FR2647594A1 - Ion source of very high intensity - Google Patents

Abstract

Ion source with ionisation by electron bombardment, in which the combined action of a uniform magnetic induction B, and a radial electrostatic field E, perpendicular to B, makes it possible, based on electron emission from a short filament of length I, to establish an ionising space charge over the whole outline of the source. The ions accelerated by E towards the centre of the source are then focused by a suitable optic on the axis of the system which exhibits axisymmetry. If the radius of the source is R, the ion current extracted is 2 pi R/l times larger than the current extracted from a conventional source using the same filament.

Description

VERY HIGH INTENSITY IONIC SOURCE
In conventional ion sources, the useful ionization volume is proportional to the very limited length of the filament emitting ionizing electrons.

The present invention provides a source with a very large ionization volume, independent of the length of the filament, thus having a much higher efficiency.

The source (fig I and 11) consists essentially of a long anode a and a grid b parallel to a. The anode has a section in
: the horizontal parts a are drilled over almost their entire length by two slots m opposite. Finally, an electrode c completely frames a. The electron-emitting filament f is stretched opposite and parallel to m, at one end thereof and between a and c.

The whole is bathed in a uniform magnetic induction B, perpendicular to the plane of a '.

An almost uniform electrostatic field E perpendicular to B is established between a and b. The filament f is negatively polarized with respect to a and the electrode c (electron repeller) is negatively polarized with respect to f.

The electrons emitted by f and injected between a and b, parallel to B are subjected to the action of a system of crossed fields E, B. The projection of the movement in a plane perpendicular to B is a very tight cycloid around an equipotential line of E (circular motion combined with a speed drift v = - - in
B
a direction perpendicular to the plane E, B).

At the same time, under the effect of the repulsive field between a and c, they
oscillate in a plane parallel to 3, defined by the slots m. A ribbon
very small thickness electronic space charge
equal to that of f is thus established in coincidence with a surface
equipotential of E over the entire length L of the anode a. the ions
formed and accelerated through grid b are therefore almost
monocinetics.

The output of such a source can be, with a filament of the same
length 1, L times larger than that of conventional sources.

A similar device can be produced with axial symmetry
(fig. 111). The electrodes a, b, c are then cylinders and the field E
is no longer uniform but radial.

The electronic space charge becomes a closed circular ribbon on
himself.

With this geometry, the ions injected into the space limited by b can be easily focused and introduced, for example, into a mass spectrograph. Figure IV shows schematically such a device: inside the volume b, a cylindrical grid d slows down the ions which are then easily focused by the two electrodes - holes g and h; The axial opening in h can be very small, which makes it possible to maintain a large pressure gradient between the source and the space of use of the ion beam.

The source and focusing system assembly has the symmetry of revolution around an axis parallel to B.

Note again that for suitable values of E and B, it is easy to block the introduction into the focusing device d, g, h of light ions such as He, which constitutes an important advantage for certain applications.

This new very high intensity ion source is intended to power mass spectrographs and ion cannons.

Claims (2)

CLAIMS 1- Ion source, with electron bombardment ionization, characterized in that the ionization chamber consists on the one hand, by an anode (a) of U-section, of length L, of which the two horizontal blanks ( a ') are provided with two parallel slots (m) facing each other, of length almost equal to L; on the other hand, by a grid (b) parallel to (a); by the fact that an electrode (c) completely frames the anode (a); by the fact that the electron-emitting filament (f) of length I, is stretched between (a) and (c), in parallel and opposite (m); by the fact that an electrostatic field E is applied between (a) and (b); by the fact that the whole bathes in a magnetic induction field B uniform and perpendicular to the field E; by the fact that (f) is negatively polarized with respect to (a) and that (c) is negatively polarized with respect to (f); by the fact that the electrons are injected parallel to B, through the slits m, in the space between (a) and (b); by the fact that in the system of crossed fields B, E between (a) and (b) and also under the effect of the repulsive field between (c) and (a), the electrons form a charge of electronic space in form tape over the entire length L of the system, with a thickness approximately equal to that of (f) and superimposed on an equipotential surface of the field E; by the fact that the ions accelerated by E are quasi monocinetic. The intensity of such a source is L / I at least greater than that of a conventional source using a filament of the same length 2 - Ion source according to claim 1, characterized in that the system has axial symmetry , The axis of symmetry being parallel to the induction B; by the fact that the charge of electronic space is thus a ribbon closed on itself. 3 - Ion source according to claim 1 and 2, characterized in that, in the space delimited by (b), a grid (d) slows down the ions which are then focused by two electrode-holes (g) and (h ) on the very small axial opening of (h); by the fact that the system (d) (g)  (h) is coaxial with the source.  4 - Ion source according to claims 1,2 and 3, characterized by  the fact that the quasimonokinetic ion beam from the opening  very small axial of (h), feeds a mass spectrograph.