Electron gun driver

Abstract

A technique for an electron gun driver is described, the electron gun driver comprising a half-bridge driver circuit and a drive controller. The half-bridge driver circuit comprises: a drive circuit configured to generate a gate drive voltage for a gate connection of an electron gun; and a cutoff circuit configured to generate a gate cutoff voltage for the gate connection of the electron gun; and a gate driver configured to switch between the gate drive voltage and the gate cutoff voltage. The drive controller is configured to generate a pulse input to the drive circuit and the cutoff circuit and a gate switching signal for the gate driver.

Description

Background Art

[0001] Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in the present disclosure and are not admitted to be prior art by inclusion in this section.

[0002] Linear accelerators (i.e., linear accelerators) are used in systems such as precision medicine, security inspections, communications, and radar systems. Linear accelerators can be used as part of a system that generates x-rays or amplifies radio frequency (RF) or microwave electromagnetic signals. Some linear accelerators generate pulses of accelerated particles by pulsating the power supplied to a particle source (e.g., an electron gun) and the power supplied to an RF source (e.g., a magnetron). Some linear accelerators have fixed voltage levels and timing for the power supplied to the particle source and the power supplied to the RF source, thereby fixing the energy and dose rate (e.g., timing and amplitude) of the pulse. Other linear accelerators can switch between two or more factory-defined modes, each of which has an associated power supplied to the particle source and a power supplied to the RF source. For each mode, the timing of the supplied power is the same. In addition, the mode is switched based on a predefined pattern that alternates between the two modes. The power and pulses provided to the electron particle source, also referred to as an electron gun (e.g., a diode gun or a triode gun), are typically provided by an electron gun driver (also referred to as an electron gun modulator). BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Figure 1 A schematic or block diagram of a triode gun driver is shown according to some embodiments.

[0004] Figure 2 A schematic or block diagram of a high side power supply is shown according to some embodiments.

[0005] Figure 3 A schematic diagram or block diagram of an alternative driver module for a triode gun driver according to some embodiments is shown.

[0006] Figure 4 A schematic diagram or block diagram of an alternative driver module for a triode gun driver according to some embodiments is shown.

[0007] Figure 5 is a flow chart illustrating an example of a method of controlling a triode gun driver according to some embodiments. DETAILED DESCRIPTION

[0008] Before explaining any embodiment of the present invention in detail, it should be understood that the present invention is not limited in its application to the details of construction and arrangement of the components set forth in the following description or shown in the following drawings. The present invention is capable of other embodiments and can be implemented or carried out in various ways. The numbers provided in the flow charts and processes are provided to clearly illustrate the steps and operations and do not necessarily represent a particular order or sequence. Unless otherwise defined, the term "or" can refer to a selection of options (e.g., a disjunctive operator or an exclusive or) or a combination of options (e.g., a concatenative operator, and / or, a logical or, or a Boolean or). DC refers to direct current, while AC refers to alternating current.

[0009] The present disclosure relates to triode electron gun drivers that are capable of modulating the amplitude, width, and delay of pulses of the electron gun gate from one pulse to the next at high switching speeds. The disclosed embodiments generally relate to mechanisms, methods, and systems for driving the gate of a triode gun with different pulse amplitudes, widths, and delays from one pulse to the next. The disclosed embodiments also generally relate to gate driver circuits for electron guns.

[0010] Linear accelerators typically use a particle source, such as an electron source, configured to generate a particle beam. The particle beam is directed through an accelerator structure. The accelerator structure is a resonant structure that uses an input RF signal to accelerate particles in the particle beam. The accelerated particle beam is generated by pulsing the particle source to generate a particle pulse directed to the accelerator structure. The RF signal accelerates the particles to generate an accelerated particle beam. As will be described in further detail below, the electron particle source can be controlled by a gun driver. In addition, the gun driver can be configured to provide pulses with variable amplitude, width and delay, which will be described in further detail below.

[0011] Typically, the particle source of a linear accelerator uses a hot cathode or thermionic cathode, which is a cathode electrode with a heating element or filament that is heated to emit electrons due to thermionic emission. The heating element is typically an electric filament that is heated by an electric current passing through it. Two types of hot cathodes can be used in vacuum equipment: directly heated cathodes and indirectly heated cathodes. In a directly heated cathode, the filament is the cathode and emits electrons directly. In an indirectly heated cathode, the filament is not the cathode, but a separate cathode, such as a thin sheet metal cylinder surrounding the filament, is heated, and the filament or cylinder emits electrons. Typically, linear accelerators use indirectly heated cathodes.

[0012] For a linear accelerator to be useful in material discrimination applications such as cargo screening, the x-ray pulses need to have their pulse energy and dose per pulse precisely controlled from one pulse to the next. To control the dose and energy of each pulse in a linear accelerator, the amplitude, width, and delay of the pulses to the radio frequency (RF) source (e.g., a magnetron) and electron gun (e.g., a diode gun or a triode gun) need to be modulated on a pulse-by-pulse basis.

[0013] Two types of electron guns can be used in linear accelerators: diode guns and triode guns (or grid-controlled guns). A diode gun or diode gun has two independent potentials: a cathode and a focusing electrode, which are set to a certain negative voltage (usually on the order of tens of kilovolts (kV)); and an anode, which is held at or near the ground. In some embodiments, the cathode connection may have two leads: a cathode lead and a heater lead (or filament lead). Sometimes, the two separate potentials of a diode gun refer to the cathode potential and the heater potential. In a triode gun or triode gun, a control grid (or grid) is added just above the cathode surface. The grid is held at a third potential, typically within about 100 volts (V) of the cathode potential. Although diode guns may be suitable for use in simple low-energy linear accelerators and x-ray sources, most high-energy linear accelerators utilize triode guns because triode guns allow more control and flexibility over the energy and timing of pulses than diode guns by using a grid. The grid is an electrode between the cathode and anode in the vacuum enclosure that acts as a "gate" to control the electron current reaching the anode. A more negative voltage on the grid repels electrons back to the cathode, so fewer electrons reach the anode. A less negative or positive voltage on the grid allows more electrons to pass, increasing the anode current (also called beam current).

[0014] As will be described in further detail below, the gun driver can be configured to control the cathode, heater, and grid. As used herein, the heater may also be referred to as a filament or cathode filament, which produces electron emission when heated or becomes hot. Typically, the gun driver does not control the focus electrode, and control of the focus electrode is provided by other components or power supplies.

[0015] Since three voltage potentials (e.g., cathode, heater, and grid) are used in a triode gun relative to a reference (e.g., anode), at least four inputs or controls may be considered when designing and operating a triode gun. First, the anode is referenced to chassis ground, or the accelerator body on which the gun is mounted, which serves as a ground connection. Second, the cathode needs to be raised to a high negative voltage relative to the anode. In one example, the maximum cathode voltage has a voltage of -12kV to -15kV. In another example, the cathode voltage has a voltage range of 0V to -18kV. In one example, high voltage may refer to a voltage amplitude within the range of the cathode voltage relative to the anode. For example, high voltage may refer to a voltage amplitude (positive or negative) greater than 1kV. Third, the heater is driven with a voltage amplitude lower than the cathode, which may be positive or negative. In one example, the heater has a voltage amplitude between 2V and 10V relative to the cathode or a voltage amplitude from 4V to 7V relative to the cathode. Fourth, the grid has a voltage of -200V to 200V relative to the cathode. For example, in some designs, when the cathode is at high voltage, the gate may generally prevent the flow of beam current having a gate voltage driven to between -50V and -70V relative to the cathode (also referred to as a cutoff voltage), and when the cathode is at high voltage, the gate may generally allow the flow of beam current having a gate voltage driven to between 50V and 100V relative to the cathode (also referred to as a drive voltage). In other examples, the cutoff voltage may cut off beam current having a voltage greater than -50V (or a voltage magnitude less than -50V) or less than -70V (or a voltage magnitude greater than -70V), and the gate may allow full beam current having a voltage less than 50V or greater than 100V. In one example, the high voltage associated with the gate voltage may have a magnitude greater than 50V.

[0016] For some applications, the gate needs to generate pulses at a programmed amplitude at a fast rate by switching from a cutoff voltage to a drive voltage and back to the cutoff voltage at a specified pulse width with a fast rise time and fall time (to avoid pulse distortion), which can reduce the efficiency of the system. In one example, the pulse width may need to be between 0.5 microseconds (μS) and 5 μS, with a rate of up to 500 pulses per second (pps) or preferably up to 2000 pulses per second. In other examples, the gate pulse width and / or pulse rate may be different. In addition, the adjustability or programmability of the gun driver to the cathode voltage, heater voltage, gate drive voltage, gate cutoff voltage, gate pulse delay, and gate pulse width can give the user greater control over the pulse energy and dose, which can provide more functionality and applications for electron guns or systems (e.g., linear accelerators).

[0017] Conventional gun drivers provide some adjustment of amplitude, width, and delay parameters, but typically on very long time scales (on the order of seconds), which makes them unsuitable for use in material discrimination x-ray imaging systems, where gate adjustment needs to be performed on the millisecond (ms) or sub-millisecond (μS) scale, preferably modulated or adjusted on a pulse-to-pulse basis. For example, a conventional gun driver may have a pulse-to-pulse modulated gate drive voltage, but may only switch between two different voltages or modes, also referred to as interleaved modes, as described by U.S. Patent 9,661,734, entitled “Linear Accelerator System with Stable Interleaved and Intermittent Pulsing,” issued May 23, 2017 (referenced herein as the “Nighan Patent”), the entire disclosure of which is incorporated herein by reference. As disclosed in the Nighan Patent, the driver for the gate uses a voltage generated directly by a power supply, and switches between these two fixed voltages (referred to as modes) on a pulse-by-pulse basis. Power supplies are typically only capable of switching voltage amplitudes in at least tens (10s) or hundreds (100s) of milliseconds (ms) at best, which is insufficient to switch between more than two voltage amplitudes at a rate of at least 500 pulses per second. The two voltage amplitude limitation of a dual-mode gun driver at fast switching speeds (in the millisecond and sub-millisecond range) can be mitigated by adding power supplies for each additional mode and switching between fixed voltages of those power supplies. However, this approach adds more design complexity and cost, especially as the number of different modes increases. In addition, the number of different modes that can be used is still limited by the number of power supplies used.

[0018] In other conventional gun driver examples (not shown or referenced), the gun driver may use a single power supply that uses relatively expensive solid-state switches to switch between high voltage capacitor banks to drive the gate, where each capacitor bank is designed to produce a specific voltage amplitude or pattern. Similarly, gun drivers that use multiple high voltage capacitor banks to drive the gate have the limitation that the number of modes that can be used is limited by the number of high voltage capacitor banks used and the associated design complexity and cost.

[0019] In contrast, the disclosed design allows both gate drive voltage and gate cutoff voltage to be adjusted on a sub-millisecond level, making these two parameters (e.g., gate drive voltage and gate cutoff voltage at some limited resolution within the available dynamic range of the gun driver) available to the user on a pulse-by-pulse basis.

[0020] Typically, a system (e.g., a linear accelerator) that can switch between two modes based on a pulse-by-pulse basis is referred to as an interleaved system or an interleaved system, wherein each x-ray mode has a specified or limited dose and energy of an x-ray beam. Typically, the dose is determined by the RF source pulse amplitude and width in combination with the electron gun pulse amplitude, width, and delay. The energy is primarily determined by the RF source pulse amplitude, wherein the electron gun pulse amplitude, width, and delay may also have an impact. For example, an interleaved linear accelerator may be configured to switch pulse by pulse between an x-ray beam of dose A and energy A and another x-ray beam of dose B and energy B. A gun driver with interleaving capability allows the linear accelerator to select pulse by pulse between two pulse modes. Therefore, the first pulse mode is a pulse of amplitude A, width A, and delay A, while the second pulse mode may be amplitude B, width B, and delay B.

[0021] In contrast, a system with interleaving capability (e.g., a linear accelerator) can select between more than two modes (i.e., n modes, where n is a positive integer) on a pulse-by-pulse basis. A gun driver with interleaving capability can generate pulses of any amplitude, width, and delay within its dynamic range (with some finite resolution) on a pulse-by-pulse basis. A gun driver with interleaving capability (together with a magnetron modulator or RF modulator) allows the system to operate as an interleaved system, which provides greater versatility and functionality for x-ray imaging (such as material discrimination) relative to an interleaved or staggered system.

[0022] In one embodiment, if Figure 1 As shown, the triode gun driver 100 is divided into at least two major parts: (1) a control side or low voltage side 102, which may include a control board, control circuit or control module 110 (or control board 110 when formed as a single printed circuit board) and (2) a high voltage side 140, sometimes referred to as a hot platform side (as another reference to the high voltage). The "low voltage side" 102 and the "high voltage side" 160 have references with voltage amplitudes relative to system ground (e.g., linear accelerator system ground). The low voltage side 102 is referenced to the same chassis ground (or linear accelerator system ground) 116 and signal ground 108 used in the rest of the system, while the high voltage side 140 is referenced to a high voltage output terminal 146 (e.g., a negative voltage) of a high voltage capacitor charging power supply, high voltage capacitor charging module or capacitor charging power supply (CCPS) 144.

[0023] The CCPS charges the high voltage capacitor 106. The high voltage capacitor 106 is a storage capacitor that accumulates charge used to provide instantaneous current during a pulse that flows primarily from the cathode to the anode of the gun, and partially from the gate to the anode when the gate is on. Since the pulse width is typically much smaller than the time between pulses (e.g., the pulse duty cycle, or the ratio of the pulse "on" time to the pulse "off" time can be in the range of 0.0001 to 0.05), the high voltage capacitor 106 can be charged slowly (relative to the pulse width) between pulses, and then discharged quickly or partially during the pulse. The high voltage capacitor 106 allows the system to use a much smaller high voltage power supply than would be required if the high voltage power supply for the cathode itself had to provide the peak current required during the pulse rather than a trickle charge for charging the high voltage capacitor 106.

[0024] Both the low voltage side 102 and the high voltage side 140 may use low voltage control circuits, such as a microcontroller or field programmable gate array (FPGA) 120, 160 and low voltage power supplies 104, 148, 147. Although the low voltage controller 120 may be referenced by the example of the FPGA 120. Similarly, the high voltage controller 160 is referred to as the FPGA 160. On the high voltage side 140, the "ground" or "reference" for the low voltage control circuit is the output terminal (or cathode voltage) of the CCPS 144, because the control circuit is configured to drive the heater 194 and the gate 192, these voltages are specified relative to the cathode 196. Therefore, the low voltage side 102 is isolated from the high voltage side 140 and is referred to as two separate parts or sides. In some examples, a high voltage enclosure is used to isolate the high voltage side 140 components from the low voltage side 102 components. In other examples, the high voltage side 140 components and the low voltage side 102 components may be in the same enclosure or housing, wherein at least some of the high voltage side 140 components use high voltage mounts as separation and isolation from the low voltage side 102 components. The isolated power supply 130 supplies power to the high voltage side 140 and provides voltage isolation between the low voltage side 102 and the high voltage side 140. In one example, the isolated power supply 130 may be a DC / DC converter. The isolated voltage rating of the power supply 130 should be greater than the voltage output of the CCPS 144 (usually by a certain factor). For example, the CCPS 144 is configured to generate a cathode voltage of up to -18kV, and the isolated power rating may be 30kVDC.

[0025] The high side 140 may include a driver module 150 having a gate driver module 161 and a heater driver 176 as well as communication circuits 152, 154, 156 and conversion circuits (e.g., analog-to-digital converters (ADCs) and digital-to-analog converters (DACs)) 158, 166. The gate driver module 161 may include circuitry that provides interleaving capability, which may be configured to generate pulses of any amplitude, width, and delay within its dynamic range. For example, the gate driver module 161 may include a drive controller 160, a drive voltage amplifier 172, a cutoff voltage amplifier 174, a gate driver 180, and switches 182, 184. The gate driver module 161 may be configured as a half-bridge circuit, wherein the gate driver 180 rapidly controls the switches 182, 184 to apply the voltage 168 of the drive voltage amplifier 172 or the voltage 170 of the cutoff voltage amplifier 174, thereby generating a pulse on the gate connection 186 of the gate 192. The drive voltage amplifier 172 may be powered by the drive amplifier power supply 143, and the cutoff voltage amplifier 174 may be powered by the cutoff amplifier power supply 145. The input of the drive voltage amplifier 172 may be configured by the drive DAC 162, and the input of the cutoff voltage amplifier 174 may be configured by the cutoff DAC 164. The drive controller 160 may apply parameters from the user interface 114 to adjust the pulse amplitude on a pulse-by-pulse basis through the inputs to the drive DAC 162 and the cutoff DAC 164, and to adjust the pulse width and delay via the gate driver 180 and switches 182, 184.

[0026] One advantage of using high voltage power amplifiers 172 and 174, especially compared to a direct connection of the output of the high voltage power supply (using a switch) to the gate, is that the amplifier output can be quickly changed or reconfigured on a pulse-by-pulse basis at a rate of up to 500 pulses per second. In some examples, the output of the high voltage power amplifiers 172 and 174 can be changed or reconfigured on a pulse-by-pulse basis at a rate of up to 1000 pulses, 2000 pulses, 4000 pulses, or 8000 pulses per second. Some high voltage power amplifiers 172 and 174 can have a slew rate greater than 25V / μS, thereby providing fast amplifier output rise and fall times. Therefore, the pulse amplitude of each pulse can be varied, allowing a configurable mode to be at a rate of up to 500 pulses per second.

[0027] The slow switching speed (of voltage) of the components of conventional gun drivers is a limitation to performing gate switching functions (similar to the functions of the gate driver module 161) at usable pulse rates (e.g., greater than 500 pps) using the interleaving capability in the system. The use of high voltage power amplifiers 172 and 174 can shift the pulse rate limitation of the gun driver from the gate driver module 161 to the recharge speed of the high voltage capacitor 106. In some examples, the recharge speed of the high voltage capacitor 106 after being discharged during a pulse is about 8000 pps. Therefore, in some examples, the output of the high voltage power amplifiers 172, 174 is changed or reconfigured on a pulse-by-pulse basis at a rate of up to 8000 pulses per second.

[0028] The drive controller 160 may also provide application parameters to vary the input to the heater DAC 166, which may generate an input to the heater amplifier 176, thereby generating a heater voltage 178. The heater amplifier 176 may be powered by a heater amplifier power supply 147.

[0029] As previously described, the high side 140 may include one or more high side power supplies 142 . Figure 2 Some power supplies that may be included in one or more high-side power supplies 142 are shown, such as one or more low-voltage power supplies 148, a driver amplifier power supply 143, a cutoff power supply 145, and a heater amplifier power supply 147; however, in other embodiments, the number and type of power supplies may be different. In one example, the high-side power supply 142 may generate voltages of 3.3V, + / -15V, -10V (e.g., heater amplifier power supply 147), 24V, and + / -200V (e.g., driver amplifier power supply 143 and cutoff amplifier power supply 145).

[0030] The following provides additional details about the functionality, connections, and interfaces of the triode gun driver 100. Figure 1, control functions and circuits may be split between the low side 102 and the high side 140. For example, control functions and circuits may be split between the control module 100 and the driver module 150. In one example, the low side controller 120 may be configured to: trigger control pulse rate and width (when in external trigger mode); trigger the generator (when in internal trigger mode); monitor interlock signals to enable or disable certain gun driver functions, interact with the user interface 114 to process supervisory user data; interact with a user human machine interface (HMI) for service; interact with other discrete user signals; control the CCPS; interact with the high side controller 160 via the fiber optic communication link 122; interact with the analog-to-digital converter (ADC) 128; and interact with the digital-to-analog converter (DAC). The high side controller 160 may be configured to: receive a trigger signal from the controller 120 and use the trigger signal to generate gate drive signals for the switches 182, 184 in the half bridge; interact with a user interface that contains pulse amplitude, width, and delay parameters from the user to be applied to the next pulse; interact with the ADC 158 that provides sensor or electrical readings or measurements of various components such as heater voltage and current, gate drive and cutoff amplifier voltages, gun current, and gate drive and cutoff supply voltages; interact with a DAC that programs the gate drive and cutoff amplifiers and heater supply; and turn the heater on and off.

[0031] The gun driver 100 may include functions used in conventional gun drivers to be backward compatible with conventional gun drivers, so that the disclosed gun driver may also be used as a replacement for conventional gun drivers and provide additional mode functions. For example, certain analog signals may be generated by the CCPS 144 (e.g., voltage and current monitoring signals) or the user interface 114 (e.g., heater settings, cathode voltage settings, gate drive voltage settings, and gate cutoff voltage settings). The ADC 128 may convert those analog signals into a digital format for processing by the processor 120. The analog user signals may be used in a scenario where pulse-to-pulse interleaving is not used. The processor 120 may convert the digital signals via a DAC (not shown), which may be transmitted to the CCPS 144 or the user interface 114.

[0032] The low voltage side 102 uses the power input 112 and the user interface 114 to interact with the user (e.g., the linear accelerator control system), uses the CCPS control device 118 to control the CCPS, and provides communication 122, trigger 124, and possible additional signals to the high voltage side 140. In one example, the power input 112 can be configured to generate 15V or 24V DC. The low voltage side 102 includes a controller or processor, such as a microcontroller or FPGA 120 and an ADC 128. The user interface 114 is coupled to the low voltage controller 120 and exchanges various communication signals, such as trigger signals, interlock signals, discrete input / output (I / O) signals, and safety signals, and various communication protocols, such as Ethernet, can be used. Ethernet is a computer networking protocol family commonly used in local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs). The Internet Protocol (IP) is usually carried on Ethernet, and therefore it is considered to be one of the key technologies constituting the Internet. The trigger is a user trigger signal used to pulse the gate when in external trigger mode. The standby interlock should be met to allow the user to turn on the heater. The trigger interlock should be met to allow the trigger gate. The high-voltage interlock should be met to allow the user to turn on the cathode high voltage. Discrete I / O signals allow the user to control certain functions of the gun driver, which would otherwise be controlled via the low-voltage side controller 120 (e.g., high-voltage connection, heater opening, trigger enable / disable, and fault reset). The safety signal can allow the user to monitor certain states, which would otherwise be monitored via the low-voltage side controller 120 (e.g., interlock state, fault state, high-voltage connection state, trigger state, preheat state, and heater state). In addition, additional user analog outputs can be used so that the user can optionally monitor the heater voltage, heater current, cathode voltage, and gate drive voltage. Although Ethernet is used as an example, in other embodiments, other communication protocols can be used.

[0033] Some fiber optic links between the low voltage side 102 and the high voltage side 140 provide communication means (e.g., fiber optic communication link 132, low voltage side or control fiber optic communication link [connector or interface] 122, and high voltage side fiber optic communication link [connector or interface] 152) between the two sides (i.e., low voltage side 102 and high voltage side 140) and trigger signals (e.g., fiber optic trigger link 134, low voltage side or control fiber optic trigger link [connector or interface] 124, and high voltage side 140 fiber optic trigger link [connector or interface] 154) and optionally some additional signals and their associated links (connectors or interfaces). The fiber optic communication link 132 and the fiber optic trigger link 134 are shown as being between the low voltage side controller 120 and the high voltage side controller 160. In one example, the fiber optic communication link 136 (including the low voltage side or control fiber optic communication link [connector or interface] 126 and the high voltage side fiber optic communication link [connector or interface] 156) can couple the user interface 114 to the high voltage controller 160. In one example, the communication link 132 between the controllers 120 and 160 can be transmitted on a relatively "slow" bus that is used to transmit slower data (e.g., heater settings, system status, and cathode voltage settings) from the user that does not need to be adjusted at a pulse rate. The communication link 136 between the user interface 114 and the controller 160 can use a "fast" bus that is configured to set adjustable parameters (e.g., gate pulse amplitude, width, and delay) based on a pulse-by-pulse basis. The bus protocol can be operated so that the controller 160 can receive and / or process new messages from the user on the communication link 136 before each pulse. In one example, the communication links 132 and 136 and the trigger link 134 can use synchronous or asynchronous communication protocols. For example, the communication link 132 can use a universal asynchronous receiver-transmitter (UART), while the communication link 136 can use a flexible communication bus, such as a controller area network (CAN) bus, a transmission control protocol / internet protocol (TCP / IP) bus, an internal integrated circuit (I2C) bus, a serial peripheral interface (SPI) bus, or any other suitable communication bus. The CAN bus is a robust bus standard originally designed for vehicles to allow microcontrollers and devices to communicate with each other in applications without a host computer. The CAN bus can provide reliable communication over a noisy communication channel (e.g., physical layer) that can occur in imaging systems (including linear accelerators). CAN bus signaling can also occur between the user interface 114 and the low voltage controller 120. Although fiber optic communication links, connectors, and interfaces have been used as examples, other types of isolated communication links, whether optical or non-optical, can also be used.

[0034] The high side 140 includes one or more high side power supplies 142 and other high side components, such as a high voltage controller 160 , high speed digital-to-analog converters (DACs) 162 , 164 , and 166 , amplifiers 172 , 174 , and 176 , gate drivers 180 and switches 182 and 184 , and an analog-to-digital converter (ADC) 158 .

[0035] The high-side 140 components may be located separately, such as included on at least two printed circuit boards (PCBs). One PCB may include a power board with one or more high-side power supplies 142, which may use the low-voltage output (e.g., 24V) from the isolated power supply 130 to generate some of the voltages used on the second board, the high-side board, the driver board, or the driver module 150. More specifically, the one or more high-side power supplies 142 on the power board take the low-voltage output from the isolated power supply 130 as input and generate voltage rails for driving voltage amplifiers 172 (e.g., ~+200V and ~-15V), cutoff voltage amplifiers 174 (e.g., ~+24V and ~-200V) and heater drivers 176. A power rail or voltage rail refers to a single voltage provided by a power supply. In another example, the driving voltage has a range from 0V to 120V, and the cutoff voltage has a range from 0V to -120V. In one example, one or more high-side power supplies 142 are integrated with the driver module 150 in a single PCB (referred to as driver board 150). One of the functions of the driver board is to generate the filament voltage for the heater 194 and the gate cutoff voltage and gate drive voltage for the gate 192. In some embodiments, these functions may be some of the main functions of the driver board 150. The driver board 150 takes the CCPS output 146 (e.g., -12 kV to -15 kV) and uses this voltage as its "ground" or reference voltage, while also passing the reference voltage to the cathode 196 of the electron gun 190. As previously described, the anode 198 is referenced to the chassis ground, or the body of the linear accelerator in which the gun is mounted, which serves as the ground connection. The method of generating the gate drive voltage 168 and the gate cutoff voltage 170 is to generate the high and low voltage rails of the half-bridge driver circuit by using two high voltage power amplifiers (one amplifier for drive 172 [or drive amplifier], and one amplifier for cutoff 174 [or cutoff amplifier]). These amplifiers 172 and 174 are configured to generate square waves at a frequency of at least 1 kHz and can be changed at the desired pulse rate of the gun driver. In one example, a high voltage amplifier can provide speed and dynamic voltage range limits for a gun driver, which can have a supply voltage range of up to 400V (+ / -200V rail), with a slew rate of 50V / microsecond (μS) and a gain of 100. Between pulses, a user can send a message (e.g., a serial message) to the gun driver requesting the desired pulse amplitude, width, and delay for the next pulse, as well as changing the cutoff voltage at a rate up to the desired pulse rate. The control board 110 then relays the required information to the driver board 150. The FPGA 160 on the driver board 150 can then set the outputs of high speed digital-to-analog converters (DACs) 162 and 164, which drive the half-bridge amplifiers to prepare for the next pulse.When the leading edge of the trigger is received from the user, an appropriate delay (as previously requested by the user) is applied, and an appropriate signal is applied by the gate driver 180 to the gates of the switches in the half bridge (e.g., the drive switch 182 and the cutoff switch 184) to generate a pulse whose width was previously requested by the user. The gun driver may also have a feedthrough mode, in which the output pulse will simply follow the rising and falling edges of the input trigger signal 134. The drive switch 182 and the cutoff switch 184 may include high voltage n-channel enhancement field effect transistors (FETs) or metal oxide semiconductor FETs (MOSFETs), insulated gate bipolar transistors (IGBTs), or similar high power transistors. The heater amplifier 176 may be similar to the drive amplifier 172 or the cutoff amplifier 174, or may have a slower response time. For example, the heater amplifier may be driven by a DC input. The heater DAC 166 may be similar to the drive DAC 162 or the cutoff DAC 164, or may have a slower response time, a lower dynamic range, and / or a lower resolution. The filament voltage 178 and cathode voltage 146 may also be programmable by the user, although these voltages may not respond at the same high rate as the gate voltage.

[0036] Figure 3 Shows something like Figure 1 Schematic diagram or block diagram of an alternative driver module 250 of a triode gun driver of the triode gun driver 110 shown, in which the gate driver module 161 is replaced by a gate driver module 261. The gate driver module 261 may include the drive controller 160, a gate DAC 262, and a gate voltage amplifier 272, which may be coupled to the gate connection 186 of the gate 192. The gate voltage amplifier 272 may be powered by both the drive amplifier power supply 143 and the cutoff amplifier power supply 145 (or a power supply that provides both negative high voltage and positive high voltage to the gate voltage amplifier 272). The input of the gate voltage amplifier 272 may be configured by the gate DAC 262. The drive controller 160 may apply parameters from the user interface 114 to adjust the pulse amplitude on a pulse-by-pulse basis through the input to the gate DAC 262, and to adjust the pulse width and delay via the response time of the gate voltage amplifier 272. The dynamic range of the gate voltage amplifier 272 may limit the pulse amplitude or pulse width achieved by the gate voltage amplifier 272 because the gate voltage amplifier 272 needs to swing from a large negative cutoff voltage (e.g., <-50V) to a large positive drive voltage (e.g., >50V). Figure 1In the half-bridge configuration gate driver module 161 shown in , the swing of the output voltage of the gate voltage amplifier 272 can be approximately twice the voltage swing from the driver amplifier 172 or the cutoff amplifier 174, which can result in a longer pulse width of the gun driver (e.g., greater than 0.5 μs), longer pulse edge rise and fall times (e.g., greater than 100 ns), greater pulse shape distortion (e.g., less than a rectangular pulse shape), or a slower pulse rate capability (e.g., less than 500 pps).

[0037] Figure 4 Shows something like Figure 1 Schematic diagram or block diagram of an alternative driver module 252 of a triode gun driver of the triode gun driver 110 is shown, in which the gate driver module 161 is replaced by a gate driver module 263. The gate driver module 262 may include the driver controller 160, a gate DAC 264, an analog switch 280, and a gate voltage amplifier 274, which may be coupled to the gate connection 186 of the gate 192. The gate voltage amplifier 274 may be powered by both the drive amplifier power supply 143 and the cutoff amplifier power supply 145 (or a power supply that provides both a negative high voltage and a positive high voltage to the gate voltage amplifier 274). The input of the gate voltage amplifier 274 may be configured by the gate DAC 264 having at least two outputs to generate an input to the gate voltage amplifier 274 (via the analog switch 280) to generate a gate drive voltage (e.g., a higher high voltage) and a gate cutoff voltage (e.g., a lower high voltage). The drive controller 160 can apply parameters or trigger signals from the user interface 114 to adjust the pulse amplitude on a pulse-by-pulse basis through the input to the gate DAC 264, and adjust the pulse width and delay via the analog switch 280. The dynamic range of the gate voltage amplifier 274 can limit the pulse amplitude or pulse width achieved by the gate voltage amplifier 274 because the gate voltage amplifier 274 needs to swing from a large negative cutoff voltage (e.g., <-50V) to a large positive drive voltage (e.g., >50V). Figure 1 In the half-bridge configuration gate driver module 161 shown in , the swing of the output voltage of the gate voltage amplifier 274 can be approximately twice the voltage swing from the driver amplifier 172 or the cutoff amplifier 174, which can result in a longer pulse width of the gun driver (e.g., greater than 0.5 μs), longer pulse edge rise and fall times (e.g., greater than 100 ns), greater pulse shape distortion (e.g., less than a rectangular pulse shape), or a slower pulse rate capability (e.g., less than 500 pps).

[0038] like Figure 1-4As shown, the disclosed gate driver circuit provides high-speed changes in pulse amplitude and timing relative to conventional gun drivers. The gate driver circuit provides the user with the ability to select any drive voltage and cutoff voltage within its dynamic range on a pulse-by-pulse basis. One limitation on the number of modes available to the user within the dynamic range of the driver is the resolution of the DAC 162, 164, 262 that drives the half-bridge rail amplifier 172, 174 or the gate voltage amplifier 272. For example, a 10-bit DAC will provide the user with 1024 drive voltages and 1024 cutoff voltages to select from in the half-bridge configuration gate driver module 161. For example, a 10-bit DAC will provide the user with 1024 gate voltages to select from the gate amplifier configuration gate driver module 261. For example, a drive voltage dynamic range of 0V to 120V using a 10-bit DAC will provide the user with a gate drive resolution of 117mV. In embodiments using different DACs, the gun driver circuit is capable of switching between 1024 and 16384 different voltage levels.

[0039] Embodiments of the disclosed gun driver provide these functions for useful operation of the electron gun. In one example, the cathode voltage, heater voltage, gate drive voltage, gate cutoff voltage, gate pulse delay, and gate pulse width are each adjustable, wherein the gate drive voltage, gate cutoff voltage, gate pulse delay, and gate pulse width are each programmable at a rate of at least 500 Hertz (Hz) for pulse-by-pulse adjustment. In some examples, the gate drive voltage, gate cutoff voltage, gate pulse delay, and gate pulse width are each programmable at a rate of at least 1000 Hz or 2000 Hz for pulse-by-pulse adjustment.

[0040] In one example, pulses from an electron gun (typically in the kilovolt range) are amplified by a linear accelerator to produce pulses with energies of 0.5 MeV to 10 MeV.

[0041] Figure 5 A flow chart of a method 300 for controlling an electron gun driver according to some embodiments is shown. Figure 1 Taking the electron gun driver 110 of FIG. 1 as an example, in 310, the drive controller 160 and the drive DAC 162 set the gate drive voltage on the drive high voltage power amplifier 172 for the gate connection 186 of the electron gun 190. In 320, the drive controller 160 and the cutoff DAC 164 set the cutoff voltage on the cutoff high voltage power amplifier 174 for the gate connection 186 of the electron gun 190. In 320, the drive controller 160, the drive power switch 182, the cutoff power switch 184 and the gate driver 180 provide switching between the gate drive voltage and the gate cutoff voltage to generate a pulse on the gate connection 186.

[0042] Some embodiments include an electron gun driver comprising: a half-bridge driver circuit comprising: a drive circuit configured to generate a gate drive voltage (e.g., a higher high voltage) 168 for a gate connection 186 of an electron gun 190; and a cutoff circuit configured to generate a gate cutoff voltage (e.g., a lower high voltage) 170 for a gate connection 186 of the electron gun 190; and a gate driver 180 configured to switch between the gate drive voltage 168 and the gate cutoff voltage 170; and a drive controller 160 configured to generate pulse inputs to the drive circuit and the cutoff circuit and a gate switching signal for the gate driver 180.

[0043] In some embodiments, the driver circuit further includes: a driving high voltage power amplifier 172 configured to provide a gate drive voltage (e.g., a higher voltage) to the half-bridge driver circuit; a driving high speed DAC 162 configured to generate a programming voltage to the driving high voltage power amplifier 172; and a driving power switch 182 configured to apply a drive voltage to a gate connection 186. The cutoff circuit further includes: a cutoff high voltage power amplifier 174 configured to provide a gate cutoff voltage (e.g., a lower voltage) to the half-bridge driver circuit; a cutoff high speed DAC 164 configured to generate a programming voltage to the cutoff high voltage power amplifier; and a cutoff power switch 184 configured to apply a cutoff pulse to the gate connection 186. The gate driver 180 is configured to apply a gate control signal to the driving power switch 182 and the cutoff power switch 184.

[0044] In some embodiments, the electron gun driver also includes: a heater circuit configured to generate a heater voltage 178 for a heater connection 188 of the electron gun 190, the heater circuit including: a heater power amplifier 176 configured to provide the heater voltage 178 to the heater connection 188 of the electron gun 190; a heater high speed DAC 166 configured to generate pulses to the heater power amplifier 176; and wherein the drive controller 160 is configured to generate a heater input to the heater circuit.

[0045] In some embodiments, the electron gun driver further includes: a control circuit 110 configured to convert user inputs into driver controller inputs, the control circuit including: a user interface 114 configured to receive linear accelerator control system inputs; a low voltage side controller 120 configured to generate drive control signals for a drive controller 160; and a capacitor charging power supply (CCPS) controller 118 configured to generate CCPS control signals for CCPS 144. In some embodiments, the drive control signals include fiber optic communication links 132, 136 and a fiber optic trigger link 134. In some embodiments, the electron gun driver further includes: an isolated power supply 130 configured to provide voltage isolation between the control circuit 110 and the half-bridge driver circuit.

[0046] In some embodiments, the drive controller 160 is configured to adjust the amplitude, width, and delay of each pulse generated by the gate drive voltage and the gate off voltage, wherein each pulse can be configured to be different from the previous pulse.

[0047] In some embodiments, at least one of the amplitude, width, or delay of each pulse generated by the gate drive voltage and the gate off voltage is configured to vary between pulses.

[0048] In some embodiments, at least one of the amplitude, width, or delay of each pulse generated by the gate drive voltage and the gate off voltage is configured to change at a rate of at least 500 pulses per second.

[0049] Some embodiments include a system comprising: an electron gun driver, the electron gun driver including a driver module 150; a high voltage capacitor 106; a capacitor charging power supply (CCPS) 144, the capacitor charging power supply configured to charge the high voltage capacitor; one or more high voltage side power supplies 142, the one or more high voltage side power supplies configured to generate power for the high voltage side 140 of the electron gun driver; and an electron gun 190, the electron gun including: an anode 198, the anode coupled to the ground 108; a cathode 196, the cathode coupled to the output terminal 146 of the CCPS; a gate 192, the gate coupled to the gate connection 186; and a heater 194.

[0050] Some embodiments use a method for controlling a gun driver, wherein the method includes: setting a gate drive voltage on a driving high voltage power amplifier 172 for a gate connection 186 of an electron gun 190; setting a gate cutoff voltage on a cutoff high voltage power amplifier 174 for a gate connection 186 of an electron gun 190; and switching between a gate drive voltage pulse and a gate cutoff voltage pulse to generate a pulse on the gate connection 186.

[0051] In some embodiments, the method further includes adjusting the amplitude, width, or delay of each pulse generated by the gate drive voltage or the gate cutoff voltage, wherein at least three different amplitudes, at least three different widths, and at least three different delays can be used.

[0052] In some embodiments, the method further includes varying at least one of an amplitude, width, or delay of the gate drive voltage pulses and the gate off voltage pulses between pulses at a rate of at least 500 pulses per second.

[0053] In some embodiments, at least one non-transitory machine-readable storage medium comprising a plurality of instructions is adapted to be executed to implement the above-described methods.

[0054] Some embodiments include an electron gun driver including: a gate voltage generating device for generating a gate drive voltage (e.g., a higher high voltage) and a gate cutoff voltage (e.g., a lower high voltage) for a gate connection of an electron gun; a switching device for generating a pulse on the gate connection by switching between the gate drive voltage and the gate cutoff voltage; and a voltage control device for generating inputs to the gate voltage generating device and the switching device. Examples of the gate voltage generating device include a driving high voltage power amplifier 172, a cutoff high voltage power amplifier 174, a gate voltage amplifier 272, a gate voltage amplifier 274, a driving amplifier power supply 143, and a cutoff amplifier power supply 145. Examples of the switching device include a gate driver 180, a driving power switch 182, a cutoff power switch 184, a driving controller 160, and an analog switch 280. Examples of the voltage control device include the driving controller 160.

[0055] In some embodiments, the electron gun driver further includes a conversion device for converting the input to the gate voltage generating device into an analog input from the digital output of the voltage control device. Examples of the conversion device include a drive high speed DAC 162, a cutoff high speed DAC 164, a gate DAC 262, and a gate DAC 264.

[0056] In some embodiments, the electron gun driver further includes a command control device for converting user input into an input of the voltage control device. Examples of the command control device include the user interface 114 and the low-side controller 120 .

[0057] In some embodiments, the electron gun driver is configured to adjust the amplitude, width and delay of each pulse generated by the voltage control device, the gate voltage generating device and the switching device, wherein each pulse can be configured to be different from the previous pulse, and each of the amplitude, width and delay can be changed between at least three different values.

[0058] In some embodiments, the electron gun driver is configured to vary at least one of the amplitude, width, and delay of each pulse between pulses at a rate of at least 500 pulses per second.

[0059] The summary provided above is illustrative and is not intended to be limiting in any way. In addition to the foregoing examples, other aspects, features, and advantages of the present invention will become apparent by reference to the drawings, the following detailed description, and the appended claims.

[0060] Circuitry may include hardware, firmware, program code, executable code, computer instructions and / or software.A non-transitory computer-readable storage medium may be a computer-readable storage medium that does not include a signal.

[0061] It should be understood that many of the functional units described in this specification are labeled as modules in order to more specifically emphasize their implementation independence. For example, a module can be implemented as a hardware circuit including a custom very large scale integration (VLSI) circuit or gate array, including but not limited to logic chips, transistors or other components. A module can also be implemented in a programmable hardware device, including but not limited to a field programmable gate array (FPGA), programmable array logic, a programmable logic device or a similar device.

[0062] References to "examples" or "embodiments" throughout the specification mean that a particular feature, structure, or characteristic described in conjunction with the example is included in at least one embodiment of the present invention. Therefore, the words "examples" or "embodiments" that appear in various parts of this specification do not necessarily all refer to the same embodiment.

[0063] In addition, the described features, structures or characteristics can be combined in a suitable manner in one or more embodiments. In the following description, many specific details (e.g., examples of layout and design) are provided to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the relevant art will recognize that the present invention can be practiced without one or more specific details, or by other methods, parts, layouts, etc. In other cases, known structures, parts or operations are not shown or described in detail to avoid blurring the various aspects of the present invention.

[0064] The claims following this written disclosure are hereby expressly incorporated into this written disclosure, with each claim standing on its own as a separate embodiment. This disclosure includes all permutations of independent claims and their dependent claims. In addition, additional embodiments that can be derived from subsequent independent and dependent claims are also expressly incorporated into this written description. These additional embodiments are identified by replacing the dependencies of a given dependent claim with the phrase "any of the claims beginning with claim [x] and ending with the claim immediately preceding said claim", where the term "[x]" in parentheses is replaced with the number of the most recently cited independent claim. For example, for the first claim group beginning with independent claim 1, claim 4 can be dependent on any of claims 1 and 3, and these independent dependencies produce two different embodiments; claim 5 can be dependent on any of claims 1, 3, or 4, and these independent dependent claims produce three different embodiments; claim 6 can be dependent on any of claims 1, 3, 4, or 5, and these independent dependent claims produce four different embodiments; and so on.

[0065] The recitation of the term "first" with respect to a feature or element in a claim does not necessarily imply the presence of a second or additional such feature or element. Elements specifically recited in means-plus-function format, if any, are intended to be interpreted under 35 USC §112(f) to cover the corresponding structures, materials, or acts described herein and their equivalents. Embodiments of the invention claiming exclusive attributes or characteristics are defined as follows.

Claims

1. An electron gun driver, comprising: A half-bridge driver circuit, the half-bridge driver circuit comprising: A drive circuit configured to generate a gate drive voltage for a gate connection of an electron gun; the drive circuit comprising: a driving high voltage power amplifier configured to provide the gate drive voltage to the half-bridge driver circuit, a driving high speed digital-to-analog converter (DAC) configured to generate a programming voltage to the driving high voltage power amplifier, and a drive power switch configured to apply the gate drive voltage to the gate connection; and a cutoff circuit configured to generate a gate cutoff voltage for the gate connection of the electron gun; and a gate driver configured to switch between the gate drive voltage and the gate cutoff voltage; and A drive controller is configured to generate pulse inputs to the drive circuit and the cutoff circuit and a gate switching signal for the gate driver.

2. The electron gun driver according to claim 1, wherein the cutoff circuit further comprises: a cut-off high-voltage power amplifier, the cut-off high-voltage power amplifier being configured to provide the gate cut-off voltage to the half-bridge driver circuit, a cutoff high speed DAC configured to generate a programming voltage to the cutoff high voltage power amplifier, and a cut-off power switch configured to apply the cut-off voltage to the gate connection; and The gate driver is configured to apply a gate control signal to the driving power switch and the turning-off power switch.

3. The electron gun driver according to claim 1, further comprising: a heater circuit configured to generate a heater voltage for a heater connection of the electron gun, the heater circuit comprising: a heater power amplifier configured to provide the heater voltage to the heater connection of the electron gun, a heater high speed DAC configured to generate a programming signal to the heater power amplifier; and Wherein the drive controller is configured to generate a heater input to the heater circuit.

4. The electron gun driver according to claim 1, further comprising: A control circuit configured to convert a user input into a driver controller input, the control circuit comprising: a user interface configured to receive a linear accelerator control system input; a low-voltage side controller configured to generate a drive control signal for the drive controller; and A capacitor charging power controller is configured to generate a capacitor charging power control signal for a capacitor charging power supply.

5. The electron gun driver of claim 4, wherein the drive control signal comprises a fiber optic communication link and a fiber optic trigger link.

6. The electron gun driver according to claim 4, further comprising: An isolated power supply is configured to provide voltage isolation between the control circuit and the half-bridge driver circuit.

7. The electron gun driver of claim 1, wherein the drive controller is configured to adjust the amplitude, width and delay of each pulse generated by the gate drive voltage and the gate off voltage, wherein each pulse is configurable to be different from a previous pulse.

8. The electron gun driver of claim 1, wherein at least one of an amplitude, a width, or a delay of each pulse generated by the gate drive voltage and the gate-off voltage is configured to vary between pulses.

9. The electron gun driver of claim 1, wherein at least one of an amplitude, a width, or a delay of each pulse generated by the gate drive voltage and the gate-off voltage is configured to change at a rate of at least 500 pulses per second.

10. A system for controlling an electron gun driver, comprising: The electron gun driver according to claim 1; High voltage capacitors; a capacitor charging power supply configured to charge the high voltage capacitor; one or more high-side power supplies configured to generate power for a high-side of the electron gun driver; as well as An electron gun, comprising: an anode coupled to ground; a cathode coupled to an output terminal of the capacitor charging power supply; a gate coupled to the gate connection; and Heater.

11. A method for controlling an electron gun driver, the method comprising: For the gate connection of the electron gun, a gate driving voltage is set on the driving high voltage power amplifier, and the setting of the gate driving voltage includes: Use a driver high-speed digital-to-analog converter (DAC) to generate the programming voltage, and amplifying the programming voltage using the driving high voltage power amplifier, the driving high voltage power amplifier being configured to generate the gate driving voltage; For the gate connection of the electron gun, setting a gate cut-off voltage on a cut-off high voltage power amplifier; and Switching between the gate drive voltage and the gate off voltage generates a pulse on the gate connection.

12. The method of claim 11, further comprising: The amplitude, width or delay of each pulse generated by the gate drive voltage or the gate cutoff voltage is adjusted, wherein at least three different amplitudes, at least three different widths and at least three different delays can be used.

13. The method of claim 11, further comprising: At least one of an amplitude, a width, or a delay of the pulse is varied at a rate of at least 500 pulses per second, wherein each of the amplitude, the width, and the delay is variable between at least three different values.

14. At least one non-transitory machine-readable storage medium comprising a plurality of instructions adapted to be executed to implement the method of claim 11.

15. An electron gun driver, comprising: A gate voltage generating device, the gate voltage generating device is used to generate a gate drive voltage and a gate cut-off voltage for the gate connection of the electron gun; a switching device for generating a pulse on the gate connection by switching between the gate drive voltage and the gate cut-off voltage; as well as a voltage control device for generating inputs to the gate voltage generating device and the switching device; The gate voltage generating device comprises: conversion means for converting the input to the gate voltage generating means into an analog input from a digital output of the voltage control means; as well as An amplifying device is used to generate the gate drive voltage in response to the analog input.

16. The electron gun driver according to claim 15, further comprising: a heater voltage arrangement for generating a heater voltage for a heater connection of the electron gun; and Wherein the voltage control means generates an input to the heater voltage means.

17. The electron gun driver according to claim 15, further comprising: A command control device is provided for converting user input into input for the voltage control device.

18. An electron gun driver as described in claim 15, wherein the electron gun driver is configured to adjust the amplitude, width and delay of each pulse generated by the voltage control device, the gate voltage generating device and the switching device, wherein each pulse can be configured to be different from the previous pulse, and each of the amplitude, the width and the delay can be changed between at least three different values.

19. The electron gun driver of claim 15, wherein the electron gun driver is configured to vary at least one of the amplitude, width, and delay of each pulse between pulses at a rate of at least 500 pulses per second.

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