US3020431A

US3020431A - Ion source and plasma generator

Info

Publication number: US3020431A
Application number: US697679A
Authority: US
Inventors: Eugene F Martina
Original assignee: American Radiator and Standard Sanitary Corp
Current assignee: American Radiator and Standard Sanitary Corp
Priority date: 1957-11-20
Filing date: 1957-11-20
Publication date: 1962-02-06
Anticipated expiration: 1979-02-06
Also published as: FR1207999A; BE573103A

Description

Feb. 6, 1962 E. F. MARTINA 3,020,431

10N souRcE AND PLASMA GENERATOR Filed Nov. 2o, 1957 s sheets-sheet 1 v 1NVENToR. Eugene E Martma Attorney 5 Sheets-Sheet 2 JNVENTOR' Eugene F Martina Attorney E. F. MARTINA ION SOURCE AND PLASMA GENERATOR Feb. 6, 1962 Filed Nov. 20, 1957 eooreui 3:22a noo 953.21 o Envoi N o e Q o.. f U/f/O/ w/////////////// W -N //H/ m7 mm. ff m .e A ////,//////////H/ Q \\\\\HM.HU.ll/l/ f q. M /f/H/ .No .w wm I9 .SW W. v, m ,//f//l/J/LHM Q v Q N .A NV

Feb. 6, 1962 E. F. MARTINA 3,020,431

ION SOURCE AND PLASMA GENERATOR l Filed Nov. 20, 1957 5 Sheets-Sheet 5 D3 355 30. on. LL l INVENTOR. Eugene E Martina BY @QM Attorney equipment, including special power supplies.

nite States 3,020,431 Patented Feb. 6, 1962 can Radiator & Standard Sanitary Corporation, a corporation of Delaware Filed Nov. 2t), 1957, Ser. No. 697,679 13 Claims. (Cl. 313-63) This invention relates to ion sources and to methods and devices for producing ions. More particularly it pertains to a novel process and device for producing a pulse of ions of high intensity for short periods of time which is simple, rugged, reliable and of relatively small dimensions.

Ions of the type produced by this invention have many uses in pure applied research in connection with particle accelerators, reactor physics `and fusion vas well as practical applications in the iields of instrumentation, isotope separation, geophysical exploration and many others connected with nuclear physics and atomic energy.

ion sources of the type covered by this invention utilize an electric arc or glow discharge to produce a plasma of ionized gas. In conventional sourcesl of this type a lilament and electro-magnet are often used to maintain the are, necessitating considerable extra and troublesome In others, beta emitting nuclear sources lare utilized but these either have a limitedrlifetime or are hazardous to use as Well as not easily controlled. In existing devices, moreover, either the intensity of the ion beam or the useful llife of the device is limited or else it must be of relatively large size. Devices such as these are covered by Crawford Patent 2,764,707 and Laurence Patent 2,785,311.

It isy consequently an object of my invention to provide anion source which would be simple and rugged.

It is a further object of my invention to provide an ion source of relatively small dimensions. v

lt is another object of my invention to provide an ion source which would 'produce a high intensity pulsed beam of ions having a relatively long useful life.

ment known as an emitter, the walls of which are permeable to the gas, at the same time that a pulsed electrical current is caused to iiow through the Walls of the emitter so that the heating action of the current aids the diffusion vof the gas through the walls. The opposite side of the chamber is surrounded by an evacuated vessel, the pressure in which s caused to increase by the leakage of gas through the walls of the chamber. The pressure close to the emitter rises until a voltage breakdown occurs, generating an arc plasma on the surface of the emitter.

More particularly referring to the accompanying iigures, 11 is the body of the ion source which may be made of copper, stainless steel or other suitable metal and 12 is a reservoir containing a supply of the gas to be ionized, which may be hydrogen or one of its isotopes, deuterium or tritium, although other gases maybe used. The reservoir 12 connects by means of the gas tube 13 to the ion emitter 14. The latter is formed from a metal belonging to the so-called transition group such as palladium, zirconium, titanium, tantalum or others having the characteristic of being permeable to certain gases.

The gas tube 13 is supported in the body 11 by the insulating tube` 15 which may 4be of magnesium oxide or other insulating and refractory material.' i

One end of the emitter 14 is'V supported by the metal spider 16 while the tube 11 is joined to vacuum tank wall 17 to which'is attached also the ion duct 18. The latter two items may be components of a cyclotron, linear accelerator or other related devicef f All metallic joints are made by soldering, brazing,

V weldingor otherv similar process adapted to ,the lmetals It is still another object of my invention to providev an 'l ion vsource which can be easily regulated and controlled without the use of elaborate electrical circuitry and magnetic fields.

t is yet another object of my invention to provide an ion source which utilizes the permeability of some metals to certain gases sought to be ionized by supplying one of said gases from an external source to one surface of said permeable metal,'rnaintaining a vacuum on a second surfacev of said permeable metal, applying a high diierence of potential to said metal, therebycausing a diiusion of said gas through said metal, resulting in a decrease in vacuum on said second surface causing anlelectric arc discharge on said second surface, thereby producing ions of the said gas. l i

Various other objects and advantages of my invention will be apparent to those skilled in the art from a study of the following description and` accompanying drawings wherein:

FIG. 1 is a longitudinal section showing the complete assembly of one embodiment of the invention.

v FIG. 2 is an enlarged section and end view of the ion emission end of the device.

FIG. 3 is a curve showing the relation'between breakdown potential and the product of pressure and gap distance for the embodiment shown in FIGURE 1 in accordance with Paschens Law.

FIG. 4 is a longitudinal section showing an alternate embodiment for eecting the objectives of lthe invention.

In general, according to my invention the gas to be ionized is caused to be compressed into a chamber or ele- A power supply Aconsisting of a source of high voltagel pulsed current is connected tov the gas tube `13 and vacuum tank wall 17 as showni y v In vthe embodiment shown 'on FlGfl, I, have used a copper reservoir 12 of Ispherical shape approximately' 11/2 in diameter, a body 11 of copper 3/s" in diameter and 1%." long,` and a palladium emitter .028 inside diameter by .032" outside diameter `by .125 effective length. The ion duct 18 is 11/2 in diameter and extends 2" beyond the'end of tube 18. The area reprmented by 22 is maintained under a vacuum of 10.5v mm. of mercury by a suitable p'ump not shown. l

In the operation ot the above embodiment, deuterium gas 20 is supplied toreservoir 12 at a pressure. of 200 lbs.

into the vacuum space 22. The result is to increase the absolute pressure as shown at 21, FIG. 2. Forthe embodiment shown, when the pressure reaches 1.5 mm. of mercury an arc-over yor breakdown 23 will take place along the emitter 14. The breakdown potentialis a unction of the pressure and iength of the gap in accordance with Paschens Law previously mentioned. For the embodiment shown I have found these values to be as shown on the curveFIG. 3.

Vi have measured the ions produced by the arc Plasma 23 and found that they have average energies of 2 electron volts and arrive at the end of the Vion duct 1 microsecond before ,the gas moleculesl do. I have measured also the output of deuterons per microsecond pulse and found it to be 1015 ions.

I have found still further that with the embodiment shown and described above I can produce 10 pulses per second and using the gas supply as shown, I can produce approximately 1,000,000 pulses, thus providing continuous operation of the device for well over 24 hours despite the fact that the greatest dimension of my device is not over 6".

In the alternate embodiment shown in FIG. 4, I introduce the gas to be ionized around the outside of an emitter chamber 14. In this embodiment I utilize a rod 41 of copper or other suitable conducting material to connect the emitter `145 with the power supply through a special insulator 42, a bushing 43 and a seal 44.

The operation of this alternate embodiment is very similar to that described above with the principal exception that the gas to be ionized diffuses from the outer to the inner surface of the emitter and the are plasma is consequently generated on the latter. I thus utilize the nozzle effect of the emitter, which may be of any convenient geometry, to help discharge the ions into the duct 18. With this embodiment I still retain the large ion extraction area which is an important feature of my invention.

Although I have described a preferred embodiment of my invention and have thus illustrated the operation of the process, many modifications will be obvious to those skilled in the art and, therefore, I do not limit myself to the details and arrangements shown here, exceptas I do so by the claims which follow.

What I claim is:

l. An ion source comprising a chamber at least one wall of which is composed of a metal permeable to a gas sought to be ionized, means of directing said gas to one surface of said wall, means of maintaining a high vacuum at a second surface of said wall, means of applying a high difference of potential between two points on said second surface, said points being so spaced as to cause rapid diffusion of said gas through said wall and create a sudden increase in pressure at said second surface, thereby causing an electric arc discharge of short duration between the two said points on said second surface.

2. The ion source of claim 1 wherein the gas sought to be ionized is an isotope of hydrogen selected from the group consisting of hydrogen, deuterium and tritium.

3. The ion source of claim l wherein the metal permeable to a gas sought to be ionized is selected from the group consisting of palladium, zirconium, titanium and tantalum.

4. A plasma generator comprising a chamber at least one wall of which is permeable to a gas sought to be ionized, means of directing said gas to one surface of said permeable wall, means of maintaining a vacuum on another surface of said wall, means of applying a difference of potential between two points on said wall, means of controlling said potential and said vacuum so that an arc plasma is formed on one surface.

5. An ion source comprising a chamber at least one wall of which is permeable to gas sought to be ionized, means of directing said gas to one surface of said permeable Wall, means of maintaining a vacuum on another surface of said wall, means of applying a difference of potential between two points on said wall, means of controlling said potential and said vacuum so that an arc plasma is formed on one surface, means of removing the ions so formed.

6. A plasma generator comprising a chamber at least one wall of which is permeable to a gas sought to be ionized, means of directing said gas to one surface of said permeable wall, means o f maintaining a vacuum on another surface of said permeable wall, means of applying a difference of potential between two points on said wall whereby diffusion of said gas through said wall produces an arc plasma on one surface of said wall.

7. An ion source comprising a chamber at least one wall of which is permeable to a gas sought to be ionized, means of directing said gas to one surface of said permeable wall, means of maintaining a vaccurn on another surface of said permeable wall, means of applying a difference of potential between two points on said wall, whereby diffusion of said gas through said wall vproduces an arc plasma on one surface of said wall, means of removing the ions so formed.

8. An ion source comprising a hollow chamber permeable to a gas sought to be ionized, an external source of said gas, means of directing said gas to one side of said hollow chamber, means of maintaining a vacuum on another side of said chamber, means of applying a difference of potential between two points on said chamber, so arranged that diffusion of said gas from said chamber produces an electrical discharge on onesurface of said chamber.

9. The ion source of claim 8 in which the means of applying adilerence of potential between two points on a permeable chamber comprises a pulse forming network adapted to provide a source of high potential pulsed current to said chamber.

10. A method of producing an are plasma comprising means of introducing a gas sought to be ionized to the surface of a wall of a chamber, said wall being composed of a material permeable to said gas, means of maintaining a vacuum on an opposite surface of said wall, means of applying a difference of potential between two points on said wall so that said gas is caused to diffuse through said wall and form an arc plasma on said opposite surface of said wall.

ll. A method of producing ions comprising means of introducing a gas `sought to be ionized to the surface of a Wall of a chamber, said wall being composed of a material permeable to said gas, means of maintaining a vacuum` on an 4Opposite surface of said wall, means of applying a difference of potential between two points on said wall so `that said gas is caused to diffuse through said wall and form an arc plasma on said lopposite surface of said wall and means for removing the ions so formed.

l2. In a method for producing an arc plasma involving the diffusion of an ionizable gas through a permeable metal the improvement comprising an externalsource of supply of said gas, means of maintaing a vacuum on one surface of said metal, means of applying a difference of potential to said metal, means of controlling `said po tential and said vacuum so that an arc plasma is formed on said surface of said metal.

13. In av method for producing ions involving the diffusion of an ionizable gas` through a permeable metal the improvement comprising an external source of supply of said gas, means of maintaining a vacuum on one sur` face of said metal, means of applying a difference of potential to said metal, means of controlling said poten tial and said vacuum so that an arc plasma is formed on said surface of said metal and means of removing the ions so formed` References Cited in the le of this patent UNITED STATES PATENTS 2,677,061 Wilson Apr. 27, 1954 2,817,032 Batteau Dec. 17, 1957 2,826,708 Foster Mar. 1l, 1958 2,831,996 Martina Apr. 22, 1958