Operation of a system for generating electromagnetic waves in the microwave range

Abstract

The invention relates to a method for operating a system for generating electromagnetic waves in the microwave range, wherein the system comprises a pulse generator for generating electrical pulses, a microwave generator (14) for generating microwaves, and a transmission line (13) between the pulse generator (10) and the microwave generator (14), wherein the method comprises: blocking a voltage output from the pulse generator (10) to the transmission line (13); after the blocking of the voltage output: outputting a voltage from the pulse generator (10) to the transmission line (13), wherein the voltage is below an ignition voltage of the microwave generator (14), in order to precharge the transmission line (13); after the precharging of the transmission line (13): outputting a voltage to the transmission line (13), said voltage being above the ignition voltage of the microwave generator (14), such that the microwave generator (14) generates electromagnetic waves in the microwave range.

Description

[0001] Description

[0002] Operating a system for generating electromagnetic waves in the microwave range

[0003] The invention relates to a method for operating a system for generating electromagnetic waves in the microwave range, a control device for controlling a pulse generator of a system for generating electromagnetic waves in the microwave range, a system for generating electromagnetic waves in the microwave range and a therapy and / or imaging device.

[0004] For example, in radiation therapy as well as in non-destructive material testing, transit-time tubes, such as magnetrons or klystrons, are used to generate electromagnetic fields in the microwave range. These transit-time tubes can be operated in pulsed mode to achieve high power levels, particularly in the megawatt range. A challenge lies in transmitting the corresponding current or voltage pulses from a pulse generator, especially a modulator, to a beam head or radiation source. In particular, it is often necessary to position the pulse generator and the beam head separately, for example, to adjust the system's center of gravity or for radiation protection reasons (e.g., to protect the electronics from neutrons).The electrical characteristics of a delay tube can change abruptly as soon as an applied supply voltage exceeds a threshold value of the delay tube, which can be referred to as the ignition voltage or breakdown voltage. In pulsed operation, this effect typically occurs with each voltage pulse. This can lead to undesirable fluctuations in the supply current or supply voltage of the delay tube.

[0005] To address this problem, the prior art offers an approach of impedance-matched transmission. Impedance matching can be achieved, in particular, by a transformer at the radiation source. Another possibility is dynamic impedance matching. For example, modulators based on Marx topology (Marx generators) with integrated matching transformers and unmatched transmission lines can be used. This variant is described in DE 10 2011 086 551 A1.

[0006] A device for generating sputtering of a target to produce a coating on a substrate is described in US 2008 / 135 400 A1. The device includes a magnetron with a cathode and an anode. A power supply is operationally connected to the magnetron, and at least one capacitor is operationally connected to the power supply. The device also includes an inductor that is operationally connected to the at least one capacitor. A first and a second switch are also provided. The first switch operationally connects the power supply to the magnetron to charge the magnetron and is configured to charge the magnetron according to a first pulse. The second switch is operationally connected to discharge the magnetron. The second switch is configured to discharge the magnetron according to a second pulse.

[0007] EP 4 069 117 B1 relates to a bipolar pulse generator circuit for an electrosurgical generator for producing a waveform suitable for electroporation of biological tissue. The bipolar pulse generator circuit comprises a voltage source that can be connected to a load via a switching element, and a coaxial transmission line whose inner conductor is separated from an outer conductor by a dielectric. The inner conductor has a first end that is connected between an input of the switching element and the voltage source, and a second end that is in an open circuit, allowing the coaxial transmission line to be charged by the voltage source when the switching element is in the OFF state and discharged when the switching element is in the ON state.The bipolar pulse generator circuit further comprises a first output, connectable to the load, wherein this first output is located between an output of the switching element and ground to assist in a positive pulse when the coaxial transmission line is discharged, and a second output, connectable to the load, wherein this second output is located between the outer conductor of the coaxial transmission line and ground to assist in a negative pulse when the coaxial transmission line is discharged. The characteristic impedance of the coaxial transmission line is designed to be equal to the sum of (i) the resistance of the switching element, (ii) the resistance of the load at the first output, and (iii) the resistance of the load at the second output.

[0008] While the described solutions can generally solve the problem of unwanted fluctuations, it would be desirable to find an improved solution. An improved solution could allow for more possibilities in the design of corresponding systems, in particular, it could respond more flexibly to requirements such as available space, components to be used, etc. For example, the improved solution should preferably also be able to function without impedance-matched, conducted high-voltage pulse transmission and / or without a matching transformer. It is therefore an object of the present invention to find an improved solution for the transmission of electrical pulses from a pulse generator or modulator to a beam head or a beam source. Furthermore, it would be desirable to find a solution with which some components used according to prior art solutions are not required or are replaced.which can save installation space and / or weight.

[0009] This problem is solved by a method according to claim 1, a control device according to claim 8, a system according to claim 9, and a therapy and / or imaging device according to claim 15. Further features and advantages will become apparent from the dependent claims, the description, and the accompanying figures.

[0010] According to a first aspect of the invention, a method for operating a system for generating electromagnetic waves in the microwave range is provided, wherein the system comprises a pulse generator for generating electrical pulses, in particular electrical voltage pulses and / or electrical current pulses, a microwave generator for generating microwaves, and a transmission line between the pulse generator and the microwave generator. The method comprises the following steps:

[0011] - Blocking a voltage output from the pulse generator to the transmission line, wherein the output of the voltage to the transmission line is controlled by means of an adjustable voltage divider, the adjustable voltage divider comprising an adjustable first partial resistor at the output of the pulse generator and a second partial resistor connected behind the adjustable first partial resistor and in parallel to the microwave generator, wherein the output of the voltage is controlled by adjusting the adjustable first partial resistor;

[0012] - after blocking the voltage output: outputting a voltage from the pulse generator to the transmission line, where the voltage is below an ignition voltage of the microwave generator, to precharge the transmission line;

[0013] - After precharging the transmission line: Applying a voltage to the transmission line that is at or above the ignition voltage of the microwave generator, in particular increasing the voltage to the voltage at or above the ignition voltage, so that the microwave generator produces electromagnetic waves in the microwave range.

[0014] Advantageously, a non-impedance-matched transmission line can thus be used to implement voltage pulse transmission, particularly high-voltage pulse transmission, to the microwave generator. It has been found that excessive overshoot at the beginning of the electrical pulses can be largely prevented by precharging the transmission line according to the invention. Specifically, pulse transmission can be implemented without a matching transformer. This means, in particular, that a corresponding system can be designed such that both the pulse generator and the transmission line or the pulse transmission chain can be designed without a transformer, especially without a high-voltage transformer. This results in savings in the required installation space and weight.In general, the method is flexible with regard to the length of the transmission line, allowing for distances between the pulse generator and microwave generator on the order of meters as well as centimeters. Pulse transmissions over several meters, for example up to 30 meters, can also be achieved using this method. In particular, the method can be computer-implemented. In other words, the process steps can be controlled by a computer and / or a suitably programmed control device.

[0015] The system used for the process comprises a pulse generator for generating electrical pulses. These pulses can be, in particular, electrical voltage pulses and / or electrical current pulses. The pulse generator can also be referred to as a pulse generator. Generally, the pulse generator can be understood as a device designed to generate electrical pulses. The pulse generator can be a modulator for generating and / or modulating electrical pulses, in particular voltage pulses and / or current pulses. The pulse generator can be provided without an HV transformer. HV stands for high voltage. High voltage refers in particular to voltages above 30 volts. Within the scope of this process, voltages of the transmitted voltage pulses in the kilovolt range can be provided. The pulse generator is electrically connected to the microwave generator via the transmission line.

[0016] A microwave generator is generally a device designed to generate microwaves or electromagnetic radiation in the microwave range. In particular, the microwave generator is designed to generate microwaves based on electrical pulses. The microwave generator can, in particular, be a transit-time tube. A transit-time tube can generally be understood to be an electron tube that generates or amplifies microwave signals or radio frequency signals based on the transit time of electrons. In particular, the microwave generator can be a magnetron or a klystron. Preferably, the microwave generator can be designed to generate microwaves with a frequency in the gigahertz range, particularly in the range of 1 GHz to 20 GHz, and more preferably in the range of 3 GHz to 10 GHz. The microwave generator can also be referred to as an RF source (RF for radio frequency).The microwave generator can be part of a beamhead of the system, or the system can include a beamhead in which the beamhead includes the microwave generator. The microwave generator has a trigger voltage. The trigger voltage is the minimum voltage at which the microwave generator begins operating, i.e., generating microwaves. In other words, the microwave generator enters a microwave-generating operating mode at or above the trigger voltage. Below the trigger voltage, the microwave generator accordingly does not generate microwaves, or at least not significant amounts of microwaves. In particular, below the trigger voltage, the microwave generator can be in a standby mode, waiting for the next electrical pulse. The trigger voltage can also be referred to as the breakdown voltage of the microwave generator.Typically, below the ignition voltage, the microwave generator essentially conducts no current or draws essentially no current.

[0017] A transmission line is provided between the pulse generator and the microwave generator for transmitting the electrical pulses. This transmission line can be, in particular, a transmission cable. Specifically, the transmission line is an electrical conductor. For example, the transmission line can be a coaxial cable. The length of the transmission line can be in the range of meters, particularly in the range of 10 to 30 meters. This length of transmission line can be advantageous because it allows for spatial separation of the pulse generator and the microwave generator. For example, the electronics of the pulse generator can thus be protected from neutrons generated in a beam head of the system by the spatial separation.Furthermore, a sufficiently long transmission line can enable spatial separation of the components, which in particular allows individual system parts to be lighter. This can facilitate installation, maintenance, and / or replacement of components. However, a shorter transmission line, for example, with a length on the order of centimeters, is also possible within the scope of the invention.

[0018] During the process, a voltage output from the pulse generator to the transmission line is initially blocked. This blocking of the voltage output can be achieved by blocking a line connection. The blocking and output of a voltage can be cyclically repeated, particularly in pulsed operation. In other words, the process steps can be repeated multiple times.

[0019] After the voltage output is blocked, a voltage is output from the pulse generator to the transmission line. This voltage output can also be linked to an output of an electric current. The voltage is below the ignition voltage of the microwave generator. For example, a nominal voltage value can be between 50% and 95%, preferably 70% and 90%, and particularly preferably 75% and 85%, of the microwave generator's ignition voltage. Advantageously, the voltage, initially below the ignition voltage, can be used to pre-charge the transmission line. A sudden switch-on of the voltage typically leads to a fluctuation in the current introduced into the transmission line, which can thus rise, particularly temporarily or at the beginning, to higher values ​​than the intended nominal current value.Advantageously, selecting a voltage below the ignition voltage prevents a significant increase in the microwave generator's current. Specifically, below the ignition voltage, the microwave generator typically has such a high impedance that no substantial operating current flows through it. Therefore, the microwave generator's current can be kept at a negligible low level.

[0020] After the transmission line has been pre-charged, a voltage is applied to the transmission line that is at or above the ignition voltage of the microwave generator. The term "above the ignition voltage" is to be interpreted broadly. Specifically, it means that the voltage is increased sufficiently for the microwave generator to enter an operating mode in which it generates microwaves or electromagnetic waves in the microwave range. Setting the voltage below the ignition voltage can, particularly due to the pre-charging process, lead to a delayed actual voltage increase during pre-charging. It may be possible to initiate an increase in the voltage above the ignition voltage once a nominal output voltage value is reached. This increase in voltage above the ignition voltage may be implemented abruptly."Jump-type" here refers to the limitations of the electronic components' technical capabilities, meaning that a certain technically induced delay is also included. Pre-charging the transmission line significantly reduces current and voltage overshoots in the microwave generator. This is achieved through a two-stage, and especially dynamic, application of the voltage or voltage pulse. It has been found that pre-charging to 70% to 90%, and particularly 75% to 85%, of the ignition voltage is especially advantageous for preventing oscillations. For example, the microwave generator can operate at a voltage of 40 kV, and the voltage is initially set to 32 kV for pre-charging before being increased to 40 kV. It can be implemented that the output voltage of the pulse generator is blocked again at the end of the voltage pulse.Re-blocking can optionally be implemented abruptly.

[0021] According to one embodiment, the voltage output to the transmission line is controlled by means of an adjustable voltage divider. An adjustable voltage divider can provide a simple way to adjust the voltage on the transmission line. In particular, the voltage divider can be used to adjust the voltage applied to the microwave generator. For example, the adjustable voltage divider can comprise an adjustable first resistor and a second resistor, with one of the two resistors connected at the output of the pulse generator and the other resistor connected downstream of the first resistor and in parallel with the microwave generator. In this case, the voltage output can be controlled by adjusting the first resistor.

[0022] According to one embodiment, the adjustable voltage divider comprises an adjustable first resistor at the output of the pulse generator and a second resistor connected downstream of the adjustable first resistor and in parallel with the microwave generator, the voltage output being controlled by adjusting the first resistor. The second resistor can optionally be connected upstream of the transmission line. In other words, the second resistor can be placed between the first resistor and the transmission line. Alternatively, the second resistor can be placed downstream of the transmission line. If the second resistor is placed upstream of the transmission line, it can optionally be provided that at least one intrinsic resistance of the pulse generator is used as the second resistor. The adjustable resistor can thus function as a switch.In particular, the adjustable partial resistor can be set to a very high resistance value or to a (virtually) infinitely high resistance value to block a voltage output. A very high resistance value can preferably be a resistance value that is greater than the resistance value of the second partial resistor, in particular by an order of magnitude or more. Within the scope of this invention, an order of magnitude is to be understood in particular as an order of magnitude in the decimal number system. Accordingly, an order of magnitude denotes a factor of essentially 10. Preferably, the resistance value of the second partial resistor is greater, in particular by at least an order of magnitude, than the resistance of the microwave generator in operating mode.For example, the second resistor can have a resistance value in the kiloohm range (kΩ range), particularly in the range of 2 kΩ to 20 kΩ, preferably in the range of 5 kΩ to 15 kΩ. A magnetron, for instance, can have an operating resistance of 400 Ω. In this case, the second resistor can, for example, have a resistance value of 10 kΩ. By making the resistance value of the second resistor larger, particularly by at least an order of magnitude, than the resistance of the microwave generator, it can be ensured that a substantial portion of the current, in particular almost the entire current, flows through the microwave generator during operation. The adjustable resistor can comprise a series connection of adjustable resistors. Advantageously, the required high voltages can thus be controlled even with relatively simple components.

[0023] According to one embodiment, the adjustable first partial resistance for outputting the voltage to the transmission line, which is below the ignition voltage of the microwave generator, is set to a first substantially constant resistance value, wherein the adjustable first partial resistance for outputting the voltage to the transmission line, which is at or above the ignition voltage of the microwave generator, is set to a second substantially constant resistance value, the second resistance value being lower than the first resistance value. In particular, the second resistance value can be lower than the first resistance value by a factor of at least 10, preferably at least 1,000, and most preferably at least 100,000. In other words, the output voltage can thus be controlled by adjusting the resistance value, with a lower resistance enabling a higher voltage.A factor of at least 100,000 (100k) is particularly advantageous. It has been found that this effectively prevents excessive fluctuations in the current from the microwave generator.

[0024] According to one embodiment, the first resistance value is between 10 ohms and 100,000 ohms, preferably between 100 ohms and 10,000 ohms, and particularly preferably between 500 ohms and 5,000 ohms. Additionally or alternatively, the second resistance value is less than 1 ohm, preferably less than 0.1 ohms, and particularly preferably less than 0.01 ohms. In particular, the second resistance value can be adjusted so that it is effectively almost zero. According to one embodiment, the adjustable first partial resistance comprises at least one transistor, in particular at least one bipolar transistor and / or at least one MOSFET (metal-oxide-semiconductor field-effect transistor), and the resistance is adjusted by setting the gate voltage of the at least one transistor. It has been found that transistors, and in particular bipolar transistors or MOSFETs, are particularly well suited to enable switching and targeted voltage division.Controlling the gate voltage provides a relatively simple and effective way to precisely adjust a resistance.

[0025] According to one embodiment, the adjustable first partial resistor comprises a series connection of transistors, in particular bipolar transistors and / or MOSFETs. In particular, it can be provided that the series-connected transistors are switched simultaneously to adjust an output voltage. Advantageously, larger voltages can be controlled by connecting transistors in series, especially without exceeding the breakdown voltage of individual transistors. Particularly at higher voltages, e.g., in the range of 40 kV, the total voltage can thus be distributed across several transistors, so that the load on each individual transistor is lower. For example, 10 to 200, preferably 40 to 120, and particularly preferably 60 to 100, transistors can be connected in series. It can optionally also be provided to connect transistors in parallel.Parallel connection allows for more precise voltage control. For example, 2 to 20, preferably 3 to 8, transistors can be connected in parallel. In a specific example, four parallel rows of 80 transistors each connected in series can be provided.

[0026] According to one embodiment, the pulse generator comprises at least one storage capacitor for generating the electrical pulses. The storage capacitor can be designed to be charged, in particular to be repeatedly charged cyclically with the generated pulses, so that energy is stored in the capacitor and released for the respective pulses.

[0027] Another aspect of the invention is a control device for controlling a pulse generator of a system for generating electromagnetic waves in the microwave range, wherein the control device is configured to control the system for generating electromagnetic waves in the microwave range, particularly as described herein, and / or the pulse generator, particularly as described herein, such that a method as described herein is carried out. In particular, the control device can be configured so that a method as described herein can be or is carried out automatically. All advantages and features of the method can be transferred analogously to the control device and vice versa. The control device can, for example, comprise a microcontroller. A control program can be implemented in the microcontroller, which includes commands to control the system or the pulse generator.to cause the pulse generator to execute a procedure as described herein. However, the control device may also be configured differently. For example, the control device may comprise a computer or be part of a computer, and / or the control device may be part of a Kontra II system of the system. The control device may optionally be provided as a component of the system, in particular as a component of the pulse generator.

[0028] Another aspect of the invention is a system for generating electromagnetic waves in the microwave range. The system comprises a pulse generator for generating electrical pulses, in particular electrical voltage pulses and / or electrical current pulses; a microwave generator for generating microwaves based on the electrical pulses when an ignition voltage of the microwave generator is exceeded; a transmission line, in particular a transmission cable, between the pulse generator and the microwave generator for transmitting the electrical pulses from the pulse generator to the microwave generator; and a control device as described herein. All advantages and features of the method and the control device can be transferred analogously to the system and vice versa. The control device can optionally be a component of the system, in particular a component of the pulse generator.The system can include a beamhead, wherein the beamhead in particular includes the microwave generator and a particle accelerator.

[0029] According to one embodiment, the system includes an adjustable voltage divider for controlling the voltage output to the transmission line. In particular, the system can include an electrical circuit configured to block voltage output to the transmission line in a blocking mode, to set it to a voltage below the ignition voltage in a first output mode, and to a voltage at or above the ignition voltage in a second output mode using the adjustable voltage divider.

[0030] According to one embodiment, the adjustable voltage divider comprises an adjustable first partial resistor at the output of the pulse generator, which is in particular part of the pulse generator, and a second partial resistor connected behind the adjustable first partial resistor and in parallel to the microwave generator, wherein the control device is configured to control the output of the voltage by causing the adjustable first partial resistor to be adjusted.

[0031] According to one embodiment, the control device is configured to adjust the adjustable first partial resistance for outputting the voltage to the transmission line, which is below the ignition voltage of the microwave generator, to a first substantially constant resistance value, and to adjust the adjustable first partial resistance for outputting the voltage to the transmission line, which is at or above the ignition voltage of the microwave generator, to a second substantially constant resistance value, wherein the second resistance value is lower than the first resistance value, in particular by a factor of at least 10, preferably at least 1000, particularly preferably at least 100000.

[0032] According to one embodiment, the first resistance value is between 10 ohms and 100,000 ohms, preferably between 100 ohms and 10,000 ohms, and particularly preferably between 500 ohms and 5,000 ohms. Additionally or alternatively, the second resistance value is less than 1 ohm, preferably less than 0.1 ohms, and particularly preferably less than 0.01 ohms.

[0033] According to one embodiment, the adjustable first partial resistance comprises at least one transistor, in particular at least one bipolar transistor and / or at least one MOSFET, wherein the resistance is adjustable by adjusting the gate voltage of the at least one transistor, in particular by the control device.

[0034] According to one embodiment, the adjustable first partial resistance comprises a series connection of transistors, in particular bipolar transistors and / or MOSFETs.

[0035] According to one embodiment, the pulse generator includes at least one storage capacitor for generating the electrical pulses.

[0036] Another aspect of the invention is a therapy and / or imaging device comprising a system for generating electromagnetic waves in the microwave range as described herein. All advantages and features of the method, the control device, and the system can be transferred analogously to the therapy and / or imaging device and vice versa. All embodiments described herein can be combined with one another unless explicitly stated otherwise.

[0037] The following describes embodiments with reference to the attached figures.

[0038] Fig. 1 shows a circuit diagram of a system for generating electromagnetic waves in the microwave range;

[0039] Fig. 2 shows a resistance curve for generating a pulse for generating electromagnetic waves in the microwave range, not according to the invention;

[0040] Fig. 3 shows the voltage and current profile during a method for operating a system for generating electromagnetic waves in the microwave range, not according to the invention;

[0041] Fig. 4 shows a circuit diagram of a system for generating electromagnetic waves in the microwave range according to an embodiment of the invention;

[0042] Fig. 5 shows a resistance curve for generating a pulse for generating electromagnetic waves in the microwave range according to a method according to an embodiment of the invention;

[0043] Fig. 6 shows the resistance, voltage and current profiles during a method for operating a system for generating electromagnetic waves in the microwave range according to an embodiment of the invention; and

[0044] Fig. 7 shows a therapy and / or imaging device according to an embodiment of the invention.

[0045] Figure 1 shows a circuit diagram of a system for generating electromagnetic waves in the microwave range. The system comprises a pulse generator 10, which is configured as a direct-switch modulator. The pulse generator 10 includes a high-voltage power supply with a filter choke 11 and a switch 12 with a storage capacitor (here configured as a direct switch) and is designed to generate electrical pulses, in particular voltage and current pulses. The electrical pulses are transmitted to a microwave generator 14, in particular a magnetron, via a transmission line 13. For example, the transmission line 13 can have a length of 10 to 30 meters. In this example, the switch 12 comprises a series connection 15 of transistors, such as bipolar transistors or MOSFETs. The number of transistors shown here (4 transistors) is for illustrative purposes only.In particular, a different number of transistors, for example, a significantly larger number than shown (e.g., 40-100 transistors), can be provided. The transistors are controlled via their gate voltage to block or output a voltage. By controlling the gate voltage, a total resistance of the series circuit is set. A corresponding resistance curve is shown in Figure 2, where the resistance curve for a pulse is shown. Initially, when the voltage is to be blocked, the resistance is set to "infinity." In contrast to this invention, in this example from Figure 2, the resistance is then directly reduced to zero, so that the output voltage is above the ignition voltage of the microwave generator 14. Both a resistance value of infinity and a resistance value of zero can be considered idealized values ​​here, i.e.,In practice, the resistance value can also be set to near or quasi-infinity and near or quasi-zero. At the end of the electrical pulse, the resistance value is set back to infinity. The resulting output circuit voltage 31 (Us) and the corresponding circuit current 32 (Is) are shown in Figure 3 above. Circuit voltage 31 and circuit current 32 are the values ​​that are directly output at the output of the pulse generator 10 or can be measured there. As soon as the resistance is set to zero, there is a sudden increase in the circuit voltage 31, which then drops again after the switch is closed or the resistance is set back to infinity. The waveform of the circuit current 32 shows that it increases sharply as soon as the circuit voltage 31 is activated.It can also be seen that the circuit current 32 initially rises to a significantly higher value and only then gradually stabilizes at its constant value. This results in overshoots at the beginning of the emitted electrical pulse. Figure 3 below shows the corresponding magnetron current 34 and magnetron voltage 33 of a magnetron connected via transmission line 13. It can be seen that here, too, there are significant overshoots at the beginning of the pulse. Only after these overshoots do the magnetron current 34 and magnetron voltage 33 gradually stabilize at a constant value. The magnetron current 34 briefly rises to a value of approximately 300 A before stabilizing at just over 120 A.

[0046] It would be desirable, however, to significantly reduce this overshoot of the magnetron current 34 and the magnetron voltage 33. This can be achieved, according to the invention, by increasing the output voltage in two stages. Specifically, the circuit voltage 31 is first set to a voltage value below the ignition voltage of the microwave generator 14, in this example the magnetron, and then increased to a voltage above the ignition voltage. This can be accomplished, for example, by a voltage divider with an adjustable partial resistance, as shown in Figure 4. Figure 4 shows a circuit diagram of a system for generating electromagnetic waves in the microwave range according to an embodiment of the invention. Here, the switch 15, as the first partial resistance, together with a second partial resistance 16, form a voltage divider.Optionally, the second partial resistor can also be arranged upstream of the transmission line 13, which is indicated here by an alternative dashed second partial resistor 16a. The voltage divider allows the output voltage to the transmission line 13 to be controlled. The second partial resistor 16 can, for example, have a resistance value of 10,000 ohms. As in the embodiment of Figure 1, the switch 12 in this embodiment comprises a series connection 15 of transistors. The resistance of the series connection 15 of transistors can be adjusted by controlling the gate voltage of the transistors; the series connection thus represents an adjustable first partial resistor. The circuit shown in Figure 4 differs from that shown in Figure 1 by the second partial resistor 16. The other aspects of this embodiment can, in principle, be designed analogously to Figure 1.To achieve a two-stage voltage adjustment, the transistors in series circuit 15 are controlled for the output of an electrical pulse as shown in Figure 5. Initially, the resistance is set to "infinity" or virtually "infinity." A specific example of the resistance curve is shown above in Figure 6, where the resistance is plotted logarithmically. In this specific example, a resistance value of virtually "infinity" means that the resistance is set to approximately 500,000 ohms. This is significantly higher than the resistance value of 10,000 ohms used in this example for the second partial resistor 16. A voltage output from the pulse generator 10 to the transmission line 13 is thus essentially blocked.The resistance of the series circuit 15 is then reduced to a value of 1000 ohms by uniformly controlling the gate voltage of the transistors. This resistance is now lower than that of the second partial resistance 16 (10,000 ohms). Accordingly, the circuit voltage 31 (see middle part of Figure 6) and the magnetron voltage 33 (see lower part of Figure 6) also increase. These two voltages rise essentially simultaneously until they each reach a value of 32 kV. This voltage value of 32 kV is below the magnetron's ignition voltage of 40 kV. Although an increase in both the circuit current 32 and the magnetron current 34 is initially observed, the increase in the magnetron current 34 is relatively small. The current can essentially flow away through the second partial resistance 16.After reaching a voltage of 32 kV, the resistance of the series circuit 15 is further reduced. At this point, or shortly before, the transmission line 13 is "pre-charged," and a relatively small current of less than 10 A flows through it. As soon as the resistance is set to zero, or in this example to 0.001 ohms, the circuit voltage 31 and the magnetron voltage 33 rise almost instantaneously to approximately 40 kV. This voltage is above, or reaches, the magnetron's ignition voltage, causing the magnetron current 34 to also increase abruptly, in this example to just over 120 A. It is clearly evident that the magnetron current 34 exhibits only very slight overshoots, especially when comparing this current waveform with that shown in Figure 3.The magnetron current 34 never exceeds 130 A. Advantageously, almost the entire current flows through the magnetron because its resistance (approx. 400 ohms) in operating mode is significantly lower than the resistance of the second partial resistor 16. In other words, the magnetron current 34 is only slightly lower than the circuit current 32, which in this example is just over 125 A. Finally, at the end of the electrical pulse, the resistance is set back to "infinity," or 500,000 ohms. Thus, the voltage 31, 33 drops again, and the current 32, 34 is reduced back to approximately 0 A, thereby completing a pulse. Advantageously, by adjusting the voltage in two stages, in this example by a voltage divider 16, overshoots of the magnetron current 34 can be largely avoided.

[0047] Figure 7 shows a therapy and / or imaging device in the form of a medical linear accelerator with a system for generating electromagnetic waves in the microwave range according to an embodiment of the invention. In particular, the device can comprise a system as described with reference to Figure 4. Electron beams can be generated or accelerated with the beam head 20, for example, for examining or treating a patient on a patient table 21. The electrons can be accelerated using microwave fields generated by the microwave generator 14. A pulse generator 10 (see Figure 4) can be controlled by a control device (not shown here) to carry out a method according to the invention for operating the system.

[0048] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

Claims

Patent claims 1. Method for operating a system for generating electromagnetic waves in the microwave range, wherein the system comprises a pulse generator for generating electrical pulses, a microwave generator (14) for generating microwaves and a transmission line (13) between the pulse generator (10) and the microwave generator (14), wherein the method comprises: - Blocking a voltage output from the pulse generator (10) to the transmission line (13), wherein the output of the voltage to the transmission line (13) is controlled by means of an adjustable voltage divider, the adjustable voltage divider comprising an adjustable first partial resistor at the output of the pulse generator (10) and a second partial resistor (16) connected behind the adjustable first partial resistor and in parallel to the microwave generator (14), wherein the output of the voltage is controlled by adjusting the adjustable first partial resistor; - After blocking the voltage output: Outputting a voltage from the pulse generator (10) to the transmission line (13), where the voltage is below an ignition voltage of the microwave generator (14), to precharge the transmission line (13); - after precharging the transmission line (13): outputting a voltage to the transmission line (13) that is at or above the ignition voltage of the microwave generator (14) is located so that the microwave generator (14) generates electromagnetic waves in the microwave range.

2. Method according to claim 1, wherein the voltage below the ignition voltage is at 50 to 95%, preferably 70% to 90%, particularly preferably 75% to 85%, of the ignition voltage of the microwave generator.

3. Method according to one of the preceding claims, wherein, after blocking the voltage output, the voltage is applied to the transmission line. (13) The output voltage is increased in two stages by first outputting the voltage below the ignition voltage of the microwave generator (14) and then outputting the voltage at or above the ignition voltage of the microwave generator. (14) is issued.

4. Method according to any one of the preceding claims, wherein the adjustable first partial resistance for outputting the voltage to the transmission line (13), which is below the ignition voltage of the microwave generator (14), is set to a first substantially constant resistance value, wherein the adjustable first partial resistance for outputting the voltage to the transmission line (13), which is at or above the ignition voltage of the microwave generator (14), is set to a second substantially constant resistance value, wherein the second resistance value is lower than the first resistance value, in particular by a factor of at least 10, preferably at least 1000, particularly preferably at least 100000.

5. Method according to claim 4, wherein the first resistance value is between 10 ohms and 100,000 ohms, preferably between 100 ohms and 10,000 ohms, particularly preferably between 500 ohms and 5,000 ohms, and / or wherein the second resistance value is less than 1 ohm, preferably less than 0.1 ohms, particularly preferably less than 0.01 ohms.

6. Method according to one of the preceding claims, wherein the adjustable first partial resistance comprises at least one transistor, in particular at least one bipolar transistor and / or at least one MOSFET, and wherein the resistance is adjusted by adjusting the gate voltage of the at least one transistor.

7. Method according to claim 6, wherein the adjustable first partial resistance comprises a series connection (15) of transistors connected in series, in particular bipolar transistors and / or MOSFETs.

8. Control device for controlling a pulse generator (10) of a system for generating electromagnetic waves in the microwave range, wherein the control device is configured to control the system and / or the pulse generator (10) in such a way that a method according to one of the preceding claims is carried out.

9. System for generating electromagnetic waves in the microwave range comprising - a pulse generator (10) for generating electrical pulses; - a microwave generator (14) for generating microwaves based on the electrical pulses when an ignition voltage of the microwave generator (14) is exceeded; - a transmission line (13) between the pulse generator (10) and the microwave generator (14) for transmitting the electrical pulses from the pulse generator (10) to the microwave generator (14); wherein the system comprises an adjustable voltage divider for controlling the output of the voltage to the transmission line (13), wherein the adjustable voltage divider comprises an adjustable first partial resistance at the output of the pulse generator (10) and a second partial resistance connected behind the adjustable first partial resistance and in parallel with the microwave generator (14), wherein the control device is configured to control the output of the voltage by causing the adjustable first partial resistance to be adjusted.

10. System according to claim 9, wherein the adjustable first partial resistance comprises at least one transistor, in particular at least one bipolar transistor and / or at least one MOSFET, and wherein the resistance is adjustable by adjusting the gate voltage of the at least one transistor, in particular by the control device.

11. System according to claim 10, wherein the adjustable first partial resistance comprises a series connection (15) of transistors connected in series, in particular bipolar transistors and / or MOSFETs.

12. System according to one of claims 9 to 11, wherein the pulse generator (10) comprises at least one storage capacitor for generating the electrical pulses.

13. System according to any one of claims 9 to 12, wherein the system further comprises a control device according to claim 8.

14. System according to one of claims 9 to 13, wherein the adjustable first partial resistance is part of the pulse generator (10).

15. Therapy and / or imaging device comprising a system according to any one of claims 9 to 14.

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