Disclosure of Invention
The invention aims to provide a pulse modulator in a compact oil cylinder, so as to further reduce the volume of the pulse modulator and improve the stability and the EMI performance of the pulse modulator.
In order to achieve the above object, the present invention provides a pulse modulator, comprising an oil cylinder box, wherein a capacitor charging power supply is arranged outside the oil cylinder box, a pulse forming network and a primary coil of a pulse transformer are arranged in the oil cylinder box, the pulse forming network and the primary coil of the pulse transformer are sequentially connected with the capacitor charging power supply through a main cable, the main cable between the capacitor charging power supply and the pulse forming network is connected with a trigger circuit positioned inside the oil cylinder box, a secondary coil of the pulse transformer is connected with a load klystron, a pair of external interface boxes are inserted on the oil cylinder box, and the parts of the external interface boxes inserted into the oil cylinder box are connected with the trigger circuit.
The pulse forming network is formed by sequentially connecting multiple stages of pulse capacitors in parallel, an inductor is respectively connected between one electrode of each stage of pulse capacitor and the corresponding electrode of the next stage of pulse capacitor, two ends of the last stage of capacitor are connected with a tail cutting circuit in parallel, and the part of the outer interface box inserted into the oil cylinder box body is connected with the tail cutting circuit.
The primary coil of the pulse transformer is grounded and connected with a damping and matching network in parallel, and the part of the external interface box inserted into the oil cylinder box body is connected with the damping and matching network.
And a power supply protection circuit positioned in the oil cylinder box body is arranged on a main cable between the capacitor charging power supply and the pulse forming network, and the part of the external interface box inserted into the oil cylinder box body is connected with the power supply protection circuit.
The power supply protection circuit comprises a first diode, a first resistor and a second diode, wherein the first diode, the first resistor and the second diode are sequentially arranged on the main cable, the second diode is connected with the main cable, one end of the second diode is grounded, and a first capacitor and a first RC filter are connected in parallel on the second diode; the tail cutting circuit comprises a third diode and a second resistor which are connected in series; and the damping and matching network comprises an RC filter, and a fourth diode and a third resistor which are connected in series are connected in parallel at two ends of the RC filter.
The power protection circuit, the ELOC circuit and the damping and matching network are formed by connecting a plurality of protection board modules in series, each protection board module is formed by connecting a plurality of diodes integrated on the same circuit board in series, and each diode is respectively connected with a voltage equalizing capacitor and a voltage equalizing resistor in parallel.
The external interface box adopts an N-type connector or an SMA connector as an external connecting hole thereof.
The trigger circuit includes a high voltage switching thyristor.
The oil cylinder box body is internally filled with insulating oil, a water cooling plate and an observation window are arranged on the side wall of the oil cylinder box body, and the distance between the water cooling plate and the pulse forming network and the pulse transformer is at least the electric insulation distance in an insulating oil environment.
The water cooling plate consists of an outer layer stainless steel plate, a plurality of inner layer copper plates fixed on the inner surface of the outer layer stainless steel plate, a cooling water pipe which is attached and fixed between the outer layer stainless steel plate and the plurality of inner layer copper plates and cooling fins fixed on the inner layer copper plates.
The pulse modulator of the invention installs the pulse forming network, the pulse transformer, the klystron and the like in a sealed oil cylinder filled with insulating oil, thereby the volume of the pulse modulator can be less than half of the volume of the existing pulse modulator, and the volume is compact; and the integrated oil cylinder design is adopted, the chance of electromagnetic interference leakage to the outside of the high-voltage cabinet is reduced, the high-voltage cabinet exchanges external signals with external signals only through the external interface box, and the external interface box adopts an external connecting hole and an N-type connector or an SMA connector as an external connecting hole, so that the EMI performance is good. In addition, the cooling mode of the pulse modulator is changed from the traditional fan cooling mode to the constant-temperature cooling water cooling mode, so that the influence of temperature drift on the stability of the pulse modulator can be effectively improved, and the output high-voltage repetition stability of the pulse modulator can be obviously improved.
Detailed Description
Referring to fig. 3, a pulse modulator according to an embodiment of the present invention is applied to VKX-8311 of CPI corporation in the united states, E37202 of toshiba corporation in japan, E3730A of mitsubishi corporation in japan, etc. a high-power pulse klystron includes a cylinder case 101, a capacitor charging source 1 (CCPS, capacitor charging power supply) is provided outside the cylinder case 101, insulating oil is filled in the cylinder case 101, a pulse forming network 2 (PFN, pulse Forming Network) and a primary winding 31 of a pulse transformer 3 are sequentially connected to the capacitor charging source 1 through a main cable L, a secondary winding 32 of the pulse transformer 3 is connected to a load klystron 4, a hot cathode electron gun portion of the load klystron 4 is disposed inside the cylinder case 101, and the rest is disposed outside the cylinder case 101. A power protection circuit 5 positioned in the cylinder box 101 is arranged on a main cable L between the capacitor charging power supply 1 and the pulse forming network 2 and is connected with a trigger circuit 6 positioned in the cylinder box 101.
Accordingly, the capacitor charging power supply 1 charges the pulse shaping network 2 first, and after the charging voltage of the pulse shaping network 2 reaches a set value, the charging is stopped and the discharging is awaited. An external trigger signal triggers the trigger circuit 6 to be conducted, so as to control the pulse forming network 2 to discharge. The discharging process of the pulse shaping network 2 forms a high-voltage pulse signal determined by the pulse shaping network 2 and the load klystron 4 on the primary coil 31 of the pulse transformer 3, and the high-voltage pulse signal is boosted by the pulse transformer and then used as cathode injection voltage of the load klystron.
The primary coil 31 of the pulse transformer 3 is grounded and connected in parallel with a damping and matching network 7 for discharging residual magnetism in the transformer after pulse, so as to realize matching of the characteristic impedance of the pulse forming network 2 and the primary impedance of the pulse transformer 3. Since the primary voltage of the pulse transformer is only half the front-end charging voltage. The withstand voltage requirement of the damping and matching network 7 is half the charging voltage of the capacitive charging source 1. In order to make the pulse transformer 3 have as small distribution parameters as possible under the condition of meeting the basic voltage and current parameters to obtain better pulse waveforms, the transformation ratio of the pulse transformer 3 is between 1:10 and 1:20, and is 1 in the embodiment: 19, and the leakage inductance and the distributed capacitance of the pulse transformer 3 are set as small as possible.
The trigger circuit 6 comprises a high voltage switching thyristor 61 and a thyristor auxiliary circuit 62. In order to meet the use problem in the oil cooling environment and meet the requirement of 5ns on the vibration of the RMS switch, the high-voltage switch thyristors 61 are hydrogen thyristors, and have the advantages of large pulse current, rapid ignition, good reliability and the like, and the model is the oil cooling CX1836 of E2V company. The thyristor auxiliary circuit 62 converts the trigger signal into a trigger level signal acceptable to the high-voltage switching thyristor 61 on the one hand, and on the other hand, this part of the circuit functions as a protection thyristor.
The Pulse Forming Network (PFN) 2 is formed by sequentially connecting multiple pulse capacitors C1, C2, …, CN in parallel, and an inductor L2, L3, …, LN is respectively connected between one electrode of each pulse capacitor CN and a corresponding electrode of the next pulse capacitor cn+1, in this embodiment, the number of pulse capacitor stages N is 10, n=1, 2, …,9. In addition, a tail-off (ELOC) circuit 21 is connected in parallel across the last stage capacitor.
Specific performance indicators of the pulse modulator of the present invention are summarized below. Where RMS refers to Root Mean Square (Root Mean Square).
| Pulse voltage | 420KV | Pulse current | 340A |
| Pulse power | 142MW | Pulse leading edge jitter RMS | 5ns |
| Highest repetition frequency | 10Hz | Pulse amplitude stability RMS | 300ppm |
| Pulse width at half maximum | 3us | Pulse top width @99% | 1us |
In order to achieve the performance index, the pulse shaping network 2 of the pulse modulator adopts a lumped LC parameter transmission line simulation method to design parameters, and the parameters of the pulse shaping network 2 include characteristic impedance of the pulse shaping network 2, capacitance level of the pulse shaping network 2, charging voltage of the pulse shaping network 2, and the like.
1) The characteristic impedance of the pulse shaping network 2 is typically set to match the impedance of the load (i.e. the load klystron 4) equivalent to the primary winding of the pulse transformer 3, so the characteristic impedance ZPFN of the pulse shaping network 2 is:
Wherein Vkly is the pulse voltage of the load klystron 4, the unit is V, Ikly is the pulse current of the load klystron 4, the unit is A, Tpulse is the pulse half width, the unit is s, and N is the transformation ratio of the pulse transformer.
The inductance value L of each inductor of the pulse shaping network 2 and the capacitance value C of each pulse capacitor 3 can be determined according to the PFN characteristic impedance ZPFN, where the inductance value L of the pulse shaping network 2 and the capacitance value C of the pulse capacitor satisfy:
WhereinPFN is PFN characteristic impedance, the unit is Ω, L is the inductance value of each inductor of the pulse shaping network 2, the unit is H, C is the capacitance value of each pulse capacitor of the pulse shaping network 2, and the unit is F.
In this embodiment, the pulse voltage Vkly of the load klystron 4 is 420KV, the pulse current Ikly of the load klystron 4 is 340A, and the transformation ratio of the pulse transformer 3 is 1:19, n is 19, whereby the characteristic impedance ZPFN of the pulse shaping network 2 can be found to be 3.4Ω by the formula (1). A set of optional LC parameters can then be determined from equation (2): the inductance value l=520 nH of each inductance of the pulse shaping network 2, and the capacitance value c=45 nF of each pulse capacitance of the pulse shaping network 2. In other embodiments, the inductance L can be in the range of 50nH-2uH, and the capacitance C can be in the range of 20nF-1uF. The selection of the inductance and capacitance parameters, particularly the selection of the capacitance, combines the inductance and capacitance parameters which can be found in the market.
2) The charging voltage VPFN of the pulse shaping network 2 is determined by the klystron pulse voltage Vkly and the pulse transformer transformation ratio N. The charging voltage of the pulse shaping network 2 is:
Wherein Vkly is the pulse voltage of the load klystron 4, the unit is V, and N is the transformation ratio of the pulse transformer.
In this embodiment, the pulse voltage of the load klystron 4 is 420KV, and the transformer transformation ratio is 1:19, the calculated charging voltage VPFN of the pulse shaping network 2 is 44.2KV, so that a charging power supply with an output voltage of 0-50KV is selected according to the calculation result.
3) The number of capacitance stages of the pulse shaping network 2 is determined by the total energy storage capacitance of the pulse shaping network 2, and the total energy storage capacitance of the pulse shaping network 2 is determined by the pulse half-width. Theoretically, the total energy storage capacitance is:
Wherein Vkly is the pulse voltage of the load klystron 4, the unit is V, Ikly is the pulse current of the load klystron 4, the unit is A, Tpulse is the pulse half-width, the unit is s, and VPFN is the charging voltage of the pulse shaping network 2, and the unit is V.
In this embodiment, the pulse half width Tpulse is 3us, VPFN is 44.2KV of the charging voltage VPFN of the pulse shaping network 2, and thus Ctotal =555 nF can be obtained according to formula (4). In practical situations, since the rising edge and the falling edge of the pulse waveform are relatively fast, the spice simulation tool calculates to know that the capacitance value of 555nF can obtain the pulse evaluation width of 2.5 us. And finally, selecting 450nF for the total capacitance value according to the design requirement of the 1us flat top width, namely, the number of capacitance stages of the pulse forming network 2 is 10, and each section consists of 45nF of capacitance and 520nH of inductance. Furthermore, in other embodiments, the number of capacitive stages of the pulse forming network 2 may range from 5 to 25 knots.
4) The resulting charging current I of the capacitive charge source 1 is:
Wherein, Ctotal is the total energy storage capacitance, the unit is F, VPFN is the charging voltage of the pulse forming network 2, the unit is V, TC is the charging time, and the unit is s.
Since the charging voltage range of the capacitor charging power supply 1 is 0-50KV, the repetition frequency of the pulse modulator is designed to be 50Hz, and the waiting and discharging time of 5ms is generally required to flow out, so that the charging time TC of the capacitor charging power supply 1 is 15ms at the most, and the charging current I is 1.54A calculated by the formula (5), that is, the pulse shaping network 2 is required to satisfy the charging current not less than 1.33A. A waveform diagram of the charging voltage of the capacitor charging power supply 1 according to the calculation is shown in fig. 4.
Referring again to fig. 3, the power protection circuit 5, the ELOC circuit 21 and the damping and matching network 7 are all protection circuits of the pulse modulator according to the present invention. In one embodiment, the power protection circuit 5 includes a first diode 51, a first resistor 52, and a second diode 53 connected to the main cable and having one end grounded, which are sequentially disposed on the main cable L, and a first capacitor 54 and a first RC filter 55 are connected in parallel to the second diode 53, and are used for the capacitor charging power supply 1, where the withstand voltage requirement is at least 50kV; the tail-biting circuit 21 comprises a third diode 211 and a second resistor 212 connected in series with each other, the withstand voltage requirement of which is at least 50kV; and the damping and matching network 7 comprises an RC filter 71, and a fourth diode 72 and a third resistor 73 connected in series with each other are connected in parallel to two ends of the RC filter 71, and the withstand voltage requirement is at least 25kV.
In another embodiment, as shown in fig. 5 and 6, the structures of the other components of the pulse modulator of the present invention are the same, but for the sake of uniformity of design and convenience of replacement, the power protection circuit 5, the eloc circuit 21 and the damping and matching network 7 are respectively formed by connecting one protection board module 700 or a plurality of protection board modules 700 in series. Each protection board module 700 is formed by connecting a plurality of diodes 701 integrated on the same circuit board in series, and each diode is connected in parallel with a voltage equalizing capacitor 702 and a voltage equalizing resistor 703 to realize voltage equalizing protection. Wherein the number of the diodes 701 is 30, and the withstand voltage of the diodes 701 is 1700V, and the model is DSA17-18A, so that the protection board module 700 has a withstand voltage of 50 kV; the capacitance value of the voltage equalizing capacitor 702 is 0.33uF; and the resistance of the equalizing resistor 703 is 5mΩ. In consideration of redundancy of the protection circuit, the power protection circuit 5 and the ELOC circuit 21 with withstand voltage requirements of at least 50kV are formed by connecting two protection board modules 700 with withstand voltage of 50kV in series, and the damping and matching network 7 with withstand voltage requirements of at least 25kV adopts one protection board module 700 with withstand voltage of 50 kV.
Fig. 7 is a perspective view of the pulse modulator shown in fig. 3. The side wall of the cylinder box 101 is provided with a water cooling plate 102 and an observation window 103, and the observation window 103 is used for observing internal faults possibly occurring in the running process of the pulse modulator, such as ignition, device damage and the like. The water cooling plates 102 are located at the left and right sides of the cylinder box 101 and are used for heat dissipation of the pulse forming network 2 and the pulse transformer 3 of the pulse modulator of the invention respectively. The water cooling plate 102 is at least electrically insulated from the pulse shaping network 2 and the pulse transformer 3 described above in an insulating oil environment. In addition, the water cooling plate 102 also ensures that the temperature change of insulating oil and various components in the oil cylinder box body 101 is not too large, which is beneficial to the improvement of the performance of the pulse modulator, and particularly can improve the problem of poor stability caused by temperature. In addition, an external interface box 104 using an N-type connector or an SMA connector as an external connection hole thereof is inserted on the cylinder case 101 for signal exchange between the inside and the outside of the cylinder case 101. The portions of the pair of external interface boxes 104 inserted into the cylinder case 101 are respectively connected with the above-described power protection circuit 5, tail-cutting circuit 21, damping and matching network 7, trigger circuit 6 and secondary of the pulse transformer 3. It receives the current monitoring signal in the power protection circuit 5 (in one embodiment, through diode 53), the current monitoring signal in the tail-biting circuit 21, the current monitoring signal in the damping and matching network 7 (in one embodiment, through diode 72), through which the three current monitoring signals are used for chain protection, while it sends an input trigger signal to the trigger circuit 6 for triggering the thyristor to conduct discharge, and receives the current voltage monitoring signal of the secondary of the pulse transformer 3 for external observation of pulse voltage and current.
The water-cooled plate 102 has a specific structure as shown in fig. 8, and the water-cooled plate 102 is composed of an outer stainless steel plate 1021, a plurality of inner copper plates 1022 fixed on the inner surface of the outer stainless steel plate 1021 by bolts, a cooling water pipe 1023 attached and fixed between the outer stainless steel plate 1021 and the plurality of inner copper plates 1022, and cooling fins (not shown) fixed on the inner copper plates 1022 for increasing the heat dissipation area. Wherein, the cooling water pipe 1023 and the cooling fin are fixedly connected with the inner copper plate 1022 through brazing. Further, a sealing ring 1024 is provided at the periphery of the inner surface of the outer stainless steel plate 1021.
Therefore, the pulse modulator solves the problems of large volume, low repeated stability and high EMI noise of the high-voltage pulse modulator. Specifically, the volume is less than half that of the existing design, and the repeated stability is better than 300ppm. The novel pulse modulator has the characteristic of compact volume, and can reduce the space occupied by equipment, thereby saving the cost. The high stability is especially suitable for occasions with high requirements on beam quality, such as free electron laser devices, synchrotron radiation light source devices and medical electron linear accelerator devices.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and various modifications can be made to the above-described embodiment of the present invention. All simple, equivalent changes and modifications made in accordance with the claims and the specification of this application fall within the scope of the patent claims. The present invention is not described in detail in the conventional art.