US3789253A

US3789253A - Crucible for vaporizing chemically active elements method of manufacturing the same and ion source including said crucible

Info

Publication number: US3789253A
Application number: US00265303A
Authority: US
Inventors: J Kervizic; R Masic; A Shroff; R Warnecke
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1971-07-06
Filing date: 1972-06-22
Publication date: 1974-01-29
Anticipated expiration: 1991-01-29
Also published as: NL7209307A; GB1369749A; DE2233275A1; FR2145012A5

Abstract

The invention relates to ion sources having two ionization chambers and more particularly to chemical and heat resistant crucibles for use with said sources. The crucible in accordance with the invention is a hollow box of pyrolytic tungsten having two opposite openings in its lateral wall. The crucible is manufactured from a pyrolytic tungsten deposite made on a copper mandrel which is dissolved in an etching bath.

Description

United States Patent [191 Kervizic et al.

[ CRUCIBLE FOR VAPORIZING CHEMICALLY ACTIVE ELEMENTS METHOD OF MANUFACTURING THE SAME AND ION SOURCE INCLUDING SAID CRUCIBLE [75] Inventors: Jacques Kervizic; Rene Masic;

Arvind Shroff; Robert Jean Wamecke, all of Paris, France [73] Assignee: Thomson-CSF, Paris, France [22] Filed: June 22, 1972 [21] Appl. No.: 265,303

[30] Foreign Application Priority Data July 6, 1971 France 7124682 [52] US. Cl 313/63, 29/5272, 263/48, 3l3/l80,313/231 [51] Int. Cl. H0511 1/02 [58] Field Of Search 313/63, 180, 231

[111 3,789,253 [451 Jan. 29, 1974 [56] References Cited UNITED STATES PATENTS 3,631,283 12/1971 Gautherm et a1 313/231 Primary Examinerl-l. K. Saalbach Assistant Examiner-Darwin R. Hostetter Attorney, Agent, or Firm.lohn W. Malley et a].

57 I ABSTRACT The invention relates to ion sources having two ionization chambers and more particularly to chemical and heat resistant crucibles foruse with said sources.

The crucible in accordance with the invention is a hollow box of pyrolytic tungsten having two opposite openings in its lateral wall. The crucible is manufactured from a pyrolytic tungsten deposite made on a copper mandrel which is dissolved in an etching bath.

4 Claims, 6 Drawing Figures PAIENIEnJmsmm sum 3 0r 3 CRUCIBLE FOR VAPORIZING CHEMICALLY ACTIVE ELEMENTS METHOD OF MANUFACTURING THE SAME AND ION SOURCE INCLUDING SAID CRUCIBLE The present invention relates to ion sources comprising two ionization chambers and more particularly to the crucible associated with the second ionization chamber, the latter making it possible to produce ions of chemically active elements.

In ion sources, for example of the Triplasmatron type, the second ionization chamber, as described by the applicants in the US. Pat. No. 3,631,283, 9th Apr. 1968, is a metal enclosure which is integral with the first ionization chamber and which contains a reservoir or crucible holding the elements which are to be ionised.

These crucibles are generally made of graphite, quartz or molybdenum. However, in certain cases, these materials are unsuitable and this is particularly so if it is necessary to raise the elements which are to be vaporised, to high temperatures. One known solution consists in using crucibles of refractory materials, but the majority of these, in the presence of chemically active elements such as boron, form an eutectic system whose melting point is very much lower than that of the material being used.

The invention overcomes these drawbacks and its object is a crucible for vaporization of a chemically active elements comprising a hollow box of pyrolytic tungsten said box having a lateral wall and bottom and top walls said lateral wall having two openings aligned along an axis crossing said lateral wall said chemically active elements beingintroduced within said box through one of said openings.

Another object of this invention is an ion source including a crucible as aforesaid, said source comprising a first ionization chamber containing a gas G a cathode located in said first ionization chamber for emitting electrons, said electrons generating within said first chamber a primary plasma due to the collisions of said electrons with particles of said gas G a second ionization chamber containing said crucible and an extraction system for extracting ions obtained in said second ionization chamber through the interaction of said primary plasma with vaporized-particles of said elements, said vaporized particles being produced with heating means associated with said crucible the axis of said openings being aligned with the mean path of the ion beam emerging from said first ionization chamber.

For the better understanding of the invention and to show how the same may be carried into effect, reference will be made to the following description accompanying the attached drawings in which a FIG. 1 illustrates in section a crucible in accordance with the invention, the crucible being provided with a support.

FIG. 2 illustrates a crucible attached to a support in a manner differing from that shown in FIG. 1.

FIGS. 3, 4 and 5 illustrate various stages in the manufacturing of a crucible.

FIG. 6 illustrates, in section, an ion source comprising a crucible associated with heating means.

FIG. 1 shows a crucible C formed by a cylindrical hollow box having a lateral wall I and top and

bottom walls

2 and 3 made of pyrolytic tungsten, the lateral wall 1 of the box being provided with two

openings

4 and 5 arranged opposite one another and having a common axis 6. The bottom wall 3 of the crucible C is brazed to a support 7 of sintered tungsten, itself integral with a tantalum tube 9, the brazing being effected through the medium of a refractory metal 8 such for example as niobium. It is possible to replace the support 7 of sintered tungsten by a brazed molybdenum cup 10 as FIG. 2 shows.

This crucible C can be carried out in the following four stages a. Machining a cylindrical hollow copper mandrel M having external dimensions corresponding to the internal dimensions of the box forming the crucible C, the mandrel M being provided with a protruding lateral support member 11 which is a tubular member in the chosen example, as shown in FIG. 3.

b. Depositing tungsten by pyrolysis onto said mandrel. The mandrel M is introduced into a quartz tube around which an HLF. heating coil slides. The quartz tube is then evacuated down to a pressure of some few millimetres of mercury.

Hydrogen is then introduced into the quartz tube and the mandrel heated to around 6009C. Then, tungsten hexafluoride WF is for example introduced into the quartz tube, triggering the chemical reaction Fluorhydric acid formed as a consequence, is then condensed out. It is possible to use tungsten chlorides or tungsten oxychlorides as well. It is equally possible to utilise the pyrolytic reaction of an organo-metallic compound. The reaction is halted when the desired thickness of tungsten deposit 12 has been produced on the mandrel M.

c. Selectively dissolving the cylindrical copper man-- drel in nitric acid. (FIG. 4).

d. And drilling a second opening 5 in the lateral wall of the cylindrical crucible C opposite the opening 4 formed by the lateral support-member l l of the copper mandrel when the mandrel and its support-member 11 have been dissolved, the

openings

4 and 5 being aligned along an axis crossing the lateral wall and being diametrally opposite (FIG. 5). The external surface of the crucible is then finished.

In FIG. 6, an ion source of the Triplasmatronf type has been shown whose second ionization chamber 14 is equipped with a crucible C. This crucible C is fixed to the tantalum tube 9. The

openings

4 and 5 in the crucible are located along the mean path of the particle beam issuing from the first ionization chamber 20, said beam being obtained, in operation, by ionizationof the gas G contained in the first chamber, through the-collisions between the electrons emitted by the cathode H and the gas particles G The device for heating the crucible C comprises a tungsten filament l5 coiled several times. The two

ends

16 and 17 of the filament 15 are connected to a direct voltage source which has not been shown in the figure. Thiskind of filament makes it'possible to raise the crucible C to a temperature greater than 2,000 C, by electron bombardment.

Trials have been carried out with an ion source comprising a crucible charged with amorphous boron. The results obtained are given here by way of example the crucible being at ambient temperature, a beam current of A formed with He ions (the first ionization chamber 20 containing helium), was measured at the output of the ion source. On raising the temperature of the crucible to 1,800 C, the total current at the output of the ion source remained constant but the proportion of He ions decreased in favour of B ions which made up around 5 percent of the total current.

at around 2,000 C, with a total current still equal to 1 l0 uA, the proportion of B ions in the particle beam was 16 percent.

at 2,l50 C, the proportion of B ions was 28 percent.

finally at 2,250" C, the beam current of 150 A was obtained, essentially composed of B ions (94 percent), the l-le ions making up around 5.5 percent.

These extremely significant results, not hitherto attainable with the conventional means since the latter do not enable boron to be raised to a sufficiently high temperature, show the advantage which is presented by a crucible of homogeneous pyrolytic tungsten, containing no bubbles or microscopic cracks, as described.

What we claim is: p

1. An ion source comprising a first ionization chamber containing a gas G a cathode located in said first ionization chamber for emitting electrons, said electrons generating within said first ionization chamber a primary plasma due to the collisions of said electrons with particles of said gas G a-second ionization chamber; a crucible within said second ionization chamber for vaporization of chemically active elements, said crucible comprising a hollow box of pyrolitic tungsten, said box having a lateral wall and bottom and top walls, said lateral wall having two openings aligned along an axis crossing said lateral wall, said chemically active elements being introduced within said box through'one of said openings and an extraction system for extracting ions obtained in said second ionization chamber through the interaction of said primary plasma with vaporized particle of said elements, said vaporized particles being produced with heating means associated with said crucible the axis of said openings being aligned with the mean path of the ion beam emerging from said first ionization chamber.

2. An ion source as claimed in claim 1, wherein said chemically active element contained in said crucible is boron.

3. An ion source comprising a first ionization chamber containing a gas G a cathode located in said first ionization chamber for emitting electrons, said electrons generating within said first chamber a primary plasma due to the collisions of said electrons with particles of said gas G a second ionization chamber; a crucible within said second ionization chamber for vaporization of chemically active elements, said crucible comprising a cylindrical hollow box of pyrolitic tungsten having a revolution axis said box having a lateral wall and bottom and top walls, said lateral wall having two openings aligned along an axis crossing said lateral wall, said chemically active elements being introduced within said cylindrical hollow box through one of said openings and an extraction system for extracting ions obtained in said second ionization chamber through the interaction of said primary plasma with vaporized particles of said elements, said vaporized particles being produced with heating means associated with said cylindrical crucible said axis of said openings formed in the lateral wall of said cylindrical crucible being aligned with the mean path of the ion beam emerging from said first ionization chamber, said mean path and said axis being perpendicular with said revolution axis of said cylindrical crucible.

4. An ion source as claimed in claim 3, wherein said chemically active element contained in said cylindrical crucible is boron.

Claims

2. An ion source as claimed in claim 1, wherein said chemically active element contained in said crucible is boron.
3. An ion source comprising a first ionization chamber containing a gas G1 ; a cathode located in said first ionization chamber for emitting electrons, said electrons generating within said first chamber a primary plasma due to the collisions of said electrons with particles of said gas G1 ; a second ionization chamber; a crucible within said second ionization chamber for vaporization of chemically active elements, said crucible comprising a cylindrical hollow box of pyrolitic tungsten having a revolution axis ; said box having a lateral wall and bottom and top walls, said lateral wall having two openings aligned along an axis crossing said lateral wall, said chemically active elements being introduced within said cylindrical hollow box through one of said openings ; and an extraction system for extracting ions obtained in said second ionization chamber through the interaction of said primary plasma with vaporized particles of said elements, said vaporized particles being produced with heating means associated with said cylindrical crucible ; said axis of said openings formed in the lateral wall of said cylindrical crucible being aligned with the mean path of the ion beam emerging from said first ionization chamber, said mean path and said axis being perpendicular with said revolution axis of said cylindrical crucible.
4. An ion source as claimed in claim 3, wherein said chemically active element contained in said cylindrical crucible is boron.