Apr 24 2024

Updates

• Laser retro-reflection checks performed with R30-4 16/30 (2 of 2) electrode front end:R30-4 gun laser retro-reflection test in LERF clean room April 23 2024: reproducibility achieved with puck retainer assembly orientation 180 deg from nominal
• Gun layout drawings comparing R28-2 with R30-4 guns show data with input from S&A. They also include now R28 (14") and R30 (18") gun chamber dimensions and show why the z coordinate for the top flange is the same for both.File:Haysg-JL0091130-0100-SECTION 01-PHOTO-GUN TO VBV2102 R30 -3 and R28-2 including chamber dimensions.pdf
• Gun fixture with alignment version 2: Carlos met with Gary Hayes and Keith Harding on April 23, 2024. We have one complete fixture version 2 assembly ready for the R30-4 gun. Two assemblies were made of this fixture version 2. One is installed in UITF with the R28-1 gun. The other is in TL1137. The feet from the fixture version 1 for the R30 gun HVC need to be transferred to fixture version 2. Carlos will coordinate this with Neil Wilson. Gary is checking drawings and models to ensure fixture version 2 will work with R30-4 gun.
• Electrodes: The four electrode front end pieces with new 16 degree Pierce focusing angle are on hand. Each piece went through the following process:

   Manufactured from ESR 316 L SS material stock provided by Matt
   Machined to 16 finish (16 micro-inches RMA)
   Polished in the lathe with 400, then 800 grit sandpaper, then diamond paste (5 micron) and finally buffered with cloth, lathe running at 800 rpms. This was very effective at removing machining marks
   Barrel polished: 2 hours coarse (green) cones, followed by 2 hours in fine (red) cones, and finished with 2 hours in corncob. This polishing process rendered the best finish I have seen bringing up the “orange peel” surface look characteristic of diamond paste polishing by hand.
   UHV clean in the SRF chem room
   Vacuum firing to 950 C for 4 hours, still per Tom Elliiot’s protocol.

The vacuum firing turns the electrodes’ surface from shiny to hazy. The same happened to the electrode set (ball, triple point junction shield, back and front end (25 deg Pierce)) used in the R30-3 gun. These electrodes were conditioned to 247 kV and demonstrated field emission free operation at up to 220 kV. So, hazy electrodes are ok for high voltage. The four new electrode pieces show also a haze, but the size of the snowflake-like surface is larger than that seen in the R30-3 gun electrodes. See attached pictures for comparison. Zoom in to see them in detail. The surface finish in the four new pieces looks great in terms of smoothness, in fact, better than the 25 deg Pierce piece used in the R30-3 gun. The only difference is the type of material, I think all of the R30-3 gun electrodes were made from regular 316 L SS.

Joe pointed out that maybe you are observing the diffusion of carbides or other oxides which remain in the ESR (heated under air) to the grains. I doubt it's ~our JLab contamination, rather process materials. Carlos' mentioned main issue found when subjecting the metal to high temperature is reducing the hardness, which I do not see as a problem for high voltage performance.

Vince worked on the 16/30 that did not fit. He opened up the ID successfully, nevertheless it seems that the bolt holes are smaller than they should.

Pictures

• 
• R30-3 gun, 25 deg cone anglec 60 deg junction angle
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• R30-4 Spare, 16 deg cone angle, 30 deg junction angle

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