Anode Installed, Switch Assembly and Testing Advance

Jul 1, 2021 | Focus Fusion, Generator

This post is also available in: Español

The LPPFusion research team has been extremely busy preparing for our next experiments—too busy in fact to put out this report until now. (If you want more frequent updates, please follow us on Wefunder and Facebook.) Our first big milestone was installing our new anode. The assembly day was May 4th. It went well—the 4th was with us! LPPFusion Research Scientist Syed Hassan, assisted by Chief Scientist Eric Lerner, removed the temporary anode plate from the top of our fusion device and then carefully replaced it with the new anode, assembled onto its own steel plate.

Our first step, inside the glove box, was to merge the anode stalk and anode base (already attached to the outer steel plate.) We achieved the low electrical resistance (micro-ohms) planned. Syed then put a custom flange on top of the anode to connect it to the upper vacuum chamber. The anode has a hole in its center to allow the escape of the electron beam, which dumps its energy into the upper vacuum chamber.

Fig. 1 The new anode in FF-2B. It is shown here through the front chamber window (the anode is the central shiny cylinder, surrounded by the cathode vanes).

Syed then put threaded rods into the temporary steel plate and with lab jacks carefully lifted it vertically, making sure that it did not hit the ceramic insulator, still inside our device. All this time we continued pumping out the vacuum chamber, so no beryllium dust (if any is still present) could escape outwards. Once a new rubber-sealed cap was put on top, we started to prepare for inserting the new anode. The anode had to be centered on the insulator to within a tenth of a mm, 1/250 of an inch, so careful planning was required.

We attached the anode assembly to a steel rod with threaded bolts and then carried it into the experimental room. Once it was aligned with other threaded rods on the machine, Syed carefully lowered the anode inside the insulator, keeping watch on two levels to keep the anode vertical, while Eric monitored from a cross-wide viewpoint. The operation, completed at 10 PM, was a complete success, with good centering.

The next two weeks in May were devoted to a bake-out of the vacuum chamber and the vacuum system. We raised the temperature with external heating coils to a gentle 120 ℃ to get rid of moisture that clings to metal parts. This brought the vacuum in the system down to only 5 microtorr, only 7 billionths of atmospheric pressure. Good vacuum is needed to exclude oxygen from the chamber when we fire.  This will prevent the formation of oxides on our electrodes and reduce erosion.

During this period, we also performed a preliminary test of the new smaller switches. We exposed them to a high voltage from our power supply to see if there would be any flashover arcing in air. It looked like the switches passed the test.

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The rest of May and early June, we concentrated on assembling the new switches onto the FF-2B device. With 16 switches, we had a lot to do, so at times LPPFusion Chief Information Officer Ivy Karamitsos and Systems Administrator Jose Varela pitched in as well. Syed also was busy preparing four new trigger cables to attach to the switches. The cables carry the trigger electrical pulse from the main trigger generator to each switch. Since we only had 12 of the large switches (and were using only 8 of them in our last experiments) we needed four more cables. Attaching them correctly was tricky, as they needed to hold a 30kV charge when the trigger system is turned on. We then successfully tested the entire trigger system, which sends a sharp 60kV spark to the switches when we fire it.

Fig. 2 The new dual switches during assembly of the switching system. The switches are the dark plastic cylinders, topped by the brass spark plugs. At this stage of assembly, they are not yet attached to the trigger system. The main trigger generator is the large brass cylinder to the left, with the trigger cables snaking out of it. 

On June 10, we took the next step and tested the whole switch and trigger system by applying a charge to the capacitor bank. We wanted to make sure there were no flashovers sparks before we made final preparations for a real shot, where we fire the capacitors, allowing huge currents to flow across our electrodes. Unfortunately, we did get a small flashover spark from one switch, right before we got to the full 40kV charge.

In retrospect, our preliminary test of just two switches was graded a bit too easy. We passed our first effort at insulating the switches against flashover sparks because we did not hear the “snap” of a large flashover spark. But we had heard a “sizzle” sound which, we realized later, was really a series of small flashovers. After another two weeks of experimenting with different ways of insulating the switches—mainly with Kapton tape—our work seems to have passed the “sizzle” test. The two test switches were quiet all the way up to 43 kV. More assembly and testing still lie ahead before we are ready to fire, hopefully soon.

This piece is part of the July 1, 2021 report. To download the report click here.













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