Fiber optic communication for embedded electronic circuits in X-ray generators.

Abstract

To solve the problem in which gun controllers need a more intelligent control system that employs digital control through digital processors, where all of these digital control subsystems need to be programmed and, if possible, also re-programmed "in the field", and, since they are typically located in a physically inaccessible high-voltage environment, this needs to be achieved remotely through the galvanic isolation provided for the high-voltage environment.SOLUTION: An x-ray source includes an optical communications link to provide a galvanically isolated communication between a system controller and a gun controller. In specific examples, the link is provided through one or more fibers. In addition, the gun controller is preferably remote-programmed by the system controller during startup. A watchdog timer is also useful for a gun digital processor of the gun controller.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Related Applications This application is related to U.S. patent application Ser. No. 17 / 238,785, filed on even date herewith, entitled "X-ray source with liquid cooled source coils," invented by Claus Flachenecker and Thomas A. Case, attorney docket number 0002.0085US1 (2020ID00440), now U.S. Patent Application Publication No. ___, and to U.S. patent application Ser. No. 17 / 238,799, filed on even date herewith, entitled "Method and system for liquid cooling isolated X-ray transmission target," invented by Claus Flachenecker, Bruce Borchers, and Thomas A. Case, attorney docket number 0002.0086US1 (2020ID00442), now U.S. Patent Application Publication No. ___.

[0002] All of the aforementioned applications are incorporated herein by reference in their entirety. [Background technology]

[0003] Background technology X-rays are widely used in microscopy due to their short wavelength and ability to penetrate objects. Typically, the best source of X-rays is a synchrotron, but these are expensive systems. Therefore, so-called tube or laboratory X-ray sources, in which a generated electron beam strikes a target, are often used. The resulting X-rays contain characteristic lines determined by the target's composition and a wide range of bremsstrahlung radiation.

[0004] X-ray microscope systems have several basic configurations. Some use a condenser to focus the X-rays onto the object being studied and / or an objective lens to image the X-rays after interaction with the object. The resolution and aberrations associated with these types of microscopes are typically determined by the spectral characteristics of the X-rays. Some microscope systems employ a projection configuration in which a small X-ray source spot is used, often with geometric magnification, to image the object.

[0005] Performance, and especially resolution, is affected by different factors. Because projection configurations lack aberrations, resolution is typically determined by the size of the X-ray source spot. Ideally, the X-ray source spot is a point spot. In practice, X-ray source spots are significantly larger. The source spot size is generally determined by the electron optics and their ability to focus the electron beam to a single point. The source spot size is typically about 50–200 micrometers (μm) with good electron optics; however, in other instances, when output is a more important figure of merit, the X-ray source spot size may be 1–5 millimeters (mm). For transmission target X-ray sources, spot sizes of several micrometers, such as 1–5 μm, are common. In fact, some transmission sources have spot sizes up to 150 nanometers (nm). In any case, the size of the X-ray source generally limits the resolution of the X-ray projection microscope.

[0006] Many microscopy applications often use transmission-target X-ray sources. In the basic configuration of an X-ray tube, thermal or field-emission electrons are generated in the cathode (filament) of a vacuum tube and accelerated to the anode (forming an electron beam that is shaped by different electrostatic and (electro)magnetic-optical elements). For example, magnetic lenses often use a coil of copper wire inside an iron pole piece. Current passing through the coil generates a magnetic field within the bore of the pole piece. Electrostatic lenses use a charged dielectric to generate an electrostatic field. The electron beam then strikes the backside of a typically thin target. Common target materials are tungsten, copper, and chromium. X-rays emitted from the front side of the target are then used to irradiate the object.

[0007] X-ray sources typically require control electronics that regulate, control, and / or monitor the electron emission system (or electron "gun"). These electronics are often called a "gun controller."

[0008] The gun controller is electrically attached to the electron gun components, such as the filament, suppressor cathode, and extractor cathode.

[0009] In many designs, during operation, the gun electronics are elevated to a high voltage potential of several kilovolts, and galvanic isolation must be provided. This is because electrons are accelerated toward the positive electrode (anode). If the target must be close to the sample, it must also be grounded to avoid arcing to the sample. As a result, the filament must be at a high negative voltage. And the gun controller must also be at a very high negative voltage.

[0010] Typically, the gun control electronics are also potted in epoxy or immersed in transformer oil. In either case, the gun control electronics are located in a location that is difficult or impossible for maintenance personnel to reach. Summary of the Invention [Problem to be solved by the invention]

[0011] Summary of the Invention More complex gun controllers require more intelligent control systems that use digital control via digital processors such as central processing units (CPUs), digital signal processors (DSPs), or field programmable gate arrays (FPGAs). All of these digital control subsystems must be programmed and, if possible, reprogrammed "in the field." Because they are typically located in physically inaccessible high-voltage environments, this must be achieved remotely through galvanic isolation provided to the high-voltage environment. [Means for solving the problem]

[0012] The present invention includes an optical communication link for providing galvanically isolated communication between the system controller and the gun controller. In a particular example, the link is provided via one or more optical fibers.

[0013] In this implementation, each fiber can transmit one or more signals together, encoding them through a special communication protocol. Bidirectional optical communication over a standard optical fiber can also be employed.

[0014] Its main advantage is the versatility of the communication method and the fact that only one or two fibers in total are needed to carry a virtually unlimited number of signals in each direction. Specific protocols include Gbit / s Ethernet over one or more optical fibers.

[0015] The present invention also includes a digital control system and remote programming of the gun controller. The gun digital processor in the gun controller requires some configuration to function. Typically, this configuration is a program (for CPUs and DSPs) or a configuration file (for FPGAs) stored in non-volatile memory close to the processor. Upon power-up, the program or configuration file is loaded and executed by the digital processor. The information may be stored directly within the processing chip or in associated memory (such as flash memory).

[0016] The only drawback to this typical setup is the fact that the gun controller may operate in a harsh X-ray environment, which makes using flash memory very dangerous. Continuous X-ray exposure will slowly erase the memory and make it unreliable. It would be better if the program could be loaded "on the fly".

[0017] In this approach, the gun controller includes a gun digital processor, and the system controller provides configuration for the digital processor at power-up. In this way, operation of the digital processor is not impaired by long-term radiation around the gun controller.

[0018] The configuration can be provided via a fiber optic link. One or more fibers of the link are then preferably used to continuously transmit data to the gun controller. Another or the same fiber can carry information back from the gun controller to the main system digital controller. This includes all desired telemetry data such as digitized voltage, current, temperature, etc.

[0019] The present invention also includes a watchdog timer for the gun digital processor, which resets the gun digital processor if no communication occurs for a certain period of time, allowing the processor to be reprogrammed at any time.

[0020] In general, according to one aspect, the invention features an x-ray source that includes a system controller, a target, an electron source for generating electrons to form a beam that impacts the target to produce x-rays, a high voltage generator for accelerating the beam, and a gun controller that controls the electron source and receives configuration from the system controller upon each start-up.

[0021] The source may comprise a source coil controlled by the gun controller. The gun controller may include a field programmable gate array (FPGA), and the system controller provides a configuration file for the digital processor upon power-up. In other cases, the gun controller includes a central processing unit (CPU) or digital signal processor (DSP), and the system controller provides a program for the digital processor upon power-up.

[0022] An optical communication link can be used between the system controller and the gun controller, over which the system controller provides the configuration to the gun controller, and can include at least a downlink fiber for transmitting data from the system controller to the gun controller and at least an uplink fiber for transmitting data from the gun controller to the system controller.

[0023] In an example, the optical communication link encodes the detected voltage of the gun controller as a frequency of light pulses. Often, the link includes at least a downlink fiber for transmitting data from the system controller to the gun controller and at least an uplink fiber for transmitting data from the gun controller to the system controller.

[0024] The gun controller may be or comprise a field programmable gate array (FPGA) or complex programmable logic device (CPLD), with the system controller providing a configuration file for the digital processor at power-up. However, the gun controller may also be a central processing unit (CPU) or digital signal processor (DSP), with the system controller providing a program for the digital processor at power-up.

[0025] In general, according to yet another aspect, the invention features an x-ray source that includes a system controller, a target, an electron source for generating electrons to form a beam for impacting the target to produce x-rays, a high voltage generator for accelerating the beam, and a gun controller for controlling the electron source and the formation of the beam under control of the system controller, the gun controller including a digital processor and a watchdog timer for resetting the digital processor after a period of no response.

[0026] In operation, the watchdog timer receives a keep-alive signal from the system controller and resets the digital processor after failing to receive the keep-alive signal.

[0027] In general, according to yet another aspect, the invention features an x-ray source including a system controller, a target, an electron source for generating electrons to form a beam for impacting the target to generate x-rays, a high voltage generator for providing acceleration of the beam, and a gun controller for controlling the electron source. A fiber optic link is used to enable communication between the system controller and the gun controller.

[0028] In general, according to yet another aspect, the invention features an x-ray source that includes a target, a system controller for monitoring a target current in the target, an electron source for generating electrons to form a beam that impacts the target to produce x-rays, a high voltage generator for powering the electron source under control of the system controller, a source coil for steering the beam, and a gun controller for controlling the electron source and the source coil and for receiving target current information used to control the source coil.

[0029] In general, according to yet another aspect, the invention features an x-ray source that includes a target; a system controller for monitoring a target current in the target; an electron source for generating electrons to form a beam that impacts the target to produce x-rays; a high voltage generator for accelerating the beam; and a gun controller for controlling the electron source, the gun controller including an analog interface unit for digitizing parameters of the gun controller and generating analog control signals.

[0030] In general, according to yet another aspect, the invention features a gun controller that controls an electron source and monitors a power supply such that the gun controller controls operation of the power supply.

[0031] In general, according to yet another aspect, the invention features a gun controller for monitoring current to an electron source.

[0032] These and other features of the invention, including various novel details of construction and combination of parts, as well as other advantages, will be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the specific methods and devices embodying the invention are shown by way of illustration and not as limitations of the invention. The principles and features of this invention can be employed in various and numerous embodiments without departing from the scope of the invention.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a schematic cross-sectional view of an X-ray source according to the present invention; [Figure 2] FIG. 1 is a schematic diagram illustrating control of an x-ray source between a system controller and a gun controller in accordance with the principles of the present invention. [Figure 3] FIG. 1 is a swim lane diagram illustrating the operation of the system digital processor 210 and the gun digital processor 305 during reset, configuration, and operation. [Figure 4] FIG. 2 is a schematic block diagram showing details of a gun controller. DETAILED DESCRIPTION OF THE INVENTION

[0035] MODE FOR CARRYING OUT THE INVENTION The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0036] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Also, all conjunctions used should be understood in the most inclusive sense possible. Accordingly, the word "or" should be understood to have the definition of a logical "or" rather than a logical "exclusive or" definition, unless the context clearly requires otherwise. Furthermore, the singular forms and the articles "a," "an," and "the" are intended to include the plural unless otherwise stated. It will be further understood that the terms "includes," "comprises," and / or "including," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Furthermore, when an element, including a component or subsystem, is referred to and / or shown as being connected or coupled to another element, it will be understood that it may be directly connected or coupled to the other element, or that intervening elements may be present.

[0037] Although terms such as "first" and "second" are used herein to describe various elements, it should be understood that these elements are not limited by these terms. These terms are used only to distinguish one element from another. Thus, an element described below could be referred to as a second element, and similarly, the second element could be referred to as a first element without departing from the teachings of the present invention.

[0038] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant art, and it will be further understood that they should not be interpreted in an idealized or overly formal sense unless expressly defined as such in this specification.

[0039] FIG. 1 is a schematic cross-sectional view of an x-ray source 100 constructed in accordance with the principles of the present invention. The illustrated embodiment is a "transmission target" source: the electron beam B strikes the target in the target assembly 500, and the x-rays X emitted from the opposite side of the target are used to illuminate the object. However, many aspects of the following innovations are equally applicable to other x-ray tube source configurations, including side windows, rotating anodes, and metal jet anodes.

[0040] Generally, the x-ray source comprises a vacuum vessel 112 and an oil vessel 114 disposed within the vacuum vessel. Preferably, the vacuum vessel 112 is metal, such as aluminum or stainless steel, for its vacuum strength. The oil vessel 114 is preferably constructed from a non-conductive material, such as a ceramic, e.g., sintered alumina, that provides electrical insulation to prevent arcing to the high voltage components contained therein.

[0041] A vacuum generator 118 is used to draw and / or maintain a vacuum on the vacuum vessel 112. In one example, an ion pump is used.

[0042] A heat exchanger 119 is located inside the oil vessel. To this end, a plate heat exchanger can be used to remove thermal energy (heat) from the oil and pass it on to a coolant, such as water, which circulates through the exchanger. Some embodiments further use a submerged pump 121 to circulate the oil within the oil vessel 114. In a preferred embodiment, a circulator 152 is used to force the coolant through the heat exchanger 119 to carry the heat away from the oil.

[0043] Generally, the vacuum vessel 112 defines a volumetric vacuum region through which the electron beam B propagates from the electron emitter 126 (filament or cathode), typically located near the distal end of the oil vessel 114, to the target held by the target assembly 500. The vacuum region also preferably surrounds at least a portion of the oil vessel, which houses high voltage components and provides high voltage insulation.

[0044] The system controller 200 is located outside both vessels 112, 114. It contains the main controller and data interfaces to external devices. It also contains a power supply for connecting to the mains power supply. It also controls the vacuum generator 118 and the circulator 152.

[0045] The high voltage generator 116 is disposed within the oil vessel 114. Its base is proximal to the oil vessel 114, allowing it to receive power from the system controller 200. The high voltage generator 116 is immersed in oil contained in the oil vessel 114 for thermal control and high voltage insulation. The oil is needed primarily to keep the generator 116 relatively small; however, the generator 116 can also be potted. Moving distally, the high voltage generator 116 is further electrically insulated from the environment by the oil and surrounding vacuum of the vacuum vessel 112.

[0046] The high voltage generator 116 in the present example generates a negative 20-160 kV acceleration voltage and powers the gun controller 300, which controls, among other things, the electron source (emitter or filament). The high voltage generator biases the entire gun controller to this large negative voltage so that the generated electrons accelerate toward the less negative voltage and ground.

[0047] The inner vessel 120 is located distal to the distal end of the high voltage generator 116. The inner vessel 120 is immersed in oil in the oil vessel 114. In the current embodiment, the inner vessel is preferably constructed from a metal such as aluminum or mild steel. It is also filled with oil, which aids in the transfer of heat from the electronics, as well as from the source coil, as will be described below.

[0048] The gun controller 300 is housed within the inner vessel 120, which also functions as a Faraday cage to electrically protect the controller 300. It drives the electron emitters and provides controls for the electron emitters, beam generation, modulation, and steering.

[0049] An electron emitter, e.g., a filament 126, is held in a filament mount 124. In the current example, the electron emitter 126 includes a lanthanum hexaboride (LaB6) crystal and a carbon heater rod, which protrudes into the vacuum of the vacuum vessel to function as a thermionic source or electron emitter (cathode). Other configurations are possible, such as W, CeB6, HfC, and carbon nanotube filaments.

[0050] The vacuum feedthrough 122 provides an electrical connection between the gun controller 300 within the inner vessel 120 and the outer wall of the oil vessel 114 through the oil contained in the oil vessel 114 .

[0051] A suppressor electrode or Wehnelt cap 127 is attached distally to the filament mount 124 and covers the filament 126. Electrons emitted from the filament 126 pass through a central aperture in the suppressor electrode 127, the voltage of which is controlled by the gun controller 300.

[0052] A protective field cap 138 has a general bell shape and extends over the electron emitter 126 and its filament mount 124, wrapping back around the distal end of the oil container 114. Its distal end carries a first or extractor anode 140. The voltage and cap of the first anode are controlled by the gun controller 300 to accelerate the emitted electrons through a central aperture 141 of the first anode 140 into beam B. Thus, during operation, the electron beam passes through the central aperture 141 of the first anode 140.

[0053] However, the first anode is not required, and the system can also be designed without this first anode and rely on other means to accelerate the electrons.

[0054] Beam B is directed through an aperture in a flight tube aperture assembly 142 in the distal wall of the vacuum vessel 112. This flight tube aperture assembly acts as a second anode and is currently held at ground potential 143. Therefore, the gun controller is biased to a large negative voltage, causing the electrons to be further accelerated in the gap between the first anode 140 and the flight tube assembly 142.

[0055] In other embodiments, the flight tube aperture assembly 142 is electrically isolated from the vacuum vessel 112 using an insulating gasket such as diamond. A voltage generator is also added to provide a controlled potential to the flight tube aperture assembly. In this configuration, the system controller 200 also controls the voltage of this second anode to provide additional control, such as additional acceleration, to the electron beam B. The flight tube assembly 400 extends the vacuum to the target assembly 500 and its target. The flight tube manifold 150 provides liquid cooling to the target assembly using a coolant, such as water, from a circulator 152 through the flight tube assembly walls.

[0056] Located along the flight tube assembly 400 is a flight tube beam steering and shaping system 600 for adjusting the electron beam and directing the beam to any desired location on the target. This is accomplished by the flight tube assembly 400 and the beam steering and shaping system 600, which directs the electron beam B to the desired angle and location through a magnetic focus lens 700. As the target is consumed during operation, the beam steering typically positions the spot at different locations on the target.

[0057] Additionally, a magnetic focusing lens 700 is positioned along the flight tube assembly 400 to focus the beam B onto the target.

[0058] Preferably, both the flight tube beam steering and shaping system 600 and the magnetic focusing lens 700 are cooled by a coolant circulated from the circulator 152 and controlled by the system controller 200 .

[0059] A pair of source coils 132N, 132S (before and after the image plane), not shown, and 132E, 132W and their respective cores 134N, 134S, 134E, and 134W, not shown, are integrated with the oil container 114, the gun controller inner container 120, and the protective field cap 138. The coils are located outside the vacuum of the vacuum container. In one example, they can be located on the outer wall of the vacuum container exposed to the ambient atmosphere. In the example shown, the source coils 132N, 132S, 132E, and 132W are located within the oil container and are therefore efficiently cooled by the contained oil, although the coils could alternatively be potted.

[0060] More generally, the oil can be replaced with potting material or other high voltage compatible cooling materials such as Fr-77 by Sigma Aldrich, Sf6-Novec 4710 by 3M, or C3F7CN.

[0061] More specifically, two source coils 132N, 132S are generally positioned above and below the filament 126. Two additional source coils 132E, 132W are positioned on the other two axes, below and above the plane of the drawing, respectively. North and south pole pieces 130N, 130S extend from cores 134N and 134S of the source coils 132N, 132S, respectively, wrap around the inside of a protective field cap 138, and converge above and below, respectively, a central aperture 141 of the first anode 140. Similarly, east pole piece 130E and west pole piece 130W (in the other two axes below and above the plane of the drawing, respectively) extend from cores 134E and 134W of source coils 132E, 132W, wrap around the inner sides of protective field cap 138, and converge to the left and right of central port 141, respectively, thus forming a magnetic circuit surrounding the emitter in vacuum.

[0062] Pole pieces 130N, 130S, 130E, and 130W can be mechanically connected to virtually anything within the emitter region. Thus, although they are carried by protective field caps in the illustrated embodiment, they need not be directly connected. However, in the present example, pole pieces 130N, 130S, 130E, and 130W are connected to protective caps that are electrically at the potential of first anode 140.

[0063] An annular ring-shaped yoke 135 is disposed proximal to the cores 134N, 134S, 134E and 134W and is fabricated as part of the container 120 to improve the magnetic circuit. Indeed, in the current embodiment, the distal end of the inner container 120 is soft iron, thus completing the magnetic circuit by directing the magnetic flux between the cores.

[0064] In a preferred embodiment, the magnetic circuit for the source coils 132N, 132S, 132E, and 132W is further improved by magnetizable or ferromagnetic wall plugs 136N, 136S, 136E, and 136W. These wall plugs are inserted into holes formed in the oil reservoir 114 opposite the distal ends of the respective cores 134N, 134S, 134E, and 134W. This improves the magnetic flux through the circuit. Specifically, the plugs minimize the gap between the coil cores 134N, 134S, 134E, and 134W and the respective pole pieces 130N, 130S, 130E, and 130W.

[0065] In some cases, plugs 136N, 136S, 136E, 136W are inserted into pre-drilled holes in ceramic oil reservoir 114. Alternatively, the same can be accomplished by welding nickel-cobalt iron alloy or soft iron plugs into pre-drilled holes in stainless steel vacuum chamber 112. Other combinations are possible.

[0066] In the current embodiment, source coils 132N, 132S, 132E, 132W are driven and operated in a current-controlled mode by gun controller 300. Feedback is obtained indirectly by measuring the amount of beam passing through the "anode aperture" and onto the target by system controller 200, which provides this information to the gun controller. The source coils are controlled by gun controller 300, which steers the electron beam near its source, specifically, steering the beam within the gap between filament 126 and first anode 140, steering the beam as it is initially accelerated.

[0067] However, it should be noted that in other embodiments, the high voltage generator may be a separate part outside the vacuum vessel.

[0068] FIG. 2 illustrates how control of x-ray source 100 is distributed between system controller 200 and gun controller 300 and their communications in accordance with the principles of the present invention.

[0069] The system controller 200 has a system digital processor 210, which functions as the main controller for the x-ray source 100. Typically, this is a central processing unit that receives user instructions via a digital interface, such as an Ethernet (IEEE 802.3) interface to a host computer. The system digital processor 210 uses system memory 212, which stores the configuration, i.e., programs, for the system digital processor, as well as gun processor configuration 214. It also typically stores system calibration data 215.

[0070] The gun processor 305 can take several different forms. If the gun processor 305 is a CPU or DSP or other type of microcontroller, the gun processor configuration 214 stored in the system memory 212 is a program that includes a boot program for the gun digital processor 305. On the other hand, if the gun digital processor 305 is an FPGA or CPLD, the gun processor configuration 214 is commonly referred to as a configuration file. In either case, the configuration for the gun digital processor 305 is stored in an environment that is safe from any radiation generated by the x-ray source 100. An additional reason for sending the configuration to the gun controller each time is on-the-fly configuration, which avoids the need to reprogram the flash memory in the gun controller. Nevertheless, in many cases, the processor 305 also includes memory 306. In some instances, radiation shielding is added to protect this memory 306.

[0071] Additionally, system controller 200 includes several other drivers and monitoring devices for operating source 100. Specifically, it includes a target current receiver 220 that detects target current from target assembly 500. Also included is a magnetic lens driver 222 that enables system digital processor 210 to control the operation of magnetic focus lens 700. Additionally, a beam steering and shaping system driver 224 enables system digital processor 210 to control beam steering and shaping system 600. A vacuum driver 232 enables the system digital processor to provide power to a vacuum generator, such as ion pump 116, to maintain vacuum. It also receives analog feedback from the vacuum pump.

[0072] The system digital processor 210 controls the high voltage generator 116 via a high voltage generator driver 226, which also includes a power supply 228.

[0073] In the high voltage generator 216, a high voltage multiplier 170 is used to generate the high voltage supplied to the gun controller 300. Additionally, an isolation transformer 172 supplies power received from the power supply 228 to the gun controller 300. This transformer isolates the power supply 228 of the system controller 200 from the high potential at which the gun controller 300 operates.

[0074] In some examples, the isolation transformer 172 is not used. Instead, power is taken from the high voltage power provided by the high voltage multiplier. However, a separate isolation transformer 172 provides the advantage that the gun controller 300, along with its gun digital processor 305, can be powered without the high voltage output from the high voltage multiplier.

[0075] On the gun controller 300, a gun digital processor 305 controls components associated with forming the electron beam. Specifically, a filament heater and driver 312 provides power to heat the filament 126. A filament U / I sensing module 314 monitors the operation of the filament 126 and provides feedback to the gun digital processor 305.

[0076] A suppressor voltage controller 316 controls the potential of the suppressor electrode 127. A first anode voltage controller 318 allows the digital processor 305 to adjust the voltage of the first anode 140. The gun digital processor 305 controls the steering of the electron beam via a source coil driver 310, which controls the source coils 132N, 132S, 132E, 132W.

[0077] A bidirectional fiber optic link 180 provides communication between the system digital processor 210 of the system controller 200 and the gun digital processor 305 of the gun controller 300. The fiber optic link is maintained between the system controller optoelectronic interface 230 and the gun controller optoelectronic interface 320. Generally, the fiber optic link comprises one or more optical fibers, typically two or more. Preferably, these are multimode optical fibers, although single-mode fiber can be used. Each of the optoelectronic interfaces 230, 330, in turn, comprises a transmitter including a diode laser that optically encodes information for transmission over the optical fiber. Additionally, each optoelectronic interface 230, 330 includes a receiver, typically a photodiode, that detects the modulated light from the other laser diode and decodes the light into electronic signals for the system digital processor 210 and the gun digital processor 305.

[0078] During operation, gun digital processor 305 reports the operation of filament 126, suppressor electrode 127, first anode 140, and emitter steering coil 132 to system digital processor via optical link 180. Generally, gun digital processor 305 transmits status bits (overcurrent, system health), temperature, supply voltage, and supply current. Meanwhile, system digital processor 210 communicates the following information to the gun digital processor: interlock status (for emergency beam extinguishing), software watchdog signal, enable bits for all subsystems, and all requested voltages and currents (Wehnelt, first anode 140, filament, source coil).

[0079] During startup, gun digital processor 305 receives power from the system controller via isolation transformer 172 and immediately begins looking for a configuration received via fiber optic link 180 through its optoelectronic interface 320. As a result, during startup, system digital processor 210 reads the gun processor configuration 214 stored in its system memory 212 and transfers it to optoelectronic interface 230 for transmission via fiber optic link 182 to gun digital processor 305. In the current example, gun digital processor 305 is an FPGA, and processor 305 is configured to be programmed to be "slave serial," receiving an asynchronous clock setting bitstream after a reset.

[0080] The gun controller also includes a watchdog 322, which monitors the communications over the fiber optic link for a periodic keep-alive clock signal sent by the system controller 200. If the watchdog 322 fails to detect a clock after a set timeout period, such as less than 5 milliseconds, the watchdog 322 resets the gun digital processor.

[0081] During reset, the output pins of the gun digital processor 305 have a specified state. The FPGA typically pulls all pins high during reset. The gun control electronics are implemented to turn off the electron beam, filament heater, and steering coils during reset.

[0082] Gun digital processor 305 controls source coils 132N, 132S, 132E, and 132W. More specifically, in the current embodiment, system digital processor 210 monitors the target current via target current receiver 220. This target current information is used to determine drive currents to the separate source coils 132N, 132S, 132E, and 132W. These desired drive currents are then relayed to gun digital processor 305 via fiber optic link 180. The gun digital processor then uses these current settings to control source coils 132N, 132S, 132E, and 132W to direct the beam through the aperture and onto the target during operation.

[0083] However, in other embodiments, the target current information is sent to the gun digital processor, which then determines the drive currents for the different coils.

[0084] FIG. 3 shows the communication between the system digital processor 210 and the gun digital processor 305 .

[0085] More specifically, during reset, no communications are sent by the system digital processor 210 over the fiber optic link 180, which in this example comprises two optical fibers F1, F2, to the gun digital processor 305. As a result, after waiting a predetermined timeout period, such as 1 second, in step 610, the gun digital processor 305 performs a self-reset and then waits for configuration in step 612.

[0086] During configuration, the first fiber F1 transmits a clock and the second fiber F2 transmits a bit stream that encodes the Gunn configuration 214 for the Gunn digital processor 305. During this communication, the Gunn digital processor 305 receives the configuration in step 614 and then executes the configuration.

[0087] During connected normal operating conditions, fibers F1 and F2 transmit a data stream to the gun digital processor 305, and a third fiber F3 carries a data stream from the gun digital processor 305 to the system digital processor 210 according to the operation provided by the gun configuration 214.

[0088] In other examples, only one fiber is used: instead of F1 (clock) and F2 (data), there is only F1 of a given bit rate and protocol, such as standard RS232 or RS485 communication.

[0089] Then, during the subsequent reset stage, if no signal is received from the system digital processor after timeout 616 , the gun digital processor 305 performs another self-reset and waits for configuration at step 618 .

[0090] FIG. 4 is a schematic block diagram showing the gun controller in detail. Bidirectional fiber optic link 180, in the illustrated example, comprises three fibers F1, F2, and F3, which terminate in optical / electronic module 320. In the present example, the system functions similarly to direct memory access, where data from the fibers is written directly to memory 306. Simultaneously, the contents of the memory are sent from Gunn digital processor 305 to system controller 200.

[0091] The gun power supply 340 receives 20 volts AC from the isolation transformer 172. This then produces 12 volts DC and 3.3 volts DC for the operation of the gun controller 300.

[0092] Analog interface unit 342 serves as an interface between gun digital processor 305 and analog components including source coil driver array 310, filament heater / driver 312, filament sense unit 314, first anode voltage controller 318, and suppressor voltage controller 316. Specifically, for this operation, analog interface 342 includes several analog-to-digital converter stages 344 and several digital-to-analog converter stages 346.

[0093] The source coil driver array 310 includes a north coil driver 348 for driving the north coil 132N, a south coil driver 350 for driving the south coil 132S, an east coil driver 352 for driving the east coil 132E, and a west coil driver 354 for driving the west coil 132W. Each of these coil drivers 348-354 receives a separate current select signal from the digital-to-analog converter stage 346. These select signals are used to set the current level for the respective driver / coil pair.

[0094] The filament heater / driver 132 includes a DC / DC converter 356, which receives 12 VDC from the gun power supply 340. A voltage select signal provided by the digital-to-analog stage 346 sets the voltage generated by the DC / DC converter 356, thereby controlling the drive current to the filament 126.

[0095] Filament U / I sensing unit 314 includes current sensor 358 and voltage sensor 360, which generate current and voltage sense signals that are digitized by analog-to-digital converter stage 344, allowing the current and voltage (generated by DC / DC converter 356) of filament 126 to be monitored by gun digital processor 305. Additionally, processor 305 can now monitor the power dissipated in the filament and use that information to indirectly estimate the filament temperature.

[0096] In one example, the gun digital processor monitors the voltage across and current through the filament 126, particularly over time. From this information, the resistance of the filament 126, particularly its change over time, is monitored to assess the wear and current condition of the filament 126. In many examples, this information is further used to optimally control the filament to improve its long-term operation and operating life. This can be particularly useful when a tungsten filament is used.

[0097] The first anode voltage controller 318 includes a DC / DC converter 362. A voltage select signal from the digital-to-analog stage 346 allows the gun digital processor 305 to set the voltage applied to the first anode 140. A voltage sense signal allows the gun digital processor 305 to monitor the actual voltage of the first anode 140 via the analog-to-digital converter stage 344.

[0098] Suppressor voltage controller 316 also includes a DC / DC converter 364 that generates the voltage applied to suppressor electrode 127. The voltage sense signal allows gun digital processor 305 to monitor the actual voltage across suppressor 127 via analog-to-digital converter stage 344.

[0099] The gun controller 300 also reads the voltage supplied by the output of the isolation transformer 172 and provides feedback control to the system controller 200's power supply 228 to adjust the voltage to a nominal 20 VAC. As the load in the gun controller changes (by changing the coil current and heating the filament at different power), this supply voltage also changes with the load. The analog interface 342 samples the voltage from the isolation transformer 172 and reports the digitized voltage to the gun digital processor 305, which sends the voltage reading back to the system controller 200. The system controller 200 then adjusts the power output from the power supply 228 to the isolation transformer 172 until feedback from the gun controller 300 indicates that the gun controller's power supply is at the desired voltage.

[0100] In this embodiment, the power supply 228 implements pulse width modulation on the isolation transformer. The "on time" during which power is supplied is varied according to the power demand from the gun controller 300. More specifically, the power supply 228 turns on the power on the positive phase of the AC for duration t1, turns it off for duration t2, turns on the power on the negative phase for duration t1, and turns it off for duration t2. The power supply controls the ratio of t1 / (t1+t2) to achieve the desired output power and voltage, and controls (t1+t2) to achieve the desired switching frequency. For the same switching frequency, as t1 increases, t2 decreases by the same amount.

[0101] While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as encompassed by the appended claims.

Claims

1. 1. An X-ray source comprising: a system controller including a system memory for storing a gun processor configuration and a system digital processor; The target, an electron source for generating electrons to form a beam for impacting the target to generate x-rays; a high voltage generator for accelerating the beam; a gun controller that controls the electron source and receives the gun processor configuration from the system controller at each power-up, the gun controller including a gun digital processor, the system digital processor reading the gun processor configuration from the system memory and providing the gun processor configuration to the gun digital processor; The x-ray source further comprising an optical communication link between the system controller and the gun controller, wherein the system controller provides the gun processor configuration to the gun controller.

2. The source of claim 1 further comprising a source coil controlled by the gun controller.

3. 2. The source of claim 1, wherein the gun controller includes a field programmable gate array (FPGA) as the gun digital processor, and the system controller provides the gun controller with a configuration file for the gun digital processor that is the gun processor configuration upon power-up.

4. 2. The supply source of claim 1, wherein the gun controller includes a central processing unit (CPU) or a digital signal processor (DSP) as the gun digital processor, and the system controller provides the gun controller with a program for the gun digital processor that is the gun processor configuration upon power-on.

5. 10. The source of claim 1, wherein the optical communication link between the system controller and the gun controller includes at least a downlink fiber for transmitting data from the system controller to the gun controller and at least an uplink fiber for transmitting data from the gun controller to the system controller.

6. 1. An X-ray source comprising: a system controller including a system memory for storing a gun processor configuration and a system digital processor; The target, an electron source for generating electrons to form a beam for impacting the target to generate x-rays; a high voltage generator for accelerating the beam; a gun controller for controlling the electron source and the formation of the beam under control of the system controller, the gun controller including a gun digital processor and a watchdog timer for resetting the gun digital processor after a period of non-responsiveness; the system digital processor reads the gun processor configuration from the system memory and provides the gun processor configuration to the gun digital processor; The x-ray source further comprising an optical communication link between the system controller and the gun controller, wherein the system controller provides the gun processor configuration to the gun controller.

7. 7. The supply of claim 6, wherein the watchdog timer receives a keep-alive signal from the system controller and resets the gun digital processor after failing to receive the keep-alive signal.

8. 7. The source of claim 6, wherein the optical communication link between the system controller and the gun controller includes at least a downlink fiber for transmitting data from the system controller to the gun controller and at least an uplink fiber for transmitting data from the gun controller to the system controller.

9. 1. An X-ray source comprising: a system controller including a system memory for storing a gun processor configuration and a system digital processor; The target, an electron source for generating electrons to form a beam for impacting the target to generate x-rays; a high voltage generator for accelerating the beam; a gun controller for controlling the electron source, the gun controller receiving the gun processor configuration from the system controller at each power-up, the gun controller including a gun digital processor, the system digital processor reading the gun processor configuration from the system memory and providing the gun processor configuration to the gun digital processor; a fiber optic link for enabling communication between the system controller and the gun controller.

10. 10. The source of claim 9, wherein the gun digital processor is a field programmable gate array (FPGA), and the system controller provides the gun controller with a configuration file for the gun digital processor that is the gun processor configuration upon power-up.

11. 10. The source of claim 9, wherein the gun digital processor is a central processing unit (CPU) or a digital signal processor (DSP), and the system controller uses the fiber optic link to provide the gun controller with a program for the gun digital processor, which is the gun processor configuration.

12. 12. The source of claim 11, wherein the fiber optic link between the system controller and the gun controller includes at least a downlink fiber for transmitting data from the system controller to the gun controller and at least an uplink fiber for transmitting data from the gun controller to the system controller.

13. 1. An X-ray source comprising: The target, a system controller for monitoring a target current of the target, the system controller including a system memory storing a gun processor configuration and a system digital processor; an electron source for generating electrons to form a beam that impacts the target to generate x-rays; a high voltage generator for powering the electron source under the control of the system controller; a source coil for steering the beam; a gun controller for controlling the electron source and the source coil and for receiving target current information used to control the source coil; the gun controller includes a gun digital processor, the gun digital processor receiving the gun processor configuration from the system controller at each power-up, the system digital processor reading the gun processor configuration from the system memory and providing the gun processor configuration to the gun digital processor; The x-ray source further comprising a fiber optic link for enabling communication between the system controller and the gun controller and for transmitting the gun processor configuration.

14. 14. The source of claim 13, wherein the system controller transfers the target current information to the gun controller over the fiber optic link.

15. 1. An X-ray source comprising: a system controller including a system memory for storing a gun processor configuration and a system digital processor; The target, an electron source for generating electrons to form a beam for impacting the target to generate x-rays; a high voltage generator for accelerating the beam; a gun controller for controlling the electron source, the gun controller including an analog interface unit for digitizing parameters of the gun controller and generating analog control signals, the gun controller including a gun digital processor, the system digital processor reading the gun processor configuration from the system memory and providing the gun processor configuration to the gun digital processor; The x-ray source further comprising an optical communication link between the system controller and the gun controller, wherein the system controller provides the gun processor configuration to the gun controller.

16. 1. An X-ray source comprising: The target, a system controller for monitoring a target current of the target, the system controller including a system memory storing a gun processor configuration and a system digital processor; an electron source for generating electrons to form a beam for impacting the target to generate x-rays; a high voltage generator for accelerating the beam; a gun controller that controls the electron supply and monitors a power supply for a gun controller to control operation of the power supply, the gun controller including a gun digital processor, the system digital processor reading the gun processor configuration from the system memory and providing the gun processor configuration to the gun digital processor; an optical communication link between the system controller and the gun controller, wherein the system controller provides the gun processor configuration to the gun controller; X-ray source.

17. 1. An X-ray source comprising: The target, a system controller for monitoring a target current of the target, the system controller including a system memory storing a gun processor configuration and a system digital processor; an electron source for generating electrons to form a beam for impacting the target to generate x-rays; a high voltage generator for accelerating the beam; a gun controller that monitors current to the electron source and controls the electron source; the gun controller includes a gun digital processor, the system digital processor reading the gun processor configuration from the system memory and providing the gun processor configuration to the gun digital processor; The x-ray source further comprising an optical communication link between the system controller and the gun controller, wherein the system controller provides the gun processor configuration to the gun controller.

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