Abstract
An apparatus for modulating the density of an electron beam as it is emitted from a cathode, comprised of connecting a source of pulsed input power to the input end of a nonlinear transmission line and connecting the output end directly to the cathode of an electron beam diode by a direct electrical connection.
Claims
1. An apparatus for modifying the density of an electron beam being emitted from a cathode comprising: a nonlinear transmission line having an output; an electrical connection for connecting the nonlinear transmission line to a source of pulsed output power; an electron beam diode having a cathode; and an electrical connection for connecting the output of the nonlinear transmission line to the cathode of the electron beam diode.
2. The apparatus as defined by claim 1, wherein the electrical connection is a direct electrical connection.
3. The apparatus as defined by claim 1, wherein the electrical connection is a capacitive or inductive coupling.
4. The apparatus as defined by claim 1, wherein the electrical connection is a direct electrical connection.
5. The apparatus as defined by claim 1, wherein the electrical connection is a capacitive or inductive coupling.
6. An apparatus for modifying the density of an electron beam as the beam is being emitted from a cathode, comprising: a nonlinear transmission line having an impedance and an output; an electrical connection for connecting the nonlinear transmission line to a source of pulsed input power; the output of the nonlinear transmission line for being connected to an impedance transformer having a transformer output; an electron beam diode having a cathode and having an electron beam diode impedance; and the transformer output for being connected to the cathode of the electron beam diode, for matching the electron beam diode impedance with the impedance of the nonlinear transmission line.
7. The apparatus as defined by claim 6, wherein the electrical connection between the nonlinear transmission line and the source of pulsed input power is a direct electrical connection.
8. The apparatus as defined by claim 6, wherein the electrical connection between the nonlinear transmission line and the source of pulsed input power is a capacitive or inductive coupling.
9. The apparatus as defined by claim 6, wherein the electrical connection between the dispersive nonlinear transmission line and the source of pulsed input power is a direct electrical connection.
10. The apparatus as defined by claim 6, wherein the electrical connection between the source of pulsed input power and the dispersive nonlinear transmission line and the source of pulsed input power is a capacitive or inductive coupling.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a conceptual drawing which describes the coupling of a nonlinear transmission line to the cathode or anode of an electron beam diode in order to allow for the generation of a modulated electron beam.
(2) FIGS. 2A, 2B and 2C comprise conceptual drawings which respectively describe the coupling of a nonlinear transmission line to the cathode or anode of an electron beam diode via an impedance transformer, a capacitive connection, and an inductive connection, to provide for the generation of a modulated electron beam.
(3) FIG. 3 is a plot of the input signal for a hypothetical non-dispersive nonlinear transmission line shock line.
(4) FIG. 4 is a plot of the output signal for a hypothetical non-dispersive nonlinear transmission line shock line. The long rise time input pulse of FIG. 3 is converted to a very short rise time voltage pulse by the shock line.
(5) FIG. 5 is plot of the predicted cathode current as a function of time for a cathode with an emission threshold of Vt.sub.0 in an electron beam diode across which the voltage waveform of FIG. 4 is applied.
(6) FIG. 6 is a plot of the input and output voltage signals for a dispersive nonlinear transmission line. The input signal is converted to a modulated output signal by the nonlinear transmission line.
(7) FIG. 7 is a plot of the output voltage signal of FIG. 6 applied as applied across an electron beam diode with voltage thresholds Vt.sub.1 and Vt.sub.2 shown.
(8) FIG. 8 is a plot of the expected current output of a cathode which is driven by the output of the nonlinear transmission line associated with the traces depicted in FIG. 6 and which has the emission threshold voltage Vt.sub.1.
(9) FIG. 9 is a plot of the expected current output of a cathode which is driven by the output of the nonlinear transmission line associated with the traces depicted in FIG. 6 and which has the emission threshold voltage Vt.sub.2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
(10) FIG. 1 is a conceptual drawing of one embodiment of the present invention in which a nonlinear transmission line 1 (NLTL) is coupled to an electron beam diode of an electron beam device 2. A first terminal 3 of the electron beam diode is connected to the output of the nonlinear transmission line (NLTL) 1 via a connection 4 which can represent either a direct connection between terminal 3 and the NLTL or a connection via a length of transmission line. In this drawing, a second terminal 5 is connected to ground 6. In the case where the modulated potential applied to the first terminal 3 is negative with respect to the grounded terminal 5, the first terminal 3 will be the cathode and the modulated electron beam 7 will travel from the cathode toward the grounded terminal or anode 5. In the case where the modulated potential applied to the first terminal 3 is positive with respect to the grounded terminal 5, the grounded terminal will be the cathode and the modulated electron beam 7 will travel from the cathode 5 toward the anode 3. The input pulser 8 provides pulsed input power to the NLTL. The NLTL may be coupled to the anode or cathode of an electron beam diode by either a direct electrical connection or via a capacitive or inductive coupling connection. The specific nature of the connection will change depending on the type of NLTL or cathode/anode used as would be apparent to one skilled in the art.
(11) The nonlinearity of the electromagnetic response of the nonlinear transmission line may be due nonlinear dielectric materials, nonlinear magnetic materials, or a combination of nonlinear dielectric and nonlinear magnetic materials. Additionally, this nonlinear transmission line may be dispersive or a shock line.
(12) FIG. 2A depicts a NLTL coupled to an electron beam diode 2 via an impedance transformer 9. This type of configuration would prove to be advantageous in cases where the electron beam diode impedance differs substantially from the output impedance of the NLTL. Alternatively, the impedance transformer 9 of FIG. 2A may simply consist of the capacitive coupling 28 shown in FIG. 2B or the inductive coupling 29 shown in FIG. 2C.
(13) The electron beam diodes depicted in FIG. 1 and FIG. 2 are greatly simplified to allow for ease of understanding of the present invention. Additionally, although the grounded terminal 5 of FIG. 1 and FIG. 2 is shown to be tied to ground for the sake of simplicity, both the cathode and anode could, in principle, be separately biased with respect to ground such that the effective voltage across the diode would be the difference of the dc biases on the cathode and anode plus the modulated voltage output of the NLTL.
(14) FIG. 3 is a plot of an input signal of a simulated nonlinear transmission line shock line. The long rise time input voltage pulse 10 is sharpened to a much shorter rise time voltage pulse 11 during its transit down the shock line as seen in FIG. 4. The voltage scales and the time scales in both plots are normalized. The voltage threshold Vt.sub.0 is chosen as an example emission threshold for a hypothetical cathode.
(15) FIG. 5 is a plot of the predicted cathode current 16 as a function of time for a cathode with an emission threshold of Vt.sub.0 in a electron beam diode, across which the voltage waveform 11 of FIG. 4 is applied. For the purposes of this illustration, it was assumed that the cathode is an idealized space-charge-limited emission cathode in which the electron emission scales as a function of voltage to the 3/2 power, V.sup.3/2. In actual practice, the emission properties and type of each individual cathode must be taken into account when calculating predicted current yields. The cathode current scale in this plot is normalized for simplicity. The time scale is the same as that used in FIG. 4.
(16) FIG. 6 is a plot of the input and output voltage signals from a simulated dispersive nonlinear transmission line. The NLTL converts the video pulse-like input signal 18 into an RF output signal or output signal consisting of a series of electromagnetic soliton-like pulses 19. A normalized voltage scale and time scale were used in this plot. The output signal 19 of the NLTL data in FIG. 6 is again shown in FIG. 7 as it is applied across an electron beam diode. The voltage thresholds Vt.sub.1 and Vt.sub.2 are also shown. These voltage thresholds represent electron emission voltage thresholds for two different hypothetical cathodes. The voltage scale and time scale are the same as those used in FIG. 6. As will be evident from the next two figures, the choice of emission threshold allows a degree of control of the modulation amplitude imposed on the electron beam.
(17) FIG. 8 is a plot of the predicted cathode current 24 as a function of time for a cathode with emission threshold Vt.sub.1 in an electron beam diode, across which the voltage waveform 19 of FIG. 7 is applied. For the purposes of this illustration, it was assumed that the cathode is an idealized space-charge-limited emission cathode in which the electron emission scales as a function of voltage to the 3/2 power, V.sup.3/2. As is evident from the plot, the cathode would emit an electron beam which is modulated at the frequency of the output of the NLTL. The cathode current scale is normalized for simplicity. The time scale is the same as that used in FIG. 6.
(18) FIG. 9 is a plot of the predicted cathode current 24 as a function of time for a cathode with emission threshold Vt.sub.2 in an electron beam diode, across which the voltage waveform 19 of FIG. 7 is applied. For the purposes of this illustration, it was assumed that the cathode is an idealized space-charge-limited emission cathode in which the electron emission scales as a function of voltage to the 3/2 power. In this case, the choice of electron emission of the cathode results in stronger relative modulation of the electron beam in that discrete electron bunches being emitted from the cathode at the frequency of the output of the NLTL. The cathode current scale is normalized for simplicity. The time scale is the same as that used in FIG. 6.
