Pulse generator for generating voltage pulses

Abstract

The invention relates to a pulse generator (1) for generating voltage pulses with a pulse shape (6) for a high-frequency power source, in particular a magnetron or klystron (8), wherein the pulse generator (1) for generating the voltage pulses comprises several controllable cells (2) each with at least one charge storage device (3), in particular a capacitor, wherein the cells (2) are configured to contribute to the output of an output voltage generating the voltage pulses in an activated state, wherein the pulse generator (1) comprises a control circuit (5) for individually switching at least a subset of the individual cells (2), wherein the pulse generator (1) is configured to selectively switch the cells (2) individually with the aid of the control circuit (5) in a time-adapted manner in order to approximate the pulse shape (6) to a desired pulse shape (60) with a substantially flat pulse surface for the high-frequency power source.

Description

[0001] The invention relates to a pulse generator for generating voltage pulses, the use of a pulse generator, a method for adapting a pulse generator for generating voltage pulses and a radiotherapy system.

[0002] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0003] To power a high-frequency power source, such as a magnetron or klystron, short voltage pulses (also called voltage pulses) with high amplitudes are typically generated using a pulse generator. Several methods exist for implementing pulse generation. For example, pulses can be generated using Blümlein circuits, pulse forming networks, or direct switch pulse cable lengths. Another example of a pulse generator is the Marx generator, which uses multiple capacitors to generate voltage pulses. To generate the voltage pulses, the capacitors are first charged with a DC voltage connected in parallel at a relatively low voltage and then connected in series for discharge. This allows the voltages of the capacitors to add up during discharge, producing a short pulse with a high voltage amplitude.The individual capacitors, typically together with their switch, can be referred to as cells or Marx cells.

[0004] DE 10 2006 060 417 A1 describes, for example, a system for generating a voltage pulse based on several cells, in particular Marx cells of a Marx generator. A DC charging voltage is used to simultaneously charge all capacitors (also known as step capacitors) of the cells, and then they are discharged in series at the same time to generate a voltage pulse. Simultaneous switching of the cells is supported by measuring the switch-on and switch-off time differences for each cell.

[0005] Ideally, the high-frequency power source should be supplied with a rectangular pulse shape featuring as vertical an edge as possible and a flat, horizontal plateau. A challenge lies in the rise and fall times of the edges, as well as the so-called flat-top requirement (pulse flatness) over the pulse duration. Due to the complexity of the typical systems, which often contain multiple components with varying properties, consistently generating a high-quality pulse shape is technically difficult.

[0006] The pulse shape is also influenced by various electrical parameters. These parameters include the switching time differences of power semiconductors, particularly their rise and fall times, as well as the storage capacity of the capacitors in the power source, which affects the pulse flatness. The energy storage device must maintain the output voltage of the power source stably over the pulse duration. For example, a linear voltage drop manifests as a deviation from pulse flatness that increases with the pulse duration, as the pulse amplitude decreases linearly.

[0007] To generate and maintain a pulse quality conforming to a specific specification, in this case specifically the pulse flatness, over the pulse propagation time, "droop compensation" is a known technique from the prior art. This "droop compensation" is implemented primarily as an matching and compensation network (ACR), which includes separate passive or active circuit components that are additionally required. This necessitates additional components and installation space. Consequently, there are additional electrical losses and increased overall system costs. Passive solutions are quasi-statically designed; that is, without adjustable inductance, they cannot be adapted to every load with varying leakage values.

[0008] It is therefore an object of the present invention to provide a means by which the described problems can be eliminated or mitigated. In particular, it is desirable to enable the best possible pulse shape with the least possible additional costs and the smallest possible additional installation space requirement. It is also desirable to achieve improved flexibility in the adjustability of such systems and / or the pulse shape.

[0009] This problem is solved by a pulse generator according to claim 1, a use according to claim 13, a method according to claim 14 and a radiotherapy system according to claim 15. Further features and advantages will become apparent from the dependent claims, the description and the accompanying figures.

[0010] The solutions according to the invention are described below with respect to the claimed pulse generator, the claimed use, and the claimed method, as well as with respect to the other aspects of the invention. Features, advantages, or alternative and combinable embodiments described with respect to one aspect may be assigned to the other aspects of the invention, and vice versa. For example, claims and embodiments of the pulse generator may be improved by features described or claimed in the context of the method, and vice versa. Functional features of the method are implemented by physical units or devices of the pulse generator.

[0011] According to a first aspect of the invention, a pulse generator is provided for generating voltage pulses with a pulse shape suitable for a high-frequency power source, in particular a magnetron or klystron. The pulse generator comprises several controllable cells, each with at least one charge storage element, in particular a capacitor, for generating the voltage pulses. The cells are configured to contribute to the output of a voltage that generates the voltage pulses when activated. The pulse generator includes a control circuit for individually switching at least a subset of the individual cells. The pulse generator is configured to selectively switch the cells individually with the aid of the control circuit in a time-adapted manner in order to approximate the pulse shape to a desired pulse shape with a substantially flat pulse surface for the high-frequency power source.Advantageously, the solution according to the invention can be implemented, in particular without additional components in the form of additional active or passive circuit components for compensation. Furthermore, adjustments can be made particularly flexibly by means of individual switching. Especially in the case of changes, such as the replacement of individual components or a change in the pulse shape, the adjustment can be made relatively easily without having to replace any additional components.

[0012] A pulse generator is generally understood to be a device designed to generate electrical pulses, particularly voltage pulses. More specifically, a pulse generator is an electronic device that first stores electrical energy, or typically accumulates this energy over a certain period, and then outputs the energy in a relatively short time, particularly as a pulse. It may be designed to employ relatively long charging times compared to the discharge time and then output the voltage pulses over this short period. Advantageously, this allows for the achievement of very high power outputs in a short time. The voltage pulses have a pulse shape that should ideally be matched to a desired pulse shape. Ideally, a rectangular pulse shape is often desirable, whereas the actual pulse shape in practice usually deviates somewhat from this.This deviation is particularly noticeable with regard to the rise and fall times, which typically have a finite length and therefore cannot occur instantaneously. The requirement that the top of the pulse waveform be as flat and straight as possible, especially corresponding to the top of a rectangle (flat-top requirement), is also often problematic. In particular, overvoltages can typically occur when the pulse is switched on and off, and falling voltage values, voltage dips, and / or drooping shoulders of the pulse waveform can occur during the pulse duration. Advantageously, this requirement of a flat and straight top can be specifically met, or even better met, by the adaptation according to the invention. The pulse waveform is typically characterized on its horizontal axis by the pulse duration and on its vertical axis by its pulse amplitude in volts or kilovolts.The desired pulse amplitude can also be referred to as the nominal pulse peak value. The pulse duration can be referred to as the pulse width. The pulse shape can, for example, have a pulse duration or pulse width of 0.5 to 100 microseconds, preferably 2 to 20 microseconds, and particularly preferably 5 to 10 microseconds. The amplitude, or plateau voltage, or nominal pulse peak value of the pulse shape can preferably be in the kilovolt range, particularly in the range of 10 kV to 600 kV, and more preferably 50 kV to 300 kV.

[0013] The pulse generator is designed for use with, or for powering, a high-frequency power source. Accordingly, the pulse generator, particularly including a magnetron or klystron, is specifically designed to generate signals in the high-frequency range. High frequency can generally be understood as a frequency above 100 kHz. The high-frequency power source can, in particular, be part of a radiotherapy system or be designed for use with a radiotherapy system. The high-frequency range can generally extend into the THz range. The high-frequency power source can, in particular, be a magnetron or a klystron. A magnetron can generate high-frequency waves very efficiently and relatively inexpensively. A klystron can be particularly flexible with regard to its achievable or adjustable power output and its power bandwidth.In particular, a klystron can be used to achieve the levels of performance typically required for radiation therapy.

[0014] To generate voltage pulses, the pulse generator comprises several controllable cells. In particular, the pulse generator can be a Marx generator, and the cells can be Marx cells. Each cell comprises at least one charge storage device. This charge storage device can be, in particular, at least one capacitor. The pulse generator is designed to allow the cells to be individually connected either in series or in parallel. A parallel connection can preferably be used to charge the cells simultaneously. A series connection can be used to add the output voltages of the cells, thus enabling higher power outputs. In particular, the number of cells connected in series simultaneously can be adjustable. Cells that are part of a series connection for voltage output can therefore be considered to be in the activated state.

[0015] The pulse generator includes a control circuit for individually switching at least a subset of the individual cells. How individual cell control can function is fundamentally described in the prior art and is explained, for example, in DE 10 2006 060 417 B4 and US 7 755 217 B2. In this publication, individual control is used in particular to synchronize the cells so that they switch simultaneously. The cells can be controlled, in particular, with a controllable semiconductor switch. For example, IGBTs (Insulated-Gate Bipolar Transistors) are particularly well-suited as semiconductor switches. However, other semiconductor switches, such as DMOS FETs, GTOs, or thyristors, can also be used. One or more semiconductor switches can be provided per cell.Within the scope of this invention, it was recognized that individual switching can advantageously be used to adapt the pulse shape, and in particular its top surface, to a desired pulse shape. Thus, the generally known individual switching of cells can be used to solve a new problem, namely, adapting the pulse shape. The pulse generator is designed to selectively switch the cells individually and in a time-adapted manner using the control circuit, in order to approximate the pulse shape to a desired pulse shape with a substantially flat pulse top surface for the high-frequency power source. The pulse top surface can, in particular, be a pulse plateau. The pulse generator can, for example, be calibrated so that the adaptation to the target platform is as reliable as possible during subsequent operation.In other words, the pulse generator can be designed to automatically apply adjusted switching states of the cells, set during calibration, in operation.

[0016] According to one embodiment, the pulse generator is designed to adjust the flatness of the pulse surface by selectively switching individual cells and / or subgroups of cells during the pulse duration, in particular to align a time-varying height of the pulse surface with a target plateau. Specifically, the pulse generator can be designed to compensate for dips, overshoots, and / or slopes of the pulse surface by individually switching the cells. For example, the pulse generator can be designed to compensate for a dip in the surface by switching on one or more additional cells. A downward slope can be compensated for, for example, by switching on an increasing number of cells.

[0017] According to one embodiment, the pulse generator is designed to implement active droop compensation by selectively switching individual cells and / or subgroups of cells. Droop compensation reduces overshoot during large voltage jumps, particularly when switching the voltage pulse on and off. For example, droop compensation can counteract overshoot during sudden power increases by selectively reducing the output voltage. This can be achieved, in particular, by selectively reducing the number of cells contributing to the output voltage. Specifically, the pulse generator can be designed to perform droop compensation selectively at the operating point. By individually adjusting the cells, an operating point can be chosen very flexibly without requiring changes to the system design or its configuration.Changes will need to be made regarding the replacement of components.

[0018] According to one embodiment, the pulse generator is designed to compensate for overshoots and / or undershoots by selectively switching individual cells and / or subgroups of cells. In the case of overshoots, individual cells or subgroups of cells can be temporarily switched off. In the case of undershoots, individual cells or groups of cells can be temporarily switched on. For example, at the beginning of the pulse, particularly directly after the rising edge, oscillations of the pulse's waveform may occur. These oscillations can, in particular, exhibit alternating overshoots above a target plateau and undershoots below the target plateau of the pulse shape. The pulse generator can be designed to selectively switch one cell or subgroup of cells on and off alternately in order to compensate for the alternating oscillations.

[0019] According to one embodiment, the pulse generator can be configured to selectively switch individual cells or subgroups of cells on and off alternately, with the signal level being controlled by the duration of the switch-on and switch-off times. Advantageously, an average voltage value can be achieved with alternating switch-on and switch-off operation, which lies between the switched-on and switched-off values. This allows, for example, a more finely tuned average value than the voltage output of a single cell or subgroup of cells. A general functionality and the technical implementation of the switch-on and switch-off operation are described in DE 10 2011 003 526 B4 and US 9 106 154 B2 in the context of a pulse-width modulated cell or subgroup of cells.

[0020] According to one embodiment, the pulse generator is designed to compensate for a time-varying pulse waveform by selectively switching individual cells and / or subgroups of cells on and off during the pulse duration. This is achieved by varying the temporary on-to-off ratio of the time the cells and / or subgroups are switched on to the time they are switched off during the pulse duration. Advantageously, this allows for a particularly precise and flexible response to varying pulse waveform amplitudes, thus enabling adjustments.

[0021] According to one embodiment, the pulse generator is designed to compensate for a falling pulse top, particularly a falling slope, at least for a portion of the pulse waveform by increasing the on-to-off ratio, and / or to compensate for a rising pulse top, particularly a rising slope, at least for a portion of the pulse waveform by decreasing the on-to-off ratio. By controlling the on and off times, an effectively near-continuous waveform can be achieved with particularly high precision through what is essentially a binary switching operation.

[0022] According to one embodiment, the pulse generator is designed to switch on individual cells and / or individual subgroups of cells with a time delay during the rise time of the pulse waveform, in particular such that the pulse waveform has a stepwise rising edge. This embodiment can be particularly advantageous for enabling slower charging or pre-charging of longer cables. With this embodiment, a cable can be charged slowly in a controlled manner, especially to avoid overcurrent events.

[0023] According to one embodiment, the pulse generator is designed to precharge a supply line to the high-frequency source during the rise time of the pulse waveform by switching on some of the individual cells and / or individual cell subgroups, so that the charge remains below the ignition voltage of the high-frequency source. This is achieved, in particular, by slowly and gradually charging the supply line by successively switching on the cells and / or cell subgroups. After precharging, the ignition voltage is exceeded by switching on a further cell or cell subgroup. Typically, several meters of cable length, sometimes up to approximately 30 meters, are used in the context of such high-frequency power sources, and these cables have a very high capacitance due to their length.The termination impedance of a sufficiently long cable can change abruptly as soon as an applied supply voltage exceeds the ignition voltage of the high-frequency power source. The effect of this can be avoided or reduced by pre-charging.

[0024] According to one embodiment, the pulse generator is designed to switch off individual cells and / or individual subgroups of cells with a time delay during the decay phase of the pulse waveform, in particular such that the pulse waveform has a stepped falling edge. Stepwise switch-off prevents overvoltages caused by a sudden shutdown.

[0025] According to one embodiment, the pulse generator comprises 2 to 100, preferably 2 to 30, and particularly preferably 3 to 10 cells. In general, the invention can be used with any number of cells. This number of cells can be particularly advantageous for combining good control and flexibility of the output voltage.

[0026] According to one embodiment, the pulse generator comprises several circuit-linked groups of cells configured to be switched synchronously and / or asynchronously. In particular, it can be provided that the cells of individual groups are switched synchronously together. By grouping cells, switching can be implemented more cost-effectively. Each group of cells can be driven by a switch, in particular a semiconductor switch such as an IGBT. Each cell in a group can comprise its own semiconductor switch.

[0027] According to one embodiment, the pulse generator is configured to check a current pulse shape, in particular at a signal input or signal output of the high-frequency power source, to compare the current pulse shape with a target pulse shape in order to determine a target-actual difference between the current pulse shape and the target pulse shape, and to precisely time the switching of the cells based on the target-actual difference in order to adapt the pulse shape to the target pulse shape. The pulse generator is specifically configured to perform the checking and adjustment repeatedly, particularly at time intervals, or continuously during operation. The checking can be performed automatically. Alternatively, it can be performed with user intervention.Checks can be performed, for example, particularly during downtime of the pulse generator and / or during at least some start-up or warm-up phases. These checks can, for instance, address changes in the system over time, such as those caused by aging. Checks can also be performed during operation. For example, they can be used to automatically monitor and adjust the pulse shape.

[0028] Another aspect of the invention is the use of a pulse generator as described herein to supply a high-frequency power source with a pulse shape, wherein droop compensation and / or improved flatness of the top surface of the pulse shape is achieved by individually controlling the individual cells or subgroups of cells. All advantages and features of the pulse generator can be transferred analogously to this use and vice versa. In particular, improved flatness can be achieved as described herein. For example, improved flatness can be achieved by compensating for over- and / or under-oscillations by switching the cells. The high-frequency power source can, in particular, be a magnetron or a klystron. The high-frequency power source can be part of a radiotherapy system.

[0029] Another aspect of the invention is a method for adapting a pulse generator, in particular a pulse generator as described herein, for generating voltage pulses with a pulse shape with which a high-frequency power source is supplied, wherein the pulse generator for generating the voltage pulses comprises several controllable cells, each with at least one charge storage device, in particular a capacitor, wherein the cells are configured to contribute to an output voltage generating the voltage pulses when in an activated state, and wherein the method comprises the following steps: - Checking a current pulse shape, especially at a signal input or signal output of the high-frequency power source, and comparing it with a target pulse shape to determine a target-actual difference between the current pulse shape and the target pulse shape; - Adjusting the pulse shape generated by the pulse generator by precisely timing the switching of the cells to generate the pulse shape based on the target-actual difference in order to produce an adapted pulse shape.

[0030] Following the procedure for adapting the pulse generator, the pulse generator can be operated with the adapted pulse shape. All advantages and features of the pulse generator and its use can be analogously transferred to the procedure and vice versa. The procedure can be carried out automatically, in particular by a computer program. Instructions for automatically executing the procedure can, for example, be stored in a computer program. The procedure can also be implemented as a computer program in memory, especially programmable memory. The procedure can be semi-automatic and / or based on user interaction. The procedure can be implemented, for example, during manufacturing or directly after manufacturing as part of a calibration process.

[0031] According to one embodiment, the steps of the method are performed repeatedly or continuously, particularly at time intervals, especially during operational breaks of the pulse generator and / or during at least some start-up or warm-up phases of the pulse generator, or during operation. Advantageously, the method allows for repeated verification of operation, particularly to monitor the performance of the pulse generator and / or the overall system. Electrical properties of the cells can change or age over their lifetime due to influences such as temperature fluctuations and damage from scattered radiation. The switching of the cells can be continuously adjusted according to the verification process to achieve the best possible match to the pulse shape.

[0032] Another aspect of the invention is a radiation-based medical system, in particular a radiotherapy system, comprising a high-frequency power source, in particular a klystron or magnetron, and a pulse generator as described herein. The pulse generator can in particular be a Marx generator. All advantages and features of the pulse generator, its use, and the method can be transferred analogously to the radiotherapy system and vice versa. The system can in particular be configured to generate a photon beam whose radiation shape corresponds to the pulse shape of the pulse generator. The energy of the photon beam is typically in the megaelectronvolt range and has a pulse width in the microsecond range.

[0033] All embodiments described herein can be combined with one another unless explicitly stated otherwise. In particular, the various embodiments for adapting the pulse shape can be combined. For example, adapting the rising and falling edges can be combined with each other and / or with adapting the pulse top. Additionally or alternatively, different variations of pulse top adaptation can be combined. For example, vibration compensation can be combined with slope compensation and / or voltage dip compensation.

[0034] The following are exemplary embodiments described with reference to the attached figures. Fig. Figure 1 shows a diagram of a pulse shape that can be an input signal for a high-frequency power source, in particular a klystron or a magnetron. Fig. Figure 2 illustrates, by way of example, the switching times of a power semiconductor in the form of an IGBT, Fig. Figure 3 shows a schematic representation of a pulse generator according to an embodiment of the invention, Fig. Figure 4 shows a schematic representation of a pulse generator according to a further embodiment of the invention, Fig. Figure 5 shows an example of switching cells of a pulse generator according to an embodiment of the invention. Fig. Figure 6 shows another example of switching cells of a pulse generator according to an embodiment of the invention. Fig. Figure 7 shows another example of switching cells of a pulse generator according to an embodiment of the invention, Fig. Figure 8 shows another example of switching cells of a pulse generator according to an embodiment of the invention, Fig. Figure 9 shows another example of switching cells of a pulse generator according to an embodiment of the invention, Fig. Figure 10 shows another example of switching cells of a pulse generator according to an embodiment of the invention, Fig. Figure 11 shows a schematic view of the working principle of a medical system according to an embodiment of the invention, Fig. Figures 12-14 show an example of adapting a pulse shape according to an embodiment of the invention. Fig. Figures 15-17 show another example of adapting a pulse shape according to an embodiment of the invention, Fig. Figure 18 shows a flowchart of a method for adapting a pulse generator according to an embodiment of the invention and Fig. Figure 19 shows a radiotherapy system according to an embodiment of the invention.

[0035] Fig. Figure 1 shows a diagram of a pulse shape 6, which can be an input signal for a high-frequency power source, in particular a klystron 8 or a magnetron. This diagram is intended to explain some basic concepts. Compared to a perfectly rectangular pulse shape 6 (compare, for example, the target pulse shape 60 shown in Figure 1), Fig. 11), a real pulse shape 6 exhibits several deviations from a rectangular shape. These include, in particular, a rise time 36, a fall time 37, and imperfect pulse flatness 34 on the pulse's top surface. Current and voltage variation can be measured on the pulse's top surface with respect to their peak values. Preferably, voltage and current should remain within the limit of a defined pulse flatness, for example, within a range of 1 kV, for the entire duration of the pulse plateau. A nominal pulse peak value 35 is the desired value that the pulse should assume on its top surface during the pulse duration. Ideally, it corresponds to the difference between the signal value before or after the pulse and the signal value during the pulse duration (provided there are no overshoots 31 or dips).The rise time 36 can be determined as the duration it takes for the signal to rise from 10% of the nominal peak value 351 to 90% of the nominal peak value 353. Similarly, the fall time 37 can be determined as the duration it takes for the signal to fall from 90% of the nominal peak value 353 to 10% of the nominal peak value 351. The half-width 38, also known as FWHM, is defined, as usual, as the signal width at which the signal exhibits 50% of the pulse's nominal peak value 35. Overshoots 31 and undershoots, respectively, can occur both when the pulse is switched on, i.e., following the rise time 36, and when the pulse is switched off, i.e., following the fall time 37. An overshoot quantity 31 is defined as the difference of the signal between the nominal peak pulse value 35 and the maximum value that the signal assumes during overshoot.An overshoot period 32 can be defined as the time from reaching 67% of the nominal peak value 352 before the overshoot until the signal falls back to the nominal pulse peak value 35 after the first overshoot 31. The difference between the actual zero signal and the minimum caused by undershoot after the decay time 37 can be defined as the peak value of the inverse 39.

[0036] The goal is to keep the rise times 36 and the fall times 37 within a defined range, or to prevent excessive fluctuations and variations in these values. Furthermore, the flatness 34 of the top surface of the pulse waveform 6 should be achieved and reproduced as reliably as possible. However, in a complex overall system with variations across multiple units, it is technically difficult to consistently generate the same high quality of the pulse waveform 6 without additional measures or actuators. Moreover, electrical parameters of the power source can influence the pulse waveform 6. These parameters include, for example, switching time differences of power semiconductors, which themselves exhibit rise times 46 and fall times 47. Fig. Figure 2 illustrates the switching times of a power semiconductor using the example of an IGBT (bipolar transistor with an insulated gate electrode). The control signal, which can be considered the intended switching behavior of the IGBT, is shown below. The actual switching behavior of the IGBT is shown above. First, there is a turn-on delay 41, meaning that the IGBT only reacts with a delay corresponding to this turn-on delay 41. Then, the IGBT typically also exhibits a rise time 46, during which the signal rises to its plateau value in a finite amount of time. At the end of the signal, a turn-off delay 42 can lead to a delayed turn-off, which can be further delayed by a fall time 37. These values ​​can vary for different IGBTs and may also change over time. Thus, the switching behavior of power semiconductors, such as...The pulse shape 6 of the pulse generator 1 is influenced by IGBTs. Other influencing factors, such as the storage capacity of energy storage devices or the capacitance of the power source, which can negatively affect the pulse flatness, can also play a role. For example, the energy storage devices must maintain a stable output voltage from the power source over the pulse duration. A linear voltage drop in the energy storage devices manifests as a deviation from the pulse flatness that increases with the pulse duration; that is, the signal value of the pulse decreases during the pulse duration, particularly linearly. Prior art approaches to maintain the pulse shape 6, especially the pulse flatness 34, using an matching and compensation network (ACR) with additional circuit components have the disadvantage that additional components (e.g.,Additional capacitors, inductors, and resistors, as well as corresponding circuitry, are required, thus necessitating additional installation space. This results in additional electrical losses, increasing the overall system costs. Furthermore, such state-of-the-art solutions are relatively inflexible and generally cannot be adapted to other requirements without modifications.

[0037] Fig. Figure 3 shows a schematic representation of a pulse generator 1, in particular a Marx generator, according to an embodiment of the invention. In this embodiment, the pulse generator 1 comprises, by way of example, five controllable cells 2, each with a charge storage device 3, in particular a capacitor, and each with a semiconductor switch (4), for example an IGBT. The cells 2 are configured to contribute to the output of an output voltage generating the voltage pulses when activated. For this purpose, the cells 2 contributing to the output voltage can, in particular, be connected in series. Conversely, the cells 2 can, in particular, be connected in parallel for charging.A control circuit 5 is also shown schematically, which configures the pulse generator 1 to individually switch the cells 2, or at least a subset of the cells 2, in order to approximate a pulse shape 6 to a target pulse shape 60 with a substantially flat pulse top. The pulse shape 6 serves to supply a high-frequency power source. It can be provided that the pulse shape 6 is continuously or at specific intervals monitored and, if necessary, adjusted based on this monitoring by using appropriate feedback (indicated by dashed lines). It can be provided that the pulse generator 1 is preconfigured within a configuration, so that it subsequently adjusts the pulse shape 6 according to the configuration by switching the cells 2 as set.The configuration can be repeated, for example, after some time in operation to compensate for changes due to aging or to meet new requirements.

[0038] Fig. Figure 4 shows a schematic representation of a pulse generator 1, in particular a Marx generator, according to a further embodiment of the invention. In this embodiment, the pulse generator 1 comprises three circuit-connected groups 7 of cells 2, which are configured to be switched synchronously and / or asynchronously together. This means, in particular, that all cells 2 of a single group 7 are switched together.

[0039] By grouping cells 2 into groups 7, switching can be implemented more cost-effectively. In this embodiment, three groups 7, each with five cells 2, are shown. However, other numbers of groups 7 are also possible. The number of cells 2 per group 7 can also differ. The number of cells 2 can vary for some or all of the groups 7. Different groups 7 of cells 2 can supply different portions of a pulse duration, allowing, in particular, a longer overall pulse duration. For example, each of the three groups shown here can be switched on for a specific time, e.g., 5 µs, to enable a total pulse duration of, e.g., 5 µs + 5 µs + 5 µs = 15 µs.

[0040] The Fig. Figures 5 to 10 each show examples of switching cells 2, in particular Marx cells, of a pulse generator 1 according to an embodiment of the invention. The horizontal axis represents the time (t) and the vertical axis represents the number (#) of cells 2 currently switched on. In the examples shown, five cells 2 are switched on in each case; however, other numbers of cells 2 can generally be provided. Fig. Figure 5 shows an example where all five cells 2 are switched on simultaneously at the beginning of a pulse and switched off simultaneously at the end of the pulse. This corresponds to an example where a pulse shape 6 is not specifically corrected or does not need to be. Fig. Figure 6 shows an example where cells 2 are switched on with a time delay. With a pulse duration of, for example, between 1.5 µs and 5.5 µs, the stepwise switching can be implemented with an offset of, for example, 20 ns to 500 ns. This time-delayed switching can create a rising edge or be used specifically to counteract a time offset that might arise, for example, due to the electronics or the transmission link. This allows the pulse to be influenced or adjusted in the rising edge region. Fig. Figure 7 shows an example where cells 2 are switched on and off with a time delay. This allows the pulse to be corrected or adjusted even during the falling edge of the pulse. Fig. 8 differs from Fig. 7 by first switching on three cells 2 one after the other, and then switching on the two remaining cells 2 simultaneously. This procedure can be used, for example, to pre-charge a supply line 9 below an ignition voltage of the high-frequency power source and then abruptly jump above the ignition voltage to activate the high-frequency power source. Fig. Figure 9 shows an example in which one of the five cells 2 is switched on and off multiple times during the pulse duration. This procedure can be used, for example, to compensate for a slope on the top of the pulse waveform 6. The on-time of the fifth cell 2 decreases over time. Fig. Figure 10 shows an example in which, during the pulse duration, two of the five cells 2 are switched on and off simultaneously multiple times in rapid succession. This can be used, for example, to compensate for overshoots 31. Switching individual cells 2 or subgroups of cells 2 (such as two cells 2 here) on and off can also be used to keep the average signal slightly lower compared to the continuously switched-on state. In this example, this can correspond to active droop compensation, whereby the average voltage signal is slightly lower at the beginning of the pulse and slightly higher towards the end (before switching off). In principle, the selection of one or more switching cells 2 can be freely chosen. For example, cells 4 and 5, or even cells 1 and 4, can be used for pulse modulation.

[0041] Fig. Figure 11 shows a schematic view of the operating principle of a medical system according to an embodiment of the invention. The rectangular pulse generated by the pulse generator 1 is influenced by its various components via a generation and transmission path, so that the pulse shape 6, which is fed into a high-frequency source, in this example a klystron 8, can deviate from the set rectangular shape or a target pulse shape 60. The pulse generator 1 can, in particular, be a Marx modulator. DCPS stands for "Direct Current Power Supply," SU stands for "Switch Unit," PrePT is a pre-pulse transformer, and PT is a pulse transformer. The switch unit is the power unit of the pulse generator, in particular a Marx modulator, which comprises the cells 2, in particular Marx cells.At an input or output of the high-frequency power source, namely the klystron 8 in this example, the actual pulse shape 6, which corresponds to a system response, is measured. This can be done, for example, with a capacitive voltage meter 64 (for example, using a CVD – “Capacitive Voltage Divider”). To approximate the actual pulse shape 6 to the target pulse shape 60, a control unit, for example, an SSM controller 63 (Solid-State Modulator controller), corrects the control of the individual cells 2 and thus adapts the resulting pulse shape 6 to the target pulse shape 60. In particular, the actual value of the charging voltage of a selected cell 2 or individual cells 2 can be measured and fed back to the DCPS via a feedback 61.A Charging Choke 62 can protect the DCPS during a pulse generation phase of the pulse generator 1, in particular Marx modulator, and protect a charging current into the parallel connected charge storage devices 3, in particular Marx capacitors, during a charging phase.

[0042] The Fig. Figures 12 to 14 together show an example of adapting a pulse shape 6. Fig. Figure 12 shows an unsuitable pulse shape 6 (solid line) which differs from a target pulse shape 60 (dashed line) on its upper surface in that the actual pulse shape 6 has a downward slope. This difference is determined by, for example, capacitive voltage measurement and then as in Fig. 13 shown corrected. In Fig. 13 is, similar to the Fig. Figures 5 to 10 show the switching on of cells 2. At the beginning of the pulse, n cells 2 are switched on or switched on. The number n can, for example, represent four cells 2. However, a different number n of cells 2 can also be specified. During the pulse duration, another cell 2 (the 1+nth cell) is alternately switched on and off to compensate for the slope. Over time, the on-times increase, resulting in an approximately linearly increasing output voltage (shown as a dashed line) on average. A temporary on-to-off ratio of this 1+nth cell increases over time. The result of this adjustment is shown in Fig. Figure 14 shows that the increasing on-to-off ratio of the 1+nth cell counteracts the linear falloff of the top surface, so that, as a result, the top surface of pulse shape 6 is again even over the entire pulse duration and thus approximates the target pulse shape 60 (see dashed line in Figure 14). Fig. 12) was approached.

[0043] The Fig. Figures 15 to 17 together show another example of adapting a pulse shape 6. Fig. Figure 15 shows a mismatched pulse shape 6 (solid line) which deviates from a target pulse shape 60 (dashed line) on its upper side in that a voltage dip occurs, particularly in the middle region of the pulse duration and at the end of the pulse duration. This deviation from the target pulse shape 60 is determined by, for example, capacitive voltage measurement and then as described in Fig. 16 shown corrected. In Fig. Figure 16 shows the switching on of cells 2. At the beginning of the pulse, n cells 2 are switched on or connected. Over the course of the pulse, another cell 2 (the 1+nth cell) is alternately switched on and off to compensate for voltage dips. The duration for which this 1+nth cell is switched on and off varies over time, resulting in a variable average output voltage (shown as a dashed line), which corresponds to the actual pulse shape shown in Figure 6. Fig. 15 is the opposite. In areas of dips, the 1+nth cell is switched on more frequently, and in areas where the target voltage is (almost) reached, the 1+nth cell is switched on for a shorter time or not at all. The result of this adjustment is in Fig. Figure 17 shows that the targeted switching of the 1+nth cell counteracts the dips on the top of the pulse shape 6, so that as a result, the top of the pulse shape 6 is again flat and straight over the entire pulse duration and thus approximates the target pulse shape 60 (see dashed line in Figure 17). Fig. 15) was approached.

[0044] Fig. Figure 18 shows a flowchart of a method for adjusting a pulse generator 1 according to an embodiment of the invention. The pulse generator 1 comprises several controllable cells 2, each with at least one charge storage device 3, in particular a capacitor, for generating voltage pulses. In a first step 101 of the method, a current pulse shape 6 is checked, in particular at a signal input or signal output of a high-frequency power source supplied by the pulse generator 1. In a further step 102, the current pulse shape 6 is compared with a target pulse shape 60 to determine a target-actual difference between the current pulse shape 6 and the target shape. In a further step 103, the pulse shape 6 generated by the pulse generator 1 is adjusted by selectively timing the switching of the cells 2 to generate the pulse shape 6 based on the target-actual difference in order to produce an adjusted pulse shape 6.Following the procedure for adapting the pulse generator 1, the pulse generator 1 can be operated with the adapted pulse shape 6.

[0045] Fig. Figure 19 shows a radiotherapy system according to an embodiment of the invention. The radiotherapy system comprises a radiofrequency power source, for example a klystron 8 or magnetron, for generating therapeutic radiation and is configured to rotate a radiation head 21 around a patient bed 20 during radiotherapy. The radiotherapy system further comprises a pulse generator 1 as described herein, which is connected to the radiofrequency power source via a supply line 9. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2006 060 417 A1

[0004] DE 10 2006 060 417 B4

[0015] US 7 755 217 B2

[0015] DE 10 2011 003 526 B4

[0019] US 9 106 154 B2

[0019]

Claims

[1] Pulse generator (1) for generating voltage pulses with a pulse shape (6) for a high-frequency power source, in particular a magnetron or klystron (8), wherein the pulse generator (1) for generating the voltage pulses comprises several controllable cells (2) each with at least one charge storage device (3), in particular a capacitor, wherein the cells (2) are configured to contribute to an output voltage generating the voltage pulses when in an activated state, wherein the pulse generator (1) comprises a control circuit (5) for individually switching at least a subset of the individual cells (2), wherein the pulse generator (1) is designed to selectively switch the cells (2) individually in a time-adapted manner using the control circuit (5) in order to approximate the pulse shape (6) to a target pulse shape (60) with a substantially flat pulse top for the high-frequency power source. [2] Pulse generator (1) according to claim 1, wherein the pulse generator (1) is configured to adjust the flatness of the pulse surface by selectively switching individual cells (2) and / or individual subgroups of cells (2) during the pulse duration, in particular to adjust a time-varying height of the pulse surface to a target plateau. [3] Pulse generator (1) according to one of the preceding claims, wherein the pulse generator (1) is configured to achieve active droop compensation by selectively switching individual cells (2) and / or individual subgroups of cells (2). [4] Pulse generator (1) according to one of the preceding claims, wherein the pulse generator (1) is configured to compensate for overshoots (31) and / or undershoots by selectively switching individual cells (2) and / or individual subgroups of cells (2). [5] Pulse generator (1) according to one of the preceding claims, wherein the pulse generator (1) is configured to compensate for a time-varying height of the pulse shape (6) by selectively switching individual cells (2) and / or individual subgroups of cells (2) on and off during the pulse duration by varying a temporary on-to-off ratio of the switched-on time to the switched-off time of the cells (2) and / or subgroups during the pulse duration. [6] Pulse generator (1) according to claim 5, wherein the pulse generator (1) is designed to at least for a section of the momentum shape (6) to compensate for a falling momentum top, in particular a falling slope of the momentum top, by an increasing on-to-off ratio and / or at least for a section of the momentum shape (6) to compensate for an increasing momentum top, in particular an increasing slope of the momentum top, by a decreasing on-to-off ratio. [7] Pulse generator (1) according to one of the preceding claims, wherein the pulse generator (1) is configured to switch on individual cells (2) and / or individual subgroups of cells (2) at a time offset during a rise time (36) of the pulse shape (6), in particular such that the pulse shape (6) has a step-like rising edge. [8] Pulse generator (1) according to claim 7, wherein the pulse generator (1) is designed to to precharge a supply line to the high-frequency source during a rise time (36) of the pulse shape (6) by switching on some of the individual cells (2) and / or the individual subgroups of cells (2) so that the charge is below an ignition voltage of the high-frequency source, in particular by slowly and stepwise charging the supply line by successively switching on the cells (2) and / or the subgroups of cells (2), and to exceed the ignition voltage after pre-charging by adding another cell (2) or a subgroup of cells (2). [9] Pulse generator (1) according to one of the preceding claims, wherein the pulse generator (1) is configured to switch off individual cells (2) and / or individual subgroups of cells (2) at a time delay during a fall time (37) of the pulse shape (6), in particular such that the pulse shape (6) has a step-like falling edge. [10] Pulse generator (1) according to one of the preceding claims, wherein the pulse generator (1) comprises 2 to 100, preferably 2 to 30, particularly preferably 3 to 10 cells (2). [11] Pulse generator (1) according to one of the preceding claims, wherein the pulse generator (1) comprises several circuit-linked groups (7) of cells (2) which are designed to be switched together synchronously and / or asynchronously. [12] Pulse generator (1) according to any one of the preceding claims, wherein the pulse generator (1) is configured to check a current pulse shape (6), in particular at a signal input or signal output of the high-frequency power source, to compare the current pulse shape (6) with a target pulse shape (60) in order to determine a target-actual difference between the current pulse shape (6) and the target pulse shape (60), and to time-controlled switching of the cells (2) based on the target-actual difference in order to adapt the pulse shape (6) to the target pulse shape (60), wherein the pulse generator (1) is designed in particular to perform the checking and adjusting, especially at time intervals, repeatedly or continuously during operation. [13] Use of a pulse generator (1) according to one of the preceding claims for supplying a high-frequency power source with a pulse shape (6), wherein droop compensation and / or improved flatness of the top surface of the pulse shape (6) is achieved by individually controlling the individual cells (2) or subgroups of cells (2). [14] Method for adapting a pulse generator (1), in particular a pulse generator (1) according to any one of claims 1 to 12, for generating voltage pulses with a pulse shape (6) with which a high-frequency power source is supplied, wherein the pulse generator (1) for generating the voltage pulses comprises several controllable cells (2) each with at least one charge storage device (3), in particular a capacitor, wherein the cells (2) are configured to contribute to an output voltage generating the voltage pulses when in an activated state, the procedure comprises the following steps: - Checking a current pulse shape (6), in particular at a signal input or signal output of the high-frequency power source, and comparing it with a target pulse shape (60) to determine a target-actual difference between the current pulse shape (6) and the target pulse shape (60); - Adjusting the pulse shape (6) generated by the pulse generator (1) by selectively timing the switching of the cells (2) to generate the pulse shape (6) based on the target-actual difference in order to generate an adapted pulse shape (6). [15] Radiation-based medical system, in particular radiotherapy system, comprising a radiofrequency power source, in particular a klystron (8) or magnetron, and a pulse generator (1) according to any one of claims 1 to 12.

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