PillBox Cavity Update(Button Tests)

Bob RimmerNFMCC CM

University of MississippiJan 13, 2009

Page 2NFMCC CM, January 13, 2009R. Rimmer

Button Test Cell,aka LBL Pillbox

• “Button” system in pillbox cavity designed for easy replacement of test materials

• Tested so far: TiN-coated Cu & Mo, bare Mo and W

• To be tested: Cu (electro-polished & unpolished), Be

• Results to date indicate that TiN can improve performance at a given B field by somewhat more than 50%

– 16.5MV/m 26MV/m

button 0.75 radius

Molybdenum buttonsMolybdenum buttons

Be window

button holder

((1.7x1.7x field field enhancemenenhancement factor on t factor on button button surface)surface)

Page 3NFMCC CM, January 13, 2009R. Rimmer

805 MHz Button (Pillbox) cavity

Refurbished

Page 4NFMCC CM, January 13, 2009R. Rimmer

805 MHz Button CellStatus

• Due to problems obtaining vacuum integrity, the 805 MHz button cell is still at TJNL.– The technicians are trying again to seal the cell using newly

machined Tin seals. This work is currently on-going.– Two attempts with new gaskets have had gross leaks on

both large flanges and pick-up probes First attempt seals were degreased with alcohol before

assembly Second attempt we deoxidized the tin deals to remove some

slight discoloration Torque is per Steve Virostek's tech note, gaskets are getting

uniform crush but not very much on the large seal Have checked that bolts are not bottoming out/ galling Have checked that cover plates go metal to metal without

gaskets, i.e. they are not hanging up anywhere

Page 5NFMCC CM, January 13, 2009R. Rimmer

Status II

• Have inspected used gaskets for imprints with the following findings:– Viewport gaskets which DO SEAL have deep imprint of milled

finish on cavity side, concentric groves on flange side.– Probe seals that leak have good imprint of machined grooves on

cavity surface but they cross the seal path. Probe side similar to viewports

– Cover seal has only light crush. Flange side shows machining marks.

– Cavity side shows light imprint of polished mating surface.– Trying to get some optical microscope pictures of each.

• Speculation:– Probe port machining marks (from facing off the cavity end

surface) cross the seal surface and although they imprint into the tin maybe there are leak paths at the bottom of the grooves.

– Cover gasket does not get enough crush for material to flow. Cavity surface may be too highly polished with nothing to "key" into.

Page 6NFMCC CM, January 13, 2009R. Rimmer

Path Forward

• Path forward:– Make a hand tool to put concentric grooves around each

probe with texture similar to mating flange (fine machined finish).

– Turn the cavity cover flange surface to mimic mating flange (fine machined finish).

– Re-clean everything– Attempt another assembly– If still leaks consider trying narrower gasket or tin wire to

increase material flow.– If leak tight on cover seals check coupling iris seal and if OK

ship to FNAL.

Page 7NFMCC CM, January 13, 2009R. Rimmer

• Other activities:

• Have received Be and extended copper buttons and flat and profiled button holders for TiN coating. Coating system is available, waiting for some Ti Foil to shield RF contact surfaces as requested by Al.

• Should receive and start coating this week.

Seal 1: viewport (sealed) x4

Reverse side of seal

Seal 2 (probe port, did not seal) (x4)

Flange side of seal

Seal 3 (big, did not seal) (x4)

Cavity side of seal

Flange side of seal