US3307062A

US3307062A - Trigger tubes

Info

Publication number: US3307062A
Application number: US261149A
Authority: US
Inventors: Paul W Stutsman
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1963-02-26
Filing date: 1963-02-26
Publication date: 1967-02-28
Anticipated expiration: 1984-02-28

Description

Feb. 28, 1967 P. w. STUTSMAN TRIGGER TUBES 5 Sheets-Sheet 2 Filed Feb. 26; 1965 ANODE VOLTAGE I GENERATOR VOLTAGE SUPPLY INVENTOR PAUL W. STUTSMA/V Feb. 28, p w S N TRIGGER TUBES Filed Feb. 26, 1963 3 Sheets-Sheet 5 EXTINCTION VOLTAGE DEPTH OF ANODE IN SLEEVE INVENTOR PAUL W .STUTSMAA/ fM 775 M AGE/VT United States Patent ()flice 3,3il7, 0 52 Patented F eb. 28, 1967 3,367,062 TRIGGER TUBES Paul W. Stutsman, Needham, Mass, assignor to Raytheon Company, Lexington, Mass, a corporation of Delaware Ffled Feb. 26, 1963, Ser. No. 261,149 6 Claims. (Cl. 313-182) This invention relates to trigger tubes, and more particularly to an improved cold cathode trigger tube which is triggered to fire by a signal applied to the tube grid and which has a very high input impedance so that only a minute amount of power is required to fire.

Heretofore, gas-filled trigger tubes including a cathode, an anode, and a triggering grid structure to which a trigger signal is applied have been employed to sense relatively small signal changes and in turn conduct relatively large currents to a load in response to the small signal changes. It is sometimes desired when using such a tube that the tube be triggered by very little input power. is in a nonconducting state or stand-by state that the amount of power used by the tube be a minimum. These features are particularly desired in applications where the tube must remain in a stand-by state for long periods of time and Where only a relatively small power supply is available. It is one object of the present invention to provide a cold cathode gas trigger tube having very high input impedance and which draws very little power to fire or in the stand-by condition.

In accordance with the present invention the tube preferably includes two grid structures, a cold cathode and an anode, one of the grid structures serving as a keep-alive grid providing a steady flow of ions to the gap between the anode and cathode and the other grid disposed between the anode and cathode and energized by the triggering signal, and further includes a body of material disposed in the proximity of the anode and which is not fixed at any particular potential but which floats in potential depending upon migration of ions thereto from the space charge within the tube.

In a preferred embodiment of the invention, the abovementioned body at a floating potential is preferably cylindrical in shape, and the anode is recessed within this body so that, as a result, ionized particles produced within the tube generally by the electric field between the keep-alive grid and the cathode and which consist of relatively heavy positive ions and electrons will be selectively separated by the very presence of the body leaving a space charge of opposite sign in the immediate vicinity of the anode during the stand-by condition. As a result, when the grid to anode potential is increased by the trigger signal, a few electrons from the cathode or grid will bombard this positive space charge causing further ionization within the space charge area which will ex perience additional separation of positive from negative ions and result in the space charge potential increasing so that the magnitude of the efiective electric field between the anode and cathode increases, and sharp triggering results.

It is theorized that the sharp triggering action of the tube results from the above-described phenomenon, and during the stand-by condition the cylindrical body assumes a charge negative with respect to the adjacent space charge and partially shields the anode from the signal grid, thus reducing leakage current flow therebetween and reducing the stand-by power requirements.

Other features of the invention will be apparent from the following specific description taken in conjunction with the figures in which:

FIG. 1 is a sectional view of the tube taken through It is also generally desired that when the tube the tube axis and showing the various locations of elements thereof;

FIG. 2 is a symbolic representation of the anode, cathode and grids identifying spacings therebetween to aid in understanding the invention;

FIG. 3 is a curve of grid to anode voltage versus grid current to show low stand-by current requirements required even at relatively high grid to anode voltages;

FIG. 4 is a plot of grid to anode firing voltage versus supply voltage to the anode;

FIG. 5 is a useful circuit employing the tube to advantage as a tetrode;

FIG. 6 is a useful circuit employing the tube to advantage as a diode voltage regulator; and

FIG. 7 is a plot of extinction voltage or regulated voltage as a function of the recession of the anode within the floating cylinder.

FIG. 1 illustrates the various electrodes in the tube and their relative locations showing the envelope partially cut away. The envelope 1 is preferably glass and is fused to a glass base 2 which carries the electric leads to the various electrodes. Two of these leads 3 and 4 support opposite ends of the cold cathode 5 and also support a getter structure 6. Lead 7 connects to the anode 8, and the surface 9 of the anode is recessed a distance denoted B within the end of a glass cylinder 11 which extends from the base 2. Lead 12 connects to control grid 13 which is disposed between the face 9 of the anode and the cold cathode 5. A second grid formed by a loop 14 connects to lead 15. The loop is preferably formed by a Ushaped wire extending adjacent the glass cylinder 11 in which the anode is located and looping up and over the cold cathode 5 in relatively close proximity thereto as shown by the dimension D. This grid 14 is sometimes called a keepalive grid and provides an extremely small but steady current to the cathode during the standby condition, thus generating a continual supply of ions which fiow to the gap between the anode and cathode producing space charge therein necessary to condition the tube so that it will fire in response to an input applied to the signal grid 13.

The structure shown within the tube in FIG. 1 supporting each of the electrodes includes glass cylinders extending from the face 2 such as the cylinder 11 in which the anode is located. Of the cylinders, only cylinder 11 serves an electrical function, as well as a supporting function within the tube, and so the

other cylinders

17, 18 and 19 could be omitted and other nonelectrically conductive structures substituted without deviating from the scope of the invention. A strap 21 encircles the cylinders 11, 17, i8 and 19 and adds rigidity to the structure within the envelope.

The cold cathode 5 preferably functions not only as a cathode but also as a second getter, and for this purpose is preferably made of Batalum. The active material in Batalum getters is barium and occurs in a compound coated on a molybdenum base. The active barium is released during the processing of the tube by electric heating of the metal base at appropriate points in the schedule of manufacture of the tube. The control grid 13 is preferably made of a tungsten wire welded to a nickel rod which forms the lead 12. The grid portion 13 is preferably tungsten because tungsten maintains rigidity during operation even under high acceleration and vibration. The keep-alive grid 14 is also preferably a tungsten wire and is mounted to the strap 21 which encompasses the glass tubes 11 and 17-19 adding rigidity to the tube structures. The anode is preferably a nickle rod mounted as shown and recessed within the open end of the tube 11.

The gas filling within the tube is preferably a mixglass ture having a relatively low sparking potential versus the product of gas pressure times the gap distance D. In other words, the mixture preferably has a broad low minimum on the Paschen curve. Such a low minimum could be provided by a mixture of krypton and xenon, but the broadness could not be provided by any combination of the two. It has been found that the broadness cannot be provided by any combination of the two, since neither has an excited state high enough to ionize the other. Good sensitivity has been obtained with a mixture of 99 percent neon and 1 percent argon. This mixture provides a reasonable minimum on the Paschens curve, and the minimum is sutficiently broad for most applications, which can be attributed to the fact that the first excited state of neon (16.6 electron volts) can easily ionize argon which has a first ionization potential of 15.7 volts. In addition, argon has a metastable state of 11.6 volts which allows ionization with the addition of only 4.l volts easily obtained from collision with excited neon atoms. When such a mixture of neon and argon is employed, it has been found that gas pressure of about 37 centimeters of mercury results in satisfactory, if not optimal performance. Furthermore, variations of a few centimeters of mercury can occur with little deleterious effect.

The important dimensions between the various electrodes within the tube denoted A, B, C, D and E are also shown in FIG. 2 which is an enlarged view of the internal parts of the tube. There are two critical dimensions between the signal grid 13 and the face 9 of the anode 8. These dimensions are denoted A and B. The distance A determines the critical grid to anode voltage. The distance B effects the maximum forward anode voltage characteristic as will be explained later. The distance A plus C when grid No. 13 is at floating potential also determines the maximum forward anode voltage. The distance C controls the transfer characteristic obtained when the grid to anode gap A is triggered. The auxiliary or keep-alive grid gap D is set at a practical minimum to reduce noise and oscillation and also to allow a low starting voltage by generating a continual source of ions, and the spacing D between the mean point of the gap D and the mean point of the gap A regulates the degree to which the stand-by conduction between the keep-alive grid 14 and the cathode can participate in the ion diffusion from the discharge between the signal grid 13 and the cathode. Hence, if the dimension E is too large, the ion diffusion from gap D to gap A may be too small for a given specified current in keep-alive grid 14-, and so the discharge in gap A will be unstable. versely, if the dimension E is too small, the gap A will be overstabilized, making the tube insensitive.

As already mentioned, the glass sleeve or cylinder 11 or at least the area inside this cylinder which lies between the anode surface 9 and the grid 13 floats in potential during operation, and so the potential of this area of the cylinder 11 during operation depends upon the amount of charge migration thereto. It has been found that the presence of the glass cylinder 11 within the gap A results in a constant current flow in the signal grid 13 over a substantial range of grid to anode voltages. For example, over ranges of 40 to 50 volts grid to anode voltage, the value of this current has been found to be substantially uniform and on an order of magnitude of 10- amps. Thus, there is provided a wide range of grid to anode operating voltages over which the signal grid current, and thus power utilized, is extremely small. This permits operation of the tube in a stand-by condition over long intervals of time during which extremely minute amounts of power are required by the tube. FIG. 3 is a plot of grid to anode voltage versus signal grid current in a tube for which the dimensions A to E are as follows: A=.040 in.; B:.020 in.; C=.Ol in.; D=.005 in.; and E=.046 in. The portion of this curve over which grid current is substantially constant is indi- Concated by a vertical line 31 which is also substantially coincident with minimum signal grid current and extends over a considerable range of grid to anode voltage.

As shown in FIG. 3, the grid to anode voltage peak at 32 along the curve occurs at very low signal grid current. In fact, this peak occurs at only 1 or 2 orders of magnitude greater than the minimum grid current, and is in advantageous condition because it permits the grid to anode voltage to be brought very near to a peak, thus bringing the tube very near to a firing position, without resulting in a substantial increase in the signal grid current, and so the tube can be held in a very sensitive condition during stand-by and still require only a minute amount of power. The applicant has discovered that it is the presence of the portion of the glass cylinder 11 in the gap A which results in this advantage. One suggested explanation of this condition is that ionization is produced throughout the tube as a result of collisions between the electrons and neutral atoms or collisions of excited atoms with neutral or other excited atoms or secondary emission or other well-known effects. If the gas pressure and the gaps within the tube are properly chosen, the random motion of these charged particles far exceeds their average motion in the direction of drift from one electrode to another. Therefore, assuming comparable ion and electron temperatures, the electrons because of their smaller masses and greater mobilities will diffuse to the various walls and surfaces within the tube much more rapidly than the heavier positive ions. For this reason, the walls become negatively charged with respect to the continguous space. When the charge becomes sufficiently negative to repel further electron migration to the wall a so-called electron-free or positive ion sheath is formed over the particular surface. The negative charges on the wall within the anode sleeve 11 or at least that portion of the sleeve lying within gap A may nearly block electron flow to the anode allowing only for electron traffic therethrough which is needed to maintain the electrostatic conditions. During the standby condition, as the grid to anode potential is increased in response to a trigger signal a few more electrons penetrate the ion sheath or barrier adjacent the anode producing a few more ions near the anode. Thus, the potential of the space adjacent the anode and between the anode and a signal grid 13 will increase, and more electrons will enter the space causing more ionization and resulting in a sharp triggering of the tube.

As stated above, the critical voltage at which the tube fires is determined by the two spacings A and B, and this, of course, presumes a given anode voltage and a given signal grid voltage. Usually, in gas trigger tubes which do not incorporate the present invention, the required signal grid voltage to fire the tube is positive. The present invention permits triggering to be accomplished by a negative signal applied to the signal grid. FIG. 5 illustrates a circuit in which the tube is used as a tetrode and is fired by a negative signal from a signal generator at very low power levels. As shown in FIG. 5, the anode 8 and cathode 5 are connected to a voltage supply 51 with a load 52 between the anode and supply. The keep-alive grid 14 is preferably coupled to the positive terminal of the source 51 by a very high resistance 56 on the order of 10 ohms. In operation, in the stand-by condition, the anode voltage derived from the source 51 and the signal from signal generator 57 combine to place tube operation at a point which lies below and to the left of the curve 42 shown in FIG. 4. This curve is a plot of anode voltage versus firing voltage for the tube having no other source of energy for forming ions within the tube than the discharge of the keep-alive electrode 14. The curve 41 in FIG. 4 shows firing characteristics with the keep-alive electrode 14 at floating potential and with no other source of energy for forming ions. An operating curve similar to curve 42 could also be obtained with the keep-alive grid floating if a source of energy such as strong light or X-ray were supplied to produce ions within the gas.

As can be seen from FIGS. 4 and 5 a reduction in the voltage from signal generator 57 will increase grid to anode voltage, and the operating point will cross curve 42 which results in the tube firing. Therefore, in operation, a negative-going signal from generator 57 applied through very low capacitance 59 across high resistance 61 between the signal grid 13 and ground will cause the tube to fire.

The present invention may also be employed as a voltage regulating diode. The applicant has discovered that the depth the anode 8 is recessed into the glass sleeve 11 can serve to sharply control diode extinction voltage. The tube shown in FIG. 1, for example, could be used with both grids disconnected and thus at floating potentials and with the anode 8 and cathode 6 coupled in a circuit as shown in FIG. 6. This circuit includes a capacitance 61 which is charged through a resistor 62 from a source 63 when the switch 64 is closed. When the charge on the capacitance exceeds the firing voltage, the tube will fire repeatedly, thus discharging the capacitance 61 until voltage on the capacitance reaches the tube extinction voltage. The charge on the capacitance will then build up again, and the tube will fire again discharging the capacitance. This sequence will be repeated continually to maintain the voltage on the capacitance 61 at a regulated value. The applicant has found that the extinction voltage of the tube varies almost directly as the depth the anode is recessed in the glass sleeve. This is shown by the plot 71 of extinction voltage versus depth in FIG. 7.

This completes the description of a few embodiments of the invention of a gas-filled electron discharge tube including a structure immediately adjacent the anode which floats in potential, the potential being determined by migration of charged particles to the structure from space charge adjacent the anode, and more particularly to certain effects the applicant has observed which result from this structure and which aiford new and improved operation and use of the tube as, for example, a gas fired trigger tube responding to a negative-going input signal or as a diode voltage regulator. It is to be clearly understood, however, that these novel applications of the applicants invention should not be construed as limitations of the invention as set forth in the accompanying claims.

What is claimed is:

1. A gas-filled cold cathode trigger tube comprising an envelope having a longitudinal axis, a rod-like anode within the envelope having one end fixed thereto and extending parallel to the axis of the envelope, an insulating cylinder closely encircling said anode and having a projecting portion extending beyond the unsupported end of the anode, said projecting portion of the insulating cylinder having an aperture therein exposing the unsupported end of the anode, a cathode extending transversely of the envelope in predetermined spaced relation with the anode and overlying the aperture in said insulating cylinder, a trigger grid electrode mounted on the envelope at one side of the cylinder and having a portion extending transversely of the tube into the interelectrode space between anode and cathode, a keep-alive grid electrode comprising an inverted U-shaped wire having leg portions extending axially of the envelope on opposite sides of said interelectrode space and having a bight portion extending over the cathode and located at a predetermined spaced relation therewith, and leads extending through said envelope and connected to said anode, cathode, and grid electrodes.

2. A tube as set forth in claim 1 wherein said envelope is filled with a gas which has a broad low minimum on the Paschen curve.

3. A tube as set forth in claim 1 wherein said envelope is filled with a mixture of neon and argon.

4. A tube as set forth in claim 3 wherein said gas mixture comprises about 99% neon and about 1% argon at a pressure of about 37 centimeters of mercury.

5. A tube as set forth in claim 1 wherein said envelope is filled with gas and the projecting portion of the insulating cylinder comprises means for intercepting and capturing ions of a given charge polarity from a space charge in said interelectrode space during operation of the tube.

6. A tube as set forth in claim 1 wherein regulated voltage is applied to said cathode and anode, and the projecting portion of the insulating cylinder is of a predetermined length in accordance with the selected magnitude of said regulated voltage.

References Cited by the Examiner UNITED STATES PATENTS 1,962,159 6/1934 Le Van 313-258 X 1,993,811 3/1935 Soundy 313-258 X 2,699,517 1/1955 Diemer 313258 X 2,883,584 4/1959 Hill 313-192 X 3,024,386 3/1962 Chauvineau 31524l X JOHN W. HUCKERT, Primary Examiner. D. O. KRAFT, Assistant Examiner.