CA1096050A - Crossed-field switch tube - Google Patents
Crossed-field switch tubeInfo
- Publication number
- CA1096050A CA1096050A CA271,171A CA271171A CA1096050A CA 1096050 A CA1096050 A CA 1096050A CA 271171 A CA271171 A CA 271171A CA 1096050 A CA1096050 A CA 1096050A
- Authority
- CA
- Canada
- Prior art keywords
- electrode
- gap
- crossed
- cathode
- ignition
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J17/00—Gas-filled discharge tubes with solid cathode
- H01J17/02—Details
- H01J17/14—Magnetic means for controlling the discharge
Landscapes
- Gas-Filled Discharge Tubes (AREA)
- Plasma Technology (AREA)
- Spark Plugs (AREA)
Abstract
Abstract of the Disclosure A crossed-field switch device which has anode, cathode and control electrodes which define a main gap and an ignition gap. The control electrode is connected through an impedance to one of the other electrodes to prevent hollow cathode discharge in the control gap. The control gap can be pulsed to ignite and the plasma passed through the intermediate electrode into the main gap to cause its ignition into the low pressure glow mode.
Description
-g This invention is directed to improvements in a ~ 10 crossed-field switch device whereby the crossed-field 11 switch device can be onswitched with voltage applied without 12 pulsing the magnetic field to.a high ~alue.
13 In recent years crossed-field switch devices 14 have been.developed into tubes which are capable of conducting 15 fairly hi~h currents and are capable of offswitchln~ a~ainst ; 16 high volta~es. Crossed-field switch devices havin~ a 10, oon : 17 ampere DC conducting capability and an offswitching capability 18 against 100 kilovolts have been desi~ned. Such switch devices 1~ are believed to have a considerable prospect in the developing ield of hi~h power electric transmission by means of direct 21 current links. Such crossed-field switch devices do not have 22 long term conducting capability, and thus must ~e paralleled 23 by an in-line switch during normal line operation. When it 24 is desired to open the circuit, the in-line switch is opened, so that it shunts the current through the crossed-field swi~ch b.s.
~ 26 device which is thereupon turned off. ~ Patent RE27557 illustrates 27 this type of circuit breaker which incorporates a crossed- :
: 28 field switch device as an off-switchin~ component.
A
13 In recent years crossed-field switch devices 14 have been.developed into tubes which are capable of conducting 15 fairly hi~h currents and are capable of offswitchln~ a~ainst ; 16 high volta~es. Crossed-field switch devices havin~ a 10, oon : 17 ampere DC conducting capability and an offswitching capability 18 against 100 kilovolts have been desi~ned. Such switch devices 1~ are believed to have a considerable prospect in the developing ield of hi~h power electric transmission by means of direct 21 current links. Such crossed-field switch devices do not have 22 long term conducting capability, and thus must ~e paralleled 23 by an in-line switch during normal line operation. When it 24 is desired to open the circuit, the in-line switch is opened, so that it shunts the current through the crossed-field swi~ch b.s.
~ 26 device which is thereupon turned off. ~ Patent RE27557 illustrates 27 this type of circuit breaker which incorporates a crossed- :
: 28 field switch device as an off-switchin~ component.
A
-2- .
.
' .
- ' ;'' : , ~ '` .
. , .
, , . .. . : ~ :
~9Çi~5QI
1 There have been a number o developments in the art 2 o the cros~ed~ield switch device which have brought it to
.
' .
- ' ;'' : , ~ '` .
. , .
, , . .. . : ~ :
~9Çi~5QI
1 There have been a number o developments in the art 2 o the cros~ed~ield switch device which have brought it to
3 this state of utility. Among the background patents on the
4 crossed-field switch devices are U.S. Paten~s 3,638,061, 3,641,384; 3,604,977; 3,558,960, 3,678,289; 3,769,537 and 6 3,7~9,978.
7 Of course it is necessary to ~nswitch the crossed-8 field swi~ch device when current flow therethrough is required.
9 Under the right conditions of applied voltage and magnetic field, initial ionization can come a~out by the action of 11 cosmic rays. However, in order to reduce the statistical 12 reliance on such events, ignition devices can supply the 13 preionization, (see~patents 3,714,510 and 3,890,520). These 14 patents covering ignition equipment are useful to reduce the ignition time delay whenever the cond~tions are within 16 ~he conductive region of the Paschen curve.
17 Sometimes it is desired to make the crossed-field 18 switch device conductive, that is onswitch the switch device, 19 when the rated line voltage is applied thereacross. This has formerly been done by pulsing the magnetic field sufficiently 21 high that even with voltage applied, the conditions in the 22 interelectrode space move in~o the conductive region. For ~J~
23 example seeApatents 3,678,289 and 3,604,977.
However, the firing or ignition of a crossed-field switch device at high voltage using a high pulse magnetic 26 field has several disadvantages. Thera is a tlme delay 27 rom the trigger ~o the ignition of the crossed~iald switch 28 device in the order of 10 microseconds. Furthermore, there , .
,..... . . ~ . .
S~
1 is significant jitter in ignition, `in the order of 1 micro-2 second. Additionall~, ik is difficult to obtain shor~
3 duration, high level magnetic pulses in the order of 4 0.1 Tesla or 1 K Gauss in crossed-field switch devices due to the eddy currents created in the electrodes. Also, 6 a high powered magnetic field pulser is a difficult and 7 expensive device, particularly at a high pulse repetition 8 frequency. These requirements also create a more complicated 9 and expensive tube construction which oten includes an internal magnetic field ~oil to minimize the above listed 11 detrimental ef~ects. Thus, it is highly desirable ~or a 12 crossed-field switch device to be ignited at high ~oltage, 13 in the order of 10 to 100 kilovolts, with a relatively low 14 magnetic ~ield, in the order of 0.01 Tesla, or 100 Gauss.
16 SUMM~RY
17 In order to aid in the understanding of this 18 invention it can be stated in essentially summary form 19 that it is directed to a gridded crossed-field switch device.
The crossed-field switch device has anode, cathode and 21 control electrodes which define a main gap and an ignition 22 gap. The control electrode is connected through an Lmpedance 23 to one of the other electrodes to prev~nt hollow cathode 24 discharge in the control gap~ The control gap can be pulsed to ignite and the plasma passes through the inter-26 mediate electrode into the main gap to cause its ignition 27 in~o the low pressure glow mode.
28 I~ is thus an obJect of this invention to provide 29 an improved gridded crossed-field switch which can s~
1 be onswitched while high voltage is applied without the 2 need for a large magnetic field pulse. It is another object 3 to provide a crossed-field switch device which has three 4 electrodes, which define an ignition gap and a main conducting gap so that ignition can be accomplished within the ignition 6 gap. It is a further object to provide a connection of 7 proper impedance between the control electrode and another 8 electrode to permit pulsing of the control electrode for 9 ignition and to prevent the initiation of hollow cathode discharge in the control gap. It is another object to 11 provide an intermediate electrode which is of gridded 12 construction with openings directly therethrough so that 13 the ignition gap and main gap are in line of sight. It 14 is a further object to provide a three electrode crossed-field switch device in which the main gap can be ignited 16 to operate in the crossed-field discharge mode without 17 requiring a pulsed magnetic ~ield.
18 Other objects and advantages of this invention 19 will become apparent ~rom a study of the ~ollowing po~tion of the speci~ication~ the claims and the attached drawings.
21 More particularly there is provided a crossed-field 22 switch tube comprising a tubular anode electrode and a coaxial 23 tubular cathode electrode spaced from said anode electrode so 2~ that the active areas of the two electrodes define a main discharge gap therebetween having a continuous closed path, 26 and means for making electrical connections to said anode and 27 said cathode electrodes and means for providing a gas at sub-28 atmospheric pressure in said main discharge gap and a magnetic 29 field above the critical value in said main discharge gap so that a glo~ mode plasma discharge can take place between said 31 anode and said cathode electrodes for conduction of said switch 32 device, characterized in that there are provided a tubular .~`` i .
6~
1 control electrode positioned adjacent to one of said anode and 2 cathode electrodes to form a continuous closed path ignition 3 discharge gap adjacent to, substantially over the whole active 4 area of and in communication with said main discharge gap, the tubular electrode positioned between the main gap and the 6 ignition discharge gap having openings therethrough so that 7 plasma can pass ~rom the ignition gap to the main gap, and 8 means for electrically pulsing said control electrode with 9 respect to its adjacent electrode on the other side of the ignition discharge gap for establishing conductive conditions 11 therein so that glow mode plasma discharge begins in the 12 ignition discharge gap and enters into substantially the entire 13 active area of the main discharge gap to cause conductive 14 condition of said main discharge gap over all of its area so that said crossed-field switch device can be turned on with 16 voltage applied thereto without magnetic field pulsing and with 17 uniform wear of said anode and cathode electrodes over their 18 entire active areas.
; 20 FIG. 1 is a longitudinal section through the gridded r 21 crossed-field switch device of ~his invention.
22 FIG. 2 is a perspective view of one of the electrodes.
23 FIG. 3 is a schematic electrical diagram showing .~
23 the connections of the gridded crossed-field switch device.
-5a-~? '~
. ~
~GQ50 1 PIG. 4 is a crossed-field breakdown curve relating 2 the conditions in the interelectrode gaps to the conductive 3 region of the breakdown curve.
4 FIG. 5 is a series of graphs showing various parameters in the gridded crossed~field switch device versus time.
7 DESCRIPTION OF_T~I~ PR~F~RRED R~IBODIMENT
8 The gridded crosse~-field switch device of this g invention i5 generally indicated at 10 in FIGS. 1 and 3. In ; 10 the schematic drawing of FIG. 3, crossed-field switch device 10 11 is shown as having an anode electrode 12, a cathode electrode 14 1~ and a control electrode 16. As will be described below, the 13 physical arrangement of the electrodes may differ, with the 1~ control electrode between the cathode and anode or even inter~
~ 15 iorly of the anode, but the preferred arrangement is as shown i 16 in ~IG. 3. These concentric electrodes define an annular space ~ 17 or gap 18 between the anode and cathode, with the annular .
1~ space 18 serving as a main ~ap in which the main glow discharge g is formed during conduction. Cathode electrode 14 and control electrode 16 define between them outer annular space 20 which 21 is the gap in which the ignition dischar~e is formed. Space 18 22 and space 20 are each in the order of 1 centimeter in the radial 23 direction. While the crossed-field switch device is shown as 24 being circular, because that is a convenient construction, other geometric constructions are also feasihle, so that the 26 gap may not be a circular annulus but may be another shape 27 such as a hollow rectangle or a hollow square. Cathode .~
28 electrode 14 has openings therethrough so that the plasma of s~ ~
l a glow discharge in one of the spaces can enter into the other 2 space. Since cathode electrode 14 is positioned between 3 anode electrode 12 and contxol electrode 16, it is n~cessarily 4 open so that the plasma can pass from the ignition gap to the main gap. The intermediate electrode has openings there-6 through which provide line of sight visibility between the 7 ignition gap and main gap.
As is seen in FIG. 3 the positive side of generator 22 9 is connected by line 24 to anode 12, while the negative side of generator 22 is connected through load 26 by line 28 ll to cathode 14. Thus~ the turning on and off of a low 12 pressure glow discharge in the main discharge gap 18 turns 13 on and off current fxom the generator through the load.
14 O course FIG. 3 is highly schematic, and the generator 22 represents any source of direc~ current. Furthermore, 16 the switchin~ on and off of the current through the load 17 is not usually accomplished only by the gridded crossed-18 field switch device lO but also by parallel in-line de~ice 19 through which the cuxrent passes during long running periods.
Control circuit 30 has line 32 connected to cathode 21 electrode 14 and line 34 connected to the control electrode 16.
22 Resistor 36 is connected between lines 32 and 34 so that unless 23 an additional voltage is supplied, controi electrode 16 is at 24 the same potential as cathode 14, by the leakage through the resistor 361 When resistor 36 is of low value, the electrodes 26 can carry substantially the same potential and a hollow 27 cathode discharge will continue in gap 20 so device lO
~8 canno~ be turned off. When resistor 36 is of too high a .
.. . .
~g6~
1 value the potential of the control electrode 16 can not be 2 properly established prior to the initial start of the 3 magnetic field pulse and spurious turn on may result~
4 A resistance value between 1 kilohm and 1 megohm typically satisfies both of these requirements~ Control circuit 30 6 permits voltage pulsing of control electrode 16 with respect 7 to cathode 14. As an example, capacitor 38, capacitor discharge rate limiting resistor 40 and switch 42 are g serially connected between lines 34 and 32. Another type of pulse supply can be substituted. A p~llse on the order 11 o 1 kilovolt is typical but voltages as low as 300V are 12 feasible.
13 FI~,. 1 shows in more detail the structure of the 14 gridded crossed-field switch device 10. Outer vessel 44 is the structural enclosure, tank or envelope which encloses the 16 electrodes and their insulated supports. Vessel 44 is vacuum 17 tight with connection 46 permittin~ drawing of a vacuum on 18 the vessel and maintenance of a proper gas supply therein at 19 a proper pressure. Usually helium at about 50 millitorr is a suitable atmosphere for the low pressure glow crossed-21 ield discharge. Vessel 44 is at cathode potential. It 22 supports cathode 14 on support ring 48 downwaxd from top 23 cover S0. Cathode electrode 14 is formed as a gr~d or 24 perforated electrode. FIG. 2 shows cathode 14 as being formed of an upper ring Sl, lower ring 52 and bars 54 26 connected therebetween to form an electrode in the form 27 of a squirrel cage. The squirrel cage intermediate electrode 28 provides a line of sight between the two gaps so that plasma 29 from the ignition gap can easily pass into the main gap.
o 1 Anode 12 is downwardly sup~orted from upper ring 50 2 on insulator 56 and is exteriorly connected by lead 58 which 3 is connected to line 24. Insulator 56 is the major insulator 4 which holds off the main anode to cathode voltage. Insulator 56 is supplied with field shaping electrodes 60 and 62 to 6 prevent glow discharge breakdown in that region.
7 Control electrode 16 is supported beneath 8 cathode 14 on insulators such as the ones shown at 64 and 9 66. Control electrode 16 is connected by lead 68 which passes through a vacuum tight insulator 70 with respect to 11 vessel 44.
12 Ionizer 72 is mounted to inject electrons into the 13 outer annular space 20 and its lead comes out through the 14 base by means of a vacuum tight insulator 74. Ionizer 72 ~/,S.
can be of the type shown in patent 3,890,52Q.
16 In accordance with the physical mechanism by which 17 the discharge operates, an axial magnetic field is provided 18 by solenoid 76. The magnetic field has a value of Bo as shown 19 in FIGs. 4 and 5, which is on the order of 100 ~auss for an interelectrode spacing of 1-2 centimeters and with a helium 21 ~as filling at S0 millitorr. The magnetic field can be 22 pulsed below the critical value Bc, (see FIGs. 4 and 5) 23 which is the leftward end of the toe of the crossed-field 24 breakdown curve 78 which separates the conductive region 80 from the nonconductive region 82.
26 The function of this equipment is best described 27 by going through an on-off cycle. Referring to FIG. 5, at 28 time to~ 9 kilovolts is first applied to the main gap 18 _g_ .
~ .
.. .. . .
3L~ 5~ ' 1 and a magnetic field of strength Bo is then applied to 2 both gaps. This places the operating condition of the 3 main gap at a point 84 in FIG. 4. This is i.n the nonconductive 4 region and therefore no current is being conducted by the gridded crossed-field switch device 10. Since control 6 electrode 16 is connected to cathode electrode 14 through 7 leak resistor 36, the voltage of the control electrode C
8 with respect to the cathode K is zero. This places the 9 operating condition of the control gap at point 89 in FIG. 4.
When on-switching is desired, for example at 11 point tl, switch 42 is closed to impress a pulse between the 12 cathode K and the control electrode C to bring the voltage 13 therebetween into the conductive region of the crossed-14 field breakdown curve, for e~ample to point 86 in FIG. 4 which represents about 1 kilovolt between the cathode and 16 the control electrode. Under these conditions, a discharge 17 in the control gap initiates~; Wi.th that gap conducting 18 in the low pressure glow discharge mode, the discharge 19 plasma seeps through the transmissive cathode structure to cause conduction of the main ,gap 18. The mechanism 21 by which the conduction starts is not clearly understood, 22 because under the initial conditions the gap is in an 23 unconducting region at point 84. However, the presence 24 of glow discharge plasma, which does not seem to need to be sufficient to reach across the entire gap, starts the 26 main gap discharge. With the beginning o~ that discharge, 27 within microseconds after the on-pulse, and thus both indicated 28 at time tl in FIG. 5, the main gap conduction current in-29 creases to 140~ and the voltage across the main gap decreases to,the discharge voltage drop, typically SOOV.
' --1 0-- , .
.:. : .
'! 1 Conduction continues either to exhaustion of t2le 2 interelectrode gas, or until magnetic field is suppressed.
3 As is seen in the bottom curve in FIG. S, the voltag~ across 4 the ignition gap quickly falls to a lower valuel due to con-duction through impedance 36, and the dis~pation of the 6 charge on capacitor 38. Conduction continues to take place 7 from the anode to both the cathode and the control electrode, 8 Off-switchin~ is then accomplished by pulsing the ma~netic ; g field below Bc. This pulsing appears at time t2 in FIG. 5 and moves the operating point to point 88 which is in the 11 nonconductive region 82 of the srosse~-field breakdown curve 12 of FIG. 4. This causes termination of the main gap discharge 13 with a buildup of voltage between the anode and cathode and 14 between the cathode and the control electrode and a termination of the current flow therebetween. Finally current flow - 16 through resistor 36 ceases and the control electrode comes 17 to the potential of the cathode and the magnetic field is 18 then reapplied. In this way the on-of cycle is completed.
~ 19 The squirrel cage type o~ structure shown in ~IG. 2 -; 20 LS an example of a preferred structure. Basically, cathode 21 electrodP 14 must have sufficient material to develop the 22 electric field and participate in the -discharge. However, 23 it must be open enough to permit the glow discharge plasma 24 to seep through from the outer ignition discharge gap to the main gap. A perforated tube can accomplish the same result.
26 The preferred maximum open area has not yet been experi-27 mentally established, however the cathode electrode 14 of 28 about 30 percent open area has been found to be feasible.
.,`.`~ ' 1 In the device actually redùced to practice, 2 resistor 36 wa`s about 1 kilohm and such a resistor seemed 3 to be necessary to produce the correct discharge. FIG. 5 4 illustrates the maximum voltage applied as being 9 kilovolts, but the limitation to this value was introduced by the 6 isolation resistors between the electrodes rather than 7 a fundamental limitation of the physical process. In fact, 8 ignition at 50 kV has been performed in the above described 9 manner.
. ~ , , . . ~
7 Of course it is necessary to ~nswitch the crossed-8 field swi~ch device when current flow therethrough is required.
9 Under the right conditions of applied voltage and magnetic field, initial ionization can come a~out by the action of 11 cosmic rays. However, in order to reduce the statistical 12 reliance on such events, ignition devices can supply the 13 preionization, (see~patents 3,714,510 and 3,890,520). These 14 patents covering ignition equipment are useful to reduce the ignition time delay whenever the cond~tions are within 16 ~he conductive region of the Paschen curve.
17 Sometimes it is desired to make the crossed-field 18 switch device conductive, that is onswitch the switch device, 19 when the rated line voltage is applied thereacross. This has formerly been done by pulsing the magnetic field sufficiently 21 high that even with voltage applied, the conditions in the 22 interelectrode space move in~o the conductive region. For ~J~
23 example seeApatents 3,678,289 and 3,604,977.
However, the firing or ignition of a crossed-field switch device at high voltage using a high pulse magnetic 26 field has several disadvantages. Thera is a tlme delay 27 rom the trigger ~o the ignition of the crossed~iald switch 28 device in the order of 10 microseconds. Furthermore, there , .
,..... . . ~ . .
S~
1 is significant jitter in ignition, `in the order of 1 micro-2 second. Additionall~, ik is difficult to obtain shor~
3 duration, high level magnetic pulses in the order of 4 0.1 Tesla or 1 K Gauss in crossed-field switch devices due to the eddy currents created in the electrodes. Also, 6 a high powered magnetic field pulser is a difficult and 7 expensive device, particularly at a high pulse repetition 8 frequency. These requirements also create a more complicated 9 and expensive tube construction which oten includes an internal magnetic field ~oil to minimize the above listed 11 detrimental ef~ects. Thus, it is highly desirable ~or a 12 crossed-field switch device to be ignited at high ~oltage, 13 in the order of 10 to 100 kilovolts, with a relatively low 14 magnetic ~ield, in the order of 0.01 Tesla, or 100 Gauss.
16 SUMM~RY
17 In order to aid in the understanding of this 18 invention it can be stated in essentially summary form 19 that it is directed to a gridded crossed-field switch device.
The crossed-field switch device has anode, cathode and 21 control electrodes which define a main gap and an ignition 22 gap. The control electrode is connected through an Lmpedance 23 to one of the other electrodes to prev~nt hollow cathode 24 discharge in the control gap~ The control gap can be pulsed to ignite and the plasma passes through the inter-26 mediate electrode into the main gap to cause its ignition 27 in~o the low pressure glow mode.
28 I~ is thus an obJect of this invention to provide 29 an improved gridded crossed-field switch which can s~
1 be onswitched while high voltage is applied without the 2 need for a large magnetic field pulse. It is another object 3 to provide a crossed-field switch device which has three 4 electrodes, which define an ignition gap and a main conducting gap so that ignition can be accomplished within the ignition 6 gap. It is a further object to provide a connection of 7 proper impedance between the control electrode and another 8 electrode to permit pulsing of the control electrode for 9 ignition and to prevent the initiation of hollow cathode discharge in the control gap. It is another object to 11 provide an intermediate electrode which is of gridded 12 construction with openings directly therethrough so that 13 the ignition gap and main gap are in line of sight. It 14 is a further object to provide a three electrode crossed-field switch device in which the main gap can be ignited 16 to operate in the crossed-field discharge mode without 17 requiring a pulsed magnetic ~ield.
18 Other objects and advantages of this invention 19 will become apparent ~rom a study of the ~ollowing po~tion of the speci~ication~ the claims and the attached drawings.
21 More particularly there is provided a crossed-field 22 switch tube comprising a tubular anode electrode and a coaxial 23 tubular cathode electrode spaced from said anode electrode so 2~ that the active areas of the two electrodes define a main discharge gap therebetween having a continuous closed path, 26 and means for making electrical connections to said anode and 27 said cathode electrodes and means for providing a gas at sub-28 atmospheric pressure in said main discharge gap and a magnetic 29 field above the critical value in said main discharge gap so that a glo~ mode plasma discharge can take place between said 31 anode and said cathode electrodes for conduction of said switch 32 device, characterized in that there are provided a tubular .~`` i .
6~
1 control electrode positioned adjacent to one of said anode and 2 cathode electrodes to form a continuous closed path ignition 3 discharge gap adjacent to, substantially over the whole active 4 area of and in communication with said main discharge gap, the tubular electrode positioned between the main gap and the 6 ignition discharge gap having openings therethrough so that 7 plasma can pass ~rom the ignition gap to the main gap, and 8 means for electrically pulsing said control electrode with 9 respect to its adjacent electrode on the other side of the ignition discharge gap for establishing conductive conditions 11 therein so that glow mode plasma discharge begins in the 12 ignition discharge gap and enters into substantially the entire 13 active area of the main discharge gap to cause conductive 14 condition of said main discharge gap over all of its area so that said crossed-field switch device can be turned on with 16 voltage applied thereto without magnetic field pulsing and with 17 uniform wear of said anode and cathode electrodes over their 18 entire active areas.
; 20 FIG. 1 is a longitudinal section through the gridded r 21 crossed-field switch device of ~his invention.
22 FIG. 2 is a perspective view of one of the electrodes.
23 FIG. 3 is a schematic electrical diagram showing .~
23 the connections of the gridded crossed-field switch device.
-5a-~? '~
. ~
~GQ50 1 PIG. 4 is a crossed-field breakdown curve relating 2 the conditions in the interelectrode gaps to the conductive 3 region of the breakdown curve.
4 FIG. 5 is a series of graphs showing various parameters in the gridded crossed~field switch device versus time.
7 DESCRIPTION OF_T~I~ PR~F~RRED R~IBODIMENT
8 The gridded crosse~-field switch device of this g invention i5 generally indicated at 10 in FIGS. 1 and 3. In ; 10 the schematic drawing of FIG. 3, crossed-field switch device 10 11 is shown as having an anode electrode 12, a cathode electrode 14 1~ and a control electrode 16. As will be described below, the 13 physical arrangement of the electrodes may differ, with the 1~ control electrode between the cathode and anode or even inter~
~ 15 iorly of the anode, but the preferred arrangement is as shown i 16 in ~IG. 3. These concentric electrodes define an annular space ~ 17 or gap 18 between the anode and cathode, with the annular .
1~ space 18 serving as a main ~ap in which the main glow discharge g is formed during conduction. Cathode electrode 14 and control electrode 16 define between them outer annular space 20 which 21 is the gap in which the ignition dischar~e is formed. Space 18 22 and space 20 are each in the order of 1 centimeter in the radial 23 direction. While the crossed-field switch device is shown as 24 being circular, because that is a convenient construction, other geometric constructions are also feasihle, so that the 26 gap may not be a circular annulus but may be another shape 27 such as a hollow rectangle or a hollow square. Cathode .~
28 electrode 14 has openings therethrough so that the plasma of s~ ~
l a glow discharge in one of the spaces can enter into the other 2 space. Since cathode electrode 14 is positioned between 3 anode electrode 12 and contxol electrode 16, it is n~cessarily 4 open so that the plasma can pass from the ignition gap to the main gap. The intermediate electrode has openings there-6 through which provide line of sight visibility between the 7 ignition gap and main gap.
As is seen in FIG. 3 the positive side of generator 22 9 is connected by line 24 to anode 12, while the negative side of generator 22 is connected through load 26 by line 28 ll to cathode 14. Thus~ the turning on and off of a low 12 pressure glow discharge in the main discharge gap 18 turns 13 on and off current fxom the generator through the load.
14 O course FIG. 3 is highly schematic, and the generator 22 represents any source of direc~ current. Furthermore, 16 the switchin~ on and off of the current through the load 17 is not usually accomplished only by the gridded crossed-18 field switch device lO but also by parallel in-line de~ice 19 through which the cuxrent passes during long running periods.
Control circuit 30 has line 32 connected to cathode 21 electrode 14 and line 34 connected to the control electrode 16.
22 Resistor 36 is connected between lines 32 and 34 so that unless 23 an additional voltage is supplied, controi electrode 16 is at 24 the same potential as cathode 14, by the leakage through the resistor 361 When resistor 36 is of low value, the electrodes 26 can carry substantially the same potential and a hollow 27 cathode discharge will continue in gap 20 so device lO
~8 canno~ be turned off. When resistor 36 is of too high a .
.. . .
~g6~
1 value the potential of the control electrode 16 can not be 2 properly established prior to the initial start of the 3 magnetic field pulse and spurious turn on may result~
4 A resistance value between 1 kilohm and 1 megohm typically satisfies both of these requirements~ Control circuit 30 6 permits voltage pulsing of control electrode 16 with respect 7 to cathode 14. As an example, capacitor 38, capacitor discharge rate limiting resistor 40 and switch 42 are g serially connected between lines 34 and 32. Another type of pulse supply can be substituted. A p~llse on the order 11 o 1 kilovolt is typical but voltages as low as 300V are 12 feasible.
13 FI~,. 1 shows in more detail the structure of the 14 gridded crossed-field switch device 10. Outer vessel 44 is the structural enclosure, tank or envelope which encloses the 16 electrodes and their insulated supports. Vessel 44 is vacuum 17 tight with connection 46 permittin~ drawing of a vacuum on 18 the vessel and maintenance of a proper gas supply therein at 19 a proper pressure. Usually helium at about 50 millitorr is a suitable atmosphere for the low pressure glow crossed-21 ield discharge. Vessel 44 is at cathode potential. It 22 supports cathode 14 on support ring 48 downwaxd from top 23 cover S0. Cathode electrode 14 is formed as a gr~d or 24 perforated electrode. FIG. 2 shows cathode 14 as being formed of an upper ring Sl, lower ring 52 and bars 54 26 connected therebetween to form an electrode in the form 27 of a squirrel cage. The squirrel cage intermediate electrode 28 provides a line of sight between the two gaps so that plasma 29 from the ignition gap can easily pass into the main gap.
o 1 Anode 12 is downwardly sup~orted from upper ring 50 2 on insulator 56 and is exteriorly connected by lead 58 which 3 is connected to line 24. Insulator 56 is the major insulator 4 which holds off the main anode to cathode voltage. Insulator 56 is supplied with field shaping electrodes 60 and 62 to 6 prevent glow discharge breakdown in that region.
7 Control electrode 16 is supported beneath 8 cathode 14 on insulators such as the ones shown at 64 and 9 66. Control electrode 16 is connected by lead 68 which passes through a vacuum tight insulator 70 with respect to 11 vessel 44.
12 Ionizer 72 is mounted to inject electrons into the 13 outer annular space 20 and its lead comes out through the 14 base by means of a vacuum tight insulator 74. Ionizer 72 ~/,S.
can be of the type shown in patent 3,890,52Q.
16 In accordance with the physical mechanism by which 17 the discharge operates, an axial magnetic field is provided 18 by solenoid 76. The magnetic field has a value of Bo as shown 19 in FIGs. 4 and 5, which is on the order of 100 ~auss for an interelectrode spacing of 1-2 centimeters and with a helium 21 ~as filling at S0 millitorr. The magnetic field can be 22 pulsed below the critical value Bc, (see FIGs. 4 and 5) 23 which is the leftward end of the toe of the crossed-field 24 breakdown curve 78 which separates the conductive region 80 from the nonconductive region 82.
26 The function of this equipment is best described 27 by going through an on-off cycle. Referring to FIG. 5, at 28 time to~ 9 kilovolts is first applied to the main gap 18 _g_ .
~ .
.. .. . .
3L~ 5~ ' 1 and a magnetic field of strength Bo is then applied to 2 both gaps. This places the operating condition of the 3 main gap at a point 84 in FIG. 4. This is i.n the nonconductive 4 region and therefore no current is being conducted by the gridded crossed-field switch device 10. Since control 6 electrode 16 is connected to cathode electrode 14 through 7 leak resistor 36, the voltage of the control electrode C
8 with respect to the cathode K is zero. This places the 9 operating condition of the control gap at point 89 in FIG. 4.
When on-switching is desired, for example at 11 point tl, switch 42 is closed to impress a pulse between the 12 cathode K and the control electrode C to bring the voltage 13 therebetween into the conductive region of the crossed-14 field breakdown curve, for e~ample to point 86 in FIG. 4 which represents about 1 kilovolt between the cathode and 16 the control electrode. Under these conditions, a discharge 17 in the control gap initiates~; Wi.th that gap conducting 18 in the low pressure glow discharge mode, the discharge 19 plasma seeps through the transmissive cathode structure to cause conduction of the main ,gap 18. The mechanism 21 by which the conduction starts is not clearly understood, 22 because under the initial conditions the gap is in an 23 unconducting region at point 84. However, the presence 24 of glow discharge plasma, which does not seem to need to be sufficient to reach across the entire gap, starts the 26 main gap discharge. With the beginning o~ that discharge, 27 within microseconds after the on-pulse, and thus both indicated 28 at time tl in FIG. 5, the main gap conduction current in-29 creases to 140~ and the voltage across the main gap decreases to,the discharge voltage drop, typically SOOV.
' --1 0-- , .
.:. : .
'! 1 Conduction continues either to exhaustion of t2le 2 interelectrode gas, or until magnetic field is suppressed.
3 As is seen in the bottom curve in FIG. S, the voltag~ across 4 the ignition gap quickly falls to a lower valuel due to con-duction through impedance 36, and the dis~pation of the 6 charge on capacitor 38. Conduction continues to take place 7 from the anode to both the cathode and the control electrode, 8 Off-switchin~ is then accomplished by pulsing the ma~netic ; g field below Bc. This pulsing appears at time t2 in FIG. 5 and moves the operating point to point 88 which is in the 11 nonconductive region 82 of the srosse~-field breakdown curve 12 of FIG. 4. This causes termination of the main gap discharge 13 with a buildup of voltage between the anode and cathode and 14 between the cathode and the control electrode and a termination of the current flow therebetween. Finally current flow - 16 through resistor 36 ceases and the control electrode comes 17 to the potential of the cathode and the magnetic field is 18 then reapplied. In this way the on-of cycle is completed.
~ 19 The squirrel cage type o~ structure shown in ~IG. 2 -; 20 LS an example of a preferred structure. Basically, cathode 21 electrodP 14 must have sufficient material to develop the 22 electric field and participate in the -discharge. However, 23 it must be open enough to permit the glow discharge plasma 24 to seep through from the outer ignition discharge gap to the main gap. A perforated tube can accomplish the same result.
26 The preferred maximum open area has not yet been experi-27 mentally established, however the cathode electrode 14 of 28 about 30 percent open area has been found to be feasible.
.,`.`~ ' 1 In the device actually redùced to practice, 2 resistor 36 wa`s about 1 kilohm and such a resistor seemed 3 to be necessary to produce the correct discharge. FIG. 5 4 illustrates the maximum voltage applied as being 9 kilovolts, but the limitation to this value was introduced by the 6 isolation resistors between the electrodes rather than 7 a fundamental limitation of the physical process. In fact, 8 ignition at 50 kV has been performed in the above described 9 manner.
. ~ , , . . ~
Claims (6)
1. A crossed-field switch tube comprising a tubular anode electrode and a coaxial tubular cathode electrode spaced from said anode electrode so that the active areas of the two electrodes define a main discharge gap therebetween having a continuous closed path, and means for making electrical connections to said anode and said cathode electrodes and means for providing a gas at sub-atmospheric pressure in said main discharge gap and a magnetic field above the critical value in said main discharge gap so that a glow mode plasma discharge can take place between said anode and said cathode electrodes for conduction of said switch device, characterized in that there are provided a tubular control electrode positioned adjacent to one of said anode and cathode electrodes to form a continuous closed path ignition discharge gap adjacent to, substantially over the whole active area of and in communication with said main discharge gap, the tubular electrode positioned between the main gap and the ignition discharge gap having openings therethrough so that plasma can pass from the ignition gap to the main gap, and means for electrically pulsing said control electrode with respect to its adjacent electrode on the other side of the ignition discharge gap for establishing conductive conditions therein so that glow mode plasma discharge begins in the ignition discharge gap and enters into substantially the entire active area of the main discharge gap to cause conductive condition of said main discharge gap over all of its area so that said crossed-field switch device can be turned on with voltage applied thereto without magnetic field pulsing and with uniform wear of said anode and cathode electrodes over their entire active areas.
2. A crossed-field switch tube according to Claim 1, wherein the cathode electrode and the control electrode are both positioned outside of the anode electrode.
3. A crossed-field switch tube according to Claim 2, wherein the cathode electrode surrounds the anode electrode, and the control electrode surrounds the cathode electrode.
4. A crossed-field switch tube according to Claim 1, 2 or 3, wherein the electrodes are cylindrical tubes so that the gaps are annular.
5. A crossed-field switch tube according to claim 1, 2 or 3 wherein an impedance is connected between said control electrode and its adjacent electrode on the other side of the ignition discharge gap, said impedance being sufficiently high so that said means for electrically pulsing the control electrode can bring the control electrode to ignition potential to start glow mode plasma discharge in the ignition discharge gap, and said impedance being sufficiently low so that said control electrode is held at the cathode potential when the tube is in the off state.
6. A cross-field switch tube according to claim 1, 2 or 3, wherein the tubular electrode positioned between the main gap and the ignition discharge gap has a squirrel-cage structure.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/659,604 US4034260A (en) | 1976-02-19 | 1976-02-19 | Gridded crossed-field tube and ignition method |
| US05/659,605 US4034261A (en) | 1976-02-19 | 1976-02-19 | Gridded crossed-field tube |
| US659,605 | 1991-02-21 | ||
| US659,604 | 1991-02-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1096050A true CA1096050A (en) | 1981-02-17 |
Family
ID=27097861
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA271,171A Expired CA1096050A (en) | 1976-02-19 | 1977-02-07 | Crossed-field switch tube |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1096050A (en) |
| DE (1) | DE2704419C3 (en) |
| GB (1) | GB1536513A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20130019006A (en) | 2005-05-04 | 2013-02-25 | 오를리콘 트레이딩 아크티엔게젤샤프트, 트뤼프바흐 | Plasma amplifier for plasma treatment plant |
| CN112777150B (en) * | 2020-12-24 | 2023-03-31 | 重庆智能机器人研究院 | Automatic machine of taking of public place gauze mask |
-
1977
- 1977-01-20 GB GB232777A patent/GB1536513A/en not_active Expired
- 1977-02-03 DE DE19772704419 patent/DE2704419C3/en not_active Expired
- 1977-02-07 CA CA271,171A patent/CA1096050A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2704419A1 (en) | 1977-09-01 |
| GB1536513A (en) | 1978-12-20 |
| DE2704419C3 (en) | 1979-07-05 |
| DE2704419B2 (en) | 1978-11-02 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR950011848B1 (en) | Ion implantation and surface processing method and apparatus | |
| US2489436A (en) | Method and apparatus for producing neutrons | |
| US5537005A (en) | High-current, low-pressure plasma-cathode electron gun | |
| US5502356A (en) | Stabilized radial pseudospark switch | |
| US4034260A (en) | Gridded crossed-field tube and ignition method | |
| US4034261A (en) | Gridded crossed-field tube | |
| US3714510A (en) | Method and apparatus for ignition of crossed field switching device for use in a hvdc circuit breaker | |
| US3949260A (en) | Continuous ionization injector for low pressure gas discharge device | |
| CA1096050A (en) | Crossed-field switch tube | |
| DE3942307C2 (en) | ||
| US4527044A (en) | Apparatus for treating a sample by a pulsed electron beam | |
| US4322661A (en) | Cross-field plasma mode electric conduction control device | |
| CA1099775A (en) | Method and apparatus for on-switching in a crossed- field switch device against high voltage | |
| US3678289A (en) | Magnetic field control circuit for crossed field switching devices | |
| EP1065502B1 (en) | Method for analyzing the breakdown characteristics of a gaseous dielectric in a highly non-uniform field | |
| US5159243A (en) | Hollow electrode switch | |
| US3030547A (en) | High voltage, high current spark gap switch | |
| US3087091A (en) | Spark gap switch | |
| US4071801A (en) | Crossed-field switch device and method for off-switching | |
| US3610989A (en) | Production and utilization of high-density plasma | |
| Gebel et al. | Triggered discharges with high arc voltages in a vacuum interrupter | |
| US3532915A (en) | High frequency ion source formed by a discharge between a secondary-emitting electrode and a grid | |
| Nazarov et al. | A source of high-density pulsed electron beams with energies up to 40 keV | |
| SU852135A1 (en) | Generator of powerful manosecond pulses | |
| US3519882A (en) | Gas discharge tube with magnetic means for extinguishing the discharge |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |