US3235170A

US3235170A - Getter supply

Info

Publication number: US3235170A
Application number: US255333A
Authority: US
Inventors: Carl G Thoresen
Original assignee: Consolidated Vacuum Corp
Current assignee: Consolidated Vacuum Corp
Priority date: 1963-01-31
Filing date: 1963-01-31
Publication date: 1966-02-15
Anticipated expiration: 1983-02-15

Description

United States Patent M 3,235,170 GETTER SUPPLY Carl G. Thoresen, Hilton, N.Y., assignor to Consolidated Vacuum Corporation, a corporation of New York Filed Jan. 31, 1963, Ser. No. 255,333 Claims. (Cl. 230-69) The present invention relates to getter supplies and, more particularly, to getter supplies for ionization vacuum pumps and to ionization vacuum pumps incorporating such getter supplies.

Ionization vacuum pumps are well known in the art and are sometimes also referred to as ionic vacuum pumps or getter-ion vacuum pumps, for instance.

Pumps of this general type usually include means for causing ionization of residual gas molecules present in a vacuum space and means for collecting or entrapping such ionized gas molecules. Frequently, these pumps are provided with a supply of getter material for aiding the collection or entrapment of the ionized gas molecules, such as on a suitable collector surface.

The getter supply means so far developed for this type of pump had either but a restricted capacity or were complicated and expensive.

The present invention provides a getter supply which is simple and inexpensive, is capable of providing a large amount of getter material in a continuous or intermittent operation, and is easily replenished with fresh getter material, when necessary.

The getter supply of the invention comprises a coiled heat-resistant Wire defining a basket structure having a substantially closed lower end, an open upper end and an internal cavity extending from such open upper end to the substantially closed lower end. A body of getter material is inserted in the aforesaid basket structure through the open upper end thereof and extends through the abovementioned cavity to the lower end of the basket structure. Expressed in other words, the body of getter material is partially surrounded by the turns of the aforesaid coiled wire and is held by the basket structure formed by such coiled wire.

The getter supply according to the invention includes means for heating the basket structure and the body of getter material. These heating means are effective at the lower end of the basket structure, so that the getter material present at and in the vicinity of such lower basket end is melted and is evaporated into the space of the aforesaid envelope.

Due to the unique basket structure of the invention, the melted getter material is able to pass through the turns of the aforesaid coiled Wire and is evaporated therefrom. Material which is evaporated inside the basket structure is also able to pass through such wire turns. It will be noted that the basket structure according to the invention also has the advantage of permitting use of relatively simple bodies of getter material that are easily manu factured.

During operation of the getter supply, the body of getter material will simultaneously move by force of gravity to the lower end of the basket structure, as the getter material of such body present at this lower end is The coiled heat-resistant wire of the aforesaid basket structure is made of a material that has a melting point higher than the temperature of evaporation of the getter material employed and that will not be damaged by con- .tinued evaporation of the getter material. While many 3,235,17h Patented Feb. 15, 1966 drical, so that it will substantially fill and easily slide in the basket structure.

The body of getter material may consist of one or more of the'well known getter materials as used in ionization vacuum pumps. In a preferred embodiment of the invention, I use a body of titanium as the body of getter material.

However, it should be understood that other getter materials, such as barium, cerium, tantalum, zirconium and any material that is capable of entrapping gas molecules and that does not form compounds which con taminate the vacuum space could be used.

Various means for heating the lower basket structure and the body of getter material in the manner mentioned above may be employed.

In a preferred embodiment, I use a filament structure which substantially encompasses the basket structure at the lower end thereof, together with means for energizing and heating the filament and for establishing a potential between the filament and the basket structure to cause electron bombardment of the lower end portion of the of the aforesaid body present thereat is melted and evaporated.

From another aspect thereof, the invention resides in an ionization vacuum pump having a getter supply with a basket structure of the aforesaid type incorporated therein.

Thus, an ionization vacuum pump in accordance with a preferred embodiment of the invention comprises an envelope for confining an evacuated space containing residual gas molecules, such as an envelope adapted to be connected to a pre-evacuated vacuum vessel. The pump includes means located in such envelope for ionizing the residual gas molecules present therein. These ionizing means may comprise an anode structure, such as a cellular anode of the type comprising a plurality of cell elements, and means for releasing electrons to such anode structure, or for establishing an electric discharge in the vicinity of molecules present in the envelope. The pump further may include means, such as a collector electrode, defining at least one surface in the envelope for collecting the ionized gas molecules. The getter supply according to the invention is also disposed in the aforesaid envelope to supply molecule-entrapping getter material into the space within the envelope or at least to the latter collecting surface or collector electrode.

The subject getter supply is also applicable to pumps comprising sputter-electrode means located in the vicinity of the latter collecting surface for releasing sputtered material to the collecting surface in response to bombardment of ionized molecules traveling to such collecting surface. Various vacuum pumps including such sputter-electrode means are described in application Serial No. 815,352, filed May 25, 1959, for Cold-Cathode Discharge Ion Pump, by Wilson M. Brubaker et al., and assigned to the subject assignee.

I have found that the incorporation of a getter supply in accordance with the subject invention in pumps of the type described in the aforesaid application results in a remarkably increased pumping speed.

The invention will become more readily apparent from the following detailed description of a preferred embodi ment thereof, illustrated by way of example in the accompanying drawings, in which:

FIG. 1 is a side view, in section, of a vacuum pump embodying the invention; and

FIG. 2 is a view along line IIII in FIG. 1.

The vacuum pump shown in FIGS. 1 and 2 has an enclosure or housing having a pipe or nipple member 11 for connection of the space within housing 10 to a vacuum space, such as to the space within a pre-evacuated vacuum vessel (not shown).

Housing 10 is preferably made of glass or metal and, in FIGS. 1 and 2, has been shown as being made of metal.

Housing 10 defines a main space 12 and a lateral wing space 13 adjoining such main space.

Located in main space 12 is a getter supply 15 according to the invention.

Getter supply 15 comprises a coiled tungsten Wire 16 which is wound to define a substantially hollow-cylindrical basket structure 17 having an open end 18 and a substantially closed end portion 19. The term substantially closed is used herein in view of the fact that the turns of coiled wire 16 have, of course, small passages from the inside to the outside of basket structure 17 located therebetween.

Basket structure 17 is mounted at its lower end portion 19 to a mounting and terminal post 21. This accomplished by winding a few turns 22 of wire 16 around post 21. These turns 22 may be welded to post 21. Post 21 extends through a feed-through and sealing bushing 23 of a suitable insulating material, such as glass, to the outside of housing 10.

A cylindrical body or slug 24 of titanium or other suitable getter material is located in basket structure 17.

A substantially circular filament structure 26 encompasses the lower portion 19 of basket structure 17. Filament structure 26 is mounted on a pair of mounting and

terminal members

28 and 29 which extend through feedthrough bushings 3t) and 31 to the outside of housing 10. Additional mounting members (not shown) may be used to mount and retain filament structure 26 in its shown position.

Located in lateral wing space 13 of housing 10 are a pair of

collector electrodes

35 and 36 having a pair of confronting

molecule collecting surfaces

37 and 38. In the shown embodiment,

collector electrodes

35 and 36 are directly mounted on and in contact with portions of metallic housing 10. If desired,

collector electrodes

35 and 36 may, however, be insulated from housing 10.

Disposed between

collector electrodes

35 and 36 is an anode structure 40. In the embodiment shown, this anode structure 40 is of the cellular type described in the aforesaid application.

A first cellular sputter-electrode structure 42 is disposed between anode 40 and collector electrode 35, and a second cellular sputter-electrode structure 43 is disposed between anode 40 and collector electrode 36. The nature and function of sputter electrodes or sputter elements of the type of sputter electrodes 42 and 43 is described in the aforesaid application. Briefly, the sputter electrodes 42 and 43 are effective to release molecule-entrapping sputtered material to

collector surfaces

37 and 38. Such release of sputtered material is brought about by ionized gas molecules which strike the sputter electrodes 42 and 43. As has been pointed out in the aforesaid application, these sputter electrodes may be made of a chemically inactive material, such as stainless steel, or, if desired, of a getter material.

Anode structure 40 is mounted on a mounting and terminal member 50 which extends through a feed-through bushing 51 to the outside of housing 10. Sputter electrodes 42 and 43 are mounted, respectively, on mounting and

terminal members

53 and 54 which extend through;

bushings 55 and 56 to the outside of housing 10. Additional mounting means (not shown) may, of course, be

-tion 19 of basket structure 17 will result.

4 employed for mounting anode 40 and sputter electrodes 42 and 43 in their shown position.

During operation of the pump, an electric discharge is established in the vicinity of anode structure 40 to ionize the residual gas molecules present in housing 10. Thus, the anode structure 40 may be positively biased by power sources 60 and 61 connected to

terminal member

50, 53, and 54 and metallic housing 10 as shown in FIG. 1. In this case, the sputter electrodes 42 and 43 will be negatively biased with respect to anode 40 so that some of the ionized molecules will impinge on sputter electrodes 42 and 43.

Collector electrodes

35 and 36 will be negatively biased with respect to anode 40 and sputter electrodes 42 and 43 so that the majority of the ionized gas molecules will travel through the cellular sputter electrodes 42 and 43 to the collector surfaces 37 and 38.

It should, of course, be understood that the application of potentials to anode 40, sputter electrodes 42 and 43 and

collector electrodes

35 and 36 by power sources 60 and 61 as illustrated is intended to be by way of example only. Thus, the application of bias potential to these electrodes may be carried out in a different manner. In fact, it has been found that a pumping action will also result if

collector electrodes

35 and 36 do not carry a high negative potential with respect to anode 40. It is believed that in this case the sputter electrodes 42 and 43 will release electrons to the anode structure 40, which electrons will strike and ionize residual gas molecules, and that such residual gas molecules will have sufficient energy to reach

collector surfaces

37 and 38. It will, therefore, be appreciated that the sputter electrodes 42 and 43 and the

collector electrodes

35 and 36 may jointly serve as electron-releasing cathode with respect to anode 40, or that such cathode function may also be performed substantially by sputter electrodes 42 and 43 alone.

As is well known, the paths of the electrons traveling to anode 40 may be extended by means of a magnetic field causing such electrons to travel in substantially helical paths, so that the probability that such electrons will strike and ionize residual gas molecules is increased. Such magnetic field may be established by means of permanent magnet 63 having pole faces 64 and 65 as shown, or by means of a similarly shaped electromagnet.

During operation of the pump, filament structure 26 is energized and heated, such as by means of heating current source 67 connected to

terminal members

28 and 29 as shown in FIG. 1. Basket structure 17 is biased positively with respect to filament structure 26, such as by means of a high voltage source 69 connected to terminal post 21 and terminal member 31 as shown in FIG. 1.

Filament structure 26 will thus bombard basket structure 17 and especially the lower end portion 19 thereof with electrons, so that heating of the lower end portion 19 of basket structure 17 and also of the titanium body or slug 24 and especially of the lower end thereof at por- This electron bombardment is continued until the material of titanium body 24 in the vicinity of lower end portion 19 will melt and evaporate.

While some of this titanium material may evaporate inside basket structure 17 and escape through the turns of wire 16, it is believed that most of the titanium material will pass such wire turns in the molten state and will be evaporated from the surface of basket structure 17.

, At any rate, the evaporated titanium material will travel substantially radially from basket structure 17. In

consequence, some of the evaporated titanium will coat the walls of housing 10 in the area of main space 12 and part of the evaporated titanium will be projected into lateral wing space 13.

The material evaporated into main space 12 will be effective to getter and entrap some of the residual gas molecules present therein, while the material evaporated into wing space 13 will significantly assist the moleculeentrapping operation taking place in wing space 13 due to the action of anode 40, sputter electrodes 42 and 43 and

collector electrodes

35 and 36. Thus, the evaporated or vaporized titanium material projected into wing space 13 will, for instance, be able to form a molecule-entrapping surface layer on

collector electrodes

35 and 36.

It will be readily appreciated that the titanium body for slug 24 will move by force of gravity toward the lower end portion 19 of basket structure 17 as material is melted and evaporated from the lower end of titanium body or slug 24.

If the titanium body or slug 24 is used up, the getter supply 15 is readily reactivated by inserting a fresh body or slug of titanium into basket structure 17. To this end, housing is provided with a removable cover or lid 80 which is fastened to a flange portion 81 of housing 10 by nut and bolt arrangements 82. A sealing member 85',

such as a conventional sealing ring, is interposed between flange portion 81 and lid 80 to assure a vacuum tight seal.

Depending on the capacity of the pump and on the desired pumping speed, the getter supply may be activated permanently or intermittently during the operation of the pump.

It will be readily appreciated that various modifications of the shown embodiment within the scope of the invention will be possible.

Thus, the housing 10 may be shaped to define more than one lateral wing portion and an ionization vacuum pump system may be located in each such wing portion. Alternatively, the housing 10 may be shaped to define a circumferentially' extending wing portion and the elements of the ionization pump system may be shaped to encompass the getter supply 15.

Also, the getter supply of the invention could be employed with ionization pump systems diiferent from that shown in FIGS. 1 and 2, such as with ionization pump systems having no sputter electrodes of the type of elec trodes 42 and 43.

Other applications of the getter supply of the invention and variations within the scope of the invention will be apparent to those skilled in the art.

I claim:

1. A getter supply for an ionization vacuum pump. comprising a coiled heat-resistant wire defining a basket structure having a substantially closed lower end, an open upper end and an internal cavity extending from said open upper end to said substantially closed lower end, a body of getter material inserted in said basket structure through said open upper end to extend through said cavity to said lower end of said basket structure, and means for heating said basket structure and said body of getter material at said lower end of said basket structure to cause melting and evaporation of the getter material of the body present at said lower end of the basket structure and simultaneous movement of said body of getter material towards said lower end of said basket structure.

2. A getter supply for an ionization vacuum pump, comprising a coiled heat-resistant wire defining a substantially hollow-cylindrical basket structure having a substantially closed lower end and an open upper end, a substantially cylindrical body of getter material inserted in said basket structure through said open end to extend to said lower end of said basket structure, and means for heating said basket structure and said body of getter material at said lower end of said basket structure to cause melting and evaporation of the getter material of the body present at said lower end of the basket structure and simultaneous movement of said body of getter material towards said lower end of said basket structure.

3. A getter supply for an ionization vacuum pump, comprising a coiled heat-resistant wire defining a substantially hollow-cylindrical basket structure having a substantially closed lower'end and an open upper end, a substantially cylindrical body of titanium inserted in said basket structure through said open end basket structure, arid means closed lower end and an open upper end,

6 for heating said basket structure and said body of titanium at said lower end of said basket structure to cause evaporation of the titanium present at said lower end of the basket structure and simultaneous movement of said body of titanium towards said lower end of said basket structure.

4. A getter supply for an ionization vacuum pump, comprising a coiled Wire of tungsten defining .a substantially hollow-cylindrical basket structure having a substantially closed lower end and an open upper end, a substantially cylindrical body of getter material inserted in said basket structure through said open end to extend to said lower end of said basket structure, and means for heating said basket structure and said body of getter material at said lower end of said basket structure to cause evaporation of the getter material of the body present at said lower end of the basket structure and simultaneous movement of said body of getter material towards said lower end of said basket structure.

5. A getter supply for an ionization vacuum pump, comprising a coiled wire of tungsten defining a substantially hollow-cylindrical basket structure having a substantially closed lower end and an open upper end, :a substantially cylindrical body of titanium inserted in said basket structure through said open end to extend to said lower end of said basket structure, and means for heating said basket structure and said body of titanium at said lower end of said basket structure to cause evaporation of the titanium present at said lower end of the basket structure and simultaneous movement of said body of titanium towards said lower end of said basket structure.

6. A getter supply for an ionization vacuum pump, comprising a coiled wire of tungsten defining a substantially hollow-cylindrical basket structure having a substantially a substantially cylindrical body of titanium inserted in said basket structure through said open end to extend to said lower end of said basket structure, a substantially circular filament spaced from said basket structure and substantially encompassing said basket structure at said lowerend thereof, and means for energizing said filament and for establishing a potential between said filament and said basket structure to cause electron bombardment of said basket structure at said lower end and evaporation of the titanium present at said lower end and simultaneous: movement of said body of titanium towards said lower end of the basket structure.

7. An ionization vacuum pump comprising an envelope for confining an evacuated space containing residual gas molecules, means in said envelope for ionizing said residual gas molecules, a coiled heat-resistant wire in said envelope defining a basket structure having a substantially closed lower end, an open upper end and an internal cavity extending from said open upper end to said substantially closed lower end, a body of getter material inserted in said basket structure through said open upper end to extend through said .cavity" to said lower end, and means for heating said basket structure and said body of getting material at said lower end of said basket structure to cause evaporation of the getter material of the body present at said lower end of the basket structure in to the space within said envelope and simultaneous movement of said body of getter material towards said lowerend of said basket structure, the evaporated getter material being effective to entrap said ionized gas molecules.

8. An ionization vacuum pump comprising an envelope for confining an evacuated space containing residual gas molecules, an anode structure in said envelope, means for releasing electrons to said anode structure to cause ionization of said gas molecules, means defining at least one surface in said envelope for collecting the ionized gas molecules, and means in said envelope for supplying ion-entrapping getter material at least to said collecting surface, said means for supplying said getter material including a coiled heat-resistant wire defining a basket structure having a substantially closed lower end, an open upper end and an internal cavity extending from said open upper end to said substantially closed lower end, a body of getter material inserted in said basket structure through said open upper end to extend through said cavity to said lower end of said basket structure, and means for heating said basket structure and said body of getter material at said lower end of said basket structure to cause melting and evaporation of the getter material of the body present at said lower end of the basket structure and simultaneous movement of said body of getter material towards said lower end of said basket structure.

9. An ionization vacuum pump comprising an envelope .for confining an evacuated space containing residual gas molecules, an anode structure in said envelope, means for releasing electrons to said anode structure to cause ionization of said gas molecules, means defining at least one surface in said envelope for collecting the ionized gas molecules, and means in said envelope for supplying ion-entrapping getter material at least to said collecting surface, said means for supplying said getter material including a coiled wire of tungsten defining a substantially hollow-cylindrical basket structure having a substantially closed lower end and an open upper end, a substantially cylindrical body of titanium inserted in said basket structure through said open end to extend to said lower end of said basket structure, and means for heating said basket structure and said body of titanium at said lower the ionized gas molecules, and means in said envelope for supplying ion-entrapping getter material at least to said collecting surface, said means for supplying said getter material including a coiled heat-resistant wire defining a basket structure having a substantially closed lower end, an open upper end and an internal cavity extending from said open upper end to said substantially closed lower end, a body of getter material inserted in said basket structure through said open upper end to extend through said cavity to said lower end of said basket structure, and means for heating said basket structure and said body of getter material at said lower end of said basket structure to cause melting and evaporation of the getter material of the body present at said lower end of the basket structure and simultaneous movement of said body of getter material towards said lower end of said basket structure.

11. An ionization vacuum pump comprising an envelope for confining an evacuated space containing residual gas molecules, a cellular anode structure in said envelope, means for releasing electrons to said anode structure to cause ionization of said gas molecules, means defining at least one surface in said envelope for collecting the ionized gas molecules, and means in said envelope for supplying ion-entrapping getter material at least to said collecting surface, said means for supplying said getter material including a coiled wire of tungsten defining a substantially hollow-cylindrical basket structure having a substantially closed lower end and an open upper end, a substantially cylindrical body of titanium inserted in said basket structure through said open end to extend to said lower end of said basket structure, and means for heating said basket structure and said body of titanium at said lower end of said hasket structure to cause evaporation of the titanium present at said lower end of the basket structure and simultaneous movement of said body of titanium towards said lower end of said basket structure.

12. An ionization vacuum pump comprising an envelope for confining an evacuated space containing residual gas molecules, an anode structure in said envelope, means for releasing electrons to said anode structure to cause ionization of said gas molecules, means defining at least one surface in said envelope for collecting the ionized gas molecules, sputter-electrode means located in the vicinity of said collecting surface to release sputtered material to said collecting surface in response to bombardment by ionized gas molecules traveling to said collecting surface, and means in said envelope for supplying ion-entrapping getter material to the area occupied by said collecting surface and said sputter-electrode means, said means for supplying said getter material including a coiled heat-resistant wire defining a basket structure having a substantially closed lower end, an open upper end and an internal cavity extending from said open upper end to said substantially closed lower end, a body of getter material inserted in said basket structure through said open upper end to extend through said cavity to said lower end of said basket structure, and means for heating said basket structure and said body of getter material at said lower end of said basket structure to cause melting and evaporation of the getter material of the body present at said lower end of the basket structure and simultaneous movement of said body of getter material towards said lower end of said basket structure.

13. An ionization vacuum pump comprising an envelope for confining an evacuated space containing residu al gas molecules, an anode structure in said envelope, means for releasing electrons to said anode structure to cause ionization of said gas molecules, means defining at least one surface in said envelope for collecting the ionized gas molecules, sputter-electrode means located in the vicinity of said collecting surface to release sputtered material to said collecting surface in response to bombardment by ionized gas molecules traveling to said collecting surface, and means in said envelope for supplying ionentrapping getter material to the area occupied by said collecting surface and said sputter-electrode means, said means for supplying said getter material including a coiled wire of tungsten defining a substantially hollowcylindrical basket structure having a substantially closed lower end and an open upper end, a substantially cylindrical body of titanium inserted in said basket structure through said open end to extend to said lower end of said basket structure, and means for heating said basket structure and said body of titanium at saidlower end of said basket structure to cause evaporation of the titanium present at said lower end of the basket structure and simultaneous movement of said body of titanium towards said lower end of said basket structure.

14. An ionization vacuum pump comprising an envelope for confining an evacuated space containing residual gas molecules, a cellular anode structure in said envelope, means for establishing an electric discharge in the vicinity of said anode structure to cause ionization of said gas molecules, means defining at least one surface in said envelope for collecting the ionized gas molecules, at least one cellular sputter-electrode structure located in the vicinity of said collecting surface to release sputtered material to said collecting surface in response to bombardment by ionized gas molecules traveling to said collecting surface, and means in said envelope for supplying ionentrapping getter material to the area occupied by said collecting surface and said cellular sputter-electrode structure, said means for supplying said getter material includinf a coiled heat-resistant wire defining a basket structure having a substantially closed lower end, an open upper end and an internal cavity extending from said open upper end to said substantially closed lower end, a body of getter material inserted in said basket structure through said open upper end to extend through said cavity to said lower end of said basket structure, and means for heating said basket structure and said body of getter material at said lower end of said basket structure to cause melting and evaporation of the getter material of the body prescut at said lower end of the basket structure and simultaneous movement of said body of getter material towards said lower end of said basket structure.

15. An ionization vacuum pump comprising an envelope for confining an evacuated space containing residual gas molecules, a cellular anode structure in said envelope, means for establishing an electric discharge in the vicinity of said anode structure to cause ionization of said gas molecules, means defining at least one surface in said envelope for collecting the ionized gas molecules, at least one cellular sputter-electrode structure located in the vicinity of said collecting surface to release sputtered material to said collecting surface in response to bombardment by ionized gas molecules traveling to said collecting surface, and means in said envelope for supplying ion- 20 entrappiug getter material to the area occupied by said collecting surface and said cellular sputter-electrode structure, said means for supplying said getter material including a coiled wire of tungsten defining a substantially hollow-cylindrical basket structure having a substantially closed lower end and an open upper end, a substantially cylindrical body of titanium inserted in said basket structure through said open end to extend to said lower end of said basket structure, and means for heating said basket structure and said body of titanium at said lower end of said basket structure to cause evaporation of the titanium present at said lower end of the basket structure and simultaneous movement of said body of titanium towards said lower end of said basket structure.

References Cited by the Examiner UNITED STATES PATENTS 2,967,012 1/1961 Connor 230-69 3,181,775 5/1965 Herb 230-69 FOREIGN PATENTS 1,261,456 4/1961 France.

DONLEY I. STOCKTNG, Primary Examiner.

Claims

7. AN IONIZATION VACUUM PUMP COMPRISING AN ENVELOPE FOR CONFINING AN EVACUATED SPACE CONTAINING RESIDUAL GAS MOLECULES, MEANS IN SAID ENVELOPE FOR IONIZING SAID RESIDUAL GAS MOLECULES, A COILED HEAT-RESISTANT WIRE IN SAID ENVELOPE DEFINING A BASKET STRUCTURE HAVING A SUBSTANTIALLY CLOSED LOWER END, AN OPEN UPPER END AND AN INTERNAL CAVITY EXTENDING FROM SAID OPEN UPPER END TO SAID SUBSTANTIALLY CLOSED LOWER END, A BODY OF GETTER MATERIAL INSERTED IN SAID BASKET STRUCTURE THROUGH SAID OPEN UPPER END TO EXTEND THROUGH SAID CAVITY TO SAID LOWER END, AND MEANS FOR HEATING SAID BASKET STRUCTURE