Status of HER Arc RF Seals

Status of HER Arc RF Seals M. Sullivan For the PEP-II team Machine Advisory Committee Review November 15-17, 2007

Outline • Quick review of status last October • Discoveries during Run 6 • Status of replacement effort • Summary

Story as of last October • We had found 5 bad RF flex flange seals and had replaced them with new (same design and material) seals • We had borescoped the beam pipe as much as we could in 2 of the 6 arcs looking for other bad RF seals and did not see any other bad seals • We were trying to think of some way of instrumenting at least some of the seals

Example of a melted RF seal These GlidCop fingers are brazed onto the SS mounting plate Inside of ring

Molten copper

RF seal from Arc 7 Inside of ring Arcing deposits enough heat to locally melt the copper

Silver melts at 1200 deg C (2200 def F) Melted the Ag plating These omega fingers are over crushed

Some Numbers from last October • Each arc has 32 cells. Each cell has a bellows module with 2 RF seals and a zero length (flex flange) bellows with one RF seal. • Arc 9 • 11 cells worth of bellows and flex flange RF seals checked • All bellows ok • 3 flex flange RF seals melted • Arc 7 • 18 cells worth of bellows and flex flange RF seals checked (8 cells checked in July of these 8 four were rechecked) • 3 bellows replaced in July 2006 • 1 bellows found with several disconnected fingers • 1 bellows found with 1-2 displaced fingers • 2 flex flange RF seals melted • Arc 1 (Some evidence of a problem but did not look) • No problems with any of the RF seals at the bellows

Mechanics Plan View Pivot Point The zero length bellows is located on the long ~5.4 m dipole chamber where it attaches to the quadrupole chamber Allowed chamber motion Fixed arm Quadrupole chamber

Findings During Run 6 • We decided to instrument the flange joint with a TC attached to the Cu as close as possible to the top bolt holding the RF seal plate even though the Cu is water cooled • We started to find remarkably high temperature readings on certain seals and decided we needed to instrument every single RF seal • By the middle of June we had attached a TC to all but about 5 joints • We found a large number of seals with temperature increases of over 50 deg F T

Location of the TC The RF seal is almost thermally isolated

More Run 6 findings • Throughout the run we identified several particular RF seals that had a very high temperature increase (as much as 100 deg F T) associated with beam aborts in the HER and with vacuum spikes in nearby pumps • We had on hand ten seals with Inconel fingers and started to replace particularly bad seals with these new seals • The new seals showed very good temperature behavior which prompted us to consider replacing a significant fraction of the 192 RF seals in the HER this fall • We initially thought we could only replace about 120-150 seals but the MFD group here at SLAC developed a production line that will give us enough seal sets to replace all 192 flex seals (minus the 5 we had already installed during the run)

Good Bad HER Current PR12 Arc 1b Tally 61 50 44 18 9 Good July 3-6, 2007 Bad 3 Days

Inspected 10jul07 Inspected 10jul07 Some melting Some melting Replaced 10jul07 Inc Inspected 10jul07 Inspected 10jul07 Looked OK Looked OK PR06 Arc 5c

Spreadsheet indicating high temperature (RED) and low temperature (Blue) RF seals for 3 different data sets. Also compared to peak temperature data. We removed this seal in order to inspect it

New RF Seal Design Same as the old design but omega fingers made out of silver plated Inconel. The entire SS plate is silver plated.

Replacement Progress • We quickly found that looking at the seals with a bore scope did not tell us whether or not the seal was damaged so we started replacing all seals soon after starting • We have replaced over 155 RF seals • So far we have found 7 seals that look OK (No visible damage like arcing, melting etc.) • Of the 155 bellows we have looked at we have had to replace about 5 due to previously identified small leaks or to bellows finger problems. None of the bellows have shown any sign of arcing and/or heating. Nor have nay of the bellows RF seals. • We are making excellent progress and still plan to replace all the RF seals in the HER before we startup next month

These pictures are from the worst RF seal found in arc 1 The SS plate is distorted Copper melts at 1080 deg C SS melts at 1540 deg C (2550 deg F)

These pictures are from the worst RF seal found in arc 5 I estimate about 200 W of power are needed to melt the SS washer

An RF seal that we replaced last fall This seal looks as bad as some of the worse seals that have been in the machine since day one

Signs of arcing These pictures are from a seal in arc 3 (PR04-6031). This is not an unusual seal.

RF seal from arc 7 Note the crushed fingers

Surface on the long dipole chamber New Inconel RF seal installed

Inconel seal that was installed July 10 This seal was not silver plated The seal looks fine. None of the fingers are damaged and all of the fingers look like they made contact with the adjoining surfaces

Summary • Last fall, in looking for bad bellows we uncovered a problem with the RF seals at the flex flange in the HER. We initially thought the problem was not as extensive as it turned out to be. • We eventually began to suspect we had a high percentage of failures when we were able to instrument most of the flex flanges with TCs sometime in May-June • During this present down the percentage of RF seals with arcing or heating problems has been found to be quite high (>95%) so we are replacing all 192 seals • Replacement progress is going well (5 of 6 arcs are done) • We have also set up motion detectors on 2 dipole chambers • Many thanks to the hard working members of MFD and MFDV who are making this replacement effort successful!!

Status of HER Arc RF Seals