CN117854750A - High-time-resolution X-ray radiation flow diagnosis system - Google Patents
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Abstract
The invention relates to a high-time resolution X-ray radiation flow diagnosis system. The system comprises a microstrip cathode, a first anode grid mesh, a vacuum drift tube, a short magnetic lens, a microchannel plate, a second anode grid mesh, an anode and a high-speed oscilloscope which are sequentially arranged on the same axis, wherein the microstrip cathode is loaded with negative direct-current bias voltage and curve broadening pulse output by a high-voltage pulse generator, the microchannel plate is loaded with gain compensation pulse, the gain compensation pulse is delayed to the broadening pulse, and the delay time is the flight time required by photoelectrons generated by the microstrip cathode to fly from the microstrip cathode to the microchannel plate in the vacuum drift tube. The invention uses the electronic pulse stretching system to stretch the time width of the photoelectric beam, realizes the time amplification of the photoelectric beam, and then uses the electronic signal sampler with ultra-fast time response to measure the time amplified photoelectric beam, thereby improving the time resolution of the system.
Description
Technical Field
The invention relates to the technical field of radiation flow ultrafast diagnosis, in particular to a high-time resolution X-ray radiation flow diagnosis system.
Background
Laser fusion is an important path for acquiring energy in the future, and is also a main path for acquiring theoretical and experimental data of thermonuclear weapons. In the laser fusion process with the duration of about 1 to 2ns, a large amount of X-ray information about time, space and energy spectrum distribution is radiated, and in order to obtain transient information of high-temperature high-density plasma and continuous space-time evolution process, ultra-fast diagnosis equipment with picosecond time resolution is required to measure the X-ray radiation, so that experimental basis is provided for fusion process analysis and the like, and fusion ignition with higher gain is realized by aid of power.
An X-ray diode (XRD) is an important laser fusion ultrafast diagnostic tool, and is also a core component of radiation flow diagnostic equipment such as a soft X-ray spectrometer, a flat response XRD, and the like. In the laser fusion experiment, radiation flow exists in the whole physical process, including black cavity physical X-ray radiation flow, implosion physical target pill self-luminescence and the like. In order to study the intensity, radiation temperature, implosion radiation symmetry and thermonuclear combustion process of the black cavity radiation source, the measurement of radiation flow is indispensable, and the measurement data are important parameters of laser fusion study.
Currently, the time resolution of practical X-ray diodes is about 100ps, which has been successfully applied to laser fusion radiometric measurements. However, with the intensive research of ICF, 100ps time resolution has failed to meet the high-precision diagnostic requirements of certain stages. For example, fusion burn duration is about 100 to 200ps, and measurement of plasma transient information at this stage requires an X-ray diode with a time resolution better than 20 ps. In addition, the vicinity of the blocking time contains abundant physical information, the physical process is drastically changed, and if detailed information of the physical process is to be measured, the X-ray diode is required to have a time resolution superior to 10 ps. Therefore, there is an urgent need to develop a higher time resolution X-ray radiation diagnostic system.
Disclosure of Invention
The invention aims to provide a high-time resolution X-ray radiation flow diagnosis system.
The technical scheme adopted for solving the technical problems is as follows: the method comprises the steps of constructing a high-time resolution X-ray radiation flow diagnosis system, wherein the high-time resolution X-ray radiation flow diagnosis system comprises a micro-strip cathode, a first anode grid mesh, a vacuum drift tube, a short magnetic lens, a micro-channel plate, a second anode grid mesh, an anode and a high-speed oscilloscope which are sequentially arranged on the same axis, the micro-strip cathode is positioned at the incident end of the vacuum drift tube, the anode is positioned at the emergent end of the vacuum drift tube, and the short magnetic lens surrounds the periphery of the vacuum drift tube; the system further comprises:
the high-voltage pulse generator is connected with the microstrip cathode, is used for generating a high-voltage direct-current power supply of negative direct-current bias voltage and generating curve broadening pulses, and the slope of the curve broadening pulses is increased and reduced along with the time; the first anode grid mesh is grounded;
the gain compensation pulse generator is connected with the input surface of the micro-channel plate and is used for generating gain compensation pulses, the gain compensation pulses are negative high-voltage pulses, photoelectrons received by the micro-channel plate are synchronous on the falling edge of the gain compensation pulses, the gain compensation pulses are delayed to the broadening pulses, and the delay time is the flight time required by the photoelectrons generated by the micro-strip cathode to fly from the micro-strip cathode to the micro-channel plate in the vacuum drift tube; the output surface of the microchannel plate is grounded;
a first power supply circuit connected with the second anode grid for generating direct current voltage, wherein the second anode grid is connected with the second anode grid through a capacitor C m Grounding;
the second power supply circuit is connected with the anode and used for generating bias voltage, the anode comprises a gold foil film and a metal conical connecting piece, the gold foil film is evaporated on the bottom surface of the metal conical connecting piece, the top of the metal conical connecting piece is connected with the second power supply circuit, and the top of the metal conical connecting piece is connected with the high-speed oscilloscope through a capacitor C;
the micro-strip cathode generates photoelectrons under the action of X-ray pulse, the photoelectrons enter the vacuum drift tube after being accelerated by an electric field between the micro-strip cathode and the first anode grid, the photoelectrons reach the micro-channel plate after being widened by the vacuum drift tube, gain output electrons of the micro-channel plate are accelerated by an electric field between an output surface of the micro-channel plate and the second anode grid, then reach the anode after being accelerated by the electric field between the second anode grid and the anode, and induced current generated by the anode is transmitted to the high-speed oscilloscope for display.
Further, in the high-time resolution X-ray radiation flow diagnosis system of the present invention, the high-voltage pulse generator includes 8 independent stretched pulse generators, each stretched pulse generator outputs stretched pulses with different amplitudes and different slopes, the stretched pulses are input to the microstrip cathode through an impedance gradual change line, and all the stretched pulses are overlapped by different delays to form the curve stretched pulse.
In the high-time resolution X-ray radiation flow diagnosis system of the present invention, the gain compensation pulse generator comprises 8 independent field effect tube negative high voltage pulse generators, each of the field effect tube negative high voltage pulse generators sends out negative high voltage pulses with different amplitudes and different slopes, and all the negative high voltage pulses are overlapped by different delays to form the gain compensation pulse.
Further, in the high-time resolution X-ray radiation flow diagnosis system of the present invention, the system further comprises a vacuum SMA connector, the top of the metal conical connector is connected to a first end of the vacuum SMA connector, a second end of the vacuum SMA connector is connected to a first end of the capacitor C through a coaxial cable, and a second end of the capacitor C is connected to the high-speed oscilloscope.
Further, in the high-time resolution X-ray radiation flow diagnosis system of the invention, the first power supply circuit passes through a current limiting resistor R m Connecting the two anode grids;
the second power supply circuit is connected with the top of the metal conical connecting piece through a series current limiting resistor R2 and a pulse blocking inductor L2;
the high-voltage direct-current power supply is connected with the microstrip cathode through a series current limiting resistor R1 and a pulse blocking inductor L1.
Further, in the high-time resolution X-ray radiation flow diagnosis system, the microstrip cathode is formed by evaporating gold or cesium iodide on a polystyrene film, and the length of the microstrip cathode is 20mm and the width of the microstrip cathode is 12mm;
the first anode grid is a metal nickel grid with the spatial frequency of 20 lp/mm.
Further, in the high-time resolution X-ray radiation flow diagnosis system according to the present invention, the short magnetic lens is in a circular ring shape, the short magnetic lens is composed of soft iron and copper coils, the outer diameter of the short magnetic lens is 110mm, the inner diameter of the short magnetic lens is 60mm, the length of the short magnetic lens in the axial direction is 50mm, and a gap with a width of 4mm is formed inside the circular ring.
Further, in the high-time resolution X-ray radiation flow diagnosis system of the present invention, the input surface of the microchannel plate is provided with a microstrip line with a length of 20mm and a width of 12mm.
Furthermore, in the high-time resolution X-ray radiation flow diagnosis system, the input impedance of the high-speed oscilloscope is 50Ω, and the bandwidth is greater than 6GHz.
Further, in the high-time resolution X-ray radiation flow diagnosis system of the present invention, the system further comprises an incidence baffle plate, the incidence baffle plate is located between the microstrip cathode and the X-ray radiation source, and the X-ray pulse generated by the X-ray radiation source is emitted to the microstrip cathode through a pinhole of the incidence baffle plate.
The high-time resolution X-ray radiation flow diagnosis system has the following beneficial effects: the invention uses the electronic pulse stretching system to stretch the time width of the photoelectric beam, realizes the time amplification of the photoelectric beam, and then uses the electronic signal sampler with ultra-fast time response to measure the time amplified photoelectric beam, thereby improving the time resolution of the system.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic diagram of a high time resolution X-ray radiation flow diagnostic system provided by an embodiment of the present invention;
FIG. 2 is a schematic diagram of a microstrip cathode and an 8-way stretched pulse input provided by an embodiment of the present invention;
FIG. 3 is a graph of the waveform and slope of a stretched pulse resulting in a 20-fold stretched magnification provided by an embodiment of the present invention;
FIG. 4 is an equivalent circuit diagram of an electronic signal sampler according to an embodiment of the present invention;
fig. 5 is a relationship between time resolution and capacitance Cm of an electronic signal sampling system according to an embodiment of the present invention;
FIG. 6 is a graph showing the relationship between the time resolution of the electronic signal sampling system and the voltage of the second anode grid according to the embodiment of the present invention;
FIG. 7 is a graph of diagnostic system time resolution versus stretched pulse slope provided by an embodiment of the present invention;
fig. 8 is a graph showing the relationship between the time resolution of the diagnostic system and the length of the drift region according to an embodiment of the present invention.
Detailed Description
For a clearer understanding of technical features, objects and effects of the present invention, a detailed description of embodiments of the present invention will be made with reference to the accompanying drawings.
In a preferred embodiment, and referring to FIG. 1, a schematic diagram of a high time resolution X-ray radiation flow diagnostic system is shown. The system consists of the following parts: an electronic pulse stretcher, an electronic booster microchannel plate (microchannel plate, MCP), an electronic signal sampling system, a high voltage pulse generator 109, a large caliber short magnetic lens 104, wherein the electronic pulse stretcher comprises a microstrip cathode 101, a first anode grid 102, and an electron drift region, which is the region between the first anode grid 102 and the microchannel plate 105 in the vacuum drift tube 103. The electronic signal sampling system includes a second anode grid 106, an anode 107, an external circuit, and a high-speed oscilloscope 108, a high-voltage pulse generator 109 for generating stretched pulses.
Specifically, the high-time resolution X-ray radiation diagnosis 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 which are sequentially arranged on the same axis, wherein the microstrip cathode 101 is positioned at an incident end of the vacuum drift tube 103, the anode 107 is positioned at an emergent end of the vacuum drift tube 103, and the short magnetic lens 104 surrounds the periphery of the vacuum drift tube 103.
Further, the system comprises 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 and curve stretching pulses, the slope of which decreases with increasing time. The first anode grid 102 is grounded. The high-voltage direct current power supply 117 is connected with the microstrip cathode 101 through a series current limiting resistor R1 and a pulse blocking inductor L1.
Further, the system further comprises a gain compensation pulse generator 110 connected to the input surface of the microchannel plate 105 for generating a gain compensation pulse, wherein the gain compensation pulse is a negative high voltage pulse, the photoelectrons received by the microchannel plate 105 are synchronous with the falling edge of the gain compensation pulse, the gain compensation pulse is delayed from the broadening pulse, and the delay time is the flight time required by 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 face of the microchannel plate 105 is grounded.
Further, the system comprises 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 the second anode grid 106 via a capacitor C m And (5) grounding.
Further, the system includes a second power supply circuit 112 connected to the anode 107 for generating a bias voltage, the second power supply circuit 112 being connected to the top of the metal taper 1072 through a series current limiting resistor R2 and a pulse blocking inductor L2. The anode 107 comprises a gold foil 1071 and a metal cone-shaped connector 1072, wherein the gold foil 1071 is evaporated on the bottom surface of the metal cone-shaped connector 1072, and the top of the metal cone-shaped connector 1072 is connected with the high-speed oscilloscope 108 through a capacitor C.
The working principle of the high-time resolution X-ray radiation flow diagnosis system is as follows:
an X-ray pulse emitted by the X-ray radiation source is directed to the microstrip cathode 101 through a pinhole 116 of an incident baffle 115, and the microstrip cathode 101 generates an optoelectronic pulse. The microstrip cathode 101 is applied with negative direct current high voltage and is overlapped with the widened pulse, and the first anode grid 102 is grounded. Because the X-ray is synchronous at the rising edge of the broadening pulse, the photoelectrons emitted earlier are synchronous at the lower position of the broadening pulse relative to the photoelectrons emitted later, so that the photoelectrons emitted earlier obtain larger accelerating voltage than the photoelectrons emitted later, namely the photoelectrons emitted earlier obtain larger energy than the photoelectrons emitted later, and the electron speed in front is faster.
After the transmission from the first anode grid 102 to the 2m electron drift region of the electron booster microchannel plate 105, the time width of the electron beam is widened, so as to realize the time amplification of the electron beam, but simultaneously make the energy of the following electrons lower. The widened electron beam enters the microchannel plate 105, and in order to compensate the gain output electron reduction generated after the electron collides with the microchannel plate 105 due to energy reduction, a negative gain compensation pulse is loaded on the input surface of the microchannel plate 105, and the output surface of the microchannel plate 105 is grounded. And, the electron beam is synchronized at the falling edge of the gain compensation pulse such that the gain of the microchannel plate 105 increases with increasing time, so that the gain output electrons of the microchannel plate 105 generated by the latter electrons (electrons having lower energy) are almost the same as the gain output of the microchannel plate 105 generated by the former electrons (electrons having higher energy).
The gain electrons enter the electron signal sampler after being accelerated by the electric field between the output face of the microchannel plate 105 and the second anode grid 106. Accelerating towards the anode 107 under the action of the electric field, inducing an electric charge on the anode 107. Thereby generating an induced current in the circuit, outputting an ultrafast pulse signal, and detecting and recording the waveform of the induced current pulse by the high-speed oscilloscope 108. Because the electron drift region has a larger transmission distance, the electron beam diverges in radial space, and in order to obtain the same electron beam spot diameter as the micro-strip cathode 101 on the micro-channel plate 105, the electron beam is formed into an equal-sized image from the micro-strip cathode 101 to the micro-channel plate 105 by adopting a large-caliber short magnetic lens 104, and the imaging multiplying power is 1:1.
Because the electron beam is amplified in time, a very high system time resolution can be obtained by using a lower time resolution electron signal sampler.
(1) Electronic pulse stretching system design scheme
The electronic pulse stretching system is composed of an electronic pulse stretcher and a high-voltage pulse generator 109, and is used for stretching the time width of the electron beam so as to realize the time amplification of the electron beam.
The electronic pulse stretcher consists of a microstrip cathode 101, a first anode grid mesh 102 and an electronic drift zone groupAnd (3) forming the finished product. In polystyrene (C) 8 H 8 ) Au (thickness is generally 60-100 nm) or CsI is evaporated on the thin film to form the transmissive microstrip cathode 101 structure. The microstrip cathode 101 has a length of 20mm and a width of 12mm. The microstrip cathode 101 has two functions, namely, has the function of a photocathode and converts incident light into photoelectrons; secondly, the microstrip transmission line is used for transmitting the broadening pulse, so that a time-varying electric field exists between the microstrip cathode 101 with the distance of 1mm and the first anode grid 102, and the time amplification of the electron beam is realized. The first anode grid 102 is a metal nickel grid with a spatial frequency of 20lp/mm and is grounded.
The microstrip cathode 101 is applied with a negative dc bias voltage (typically-3 to-10 kV) and the stretched pulses are superimposed. The stretching pulses cause the voltage at each photoelectron emission point on the microstrip cathode 101 to change with time, and the total voltage between the microstrip cathode 101 and the first anode grid 102 will decrease with time, so that the energy of the electrons emitted first is smaller than the energy of the electrons emitted later, i.e. the electrons emitted first have a faster speed, and the time width of the electron beam is amplified through the electron drift region (typically 0.5 to 2 m) from the first anode grid 102 to the time collimator.
Generation of stretched pulses: the microstrip cathode 101 is driven by adopting curve stretching pulse, so that the stretching multiplying power of the electronic pulse is consistent at each position of the slope, and the linear time amplification of the electronic beam is realized. As shown in fig. 2, in order to obtain a curved stretched pulse, stretched pulse 1, stretched pulse 2, stretched pulse 3, stretched pulse 4, stretched pulse 5, stretched pulse 6, stretched pulse 7 and stretched pulse 8, the common 8-path stretched pulse is simultaneously loaded on the microstrip cathode 101 through an impedance gradient line to form a curved stretched pulse. In the embodiment, an avalanche transistor string and a Marx pulse generator structure are adopted to develop 8 independent stretching pulse generators, each generator outputs stretching pulses with different amplitudes and different slopes, and 8 paths of stretching pulses are delayed differently and finally are overlapped to form curve stretching pulses.
Microstrip cathode 101 is loaded with a-3 kV bias voltage and stretched pulses so that each ramp position has the same electron beam time magnification of 20:1, the desired stretched pulse rising edge waveform and its slope change with time are as shown in fig. 3, and the slope of the curve stretched pulse decreases with increasing time.
(2) Large caliber short magnetic lens 104
The electron beam is imaged on the micro-channel plate 105 in an equal size from the micro-strip cathode 101 by adopting the large-caliber short magnetic lens 104, and the imaging multiplying power is 1:1, so that the diameters of the electron beam spots on the micro-channel plate 105 and the micro-strip cathode 101 are the same. The short magnetic lens 104 in the shape of a circular ring consists of soft iron and copper coils, the outer diameter is 110mm, the inner diameter is 60mm, the length in the axial direction is 50mm, a circle of slits with the width of 4mm are arranged on the inner side of the circular ring, and a magnetic field enters a drift region through the slits with the width of 4 mm.
(3) Microchannel plate 105 gain compensation
After the transmission from the first anode grid 102 to the 2m drift region of the electron booster microchannel plate 105, the time amplification of the electron beam is realized, the time width of the electron beam is widened, but the energy of the front electrons in the electron beam is larger, and the energy of the rear electrons in the electron beam is lower. The widened electron beam is imaged by the large-caliber short magnetic lens 104 to the microchannel plate 105. The electron beam with gradually decreasing energy bombards the microchannel plate 105, so that the gain of the microchannel plate 105 will gradually decrease with time, and the amplitude of the signal output from the anode 107 will sequentially decrease. And the optical signals with the same intensity are incident on the micro-strip cathode 101, the gains of the micro-channel plates 105 should be consistent, and the amplitudes of the signals output by the anode 107 should be the same. The gain of the microchannel plate 105, which is formed by the progressively lower electron energies, decreases, which will cause measurement errors.
In order to compensate for the decrease in gain output electrons generated after the subsequent electrons collide with the microchannel plate 105 due to the decrease in energy, the gain uniformity of the microchannel plate 105 is improved, the measurement accuracy of the system is improved, and a negative gain compensation pulse varying with time is loaded on the input surface of the microchannel plate 105. The microchannel plate 105 output face is grounded such that the voltages at both the input face and the output face of the microchannel plate 105 increase over time (such that the gain of the microchannel plate 105 increases over time), thereby compensating for the decrease in gain output electrons generated after subsequent electrons collide with the microchannel plate 105 due to the decrease in energy. The electron beam synchronization is at the falling edge of the gain compensation pulse such that the microchannel plate 105 gain increases with increasing time, such that the microchannel plate 105 gain output electrons generated by the latter electrons (lower energy electrons) are nearly identical to the microchannel plate 105 output generated by the former electrons (higher energy electrons). A microstrip line with a length of 20mm and a width of 12mm is fabricated on the input surface of the microchannel plate 105 to transmit gain compensation pulses.
Negative gain compensation pulses are applied to the input face of the microchannel plate 105, the output face of the microchannel plate 105 is grounded, and a time-varying acceleration field is formed between the two electrodes. The electron beam is synchronized at the falling edge of the gain compensation pulse, and electrons with lower energy will acquire more energy later, and the gain compensation pulse with the appropriate slope is selected so that the energy is almost the same after all electrons have passed through the time collimator. The gain-compensated pulses and the stretched pulses are delayed in time by an amount approximately equal to the time of flight of the electrons in the drift region.
Generation of gain compensation pulses: since the microchannel plate 105 performs gain compensation on the electron beam after time amplification, the slope of the falling edge of the gain compensation pulse is small, a plurality of field effect transistors are connected in series, and then the field effect transistor series is connected into a Marx pulse generator to generate a negative high voltage pulse as the gain compensation pulse. As with the method for obtaining curve stretched pulse in fig. 2, 8 independent field effect tube negative high voltage pulse generators are developed, each generator outputs negative high voltage pulses with different amplitudes and different slopes, and 8 paths of negative high voltage pulses are delayed differently and finally superimposed together to form gain compensation pulses corresponding to the stretched pulses.
(4) Design scheme of electronic signal sampling system
The electronic signal sampling system includes a second anode grid 106, an anode 107, an external circuit, and a high-speed oscilloscope 108, the function of which is to detect the electron beam after time amplification and gain compensation of the microchannel plate 105. The electron beam is accelerated to the anode 107 under the action of the electric field between the second anode grid 106 and the anode 107, and charges are induced on the anode 107, so that induced current is generated in the circuit, and the output ultrafast pulse signal is detected and recorded by a high-speed oscilloscope 108 with the input impedance of 50 omega and the bandwidth of more than 6GHz.
The electronic signal sampler is composed of a bias circuit, an energy storage capacitor C, a second anode grid 106, an anode 107 and an output circuit. The bias circuit is composed of a high-voltage direct-current power supply and a 1MΩ current-limiting resistor R m And 100mH resistance pulse inductance L2, and apply DC voltage V to the second anode grid 106 m (0.5-2 kV), bias voltage V is applied to anode 107 b (vm+0.5-2 kV) so that an accelerating electric field is formed between the second anode grid 106 and the anode 107 at a distance of 1mm while charging the storage capacitor C (50-150 pF). The energy storage capacitor C stores energy in a charge form and supplements energy loss caused by the current induced in the working moment of the electronic signal sampler. In addition, the energy storage capacitor C will bias the voltage V b Isolated from the high speed oscilloscope 108 such that V b Only on the anode 107 while protecting the oscilloscope. Meanwhile, the energy storage capacitor C is equivalent to a short circuit to the high-frequency induced current signal, and the induced current entirely flows into the high-speed oscilloscope 108.
The anode 107 is composed of a gold film 1071 having a diameter of 12mm and a metal taper connector 1072 (such as copper or the like), and the gold film 1071 is directly vapor-deposited on the surface of the large plane (diameter of 12 mm) side of the metal taper connector 1072. The facet side of the metal taper 1072 is connected to a vacuum 50 Ω rf ultra-small a (SMA) connector 113 that outputs the high frequency induced current pulses generated by the anode 107 out of the vacuum chamber and through a coaxial cable 114 to the high speed oscilloscope 108.
When the electron beam is accelerated to the anode 107 by the second anode grid 106, a pulse current is induced on the gold film 1071 of the anode 107, and the pulse waveform is detected and recorded by sequentially transmitting the pulse signal in the vacuum chamber to the outside through the metal cone-shaped connector 1072, the vacuum SMA connector 113 and the coaxial cable 114 to the high-speed oscilloscope 108.
Electronic signal sampler model
According to the working principle of the electronic signal sampler, after the electrons pass through the second anode grid 106, the electrons do acceleration motion to the anode 107 under the action of an electric field, and the transit time of the electrons between the second anode grid 106 and the anode 107 is as follows:
in the above, d is the distance between the second anode grid 106 and the anode 107, e is the electron charge amount, U 2 The DC voltage applied to the second anode grid 106, U 1 Applying a DC voltage to the output face of the microchannel plate 105, E 1 Is the energy of electrons emitted from the microchannel plate 105, m is the electron mass, U 3 A dc voltage is applied to the anode 107.
The positive electrode 107 output pulse has a leading edge that depends on the transit time and a trailing edge that depends on the discharge time constant of the discharge loop. The equivalent resistance of the oscilloscope is 50Ω, and the anode 107 and the second anode grid 106 can be equivalent to a capacitor C a The electronic signal sampling system may be equivalent as shown in fig. 4. From C a 、C、C m 、R L The circuit formed by (oscilloscope equivalent resistance) discharges, and the discharge time constant of the RC circuit is as follows:
interelectrode equivalent capacitance C of anode 107 and second anode grid 106 a The method comprises the following steps:
where ε is the vacuum dielectric constant 1, S is the relative area of the anode 107 and the second anode grid 106, k is the electrostatic force constant, and d is the spacing between the second anode grid 106 and the anode 107.
The circuit discharge time is:
T dc ＝2.75τ (4)
the time resolution of the electronic signal sampler is:
T anode ＝0.5(T ma +T dc ) (5)
electronic signal sampling system time resolution:
when the bandwidth of the oscilloscope is 12GHz, the distance between the 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 the anode 107 is 12mm, and the bias voltage V is b The voltage difference between the anode 107 and the second anode grid 106 was 1kV, and the output surface of the microchannel plate 105 was grounded and spaced 1mm from the second anode grid 106. When the second anode grid 106 is connected to the capacitor C m When in change, the time resolution and the capacitance C of the electronic signal sampling system after the bandwidth of the oscilloscope are considered m As shown in FIG. 5, the time resolution is a function of capacitance C m Is improved by the reduction of (2). Using a discharge capacitance C of 0.5pF m The theoretical time resolution is 98ps.
An accelerating electric field is formed between the second anode grid 106 and the microchannel plate 105, so that electrons have higher speed when entering the electronic signal sampler, the transit time of the electrons from the second anode grid 106 to the anode 107 is reduced, and the time resolution of the electronic signal sampler is improved. The voltage difference between the anode 107 and the second anode grid 106 is kept unchanged (0 kV or 1kV respectively), and when the voltage of the second anode grid 106 changes, the relationship between the time resolution of the electronic signal sampling system and the voltage of the second anode grid 106 is shown in fig. 6, where grid 2 refers to the second anode grid 106, the anode refers to the anode 107, and the time resolution in the figure increases with the increase of the voltage of the second anode grid 106. When the voltages of the second anode grid 106 and the anode 107 are both 0, the time resolution of the electronic signal sampling system is poor at 202ps. The second anode grid 106 or anode 107 is therefore charged with a positive voltage in order to reduce the electron transit time and improve the time resolution of the electron signal sampler.
X-ray radiation flow diagnostic system time resolution:
the electronic signal sampling system uses the parameters of FIG. 4 and a discharge capacitance C of 0.5pF m The time resolution was 98ps. By introducing an electronic pulse stretching technology, an electronic pulse stretching system (an electronic microstrip cathode 101 is loaded with-3 kV bias voltage and stretched pulses shown in fig. 3) is utilized to amplify the time of an electron beam, so that the time resolution of an X-ray radiation flow diagnosis system can be improved from 98ps to 4.9ps, and the angles of the stretched pulses are respectively improvedThe slope position has the same electron beam time magnification and good time resolution uniformity.
When the length of the drift region is 0.5m, the cathode bias voltage is-3 kV, and the time resolution of the electronic signal sampling system is 98ps, the relation between the time resolution of the X-ray radiation flow diagnosis system and the rising edge slope of the starting point of the curve broadening pulse slope is shown in figure 7, and the time resolution is increased along with the increase of the rising edge slope and is increased from 98ps to 2ps. The time resolution is further improved to the femtosecond level by continuously increasing the slope of the broadening pulse, for example, the time resolution is improved to 500fs when the slope is 75V/ps.
Increasing the drift region distance will also increase the time resolution, when the cathode bias voltage is-3 kV, the gradient of the broadening pulse 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 diagnosis system and the length of the drift region is shown in figure 8. As the drift region length increases, the temporal resolution increases. For example, the time resolution is improved to 696fs when the slope is 20V/ps and the drift region length is 3 m.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative elements and steps are described above generally in terms of functionality in order to clearly illustrate the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software modules may be disposed in Random Access Memory (RAM), memory, read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The above embodiments are provided to illustrate 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 the same according to the content of the present invention, and not to limit the scope of the present invention. All equivalent changes and modifications made with the scope of the claims should be covered by the claims.
Claims (10)
1. The high-time resolution X-ray radiation flow diagnosis system is characterized by comprising a micro-strip cathode (101), a first anode grid mesh (102), a vacuum drift tube (103), a short magnetic lens (104), a micro-channel plate (105), a second anode grid mesh (106), an anode (107) and a high-speed oscilloscope (108) which are sequentially arranged on the same axis, wherein the micro-strip cathode (101) is positioned at the incident end of the vacuum drift tube (103), the anode (107) is positioned at the emergent 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 comprises:
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 stretching pulse, the slope of which increases and decreases with time; the first anode grid (102) is grounded;
a gain compensation pulse generator (110) connected to the input surface of the microchannel plate (105) for generating a gain compensation pulse, the gain compensation pulse being a negative high voltage pulse, the photoelectrons received by the microchannel plate (105) being synchronized at the falling edge of the gain compensation pulse, the gain compensation pulse being delayed from the broadening pulse by a time period 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, the second anode grid (106) being connected to the second anode grid via a capacitor C m Grounding;
a second power supply circuit (112) connected with the anode (107) and used for generating bias voltage, wherein the anode (107) comprises a gold foil film (1071) and a metal conical connector (1072), the gold foil film (1071) is evaporated on the bottom surface of the metal conical connector (1072), the top of the metal conical connector (1072) is connected with the second power supply circuit (112), and the top of the metal conical connector (1072) is connected with the high-speed oscilloscope (108) through a capacitor C;
the micro-strip cathode (101) generates photoelectrons under the action of X-ray pulse, the photoelectrons enter the vacuum drift tube (103) after being accelerated by an electric field between the micro-strip cathode (101) and the first anode grid (102), the photoelectrons reach the micro-channel plate (105) after being widened by the vacuum drift tube (103), gain output electrons of the micro-channel plate (105) are accelerated by an electric field between an output surface of the micro-channel plate (105) and the second anode grid (106), then reach the anode (107) after being accelerated by an electric field between the second anode grid (106) and the anode (107), and induction 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, wherein the high-voltage pulse generator (109) comprises 8 independent stretched pulse generators, each of which outputs stretched pulses of different magnitudes and different slopes, which are input to the microstrip cathode (101) through an impedance grading line, all of which are superimposed with different delays to form the curved stretched pulse.
3. The high-time resolution X-ray radiation flow diagnostic system according to claim 1, wherein the gain compensation pulse generator (110) comprises 8 independent fet negative high voltage pulse generators, each of which emits negative high voltage pulses of different magnitudes and different slopes, all of which are superimposed with different delays to form the gain compensation pulse.
4. The high time resolution X-ray radiation flow diagnostic system according to claim 1, further comprising a vacuum SMA connector (113), a top of the metal cone connector (1072) being connected to a first end of the vacuum SMA connector (113), a second end of the vacuum SMA connector (113) being connected to a first end of the capacitor C by a coaxial cable (114), a second end of the capacitor C being connected to the high speed oscilloscope (108).
5. The high-time resolution X-ray radiation flow diagnostic system according to claim 1, wherein the first power supply circuit (111) is connected to the first power supply circuit via a current limiting resistor R m Connecting the two anode grids (106);
the second power supply circuit (112) is connected with the top of the metal conical connecting piece (1072) through a series current limiting resistor R2 and a pulse blocking inductor L2;
the high-voltage direct current power supply (117) is connected with the microstrip cathode (101) through a series current limiting resistor R1 and a pulse blocking inductor L1.
6. The high time resolution X-ray radiation flow diagnostic system according to claim 1, wherein the microstrip cathode (101) is a gold-vapor plating or cesium iodide on a polystyrene film, the microstrip cathode (101) having a length of 20mm and a width of 12mm;
the first anode grid (102) is a metal nickel grid with a spatial frequency of 20 lp/mm.
7. The high-time resolution X-ray radiation flow diagnosis system according to claim 1, wherein the short magnetic lens (104) is in a circular ring shape, the short magnetic lens (104) is composed of soft iron and copper coils, the outer diameter of the short magnetic lens (104) is 110mm, the inner diameter of the short magnetic lens (104) is 60mm, the axial length of the short magnetic lens (104) is 50mm, and a circle of gap with the width of 4mm is arranged on the inner side of the circular ring.
8. The high time resolution X-ray radiation flow diagnostic system according to claim 1, wherein the microchannel plate (105) has a microstrip line with a length of 20mm and a width of 12mm on its input face.
9. The high time resolution X-ray radiation flow diagnostic system according to claim 1, wherein the high speed oscilloscope (108) has an input impedance of 50Ω and a bandwidth of greater than 6GHz.
10. The high time resolution X-ray radiation flow diagnostic system according to claim 1, further comprising an incidence baffle (115), the incidence baffle (115) being located between the microstrip cathode (101) and an X-ray radiation source, the X-ray pulses generated by the X-ray radiation source being directed towards the microstrip cathode (101) through a pinhole (116) of the incidence baffle (115).
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