We have successfully tested a double post-hole vacuum convolute for driving z-pinch loads on Saturn (32 TW, 1.9 MV, 40 ns FWHM, and 0.11 Cl). We use the lower four insulators to feed four, conical self-magnetically insulated disk feeds (MITLs). The disk MITLs are convoluted using six anode posts (and cathode holes) to a single disk MITL (L -10 nH). A peak current of 12.5 MA was delivered to a low inductance short circuit load and 10.5 MA was delivered to a gas puff z-pinch load. Electron losses in the vacuum feed have been acceptable.
Advanced radiography capabilities can be provided by diodes in which a < 1 mm diameter cathode is immersed in a -60 T magnetic field and pulsed to -16 Mv. An electron current of -50 kA is constrained by the magnetic field to -1 mm at the anode, and produces v 1 krad at 1 m. A 16 MV, 50 ns flat-top voltage adder has been designed that is optimum to develop such &odes. The adder approach is chosen to give a relatively short risetime and low prepulse. It also has the advantage of being re-configurable to provide two 8 MV pulses. The pulser uses standard Marxes, intermediate stores, and water P E S . Novel features include an oil prepulse switch, an induction cell that is fed from one pain< and a blocking network to couple two pulses to one cell. Based on detailed simulations, a design has been completed through detailed drawings and prototype hardware will be tested next year. Figure 1 shows an "immersed diode" designed for advanced radiography applications [ 11. The negative inner conductor of a coaxial MlTL enters a strong axial magnetic field produced by a pulsed solenoid, and tapers to a cathode less than 1 mm in diameter. The magnetic field prevents the electron beam from expanding in radius sigmficantly, thereby forming a -1 mm x-ray source at the anode. The spacecharge-limited current in such an "immersed diode" system is -V/300 ohms, and at 16 MV, for example, a current of 50 kA impinging on a high-Z anode should be able to create a radiation source of > 1 kradat 1 min tens of ns.
I. RADIOGRAPHY REQUIREMENTS AND THE RITS CONFIGURATIONSExperiments at up to 50 T on Hermes I11 [2] and Sabre [3] have had considerable success in demonstrating such sources, producing as much as 114 rads at 1 m from a 1.5 mm FWHM diameter spot. Experimental progress has been limited by the availability of these accelerators and the fact that they were not designed for this application. The Radiographic Integrated Test Stand (RITS) has been designed as a 16 MV source optimized for immersed diode radiography. It can also reconfigured to deliver two pulses at 8 MV or more. Figure 1. High B, rdographic diode.Figure 2 shows the three different configurations of RITS. It is an induction voltage adder like Hermes and Sabre and uses similar drive technology. M a n generators (two) charge coaxial water transfer capacitors (TCs--two per Marx, four in all). Each TC is switched out by a laser triggered gas switch (LTGS) to fastcharge water pulse forming lines (PES --three per TC, twelve in all) that have synchronized self-brealang water output switches. *Bechtel Nevada Subcontract 18719; **JFC, Castro Valley, CA &77803-549&u99/slO.~l999 IEEE.
403Single adder configuration producing 16 MV pulse.Double adder configuration producing separate 8 MV pulses on two cathodes in common B, magnet.
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