EP2296165A1 - Zweiteilig geschaltete Elektronenkanone - Google Patents

Zweiteilig geschaltete Elektronenkanone Download PDF

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Publication number
EP2296165A1
EP2296165A1 EP10176588A EP10176588A EP2296165A1 EP 2296165 A1 EP2296165 A1 EP 2296165A1 EP 10176588 A EP10176588 A EP 10176588A EP 10176588 A EP10176588 A EP 10176588A EP 2296165 A1 EP2296165 A1 EP 2296165A1
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EP
European Patent Office
Prior art keywords
cathode
anode
focusing electrode
electron beam
switching
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.)
Withdrawn
Application number
EP10176588A
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English (en)
French (fr)
Inventor
Richard Brownell True
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
L3 Technologies Inc
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L3 Communications Corp
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Publication date
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Publication of EP2296165A1 publication Critical patent/EP2296165A1/de
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/34—Circuit arrangements not adapted to a particular application of the tube and not otherwise provided for
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/34—Travelling-wave tubes; Tubes in which a travelling wave is simulated at spaced gaps

Definitions

  • the present invention pertains to the field of electron beam tubes and more particularly to an ungridded electron gun having an electrically isolated focusing electrode and a modulating anode.
  • travelling wave tubes TWTs
  • This can be accomplished by switching the focusing electrode of the electron gun to a voltage potential that is negative with respect to the cathode.
  • the cathode voltage potential can be switched towards ground in order to establish a negative bias on the cathode with respect to the focusing electrode.
  • the anode is generally switched from essentially ground potential to a potential approximately equal to the cathode potential, thereby reducing the electron beam current effectively to zero.
  • Figure 1 is a plot of a normalized focusing electrode cutoff voltage as a function of anode microperveance.
  • the open circles, e.g., 110, are measured cutoff voltage ratios of various electron guns having different microperveance values.
  • the microperveance of a given electron gun is a function of its geometry. It can be observed from Figure 1 that the relationship of the cutoff voltage ratio to the microperveance is quite linear. This linear relationship is illustrated by curve 102, which is an empirical fit to the measured cutoff ratios of several different electron gun designs. A linear fit 106 to the data, shows that the normalized cutoff voltage is related to microperveance by a ratio of approximately 0.44. Thus, as the anode microperveance approaches a value of 2.1, the voltage that must be applied to the focusing electrode approaches the level of the cathode-to-anode voltage itself.
  • an electron beam tube comprises a tube body and a cathode mechanically affixed to the tube body through an insulating element, wherein the cathode is adapted to emit an electron beam at an operating electron beam current.
  • the cathode is further connected to a cathode bias circuit adapted to apply a cathode bias voltage to the cathode.
  • the electron beam tube further includes an anode mechanically affixed to the tube body through an insulating element wherein the anode is connected to an anode bias circuit adapted to apply an anode bias voltage to the anode.
  • the electron beam tube further includes a focusing electrode mechanically affixed to the tube body through an insulating element wherein the focusing electrode is connected to a focusing electrode bias circuit adapted to apply a focusing electrode bias voltage to the focusing electrode.
  • the electron tube includes a switching mechanism that may comprise a plurality of individual switches in some embodiments or a single switch in other embodiments. The switching mechanism is adapted to switch the bias voltage applied to at least one of the cathode, the anode, or the focusing electrode. As a result of actuating the switching mechanism and changing the selected bias voltage or voltages, the electron beam current drops from its operating current to a current that is substantially equal to zero.
  • the switching mechanism is implemented as a single switch configured to switch a floating power supply that may be connected to multiple ones of the cathode bias circuit, the anode bias circuit, and the focusing electrode bias circuit.
  • the electron tube is configured to operate at a microperveance that is greater than approximately 0.8.
  • a microperveance that is greater than approximately 0.8.
  • Two exemplary embodiments described in detail below discuss an electron gun with a microperveance of 0.87 and an electron gun with a microperveance of 2.0. While the invention is particularly useful for electron guns operating at high perveance, it applies equally to a gun of any perveance value.
  • the switching mechanism is configured to switch one or more voltages by a magnitude of less than approximately 2000 volts while still achieving cutoff of the electron beam.
  • a typical system may have a maximum voltage magnitude of approximately 7500 volts applied to any of the cathode, anode, or focusing electrode during normal operation.
  • the switching mechanism is configured to switch voltages of a magnitude less than roughly one third of the maximum bias voltage employed during normal operation.
  • the invention would similarly be applicable to electron guns having a maximum operating voltage other than 7500 volts, and the switching mechanism would accordingly operate to provide beam cutoff by switching voltages smaller than roughly one third of the maximum operating voltage.
  • the switching mechanism is configured to switch the cathode bias voltage and the anode bias voltage.
  • the cathode will be switched to a voltage that is less negative and the anode will be switched to a voltage that is more negative than in normal operating mode.
  • the voltage difference between the cathode and anode will decrease to a sufficient extent, and electron beam cutoff will be achieved.
  • the magnitude by which the cathode and the anode are switched will be equal. In other embodiments, the cathode and anode may be switched by different magnitudes.
  • the switching mechanism is configured to switch the anode bias voltage and the focusing electrode bias voltage.
  • the magnitudes of the voltages by which the anode and focusing electrode are switched may be equal to one another or may differ.
  • the focusing electrode and the anode will both be switched such that their biases become more negative in order to achieve electron beam cutoff.
  • the switching mechanism is configured to switch the cathode bias voltage and the focusing electrode bias voltage.
  • the magnitudes of the voltages by which the cathode and focusing electrode are switched may be equal to one another or may differ.
  • the switching mechanism may be configured to switch the voltage biases applied to all three of the cathode, the anode, and the focusing electrode.
  • the magnitudes by which each bias is switched may or may not be equal to each other.
  • the electron gun may further include a collector unit configured to collect the spent electron beam.
  • the collector may comprise a multistage depressed collector having one or more stages that are depressed in voltage potential with respect to the tube body.
  • the invention provides an apparatus and method for switching voltages within a high-perveance electron gun to achieve full beam cutoff.
  • selective full-beam cutoff is achieved by switching both the cathode and the modulating anode voltages using two moderate-voltage switches.
  • This switching scheme is illustrated both for a gun with a microperveance of 0.87, shown parametrically in Figure 1 at marker 104, and for a gun with a high microperveance of 2.0, as illustrated at marker 108.
  • Figures 2a-2c depict a cross section of a preferred embodiment of an electron gun in accordance with the present invention that operates with a microperveance near 0.87.
  • the electron gun includes a cathode 208 that produces electrons to form an electron beam 204 that propagates within the electron gun.
  • the electron gun also includes a focusing electrode 206, and a modulating anode 210.
  • the cathode 208, focusing electrode 206, and modulating anode 210 are typically mounted on insulating elements (not shown) and thereby affixed to a tube body 202.
  • the cathode 208 is held at a potential of -7500 volts with respect to the tube body 202, which is held at ground potential, or 0 volts.
  • the focusing electrode 206 is held at -7500 volts, and the modulating anode 210 is held at body potential or ground.
  • a large electron beam current 204 is achieved.
  • a magnetic field is typically applied within the body of the device to counteract space charge effects that can disperse the beam.
  • the focused beam is generally cylindrical in shape.
  • the focusing electrode 206 is depicted as being at the same potential as the cathode 208, it may be desirable to bias the focusing electrode 206 slightly negative with respect the cathode, for example by -10 volts or so, in order to reduce electron emission from the side of the cathode and to improve uniformity of the current density near the edge of the cathode.
  • the basic switching principles presented herein do no preclude the application of such bias voltages; in fact, they may serve to enhance the switching methods described below.
  • both the cathode and the modulating anode voltages are switched by 1700 volts.
  • the voltage of the cathode 208 is switched from -7500 volts to -5800 volts, and the voltage of the modulating anode is switched from ground to -1700 volts. This double switching operation reduces the beam current to zero or near zero, as indicated at 224.
  • cathode and the modulating anode were both described as being switched by 1700 volts in the embodiment depicted in Figure 2c , it is not necessary to switch them symmetrically.
  • the cathode could be switched by 1900 volts and the modulating anode could be switched by -1500 volts, and a similar effect on the beam current would be produced.
  • Systems that are switched asymmetrically, as described above, would also fall within the scope and spirit of the present invention.
  • Figures 3a and 3b illustrate an alternative embodiment of an electron gun in accordance with the present invention for a gun with a microperveance of 2.0.
  • the focusing electrode 306 is at a potential of -5.35 kV
  • the modulating anode 310 and body 302 are set at a potential of 0 kV.
  • the cathode 308 is switched from -5.35 kV toward ground by 1.7 kV, as shown at 308, to create a potential difference of -3.65 kV between the cathode 308 and modulating anode 310.
  • element 108 a gun operating at a microperveance of 2.0 requires a cutoff voltage of 91 % of the cathode-to-anode voltage. Because 0.91 multiplied by - 3.65 kV is -3.33 kV, which is larger in magnitude than -1.7 kV, the electron beam is not fully cut off, as illustrated at 304. However, in Figure 3b , the modulating anode 310 is also switched by -1.7 kV, in accordance with the present invention. This creates a potential between the cathode and modulating anode of 1.95 kV. Multiplied by 0.91, this gives -1.78 kV as the cutoff voltage, which is very close to - 1.7 kV, resulting in the electron beam's being nearly completely cut off, as indicated at 324.
  • control of the electron beam current can be achieved by switching a single element, such as the cathode; by switching two elements, such as the cathode and modulating anode, or the focusing electrode and modulating anode; or by switching all three elements.
  • the focusing electrode would have to be switched negative by -3060 volts with respect to cathode, or to -10,560 volts with respect to ground, in order to achieve full beam cutoff.
  • K' K'/(1-K').
  • K K'/(1-2K')
  • K' 0.224670.
  • this embodiment has the advantage of leaving the cathode voltage constant. Because the cathode draws significant current, it is much simpler to switch the focusing electrode or the modulating anode than it is to switch the cathode.
  • Figure 4 is a graphical depiction of the cutoff voltage to anode voltage ratio versus the anode microperveance for cases A, B, C, and D, described above.
  • case C the first dual-switched case
  • the cutoff voltage ratio for an electron gun using any of the cutoff switching schemes A, B, C, or D can be predicted for a gun of any microperveance.
  • the dual switching schemes depicted at 360 and 370 become particularly advantageous for high microperveance guns, reducing the switching voltage required for cutoff by a factor of two or more over the standard switching mode 350.
  • Figures 5 - 10 depict the results of several electromagnetic simulations using an electron transport code known as DEMEOS of an electron gun in accordance with an embodiment of the present invention.
  • a 7500-volt electron gun is illustrated, showing that full beam cutoff can be achieved using two 1700-volt switches.
  • Figure 5 shows the gun during normal operation with 100% beam transmission.
  • the cathode 408 and focusing electrode 406 are held at a potential of -7.5 kV.
  • the modulating anode 402 and body 404 are at ground potential.
  • the periodic permanent magnet or PPM field on axis used to focus the beam in this case is shown in the figure at 412. In actuality, the average sinusoidal field level is displaced but a small amount from zero Gauss.
  • electron beam 410 is fully transmitted at a power level of 4244.3 watts and a current of 565.9 mA.
  • the focusing electrode 406 is switched 1700 volts negative with respect to the cathode 408. This results in a reduction of the electron beam flux 510.
  • the emitted beam current is approximately 39 mA, resulting in a net power in the beam of 290 watts. Since approximately 60.7% of the beam current is transmitted, net power on the body beam shaver is 114.2 watts. This may result in a heat load high enough to cause melting.
  • the remainder of the beam current that makes its way down the travelling wave tube (TWT) or other linear beam microwave tube can provide amplification of noise, which may be unacceptable.
  • TWT travelling wave tube
  • the focusing electrode 406 is switched 1700 volts negative with respect to the cathode 408, and the modulating anode 402 is also switched 1700 volts negative with respect to ground. Beam current and body power are both significantly lower in comparison to the case shown in Figure 6 .
  • the anode 402 may be biased to +7500 volts with respect to the focusing electrode 406 using a fixed-voltage floating power supply or similar device connected between the anode 402 and the focusing electrode 406.
  • the focusing electrode 406 is switched to - 1700 volts below the potential of the cathode 408, the voltage of the anode 402 will follow, bringing it to -1700 volts below ground.
  • a simplified configuration implementing this scheme according to an embodiment of the present invention is depicted in Figure 12 , described further below.
  • the cathode 408 is instead switched 1700 volts positive with respect to the focusing electrode 406.
  • the emitted beam current is 8.3 mA and the net beam power is 48.2 watts.
  • This level of current is similar to the case shown in Figure 7 .
  • the beam transmission is 64.6%, so the power load on the power shaver is 17.1 watts. While this level of body power is not unduly high and will not cause damage to the tube, the beam current progressing through the circuit can lead to increased amplified noise that may be undesirable in certain systems.
  • FIG 11 depicts an embodiment of an electron beam tube power supply switching circuit in accordance with the present invention that can be used to provide the dual switching function described above.
  • the electron tube comprises a cathode 802, a focusing electrode 804, a modulating anode 806, a main body 808, and a multi-stage depressed collector unit comprising a first collector 810 and a second collector 812.
  • a power supply 814 is used to supply current to a cathode heater 820.
  • Further voltage sources 822, 824, 826, 828, and 830 are used to bias various components of the electron tube.
  • Cathode bias circuit 840 is used to supply a bias voltage to the cathode 802.
  • Focusing electrode bias circuit 842 is used to apply a voltage bias to the focusing electrode 804, and anode bias circuit 844 is used to supply a voltage bias to anode 806.
  • focusing electrode bias circuit 842 is fixed at -7.5 kV by series power supplies 822, 824, and 830.
  • the cathode is normally at -7.5 kV, when switch 816, connected to cathode bias circuit 840, is in the position indicated by the solid arrow. By throwing the first 1700-volt switch 816 to the position indicated by the dashed arrow, the cathode voltage can be reduced in magnitude to -5.8 kV.
  • a second 1700-volt switch 818 is connected to anode bias circuit 844 and can be used to switch a bias applied to the modulating anode from ground (solid arrow position) to -1.7 kV (dashed arrow position).
  • the combined effect of the switching operation comprising changing the position of the two switches 816 and 818 results in a full cutoff of beam current, as described previously.
  • FIG 12 is a simplified schematic drawing of another embodiment of an electron beam tube power supply switching circuit in accordance with the present invention.
  • the electron tube includes a cathode 902, a focusing electrode 904, an anode 906, and a tube body 908.
  • a power supply 916 supplies current to a cathode heater 918.
  • a fixed floating power supply 914 is situated between the focusing electrode 904 and the anode 906 to maintain a constant potential difference between these two components.
  • Focusing electrode bias circuit 932 and anode bias circuit 934 are connected to the two terminals of floating power supply 914.
  • the switching mechanism comprises a single switch 920 operatively coupled to both the focusing electrode bias circuit 932 and the anode bias circuit 934.
  • Actuating switch 920 alternatively ties the negative terminal of the floating supply 914 to the negative terminal of the cathode power supply 910 or to the negative terminal of the 1.7 kV floating power supply 912.
  • the anode 906 and tube body 908 are both held at ground potential
  • the focusing electrode 904 is held at -7.5 kV by the cathode power supply 910
  • the cathode 902 is held at -7.5 kV by the cathode power supply 910.
  • Switch 920 can then be thrown to the position indicated by the dashed arrow, and both the anode bias circuit 934 and the focusing electrode bias circuit 932 are pulled negative by 1.7 kV by connection to the negative terminal of the 1.7 kV floating power supply 912.
  • the anode 906 will end up at -1.7 kV and the focusing electrode 904 will move to -9.2 kV, cutting off the electron beam current, as shown previously in the simulation depicted in Figure 7 .
  • the dual switching of the focusing electrode 904 and the anode 906 is achieved with a single switch 920.
  • the floating power supply could also be connected between elements other than the focusing electrode and the anode depending on the desired switching configuration.
  • FIG. 13 depicts an alternative embodiment of a power supply switching circuit for an electron beam tube in accordance with an aspect of the present invention.
  • the figure depicts a cathode 1002 coupled to a cathode heater 1018 and cathode heater power supply 1016.
  • the cathode 1002 is further connected to a cathode bias circuit 1030 that applies a voltage bias of -7.5 kV to the cathode via power supplies 1010 and 1014.
  • Focusing electrode 1004 is connected to focusing electrode bias circuit 1032, which is in turn coupled to switch 1020. In its normal operating position (solid arrow), switch 1020 bypasses power supply 1012 such that the focusing electrode remains at a potential of -7.5 kV.
  • FIG 14 depicts an alternative embodiment of a power supply switching circuit for an electron beam tube in accordance with an aspect of the present invention.
  • Cathode 1102 is coupled to a cathode heater 1118 and cathode heater power supply 1116.
  • the cathode 1102 is further connected to a cathode bias circuit 1130 that applies a voltage bias of -7.5 kV to the cathode via power supplies 1110 and 1114.
  • Focusing electrode 1104 is connected to focusing electrode bias circuit 1132, which is in turn coupled to switch 1120. In its normal operating position (solid arrow), switch 1120 bypasses power supply 1112 such that the focusing electrode remains at a potential of -7.5 kV.
  • anode 1106 is connected to anode bias circuit 1134, which includes a voltage divider formed by resistors R1 (1140) and R2 (1142) connected between -1.7 kV and ground. Because the anode does not draw significant current, R1 can be selected to be a large value, such as 10 M ⁇ . If R2 is then selected to have a value of 0 ⁇ , the leakage current when switch 1122 is in the normal operating position (solid arrow) is only 0.17 mA. In such a configuration, the anode 1106 is held at ground potential in normal operating mode, and when switch 1122 is opened (dashed position), the anode drops to -1.7 kV, and the leakage current drops to zero.
  • the anode when switch 1122 is closed (solid position), the anode is set to a bias voltage given by the voltage of power supply 1114 multiplied by R2 and divided by R1+R2. For example, if R2 is selected to be 1.11 M ⁇ , and R1 is set at 10 M ⁇ , the anode bias voltage when switch 1122 is closed will be -170 V. As discussed previously, it can be desirable to bias the anode 1106 to such a voltage below ground potential in order to adjust the current emitted from the electron gun in its normal beam-on operational mode. The embodiment shown in Figure 14 thus provides one method of achieving this goal. In normal operating mode with switch 1122 closed, the leakage current in this example would be only 0.153 mA.

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EP10176588A 2009-09-14 2010-09-14 Zweiteilig geschaltete Elektronenkanone Withdrawn EP2296165A1 (de)

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US24230809P 2009-09-14 2009-09-14
US87397910P 2010-09-01 2010-09-01

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4247801A (en) * 1979-03-02 1981-01-27 Raytheon Company Cathode current control system
US4323853A (en) * 1979-02-23 1982-04-06 Nippon Electric Co., Ltd. Circuit for protecting traveling-wave tubes against faults of a power supply
WO1985000074A1 (en) * 1983-06-16 1985-01-03 Hughes Aircraft Company Grid structure for certain plural mode electron guns
US4638215A (en) * 1983-03-30 1987-01-20 Siemens Aktiengesellschaft Circuit assembly for temperature-dependent cathode current tracking in traveling-wave tubes
US5744919A (en) * 1996-12-12 1998-04-28 Mishin; Andrey V. CW particle accelerator with low particle injection velocity
WO2000030145A1 (en) * 1998-11-16 2000-05-25 Litton Systems, Inc. Low-power wide-bandwidth klystron
EP1814134A2 (de) * 2006-01-31 2007-08-01 NEC Microwave Tube, Ltd. Netzteilgerät und Hochfrequenzschaltungssystem

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4323853A (en) * 1979-02-23 1982-04-06 Nippon Electric Co., Ltd. Circuit for protecting traveling-wave tubes against faults of a power supply
US4247801A (en) * 1979-03-02 1981-01-27 Raytheon Company Cathode current control system
US4638215A (en) * 1983-03-30 1987-01-20 Siemens Aktiengesellschaft Circuit assembly for temperature-dependent cathode current tracking in traveling-wave tubes
WO1985000074A1 (en) * 1983-06-16 1985-01-03 Hughes Aircraft Company Grid structure for certain plural mode electron guns
US5744919A (en) * 1996-12-12 1998-04-28 Mishin; Andrey V. CW particle accelerator with low particle injection velocity
WO2000030145A1 (en) * 1998-11-16 2000-05-25 Litton Systems, Inc. Low-power wide-bandwidth klystron
EP1814134A2 (de) * 2006-01-31 2007-08-01 NEC Microwave Tube, Ltd. Netzteilgerät und Hochfrequenzschaltungssystem

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