* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Nereus, A 250 kV, 80 kA Electron Beam Generator
Cavity magnetron wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Vacuum tube wikipedia , lookup
Electrical ballast wikipedia , lookup
Three-phase electric power wikipedia , lookup
Electrical substation wikipedia , lookup
Power electronics wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Photomultiplier wikipedia , lookup
Optical rectenna wikipedia , lookup
Mercury-arc valve wikipedia , lookup
History of electric power transmission wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Current source wikipedia , lookup
Power MOSFET wikipedia , lookup
Stray voltage wikipedia , lookup
Voltage optimisation wikipedia , lookup
Voltage regulator wikipedia , lookup
Surge protector wikipedia , lookup
Mains electricity wikipedia , lookup
Alternating current wikipedia , lookup
Buck converter wikipedia , lookup
© 1971 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. NEREUS, A 250 kV, 80 kA ELECTRON BEAM GENERATOR* K. R. Prestwich Sandia Laboratories Albuquerque, New Mexico Summary A 250 - 400 kV, 80 kA, 39 ns electron beam generator has been developed. The machine consists of a water-dielectric transmisa 600 kV Marx generator, It was sion line, a diode, and a beam drift chamber. necessary to minimize prepulse for stable diode operaSeveral cathodes were tested during development tion. Diodes with 26 and 8 nH and results are reoorted. inductance are described. Introduction Nereus is a compact, 250 kV, 80 kA, 30 ns electron beam generator developed at Sandia Laboratories. Four Nereus machines have beenfabricated and are in use in the followinq experimental areas: rapid energy deposition in materials, electron beam physics and diagnostics, diode, and plasma-electron beam interaction. Nereus The 1.5 kJ, 600 kV, oil-insulated Marx generator has twelve 50 kV, 0.10 PF stages arranged in an n=2, plus-minus charged confiquration.' Its output capacitance is 8.3 nF and the system inductance is 6.0 PH. The Marx generator charges the 1.9 n, 35 ns transmission line to 500 kV in 0.45 us. The line electrodes are stainless steel pipes with 8.63 and The center cylinder is canti11.5 inch diameters. levered from a lucite sheet that forms the oil-water To minimize resistive losses during charqinterface. ing, the resistivity of water dielectric must be At 500 kV the peak electric greater than 1 M&cm.' field in the transmission line is 160 kV/cm. The diode, switch, and prepulse resistor are shown in Fig. 3. The switches are either l/B inch or 3/16 inch sheets of low-density polyethylene that are stabbed with an array of 45 sewing machine needles. The stab depth controls the switch breakdown voltage. Seventy shots with l/8 inch sheet stabbed 0.020 inches deep had a mean breakdown voltaqe of 434 kV with a standard deviation of 29 kV. The inductance of the switch and its electrodes is of this diode was measured to 11 nH. The inductance be 26 nH. Thus for a 4 o diode imoedance. the 10 - 90 current risetime is 19 ns. Prepulse While the transmission 250 pF switch capacitance supported Cathodes -Six of the cathodes tested Fiq. 4 and some of the operational tabulated in Table I. Description A complete Nereus facility consistinq of the generator, its control panel, water and oil storage, vacuum system, and a switch stabber are shown in Fig. 1. The five ma,jor components of Nereus are: a a water-dielectric, coaxial transmisMarx generator; sion line; a polyethylene switch; a diode; and an These are shown in electron beam drift chamber. Fig. 2. *This work Comission. Thus 13% of capacitance of the diode and its base. the transmission line voltaqe (prepulse voltaoe) is across the 0.25 cm anode-cathode qap and the mean electric field in the gap is 260 kV/cm for 500 kV In this case electron emission will occur from charge. about l/16 of the cathode area and the diode will short For reliable diode operaout durinn the main pulse. tion, it was necessary to reduce the prepulse to one percent of the Marx voltaqe. This reduction was accomplished by connecting a 30 n sodium-chloride solution resistor in parallel with the diode and insertino a 5/16 inch lone section of lucite in the cathode shank to form a prepulse switch as shown in Fis. 3. is by the line is beino charged, the in series with the 1600 pF U.S. Atomic Energy Table Nereus in llereus are parameters shown are in I Cathode Operational d V I 2 J* --(cm) (kV) (kA) (n) --(kll; 1.27 1.27 .152 .190 200 320 65 74 3.1 4.4 12 14 Flame-SprayedTunqsten 1.27 1.27 .190 .254 340 250 65 130 5.3 1.9 16 4 Tunosten 1.27 1.27 .254 .254 260 330 3.3 3.3 4 A Two-Ring 1.27 1.27 .254 .254 260 330 66 67 4.0 4.9 4 4 Four-Rina 2.54 2.54 .254 .254 210 319 120 87 1.8 3.E t 2.54 2.54 .762 .635 420 400 49 57 8.5 7.0 E F Cathode Plain Plasma Brass Wires Parameters v For a given anode-cathode spacing, and at a given voltaqe. the current from the plain metal and the flamesprayed-tungsten cathodes was aoproximately 20% less than the current from the tungsten wire and the two-rino cathodes. Pinhole x-ray pictures of the anode indicated that the plain metal cathode emitted electrons from less than l/16 of its area. The flame-sprayed-tunqsten cathode, similar to the one used on the Coqen machine,Zy3 emitted uniformly unless the spacing was less than 0.15 cm; in this case it emitted only from the edge. The tunqsten wire cathode emitted from a small number of wires. A higher wire density would qive better results. The epoxy ring cathodes emit from the epoxy areas and, for the two-ring unit with a 0.25 cm anode-cathode spacin the diode. ing, a pinch always occurred Fiqure 5 shows voltage, current, and impedance waveforms for one shot with the two-rinq cathode and an anode-cathode spacing of 0.25 cm. Significant current 493 starts flowing when the anode-cathode voltage is 70 kV. The diode-voltage monitor is located at the vacuumwater interface and measures the voltage across the diode inductance plus the anode-cathode gap voltage. At times shortly after the current starts, the inducThe diode impedance decreases tive voltage is 120 kV. from an open circuit to 5 o in 20 ns, remains constant at 5 R for 20 ns, and then decreases to about 1.0 R in the next 10 ns. At higher impedances, such as that obtained with the plasma cathode and anode-cathode spacing greater than 0.E cm, pinching does not occur. Analysis of the impedance at peak current of this cathode for 32 shots with an anode-cathode spacing of 0.64 cm gave the following relationship between impedance and anodecathode voltage: z I 5.5 V-O.24 where Z is voltage in in ohms and V in megavolts. The range this data was from 0.31 to 0.43 MV. of Diodes As can be seen in Fig. 5, the peak voltage across the vacuum-water interface can be 20% higher than the peak anode-cathode voltage. In the diode shown in Fig. 3, this interface is four lucite insulators with interspersed metallic grading rings. The total insulator length is 2 inches. This tube has operated with electric fields greater than 200 kV/in. Figure 6 is a sketch of an 8 nH diode designed and fabricated for Nereus with a single radial vacuum-interface insulator. The electrodes are shaped so that a uniform voltage gradient exists across this insulator and the equipotential lines form a 45O anqle with the insulator, as is desired for maximum flashover voltage. The lower inductance decreases the inductive voltage overshoot, gives a faster current risetime, and thus more output energy'per pulse. References: 1. Unit, 2. Inc., R. S. Clark, Nereus Marx Generator, Sandia report to be published. J. Kraemer Brookline, and W. Crewson, Mass., April 3. J. Clark and S. Linke, and Entrance Conditions of Electron Beam Accelerator, LPS 23, August 1969. Cogen Final 1968. / WplTEl ITORlCl 11761 \ oEto*mER \ “AC”“I( EG&G, I. Smith, "Pulse Breakdown of an Insulator 4. in a Poor Vacuum," Proc. of the International Symposium on Insulation of High Voltage in a Vacuum, Boston, Oct. 1964. SYSTLY NEREUS Figure Report, kJ Operational Characteristics a High Current Relativistic Cornell University Report, NEREUS ELECTRON BEAM FACILITY OR” ISR a 600 kV, 1.5 1. Figure 494 2. IOO7Y150sg200- NEREUSDIODE Figure 3. $i 250300TIME BRASS ss PLAIN 1 ,I EPOXY METAL 0 FLAME (nsec) anode-cathode voltage, Figure 5. Diode and impedance versus time tage, current nereus two epoxy ring cathode. -SPRAYED TUNGSTEN TUNGSTEN WIRES FOUR RING DARK AREA XY RASS TWO WA;ER PLASMA RING Figure EPOXY 4. Nereus Figure cathodes. 495 6. Nereus low-inductance diode. volfor