US3843889A

US3843889A - High intensity proton source

Info

Publication number: US3843889A
Application number: US00420356A
Authority: US
Inventors: J Layton; G Magnuson
Original assignee: US Air Force
Current assignee: US Air Force
Priority date: 1973-11-29
Filing date: 1973-11-29
Publication date: 1974-10-22
Anticipated expiration: 1991-10-22

Abstract

A proton source in which hydrogen is heated by a tungsten filament in a chamber. The chamber is surrounded by an anode cylindrically shaped and having an orifice for the expulsion of protons. The chamber is mounted between two stainless steel support posts which are then mounted upon a supporting disk. The hydrogen is introduced to the chamber by a gas line embedded in one of the support posts. A pair of heat shields surround the anode and have orifices concentric with the anode''s orifice.

Description

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Layton et al.

f States Patent 1 Oct. 22, 1974 HIGH INTENSITY PROTON SOURCE [75] Inventors: James K. Layton; Gustav D.

Magnuson, both of San Diego, Calif. [73] Assignee: The United States of America as represented by the Secretary of the Air Force, Washington, DC. [22] Filed: Nov. 29, 1973 [21] Appl. No.: 420,356

[52] US. Cl 250/423, 250/427, 313/63, 313/230 [51 Int. Cl. HOlj 37/08 [58] Field of Search 250/427, 423, 424; 313/63, 313/230 [56] References Cited UNITED STATES PATENTS 3,610,985 l0/l97l Fleming 250/427 3,705,998 12/1972 Jennings .1 ..250/427 5 7 ABSTRACT A proton source in which hydrogen is heated by a tungsten filament in a chamber. The chamber is surrounded by an anode cylindrically shaped and having an orifice for the expulsion of protons. The chamber is mounted between two stainless steel support posts which are then mounted upon a supporting disk. The hydrogen is introduced to the chamber by a gas line embedded in one of the support posts. A pair of heat shields surround the anode and have orifices concentric with the anodes orifice.

5 Claims, 3 Drawing. Figures PATENIED URI 2 2 I974 SHEET 2 0F 2 HIGH INTENSITY PROTON SOURCE BACKGROUND OF THE INVENTION This invention relates to particle sources, and more particularly to a high intensity proton source with a low energy spread.

To perform atomic hydrogen collision experiments at low center-of-mass collision energies (0.1 to 15 eV) with a merging beam apparatus, there is a need in the art for an ion source which would produce an intense beam of protons at several keV with a small energy spread. A number of ion sources satisfies the first requirement but produces beams with energy spreads that are too large for many applications 8 eV or larger). Electron bombardment ion sources have small energy spreads 0.1 to 2 eV) but do not usually produce protons very efficiently. Typical proton beam currents are only 5 to percent of the total beam current. However, in the present invention the proton source produces beams with about 60 percent H, 38 percent H; and 1 percent Hg with an energy spread of 0.4 eV or less. Total ion currents of 80 ramps at 1 keV were extracted from the expulsion orifice of the source.

SUMMARY OF THE INVENTION The present invention is a particle source that produces protons by thermally dissociating gas molecules such as hydrogen prior to electronic bombardment ionization thereby increasing the efficiency of proton production. The hydrogen or other gas is fed to a chamber formed by an enclosed anode except for an orifice allowing for the output beam. A tungsten filament passes through the chamber and the entire chamber is mounted on a disk with stainless steel support posts.

It is therefore an object of this invention to provide a novel and improved proton source.

It is another object to provide a high intensity proton source having a low energy spread of 0.4 eV or less.

It is still another object to provide a high intensity proton source that is stable, reliable, and relatively free of noise.

These and other objects, features and advantages of the invention will become more apparent from the following description taken in conjunction with the illustrative embodiment, in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view partly in schematic of an embodiment of the invention;

FIG. 2 is a front elevation view of that shown in FIG. 1; and

FIG. 3 is a graph showing the ion current output of the proton source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 showing different views of the proton source, chamber 11 is formed by anode 13 and contains extraction orifice l5. Anode 13 is constructed of three layers of rolled 0.025 mm tungsten foil and is supported at the ends by stainless steel support posts. Extraction orifice 15 in anode 13 can be made with a fine sandblaster and finished with a 0.75 mm drill by hand. Hydrogen gas is introduced to chamber 11 by gas line 17 from source 19. Passing through chamber 11 is filament 21 which is connected to voltage source 23. Filament 21 is preferably a coil of 0.075 mm diameter tungsten wire and heliarc-welded to a straight 0.127 tungsten wire which affords support and cool operation at the ends for protection of

sapphire insulators

25 and 27. Filament 21 is connected most advantageously by winding it around the 0.127 mm tungsten wire and functions both as an electron emitter and as a heater for thermally dissociating the hydrogen molecules. Chamber 11 is surrounded by

heat shields

29 and 31 having orifices that are concentric with orifice 15 of anode 13 for allowing the passage of the proton beam.

The primary support of the proton source is diskshaped member 33 having flange 35 which includes 0- ring groove 39. Stainless

steel support posts

43 and 45 mount chamber 11 to supporting member 33 using

removable end pieces

47 and 49. One of the support posts 45 provides for gas line 17.

Support posts

43 and 45 also contain passageway 37 for a water-cooling pipe and O-

ring grooves

51 and 53. Each end of filament 21 is mounted to support members 33 by

ceramic support posts

55 and 57.

Typical operating conditions forthe proton source are: filament-heater, 6 volts and 26 amps; emission current, 2 amps; anode, 100 volts; and hydrogen pressure, microns.

The temperature of the anode is about 2,250C. Use of a magnetic field of about gauss parallel to the ion extraction direction increases the beam current by about a factor of two.

A mass spectrum of the source output current when the hydrogen was used as the source gas is shown in FIG. 3. The I-I peak here represents about 60 percent of the total beam current. Impurity ions other than H and H; constituted at most 1 percent of the total ion current. For example, the impurity ion H O which is present in all ion sources, was extremely small, probably because of the high operating temperature.

One operating characteristic is a tendency for the emission current to run away. This is apparently caused by ions being accelerated to the filament which causes further heating and consequently more emission. However, this can be prevented by using a current regulated anode supply or connecting a 50 Q, 300 watt resistor in series with the anode.

The energy spread (full-width at half-maximum) was obtained with a hemispherical electrostatic analyzer. The half-widths measured at different beam energies were extrapolated to zero beam energy to obtain the value of 0.4 eV.

This proton source is stable, reliable, and relatively noise free. For an emission current of 3 amps the filament lifetime is 25-30 hours. However, if the emission current is reduced, with of course some loss in proton beam current, the filament lifetime can be extended to well over 100 hours.

The source can be successfully operated with source gases other than hydrogen but in all cases the operation is similar to that described for hydrogen.

Because of the high operating temperature, the source may also be useful for producing ion beams of low vapor pressure materials.

What is claimed is:

l. A proton source comprising:

a. a support disk;

b. a pair of stainless steel supporting posts mounted on the supporting disk equidistant from the center;

0. a filament supported by the supporting posts;

(1. a voltage source connected to the filament;

e. an anode having a beam output orifice mounted between the supporting post and connected to the voltage source, the anode being cylindrically shaped and forming an ionizing chamber containing the filament;

f. a pair of heat shields surrounding the anode and having orifices concentric with the orifice of the anode;

g. a source of ionizing gas; and

h. a gas line embedded in one supporting post having one terminal fed by the ionizing gas source and the other terminal feeding into the ionizing chamber.

2. A proton source according to claim 1 wherein the source of ionizing gas is a hydrogen source.

3. A proton source according to claim 2 wherein the filament includes a coil of approximately 0.75 mm diameter tungsten wire heliarc-welded to straight 0.127 mm tungsten wire, the straight wire being mounted to the stainless steel support posts.

4. A proton source according to claim 3 wherein the anode consists of three layers of rolled approximately 0.025 mm tungsten foil.

5. A proton source according to claim 4 which further comprises a pair of sapphire insulators interposed between the filament and one each of the stainless steel support posts.

Claims

1. A proton source comprising: a. a support disk; b. a pair of stainless steel supporting posts mounted on the supporting disk equidistant from the center; c. a filament supported by the supporting posts; d. a voltage source connected to the filament; e. an anode having a beam output orifice mounted between the supporting post and connected to the voltage source, the anode being cylindrically shaped and forming an ionizing chamber containing the filament; f. a pair of heat shIelds surrounding the anode and having orifices concentric with the orifice of the anode; g. a source of ionizing gas; and h. a gas line embedded in one supporting post having one terminal fed by the ionizing gas source and the other terminal feeding into the ionizing chamber.