High-Pressure Gas Injector," Pribory i Te hni a Eksperi enta, No. 3, pp. 219-222, May-June, 1972. However, upon close examination of that reference, it appears clear that the description in the reference does not lead one to the fast- opening and fast-closing valve of this invention whic _* : possesses two special features, both of which contribute to a fast closing. In fact, that article appears from the drawing even to teach away from at least one of these two features. Additionally, the valve in that article includes a spring; and the operation of that valve appears to be different from that of the present invention.

Valves which require springs to slow down and close the valves generally require frequent maintenance of the springs; and the valve housing must be quite large in order to house the spring when the valve is to move at very high speeds. For example, if a valve stem having a mass of 50 grams, a stem speed of 30 meters per second, and a maximum distance of stem travel of 4 millimeters must be stopped without damage to the valve solely by use of a spring, the spring would be required to have a spring constant of about 8 tons per inch. Consider¬ ing that the coil springs of an automobile have spring con¬ stants of about one ton per inch, one can readily see that if a spring alone must stop the above-described valve stem, the spring would have to be very large and would require a very large housing in comparison with the size of the valve stem. Furthermore, when a spring is used in a valve to stop a valve stem, the valve stem is subject to bouncing; and this is

- 1 -

FAST-ACTING VALVE AND USES THEREOF

The present invention relates generally to valves and methods of producing puffs of gas and relates more particuar to a valve which can both open and close very quickly and to method of producing very well-defined puffs of gas. In work in nuclear fusion, a great need has arisen for fast-acting valve which can both open and close very quickly so as to produce a very sharply defined (i.e. , short) puff o gas. Such a puff of gas is desirable for filling a theta pinch, wherein a controlled nuclear fusion reaction takes place, plasma in a long torus or skinny tube being confined a magnetic field and shock-heated and compressed to produce the high temperatures at which fusion takes place. If a sub stantial tail is present on the. gas puff used to fill a thet pinch, the plasma will cool and its lifetime will be limited Therefore, a fast opening and fast closing valve is of great if not critical, importance to a sustained, controlled fusio reaction.

A valve described as fast-opening was disclosed in the article by G. N. Aretov et al. , "High-Speed Electrodynamic

highly undesirable when a well-defined puff of gas is sought. Furthermore, a linear spring would act to decrease the speed of the valve stem continuously as the spring is compressed, thus lengthening the opening time; and a short puff of gas. could not be produced.

An object of this invention is a valve which is both fast opening and fast closing.

Another object of this invention is a valve suitable for producing a very well-defined puff of gas, useful for exam le in a theta pinch.

Yet another object of this invention is a fast-acting valve having a long lifetime (i.e., at least several thousands of shots) .

A further object is to provide a method of producing a very well-defined puff of gas.

Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be utilized and attained by means of the instru¬ mentalities and combinations particularly pointed out in the appended claims.

To achieve the foregoing and other objects and in accor- dance with the purposes of the present invention, as embodied and broadly described herein, the valve of this invention comprises:

( a) a valve ho sing;

(b) a valve stem having a coil end and a muzzle end and b able to reciprocate within the valve housing so that the v has a fully open position, a plurality of partially open po tions and a fully closed position, the size and shape of t valve stem relative to the valve housing being such that at least one air cushion space is formed between the valve ste and the valve housing;

(c) sealing means for sealing the at least one air cushion space; and

(d) a gas reservoir which is in open communication with a space external to the valve when the valve is in an open position and which is sealed off from that external space w the valve is in its fully closed position, the valve stem having a shape such that when the valve is an open position, gas is released from the gas reservoir to the external space so as to exert a force on the valve ste tending to restore the valve to its fully closed position. Also according to the invention, the above-described valve is operated in cooperation with an actuating means located adjacent to the coil end of the above-described apparatus.

In a preferred embodiment, the actuating means is a specially produced pancake coil which can be operated with high voltage.

In a further aspect of the present invention, in accor ance with its objects and purposes, a method of producing a very well-defined puff of gas comprises :

(a) opening a valve containing a first pressurized gas when the valve stem is moving at its maximum velocity, thus allow¬ ing the first pressurized gas to flow out of the valve when the valve is in an open position; and 5 (b) slowing down the valve stem nonlinearly and closing the valve by (1) having the valve stem compress a second gas located within at least one sealed air cushion chamber located within the valve housing and (2) having the first pressurized gas exert a restoring force on the valve as it flows out of

10 the valve.

The apparatus according to the invention exhibits the advantages of having the capability of a very fast opening time (on the order of 100 microseconds) , a very fast closing time (also on the order of 100 microseconds) , and a quite long

15 lifetime (at least several thousands of valve firings) .

Additionally, because no spring need be used to slow or stop the valve stem, the size of the valve housing relative to the size of the valve stem need not be nearly so large as would be required if springs were needed to stop the valve stem; and

20 the valve is not subject to bouncing. This particular combina¬ tion of advantages is believed not to have existed in any valve known in the prior art.

Because the valve is both fast opening and fast closing and is not subject to bouncing, it can be used to produce a

25 ^. well-defined puff of gas suitable for use, for example, in filling a theta pinch vacuum vessel.

The accompanying drawings, which are incorporated in an form a part of the specification, illustrate preferred embod ments of the present invention and, together with the descri tion, serve to explain the principles of the invention. Figures 1 and 2 are schematic illustrations in cross section of a preferred embodiment of the valve (i.e., the valve stem within the valve housing) in its open and closed positions, respectively, the valve stem being axially symmet Figure 3 is a schematic illustration in cross-section o the embodiment of the valve stem shown in Figures 1 and 2 an having 6 portions.

Referring to the drawing, in Figures 1, 2, and 3, for each labeled part of the valve stem !__)_, there is a correspon ing part which is shown but which is not labeled in each cross-sectional view.

In Figure 1, showing a preferred embodiment of the valv in its closed position, a valve stem referred to generally a 10 is shown located within valve housing 12_. Valve stem 10_ has a coil end 14_ and a muzzle end lβ_ and is made of metal. The center of valve stem 10_ is preferably bored out from coi end 14_ almost through to muzzle end lj5_, so as to leave a hollow space 18_, thereby reducing the mass of- the valve and permitting faster speeds. Valve stem 1 as shown in Figure and as more clearly shown and labeled in Figure 3 preferably has six segments, each segment of which has a particular largest diameter, as described below. The six portions of

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valve stem 1J3 are first portion 2_0_, second portion 22_, third portion 2_4_, fourth portion 26_, fifth portion 28_, and sixth portion _3Q_ _r all of which are continuously connected together ^■ and machined from one piece of metal. Valve housing 12_ has three portions, first portion 32, second portion 3_4_, and third portion 3j5, formed preferably from three pieces of metal which are shaped and bolted to¬ gether so as to form one structure. Valve housing _1_ has a hollow portion therein (not shown) , within which valve stem 10_ reciprocates. The shape of the hollow portion in valve housing 2. is substantially the same as the shape of- valve stem 1O_, except that valve stem 1 is slightly smaller than the hollow portion, there are spaces in the hollow portion into which valve stem L0_ can move as it reciprocates, and the hollow portion is in open communication with a space external to the valve (for example, a vacuum vessel) at muzzle 3_8. when the valve is open. There are five spaces (shown as blanks in Figure 1) corresponding to one less than the number of por¬ tions of valve stem 10_. As the valve opens, muzzle end 16_ of valve stem _10_ moves into muzzle i ^' Z third portion 2_ moves into gas reservoir 4 ; fourth portion 26_ moves into third space 2_; fifth portion 2$_ moves into sealed air chamber 44; and sixth portion 3_0_ moves into fifth space 46.

Located around the circumference of gas reservoir 4_0_ and between front seal _52_ and rear seal 54_ are seal retainers 48 and 50. These retainers hold front seal 52 and rear seal 54

in their respective positions _. and they form the walls of gas reservoir 40.

Sealed air chamber 4_4_ is sealed on either side by first seal 5_6_ and second seal 5_8_, which are preferably o-rings/ each of which is located within a small groove cut into valve housing 12^. These grooves serve to prevent first seal 5_6_ an second seal 5_8_ from being displaced to an appreciable extent as the valve stem 1_0_ reciprocates.

Gas inlet 6_0_ is preferably continuously in open communic tion with a pressurized gas source (not shown) which feeds pressurized gas into gas reservoir 4_0_ through conduit 61.

Preferred actuating means pancake coil 62_ is held in a fixed position by means of dovetail grooves 6_3_ within third portion 2JJL °£ valve housing 12_. Third portion 36_ of valve housing 12_ houses a cylinder 6_4_ made of an insulator which is preferably machined fiberglass. Cylinder 6_4_ houses solid metal rod 6_5_, having a bore in one end, into which a high voltage connection is connected by means of a plug such as a banana plug 6_6_. Cylinder 6_4_ is slotted (not shown) at the end near valve stem 10. One end of the flattened wire formin the turns of the pancake coil is soldered into a slit in soli metal rod 65_, and the wire is next passed through the slot in cylinder 6_4_. The other end of the coil is fastened by means of set screws to third portion 3_6_ (made of metal) , thus compl ing the circuit. Cylinder 6_4_ extends beyond the usual bounda of third portion 36_; and that extending portion is housed within extending housing 7_0_, which is preferably made of

molded fiberglass and epoxy. Extending housing 7_0_ is housed within hollow outer housing 7_2_, which is connected to third portion 3j_ by screws (not shown) . Extending housing 7_0_ is con¬ nected by means of dovetail grooves 7_1 to third portion ^" 36. High voltage connection (not shown) is the inner conduct¬ ing portion of coaxial cable 7_4_ and is located within insulator 67; the outer conducting portion is terminal 7_6_. Coaxial cable 7_4_ should be grounded. Solid metal rod 6_5_ is threaded to take nut 7_8_. Solid metal rod 6_5_ continues through cylinder 64_ and it (as well as the slotted end of cylinder 6_4_) is covered by fiberglass (not shown) , over which a removable thin sheet of insulator such as Mylar (not shown) is fitted so as to cover all of the turns of the coil, solid metal rod 65, and cylinder 6_4_ when the valve is assembled. A nut 7_8_ is positioned on ^" the end of solid metal rod 6_5 near terminal 76. hen nut 7_8_ is tightened, cylinder 6_ is maintained in its position. Clamp _8_0_ is used to clamp terminal 76. onto hollow outer housing 7 Coaxial cable 7_4_ is connected to any source of changing current suitable for actuating the valve stem 10. Seals j32_ are positioned along the boundary between second portion _3 ^{a £} i first portion 22__ of valve housing 12_. Seals £!4_ are positioned around front seal 52_ and rear seal 54.

In Figure 2, showing the valve in its open position, the parts are the same as and are numbered the same as those described for Figure 1. The spaces which were described for Figure 1, however, are all closed at least partially in

Figure 2 by the respective parts of valve stem 10_ which hav moved into those spaces. Instead of the spaces shown in Figure 1, a space 36 exists in Figure 2 between coil end 1_4_ valve stem 10_ and pancake coil 6_2_. Gas from gas inlet 50_ . flows out from gas reservoir 4_0_, around muzzle end _L6_ of valve stem 1 , into muzzle _3_8_, and finally out of. valve hou - ing 12.

In Figure 3, a cross section of valve stem 10_ is schem tically shown, without showing hollow space 18_. The six portions of valve stem 1 , further described below, are labeled in Figure 3. For strength, these portions are tape as shown. This tapering is particularly important for sixt portion 3JD. _* Shown in dotted lines (for purposes of orienta tion) are fifth space 6_, sealed air chamber 44_, third spac 42_, rear seal 5_4_, and front seal 5_2_. The largest diameter first portion 20_ of valve stem 1 is a; of second portion 2 b; of third portion 2_4_, c; of fourth portion 26_, d; of fift portion 28, e; and of sixth portion 30./ f.

The operation of the valve is the following. Initiall the valve is in its closed position, as shown in Figure 1; no current flows in pancake coil 62. The pressurized gas located within gas reservoir 4_ exerts an axial force on fr seal 52_ when the valve is closed. In turn, front seal 52 exerts a radial force on muzzle end 1_6_ of valve body 1 so to prevent escape of gas from the valve when the valve is i its closed position. Next, a pulse of current is sent thro pancake coil 62_, the pulse being preferably a half sine wav

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pulse so that there is no residual current to retard the return speed; and the changing magnetic field sets up an induced current in coil end 4_ of valve stem l(h The induced current interacts with the magnetic field, and valve stem 10_ is forced away from pancake coil 6_2_; and the valve begins to open. Pressurized gas located in gas reservoir 4_0_ then flows out through the space which has opened between muzzle end _S_ and front seal 52. The valve begins to open at the same time that valve stem 13 is moving at its maximum velocity. This is achieved by the choice of the dimensions of stem 0_ and seal 52 for a particular force applied to valve stem 10_ by coil 62. It has been found that the impulse applied to the coil end of the stem causes axial compression of the stem and the stem actually is deformed at space 46. When the muzzle end of the stem reaches its maximum velocity, it has moved a distance g (shown in Figure 3) .

After valve stem 1 has reached its maximum velocity, it moves at nearly its maximum velocity for a short time and then begins to slow down because of two features in the valve. The air (now compressed) within sealed air chamber 44_ operates to slow down the valve stem, as does the feature (further des¬ cribed below) that σ be greater than a. The action of sealed air chamber _i _ performs two related functions; i.e., it provides a highly nonlinear cushioning element which stops the forward motion of the valve stem 10_ without damage to the _. , valve body and it provides a restoring force to return the valve stem to its closed position. Thus, at least one sealed

air chamber 4_4_ is required. The sealing can be done by .sea located so that one seal is on either side of the air chamb between valve stem l_p_ and valve housing 12.

The operation of sealed air chamber 4_4_ is approximatel described by ^• - the eσuation F = -PoA (—q—x -x) ₇ - k, wherein F is t retarding force of the air chamber, wherein P is the chamb fill pressure, A is the cross-sectional area of the chamber, q is the maximum stroke length, x is the distance traveled the valve stem, and k is the ratio of specific heat at cons pressure to that at constant volume of the gas in the cham¬ ber. P is atmospheric pressure when the air chamber is filled with air at atmospheric pressure, and k is 1.4 (assu ideal gas laws, which provide a rough approximation) . One readily see that the restoring force of the air chamber is quite small until x is nearly equal to q; and then the rest ing force very quickly becomes very large. This feature is extremely important for obtaining a very short puff of gas. This nonlinear restoring force is quite different from the restoring force of a spring, F = -kx, which is proportional the displacement x.

In the apparatus of the invention, to achieve proper s ing of the valve in its fully closed position without using a spring, it is required that the valve stem have a shape s that when the valve is in an open (i.e., fully or partially open) position, gas is released from the gas reservoir to a space external to the valve so as to exert a force on the va stem tending to restore the valve to its fully closed positi

This is achieved when a is greater than b and c is greater than a (where a, b, and c are shown in Figure 3) . When c is greater than a, the component of the surface area vector lying parallel to the axis of the valve stem will be larger for third portion 2_4_ than for first portion 2 . (This was not required in the Russian reference cited above, and particularly not as shown in Figure 1 of that paper. ) Hence the force exerted on third portion 2_4_ due to the gas pressure will be larger than on first portion 20_. When c is greater than a and a is greater than b and when the valve is in its open position, gas flowing out of the valve between first portion 32_ and the muzzle end 1_6_ of valve stem 10_ will exert a restoring force to help close the valve.

Although preferred, it is not required that the valve stem 1Q_ comprises six portions as shown in Figure 3. There must, however, be enough portions to form at least one air cushion space and to provide the structure on which the restor¬ ing force acts at the muzzle end (as described above) .

Front seal 5_2_ and rear seal 4_ can be formed from any material which exerts a radial force when it is stressed in the axial direction. For example, Teflon ^* can be used.

Any suitable actuating means can be used to actuate the valve. When the actuating means employs a source of electri¬ cal current, it is required that the electrical source be such that it gives rise to a changing magnetic field, which induces the current that causes the valve ste to be accelerated and to open the valve. Thus, the coil end 14 of the valve stem

must be made of metal. Any current pulse having an amplitud which is approximately zero when the valve is to begin to cl can be used, although a half sine wave pulse was used in the example below and is preferred. In a preferred embodiment, the actuating means is a pancake coil formed-from flattened copper wire, using fiber¬ glass as insulation -between the turns. The copper wire is preferably glued onto a similarly shaped strip of fiberglass and one end of the wire is soldered to metal rod 65. The wire is tightly wound around the rod, so as to maximize the number of turns in the area occupied by the coil. Fiberglas is next placed on top of and below the formed coil for insul tion. Then, the coil is inserted into third portion 6_ of valve housing 12_; and the loose end of the wire is clamped b a set screw into third portion 3_6_. The formed coil is then impregnated with epoxy.

In order to optimize the speed of the valve stem, its mass should be small- Thus, preferably the valve stem will hollow and will be made of an alloy of aluminum or of some other strong but lightweight metal. Also, to increase the speed of the valve, one can increase the amplitude of the current through the actuating means for a given pulse time length. And, preferably the cross-sectional area of the coi end will be large as compared with other sections of the val stem; and the number of turns in the coil area will be maxim In order to further increase the speed of closing of th valve, the externally applied gas pressure can be increased;

and the quantity σ can be increased with respect to the quantity a. In order to increase the restoring force of the air cushion chamber, the fill pressure P can be increased and the piston area A can be increased. However, these measures will have a minor influence on the restoring force, as com¬ p ⁼ ared with the effect of the factor (—q ^x ——x) .

In order to achieve the many advantages set forth above, preferably no spring will be used in the valve.

For convenience, the externally applied gas pressure used for closing the valve is continuously in open communication with the source of that pressurized gas. However, if desired, the pressurized gas could be turned on only during the period of time of closing of the valve.

If desired, more than one sealed air cushion space can be employed in the valve; and, if desired, a plurality of valves can be operated simultaneously to fill a theta pinch vacuum vessel, for example. Example

A valve having the design shown in Figures 1, 2, and 3 was constructed. The valve stem and valve housing were made of an aluminum alloy comprising 97.9% aluminum and normal impurities, 0.6% silicon, 0.25% copper, 1.0% magnesium, and 0.25% chromium. The valve was operated in cooperation with a pancake coil, which was made as described above. The valve ^■ stem had a mass of 50 grams, a maximum stem travel of 4 millimeters, and a cross-sectional area of the coil end 14_ of

2

20.3 cm . The pancake coil had 30 turns. The applied current

was approximately half sine wave pulses of approximately 70 μsec duration, with a maximum of 5300 amps. The applied pressure used in closing the valve was 1400 psi. The maxim speed of the valve operated under these conditions was meas to be about 18 m/sec, and the valve was used for 3000 shots without any apparent damage. Additionally, it is noted tha the volume occupied by the valve housing was only about 2100 cc and the volume occupied by the valve stem was only about 18.5 cc. The ratio of volumes was thus only about 11 This valve was used to produce puffs of gas which were used to fill a theta pinch vacuum vessel. The opening time (i.e., time from start of current to the time at maximum va opening) of the valve was 150 μsec, the closing time (i.e., the time from maximum opening to time at cessation of gas flow) was 200 μseσ, and the overall time during which any g flowed out of the valve was less than 250 μsec, (as estimat by the characteristics of the gas puff emitted by the valve

The foregoing description of preferred embodiments of the invention has been presented for purposes of illustrati and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The embodiments were chosen described in order to best explain the principles of the invention and their practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are

suited to the particular uses contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.

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