of symmetrical arrangement of object and image and perpendicular trajectories at the field boundaries expressions for the image aberrations up to the second order are given. It is shown that this special type of field has two-directional point to point focusing.

Focusing properties of magnetic sectors of the wedge type. Part II

The focusing properties of inhomogeneous magnetic sector fields with cylindrical symmetry, symmetrical arrangement of object and image and perpendicular trajectories at the field boundaries are investigated. First and second order aberrations are computed and compared with the analogous values of other stigmatic focusing magnets.

A Mass Analyzer System for the High Voltage Terminal of a Van De Graaff Heavy Ion Accelerator

A computer analysis of an electromagnetic mass analyzer system which will be mounted in the high voltage terminal of a planned 3MeV van de Graaff heavy ion accelerator at M.I.T. has been performed. Since one of the main fields of application of this new facility will be ion implantation, a stigmatic focusing analyzer with high transmission is required. It is shown that a magnetic sector field which is formed by plane inclined pole faces meets both these requirements. Second order ion optical calculations for this type of field are given and compared with two more conventional alternatives of stigmatic focusing analyzers namely the homogeneous field fringe field focusing magnet and the rotationally symmetric field with logarithmic field gradient n = 1/2. The complete ion injector system which will consist of a high temperature metal ion source, an extraction and focusing system and a stigmatic double focusing mass analyzer will have a total weight of about 400 pounds and be capable of unit mass resolution at least up to mass number 150.

Ion mass spectrometer on explorer XXXI satellite

A magnetic sector field mass spectrometer on the Explorer XXXI satellite, when calibrated in flight against electron concentration data from the Alouette II topside sounder satellite, measures the absolute concentrations of the various positive ion species in the ionosphere. The in-flight calibration is performed by comparing the total ion current measured by the mass spectrometer, corrected for internal discriminations, with the electron concentrations, first in regions of nearly pure H+, then in regions of nearly pure O+, to obtain calibration coefficients for each ion species. Data at 500 km show as many as ten different ion species in the ionosphere. Over the polar region, H+ions streaming upward at 10 to 15 km/s have been observed.

Ion optics of mass spectrometers IIB. Oblique incidence on magnetic fields

In Part IIA ion-optical properties, including magnification, dispersion, aberrations and resolution, for homogeneous magnetic sector fields were considered for the case of normal incidence. In this part these properties have been re-examined for an ion beam incident obliquely on the field boundary. All calculations are presented in graphical form.

Ion optics of mass spectrometers IIA. Normal incidence on magnetic fields

Ion-optical properties, including magnification, dispersion, aberrations and resolution, of homogeneous magnetic sector fields have been re-examined for the case of a beam incident normally on the field boundary. The calculations have been presented in graphical form with a view to being readily useful to the designer.

Calculation of the pole face profiles of inhomogeneous magnetic fields

A formula is derived which gives the pole face profiles of inhomogeneous magnetic sector fields for preselected magnetic field parameters as a power series representation up to the fifth order. A way of solving the inverse problem (i.e. determining the magnetic field parameters for a given pole shape) is also pointed out.

Construction and use of the Groningen isotope separator

The Groningen electromagnetic isotope separator which is of the so-called “Scandinavian type” with a Nielsen ion source, operates with about 50 kV acceleration potential and a homogeneous 90° magnetic sector field with a mean radius of 80 cm. Small ion sources are developed, which are interchangeable through a vacuum lock. The circular source aperture yields a line focus on the collector plate, the beam half width at the collector being about 1 mm. The beams are scanned with a thin vibrating needle; their position is stabilized. Among the applications of the isotope separator we mention studies on secondary electron emission and sputtering of metals by noble gas ions, the effects of gas desorption, the preparation of radioactive samples for nuclear spectroscopy, internal field measurements near implanted ions in magnetic materials.

Image aberrations of second order of electrostatic sector fields

The ion optical properties of electrostatic sector fields are described here in a second order approximation for three dimensional particle trajectories. All influences of the fringing fields are taken into account in the same approximation. The resultant aberrations differ considerably from older expressions as far as they have been calculated. This work is the counterpart to an article on image aberrations of a magnetic sector field 1), in which also a possibility is shown, how such aberrations can be corrected.

The correction of image aberrations of second order for mass or energy separators consisting of one single magnetic sector field

Image aberrations of second order are presented for mass separators consisting of one homogeneous or inhomogeneous 1–3) magnetic sector field, whereby the influence of the fringing fields 4, 5) are included in these expressions. Using a graphical method similar to linear programming techniques the derived aberrations can be corrected by proper choice of the curvatures of the entrance and exit boundaries of the magnet. As an example finally such a correction is carried out for a stigmatic focusing symmetric mass separator using a magnetic field with the inhomogeneity factor n = 0.5 and with perpendicular entry and exit of the ion beam into and out of the sector field.

Second order transfer matrices of real magnetic and electrostatic sector fields

With the help of second order transfer matrices 1 ) it is easily possible to calculate focusing and dispersion properties as well as second order image aberrations of any ion optical apparatus consisting of one or of several sector fields. Taking into account, in addition to the defrections in the main fields, all effects of the fringing fields 2,3 ), such transfer matrices are presented here for magnetic and electrostatic sector fields which have circular main paths in the main deflecting fields.