A high temporal resolution x-ray radiation flow diagnostic system

Abstract

This invention relates to a high-time-resolution X-ray radiation flow diagnostic system. The system includes a microstrip cathode, a first anode grid, a vacuum drift tube, a short magnetic lens, a microchannel plate, a second anode grid, an anode, and a high-speed oscilloscope, arranged sequentially on the same axis. The microstrip cathode is subjected to a negative DC bias voltage and a curve-broadening pulse output from a high-voltage pulse generator. The microchannel plate is subjected to a gain compensation pulse, which is delayed by the broadening pulse. The delay time is the flight time required for photoelectrons generated by the microstrip cathode to travel from the microstrip cathode to the microchannel plate in the vacuum drift tube. This invention utilizes an electron pulse broadening system to broaden the time width of the photoelectron beam, achieving temporal amplification of the electron beam. Then, an electron signal sampler with an ultrafast time response is used to measure the time-amplified electron beam, thereby improving the system's time resolution.

Description

Technical Field

[0001] This invention relates to the field of ultrafast radiation flow diagnostics, and more specifically, to a high time-resolution X-ray radiation flow diagnostic system. Background Technology

[0002] Laser fusion is a crucial pathway for future energy acquisition and a primary means of obtaining theoretical and experimental data on thermonuclear weapons. During laser fusion processes lasting approximately 1 to 2 ns, a large amount of X-ray information regarding temporal, spatial, and energy spectrum distribution is emitted. To obtain transient information about the high-temperature, high-density plasma and its continuous spatiotemporal evolution, ultrafast diagnostic equipment with picosecond time resolution is needed to measure X-ray radiation. This provides experimental evidence for fusion process analysis and facilitates the achievement of higher-gain fusion ignition.

[0003] X-ray diodes (XRDs) are crucial ultrafast diagnostic tools for laser fusion and core components of radiation flow diagnostic equipment such as soft X-ray spectrometers and flat-response XRDs. In laser fusion experiments, radiation flow exists throughout the entire physical process, including X-ray radiation flow in black cavity physics and target spontaneous emission in implosion physics. Measuring radiation flow is indispensable for studying the intensity, radiation temperature, implosion irradiation symmetry, and thermonuclear combustion processes of black cavity radiation sources; the measurement data are vital parameters in laser fusion research.

[0004] Currently, the time resolution of practical X-ray diodes is approximately 100 ps, ​​and they have been successfully applied to the measurement of radiation flux in laser fusion. However, with the advancement of ICF research, a time resolution of 100 ps is no longer sufficient to meet the high-precision diagnostic requirements of certain stages. For example, the duration of fusion combustion is approximately 100 to 200 ps, ​​and measuring the transient information of the plasma during this stage requires X-ray diodes with a time resolution better than 20 ps. Furthermore, the vicinity of the stagnation moment contains rich physical information, and the physical processes change drastically. To obtain detailed information about these processes, X-ray diodes with a time resolution better than 10 ps are required. Therefore, there is an urgent need to develop X-ray radiation flux diagnostic systems with higher time resolution. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high time-resolution X-ray radiation flow diagnostic system.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A high time-resolution X-ray radiation flow diagnostic system is constructed, comprising a microstrip cathode, a first anode grid, a vacuum drift tube, a short magnetic lens, a microchannel plate, a second anode grid, an anode, and a high-speed oscilloscope arranged sequentially on the same axis. The microstrip cathode is located at the incident end of the vacuum drift tube, the anode is located at the exit end of the vacuum drift tube, and the short magnetic lens surrounds the periphery of the vacuum drift tube. The system further includes:

[0007] A high-voltage DC power supply for generating a negative DC bias voltage and a high-voltage pulse generator for generating a curve-broadening pulse, the slope of which decreases with increasing time, are connected to the microstrip cathode; the first anode grid is grounded.

[0008] A gain compensation pulse generator is connected to the input surface of the microchannel plate to generate a gain compensation pulse. The gain compensation pulse is a negative high-voltage pulse. The photoelectrons received by the microchannel plate are synchronized with the falling edge of the gain compensation pulse. The gain compensation pulse is delayed by the broadened pulse, and the delay time is the flight time required for the photoelectrons generated by the microstrip cathode to travel from the microstrip cathode to the microchannel plate in the vacuum drift tube. The output surface of the microchannel plate is grounded.

[0009] A first power supply circuit connected to the second anode grid for generating a DC voltage, wherein the second anode grid is connected to a capacitor C m Grounding;

[0010] A second power supply circuit connected to the anode for generating a bias voltage, the anode comprising a gold foil and a metal conical connector, the gold foil being deposited on the bottom surface of the metal conical connector, the top of the metal conical connector being connected to the second power supply circuit, and the top of the metal conical connector being connected to the high-speed oscilloscope via a capacitor C;

[0011] The microstrip cathode generates photoelectrons under the action of X-ray pulses. The photoelectrons are accelerated by the electric field between the microstrip cathode and the first anode grid and then enter the vacuum drift tube. After being broadened by the vacuum drift tube, the photoelectrons reach the microchannel plate. The gain output electrons of the microchannel plate are accelerated by the electric field between the output surface of the microchannel plate and the second anode grid, and then accelerated by the electric field between the second anode grid and the anode before reaching the anode. The induced current generated by the anode is transmitted to the high-speed oscilloscope for display.

[0012] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system of the present invention, the high-voltage pulse generator includes eight independent broadening pulse generators. Each broadening pulse generator outputs broadening pulses with different amplitudes and slopes, which are input to the microstrip cathode through an impedance gradient line. All the broadening pulses are superimposed after different delays to form the curve broadening pulse.

[0013] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system of the present invention, the gain compensation pulse generator includes eight independent field-effect transistor negative high-voltage pulse generators. Each field-effect transistor negative high-voltage pulse generator emits negative high-voltage pulses with different amplitudes and slopes. All the negative high-voltage pulses are superimposed after different delays to form the gain compensation pulse.

[0014] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system of the present invention, the system further includes a vacuum SMA connector, the top of the metal tapered connector is connected to the first end of the vacuum SMA connector, the second end of the vacuum SMA connector is connected to the first end of the capacitor C via a coaxial cable, and the second end of the capacitor C is connected to the high-speed oscilloscope.

[0015] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system described in this invention, the first power supply circuit uses a current-limiting resistor R. m Connect the two anode grids;

[0016] The second power supply circuit is connected to the top of the metal tapered connector through a series current-limiting resistor R2 and a pulse-resisting inductor L2;

[0017] The high-voltage DC power supply is connected to the microstrip cathode via a series current-limiting resistor R1 and a pulse-resisting inductor L1.

[0018] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system of the present invention, the microstrip cathode is gold or cesium iodide deposited on a polystyrene film, and the length of the microstrip cathode is 20 mm and the width is 12 mm.

[0019] The first anode grid is a nickel metal grid with a spatial frequency of 20 lp / mm.

[0020] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system of the present invention, the short magnetic lens is in the shape of a ring, the short magnetic lens is composed of soft iron and copper coils, the outer diameter of the short magnetic lens is 110 mm, the inner diameter of the short magnetic lens is 60 mm, the axial length of the short magnetic lens is 50 mm, and there is a 4 mm wide slit on the inner side of the ring.

[0021] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system of the present invention, the input surface of the microchannel plate has a microstrip line with a length of 20 mm and a width of 12 mm.

[0022] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system described in this invention, the input impedance of the high-speed oscilloscope is 50Ω and the bandwidth is greater than 6GHz.

[0023] Furthermore, in the high time-resolution X-ray radiation flow diagnostic system of the present invention, the system further includes an incident baffle located between the microstrip cathode and the X-ray radiation source, wherein the X-ray pulse generated by the X-ray radiation source is directed toward the microstrip cathode through a pinhole in the incident baffle.

[0024] The high time-resolution X-ray radiation flow diagnostic system of the present invention has the following beneficial effects: The present invention utilizes an electron pulse broadening system to broaden the time width of the photoelectron beam, thereby realizing time amplification of the electron beam. Then, an electron signal sampler with ultrafast time response is used to measure the time-amplified electron beam, thereby improving the time resolution of the system. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0026] Figure 1 This is a schematic diagram of the high time-resolution X-ray radiation flow diagnostic system provided in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the microstrip cathode and 8-channel stretched pulse input provided in an embodiment of the present invention;

[0028] Figure 3 The present invention provides a curve broadening pulse waveform and slope that generates a 20x broadening ratio.

[0029] Figure 4 This is an equivalent circuit diagram of the electronic signal sampler provided in an embodiment of the present invention;

[0030] Figure 5 This describes the relationship between the time resolution and capacitance Cm of the electronic signal sampling system provided in this embodiment of the invention.

[0031] Figure 6 This describes the relationship between the time resolution and the second anode grid voltage of the electronic signal sampling system provided in this embodiment of the invention.

[0032] Figure 7 This describes the relationship between the temporal resolution and the slope of the broadened pulse in the diagnostic system provided in this embodiment of the invention.

[0033] Figure 8This describes the relationship between the time resolution and the length of the drift region in the diagnostic system provided in this embodiment of the invention. Detailed Implementation

[0034] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] In a preferred embodiment, reference Figure 1 This is a schematic diagram of a high-time-resolution X-ray radiation flow diagnostic system. The system consists of the following parts: an electron pulse stretcher, an electron gain unit microchannel plate (MCP), an electron signal sampling system, a high-voltage pulse generator 109, and a large-aperture short magnetic lens 104. The electron pulse stretcher includes a microstrip cathode 101, a first anode grid 102, and an electron drift region, which is the area between the first anode grid 102 and the microchannel plate 105 in the vacuum drift tube 103. The electron signal sampling system includes a second anode grid 106, an anode 107, external circuitry, and a high-speed oscilloscope 108. The high-voltage pulse generator 109 is used to generate the stretched pulse.

[0036] Specifically, the high time-resolution X-ray radiation flow diagnostic system includes a microstrip cathode 101, a first anode grid 102, a vacuum drift tube 103, a short magnetic lens 104, a microchannel plate 105, a second anode grid 106, an anode 107, and a high-speed oscilloscope 108 arranged sequentially on the same axis. The microstrip cathode 101 is located at the incident end of the vacuum drift tube 103, the anode 107 is located at the exit end of the vacuum drift tube 103, and the short magnetic lens 104 surrounds the periphery of the vacuum drift tube 103.

[0037] Furthermore, the system also includes a high-voltage DC power supply 117 connected to the microstrip cathode 101 for generating a negative DC bias voltage, and a high-voltage pulse generator 109 for generating a curve-broadening pulse, the slope of which decreases over time. The first anode grid 102 is grounded. The high-voltage DC power supply 117 is connected to the microstrip cathode 101 via a series current-limiting resistor R1 and a pulse-blocking inductor L1.

[0038] Furthermore, the system also includes a gain compensation pulse generator 110 connected to the input surface of the microchannel plate 105 for generating gain compensation pulses. The gain compensation pulse is a negative high-voltage pulse. The photoelectrons received by the microchannel plate 105 are synchronized on the falling edge of the gain compensation pulse. The gain compensation pulse is delayed by the broadened pulse, and the delay time is the flight time required for the photoelectrons generated by the microstrip cathode 101 to travel from the microstrip cathode 101 to the microchannel plate 105 in the vacuum drift tube 103. The output surface of the microchannel plate 105 is grounded.

[0039] Furthermore, the system also includes a first power supply circuit 111 connected to the second anode grid 106 for generating a DC voltage, the second anode grid 106 being connected to a capacitor C. m Grounding.

[0040] Furthermore, the system also includes a second power supply circuit 112 connected to the anode 107 for generating a bias voltage. The second power supply circuit 112 is connected to the top of the metal tapered connector 1072 via a series current-limiting resistor R2 and a pulse-blocking inductor L2. The anode 107 includes a gold foil 1071 and a metal tapered connector 1072. The gold foil 1071 is deposited on the bottom surface of the metal tapered connector 1072, and the top of the metal tapered connector 1072 is connected to a high-speed oscilloscope 108 via a capacitor C.

[0041] The working principle of this high time-resolution X-ray radiation flow diagnostic system is as follows:

[0042] X-ray pulses emitted from the X-ray radiation source are directed towards the microstrip cathode 101 through pinhole 116 of the incident baffle 115, generating photoelectron pulses. A negative DC high voltage is applied to the microstrip cathode 101, superimposed with a broadened pulse, and the first anode grid 102 is grounded. Because the X-rays are synchronized at the rising edge of the broadened pulse, the photoelectrons emitted earlier are synchronized at a lower position on the broadened pulse compared to those emitted later. This results in the earlier photoelectrons receiving a greater accelerating voltage, meaning they receive more energy, thus causing the earlier electrons to travel faster.

[0043] After transmission through the 2m electron drift region from the first anode grid 102 to the electron gain microchannel plate 105, the time width of the electron beam is broadened, achieving time amplification of the electron beam, but simultaneously resulting in lower energy for subsequent electrons. The broadened electron beam enters the microchannel plate 105. To compensate for the reduced gain output electrons generated after collisions with the microchannel plate 105 due to the lower energy of subsequent electrons, a negative gain compensation pulse is applied to the input surface of the microchannel plate 105, while the output surface of the microchannel plate 105 is grounded. Furthermore, the electron beam is synchronized with the falling edge of the gain compensation pulse, causing the gain of the microchannel plate 105 to increase with time. This ensures that the gain output electrons generated by subsequent electrons (lower energy electrons) are almost identical to those generated by preceding electrons (higher energy electrons).

[0044] Gain electrons are accelerated by the electric field between the output surface of the microchannel plate 105 and the second anode grid 106 before entering the electron signal sampler. Under the influence of the electric field, they are accelerated towards the anode 107, inducing a charge on the anode 107. This generates an induced current in the circuit, outputting an ultrafast pulse signal, which is detected and recorded by a high-speed oscilloscope 108. Due to the large transmission distance of the electron drift region, the electron beam will diverge in radial space. To obtain the same electron beam spot diameter on the microchannel plate 105 as that on the microstrip cathode 101, a large-aperture short magnetic lens 104 is used to project the electron beam from the microstrip cathode 101 to the microchannel plate 105 in an image of the same size, with an imaging magnification of 1:1.

[0045] Because the electron beam is amplified in time, a high system time resolution can be obtained by using an electron signal sampler with a lower time resolution.

[0046] (1) Design scheme of electronic pulse broadening system

[0047] The electron pulse broadening system consists of an electron pulse broadener and a high-voltage pulse generator 109. Its function is to broaden the time width of the electron beam and realize the time amplification of the electron beam.

[0048] The electron pulse broadener consists of a microstrip cathode 101, a first anode grid 102, and an electron drift region. Au (typically 60-100 nm thick) or CsI is deposited on a polystyrene (C8H8) thin film to form a transmission-type microstrip cathode 101 structure. The microstrip cathode 101 is 20 mm long and 12 mm wide. The microstrip cathode 101 serves two functions: firstly, it functions as a photocathode, converting incident light into photoelectrons; secondly, it acts as a microstrip transmission line, transmitting the broadened pulse, creating a time-varying electric field between the 1 mm-distance microstrip cathode 101 and the first anode grid 102, thus achieving temporal amplification of the electron beam. The first anode grid 102 is a grounded nickel mesh with a spatial frequency of 20 lp / mm.

[0049] A negative DC bias voltage (typically -3 to -10 kV) is applied to the microstrip cathode 101, and a broadened pulse is superimposed on it. The broadened pulse causes the voltage at each photoelectron emission point on the microstrip cathode 101 to change over time, and the total voltage between the microstrip cathode 101 and the first anode grid 102 decreases as time increases. This results in the energy of the first emitted electrons being greater than that of the later emitted electrons, meaning that the first emitted electrons have a faster velocity. After passing through the electron drift region (typically 0.5 to 2 m) from the first anode grid 102 to the time collimator, the time width of the electron beam is amplified.

[0050] Generation of broadened pulses: A curved broadened pulse is used to drive the microstrip cathode 101, ensuring that the electron pulse broadening factor is consistent across all positions of the ramp, thereby achieving linear time amplification of the electron beam. For example... Figure 2 As shown, to obtain the curve broadening pulse, eight linear broadening pulses—broadening pulse 1, broadening pulse 2, broadening pulse 3, broadening pulse 4, broadening pulse 5, broadening pulse 6, broadening pulse 7, and broadening pulse 8—are simultaneously applied to the microstrip cathode 101 through an impedance gradient line to form the curve broadening pulse. In this embodiment, eight independent broadening pulse generators are developed using an avalanche tube string and Marx pulse generator structure. Each generator outputs a broadening pulse with different amplitude and slope. After different delays, the eight broadening pulses are finally superimposed to form the curve broadening pulse.

[0051] A -3kV bias voltage and a broadened pulse are applied to the microstrip cathode 101 to ensure that each ramp position has the same electron beam time amplification factor of 20:1. The required broadened pulse rise edge waveform and its slope change with time as follows: Figure 3 As shown, the slope of the curve-broadening pulse decreases as time increases.

[0052] (2) Large-aperture short magnetic lens 104

[0053] A large-aperture short magnetic lens 104 is used to project the electron beam from the microstrip cathode 101 into an image of the same size on the microchannel plate 105, with an imaging magnification of 1:1, ensuring that the electron beam spot diameters on the microchannel plate 105 and the microstrip cathode 101 are the same. The annular short magnetic lens 104 is composed of soft iron and copper coils, with an outer diameter of 110 mm, an inner diameter of 60 mm, and an axial length of 50 mm. There is a 4 mm wide slit on the inner side of the annulus, through which the magnetic field enters the drift region.

[0054] (3) Microchannel plate 105 gain compensation

[0055] After transmission through the 2m drift region from the first anode grid 102 to the electron gain microchannel plate 105, the electron beam undergoes temporal amplification, widening its temporal width. However, this also results in higher energy electrons at the beginning of the beam and lower energy electrons at the end. The widened electron beam is then imaged onto the microchannel plate 105 by the large-aperture short magnetic lens 104. As the electron beam bombards the microchannel plate 105 with gradually decreasing energy, the gain of the microchannel plate 105 will gradually decrease over time, and the signal amplitude output from the anode 107 will decrease accordingly. Since light signals of the same intensity should have consistent gain on the microchannel plate 105 and identical signal amplitude output from the anode 107 when incident on the microstrip cathode 101, the decreasing gain of the microchannel plate 105 due to the gradually decreasing electron energy will cause measurement errors.

[0056] To compensate for the reduced gain output electrons caused by the lower energy of subsequent electrons colliding with the microchannel plate 105, thereby improving the gain uniformity of the microchannel plate 105 and enhancing system measurement accuracy, a time-varying negative gain compensation pulse is applied to the input surface of the microchannel plate 105. The output surface of the microchannel plate 105 is grounded, causing the voltage at both the input and output surfaces to increase over time (leading to an increase in the gain of the microchannel plate 105), thus compensating for the reduced gain output electrons caused by the lower energy of subsequent electrons colliding with the microchannel plate 105. The electron beam is synchronized with the falling edge of the gain compensation pulse, further increasing the gain of the microchannel plate 105 over time, ensuring that the gain output electrons produced by subsequent electrons (lower energy electrons) are almost identical to those produced by preceding electrons (higher energy electrons). A microstrip line with a length of 20 mm and a width of 12 mm is fabricated on the input surface of the microchannel plate 105 to transmit the gain compensation pulse.

[0057] A negative gain compensation pulse is applied to the input surface of the microchannel plate 105, while the output surface of the microchannel plate 105 is grounded, creating a time-varying acceleration field between the two electrodes. The electron beam is synchronized at the falling edge of the gain compensation pulse; electrons with lower energy will gain higher energy later. By selecting a gain compensation pulse with an appropriate slope, all electrons will have almost the same energy after passing through the time collimator. The gain compensation pulse and the broadening pulse have a certain time delay, which is approximately equal to the flight time of the electrons in the drift region.

[0058] Generation of the gain compensation pulse: Since the gain compensation of the microchannel plate 105 is based on the time-amplified electron beam, the falling edge slope of the gain compensation pulse is relatively small. Multiple field-effect transistors (FETs) are connected in series, and then these FETs are connected in series to form a Marx pulse generator to generate a negative high-voltage pulse, which serves as the gain compensation pulse. (This is related to the above...) Figure 2 Similar to the method used to obtain the curve broadening pulse, eight independent field-effect transistor negative high-voltage pulse generators were developed. Each generator outputs negative high-voltage pulses with different amplitudes and slopes. After different delays, the eight negative high-voltage pulses are finally superimposed to form a gain compensation pulse corresponding to the broadening pulse.

[0059] (4) Design scheme of electronic signal sampling system

[0060] The electronic signal sampling system includes a second anode grid 106, an anode 107, external circuitry, and a high-speed oscilloscope 108. Its function is to detect the electron beam after time amplification and gain compensation by the microchannel plate 105. Under the influence of the electric field between the second anode grid 106 and the anode 107, the electron beam accelerates towards the anode 107, inducing a charge on the anode 107, thereby generating an induced current in the circuit. The output ultrafast pulse signal is detected and recorded by the high-speed oscilloscope 108, which has an input impedance of 50Ω and a bandwidth of over 6GHz.

[0061] The electronic signal sampler consists of a bias circuit, an energy storage capacitor C, a second anode grid 106, an anode 107, and an output circuit. The bias circuit comprises a high-voltage DC power supply and a 1MΩ current-limiting resistor R. m Together with a 100mH pulse inductor L2, a DC voltage V is applied to the second anode grid 106. m (0.5-2kV), apply a bias voltage V to anode 107. b (Vm+0.5-2kV) creates an accelerating electric field between the second anode grid 106 and the anode 107, which are 1mm apart, simultaneously charging the energy storage capacitor C (50-150pF). The energy storage capacitor C stores energy in the form of charge, compensating for the energy loss caused by the induced current during the operation of the electronic signal sampler. Furthermore, the energy storage capacitor C applies the bias voltage Vm. b Isolation from the high-speed oscilloscope 108 makes V b The load is applied only to the anode 107 to protect the oscilloscope. At the same time, the energy storage capacitor C acts as a short circuit for the high-frequency induced current signal, and all the induced current flows into the high-speed oscilloscope 108.

[0062] The anode 107 consists of a 12mm diameter gold thin film 1071 and a metal tapered connector 1072 (such as copper). The gold thin film 1071 is directly deposited on the surface of the large plane (12mm diameter) of the metal tapered connector 1072. The small plane of the metal tapered connector 1072 is connected to a vacuum 50Ω RF sub-Miniature-A (SMA) connector 113, which outputs the high-frequency induced current pulse generated by the anode 107 to the vacuum chamber and transmits it to the high-speed oscilloscope 108 via a coaxial cable 114.

[0063] When the electron beam is accelerated from the second anode grid 106 toward the anode 107, a pulse current is induced on the gold thin film 1071 of the anode 107. The pulse current is transmitted sequentially through the metal tapered connector 1072, the vacuum SMA connector 113 (which transmits the pulse signal from the vacuum chamber to the outside), and the coaxial cable 114 to the high-speed oscilloscope 108 to detect and record the pulse waveform.

[0064] Electronic signal sampler model

[0065] According to the working principle of the electronic signal sampler, after passing through the second anode grid 106, the electrons accelerate towards the anode 107 under the action of the electric field. The transit time of the electrons between the second anode grid 106 and the anode 107 is:

[0066]

[0067] In the above formula, d is the distance between the second anode grid 106 and the anode 107, e is the electron charge, U2 is the DC voltage applied to the second anode grid 106, U1 is the DC voltage applied to the output surface of the microchannel plate 105, E1 is the energy of the electron when it exits the microchannel plate 105, m is the electron mass, and U3 is the DC voltage applied to the anode 107.

[0068] The leading edge of the output pulse from anode 107 depends on the transit time, while the trailing edge depends on the discharge time constant of the discharge circuit. The equivalent resistance of the oscilloscope is 50Ω, and anode 107 and the second anode grid 106 can be equivalently represented as capacitor C. a The equivalent circuit of the electronic signal sampling system is as follows: Figure 4 As shown. By C a C, C m R L The circuit consisting of (oscilloscope equivalent resistance) discharges, and the discharge time constant of the RC circuit is:

[0069]

[0070] The inter-electrode equivalent capacitance C of anode 107 and second anode grid 106 a for:

[0071]

[0072] In the formula, ε is the vacuum dielectric constant 1, S is the relative area of ​​anode 107 and second anode grid 106, k is the electrostatic constant, and d is the distance between the second anode grid 106 and anode 107.

[0073] The circuit discharge time is:

[0074] T dc =2.75τ (4)

[0075] The time resolution of the electronic signal sampler is:

[0076] T anode =0.5(T) ma +T dc (5)

[0077] Time resolution of electronic signal sampling system:

[0078] When the oscilloscope bandwidth is 12GHz, the spacing between anode 107 and the second anode grid 106 is 1mm, the voltage Vm of the second anode grid 106 is 1kV, the energy storage capacitor C is 100pF, the diameter of anode 107 is 12mm, and the bias voltage Vm is... b The voltage difference between the anode 107 and the second anode grid 106 is 1kV, which is 2kV. The output surface of the microchannel board 105 is grounded and 1mm away from the second anode grid 106. When the capacitor C connected to the second anode grid 106... m When the oscilloscope bandwidth is considered, the time resolution of the electronic signal sampling system and the capacitance C are considered. m Relationship such as Figure 5 As shown, the time resolution varies with the capacitance C m The decrease leads to an increase. A 0.5pF discharge capacitor C is used. m The theoretical time resolution is 98ps.

[0079] An accelerating electric field is formed between the second anode grid 106 and the microchannel plate 105, resulting in higher velocities for electrons entering the electronic signal sampler. This reduces the transit time of electrons from the second anode grid 106 to the anode 107, thereby improving the time resolution of the electronic signal sampler. Keeping the voltage difference between the anode 107 and the second anode grid 106 constant (0 or 1 kV respectively), the relationship between the time resolution of the electronic signal sampling system and the voltage of the second anode grid 106 when the voltage of the second anode grid 106 changes is as follows: Figure 6 As shown, Figure 6 In the diagram, the intermediate grid 2 refers to the second anode grid 106, and the anode refers to anode 107. The time resolution increases with the increase of the voltage of the second anode grid 106. When both the voltages of the second anode grid 106 and anode 107 are 0, the time resolution of the electronic signal sampling system is poor, at 202 ps. Therefore, a positive voltage needs to be applied to either the second anode grid 106 or anode 107 to reduce the electron transit time and improve the time resolution of the electronic signal sampler.

[0080] Time resolution of X-ray radiation flow diagnostic system:

[0081] Electronic signal sampling system Figure 4 Parameters and a 0.5pF discharge capacitor C m At that time, the time resolution was 98 ps. Electronic pulse broadening technology was introduced, utilizing an electronic pulse broadening system (electronic microstrip cathode 101 with a -3kV bias voltage and...) Figure 3 The broadened pulse shown in the figure can amplify the electron beam in time, which can improve the time resolution of the X-ray radiation flow diagnostic system from 98ps to 4.9ps. Moreover, the broadened pulse has the same electron beam time amplification factor at each ramp position, that is, the time resolution uniformity is good.

[0082] Using electronic pulse broadening technology, with a drift region length of 0.5m, a cathode bias voltage of -3kV, and an electronic signal sampling system time resolution of 98ps, the relationship between the time resolution of the X-ray radiation flow diagnostic system and the rising slope of the curve broadening pulse ramp is as follows: Figure 7 As shown, the time resolution increases with the increase of the rising edge slope, from 98 ps to 2 ps. Further increasing the pulse broadening slope will further improve the time resolution to the femtosecond level; for example, at a slope of 75 V / ps, the time resolution will increase to 500 fs.

[0083] Increasing the drift region distance also improves the time resolution. When the cathode bias voltage is -3kV, the pulse broadening slope is 10V / ps or 20V / ps, and the time resolution of the electronic signal sampling system is 98ps, the relationship between the time resolution of the X-ray radiation flow diagnostic system and the drift region length is as follows: Figure 8 As shown, the time resolution increases with the length of the drift region. For example, with a slope of 20V / ps and a drift region length of 3m, the time resolution will increase to 696fs.

[0084] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0085] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0086] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0087] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They do not limit the scope of protection of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A high time-resolution X-ray radiation flow diagnostic system, characterized in that, The system includes a microstrip cathode (101), a first anode grid (102), a vacuum drift tube (103), a short magnetic lens (104), a microchannel plate (105), a second anode grid (106), an anode (107), and a high-speed oscilloscope (108) arranged sequentially on the same axis. The microstrip cathode (101) is located at the incident end of the vacuum drift tube (103), the anode (107) is located at the exit end of the vacuum drift tube (103), and the short magnetic lens (104) surrounds the periphery of the vacuum drift tube (103). The system further includes: A high-voltage DC power supply (117) for generating a negative DC bias voltage and a high-voltage pulse generator (109) for generating a curve-broadening pulse are connected to the microstrip cathode (101), the slope of which decreases with increasing time; the first anode grid (102) is grounded; A gain compensation pulse generator (110) is connected to the input surface of the microchannel plate (105) to generate a gain compensation pulse. The gain compensation pulse is a negative high-voltage pulse. The photoelectrons received by the microchannel plate (105) are synchronized on the falling edge of the gain compensation pulse. The gain compensation pulse is delayed by the broadening pulse. The delay time is the flight time required for the photoelectrons generated by the microstrip cathode (101) to fly from the microstrip cathode (101) to the microchannel plate (105) in the vacuum drift tube (103). The output surface of the microchannel plate (105) is grounded. A first power supply circuit (111) connected to the second anode grid (106) for generating a DC voltage, wherein the second anode grid (106) is connected to a capacitor C m Grounding; A second power supply circuit (112) connected to the anode (107) for generating a bias voltage, the anode (107) comprising a gold foil (1071) and a metal conical connector (1072), the gold foil (1071) being deposited on the bottom surface of the metal conical connector (1072), the top of the metal conical connector (1072) being connected to the second power supply circuit (112), and the top of the metal conical connector (1072) being connected to the high-speed oscilloscope (108) via a capacitor C; The microstrip cathode (101) generates photoelectrons under the action of X-ray pulses. The photoelectrons are accelerated by the electric field between the microstrip cathode (101) and the first anode grid (102) and then enter the vacuum drift tube (103). The photoelectrons are broadened by the vacuum drift tube (103) and then reach the microchannel plate (105). The gain output electrons of the microchannel plate (105) are accelerated by the electric field between the output surface of the microchannel plate (105) and the second anode grid (106), and then accelerated by the electric field between the second anode grid (106) and the anode (107) before reaching the anode (107). The induced current generated by the anode (107) is transmitted to the high-speed oscilloscope (108) for display.

2. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The high-voltage pulse generator (109) includes eight independent pulse broadening generators. Each pulse broadening generator outputs pulse broadening pulses with different amplitudes and slopes, which are input to the microstrip cathode (101) through an impedance gradient line. All the pulse broadening pulses are superimposed after different delays to form the curve broadening pulse.

3. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The gain compensation pulse generator (110) includes eight independent field-effect transistor negative high-voltage pulse generators. Each field-effect transistor negative high-voltage pulse generator emits negative high-voltage pulses with different amplitudes and slopes. All the negative high-voltage pulses are superimposed after different delays to form the gain compensation pulse.

4. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The system also includes a vacuum SMA connector (113), the top of which is connected to the first end of the vacuum SMA connector (113), the second end of which is connected to the first end of the capacitor C via a coaxial cable (114), and the second end of the capacitor C is connected to the high-speed oscilloscope (108).

5. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The first power supply circuit (111) is connected to the current-limiting resistor R. m Connect the second anode grid (106); The second power supply circuit (112) is connected to the top of the metal tapered connector (1072) through a series current-limiting resistor R2 and a pulse-blocking inductor L2; The high-voltage DC power supply (117) is connected to the microstrip cathode (101) through a series current-limiting resistor R1 and a pulse-resisting inductor L1.

6. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The microstrip cathode (101) is formed by depositing gold or cesium iodide on a polystyrene film. The microstrip cathode (101) has a length of 20 mm and a width of 12 mm. The first anode grid (102) is a nickel metal grid with a spatial frequency of 20 lp / mm.

7. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The short magnetic lens (104) is in the shape of a ring. The short magnetic lens (104) is composed of soft iron and copper coil. The outer diameter of the short magnetic lens (104) is 110 mm, the inner diameter of the short magnetic lens (104) is 60 mm, the axial length of the short magnetic lens (104) is 50 mm, and there is a 4 mm wide slit on the inner side of the ring.

8. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The microchannel board (105) has a microstrip line with a length of 20 mm and a width of 12 mm on its input surface.

9. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The high-speed oscilloscope (108) has an input impedance of 50Ω and a bandwidth greater than 6GHz.

10. The high time-resolution X-ray radiation flow diagnostic system according to claim 1, characterized in that, The system also includes an incident baffle (115) located between the microstrip cathode (101) and the X-ray source, wherein the X-ray pulse generated by the X-ray source is directed toward the microstrip cathode (101) through a pinhole (116) in the incident baffle (115).

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