status of her arc rf seals
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1
HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
Status of HER Arc RF Seals
M. SullivanFor the PEP-II team
Machine Advisory Committee ReviewNovember 15-17, 2007
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
Outline• Quick review of status last October
• Discoveries during Run 6
• Status of replacement effort
• Summary
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
Example of a melted RF seal
Inside of ring
These GlidCop fingers are brazed onto the SS mounting plate
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
Molten copper
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
RF seal from Arc 7
Inside of ring
Arcing deposits enough heat to locally melt the copper
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
These omega fingers are over crushed
Melted the Ag plating
Silver melts at 1200 deg C(2200 def F)
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
MechanicsPlan View
The zero length bellows is located on the long ~5.4 m dipole chamber where it attaches to the quadrupole chamber
Pivot Point
Fixed arm
Allowed chamber motion
Quadrupole chamber
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
Location of the TC
The RF seal is almost thermally isolated
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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)
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
PR12 Arc 1b
Tally 61 50 44 18 9
July 3-6, 2007
HER Current
3 Days
Good
Bad
Bad
Good
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
PR06 Arc 5c
Inspected 10jul07
Replaced 10jul07 Inc
Inspected 10jul07
Inspected 10jul07 Inspected 10jul07
Some melting
Looked OK Looked OK
Some melting
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
PR06 Arc 5c
Inspected 10jul07
Replaced 10jul07 Inc
Inspected 10jul07
Inspected 10jul07 Inspected 10jul07
Some melting
Looked OK Looked OK
Some melting
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
New RF Seal DesignSame as the old design but omega fingers made out of silver plated Inconel. The entire SS plate is silver plated.
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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)
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
Signs of arcing
These pictures are from a seal in arc 3 (PR04-6031).
This is not an unusual seal.
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
RF seal from arc 7
Note the crushed fingers
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
Surface on the long dipole chamber
New Inconel RF seal installed
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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
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HER Arc RF sealsM. Sullivan
MAC ReviewOct. 25-27, 2006
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!!
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