CM2 Repair Status 8/13/2012 Tug Arkan 1

Latest Status After the warm end couplers were disassembled, it was decided to disassemble all the lower aluminum heat shields in order to inspect all the invar rod clamps and do a thorough assessment of the alignment of the cavities and the magnet package. During the week of July 16, CM2 was moved to Big Bertha fixture. Vacuum vessel was removed from the cold mass. 30 layers MLI was cut, 80K lower shields were ground off, 10 layers MLI was slit and rolled up, 5K shields were ground off. Magnet package was moved ~14 mm back to its specified axial location. On July 23, cold mass was moved to the red spreader bar fixture. Alignment group conducted measurements and we did not see any major (>0.5 mm) X-Y-Z shifts on the cavities location. On July 23, we had a Webex meeting with DESY colleagues to discuss the invar rod clamps designs: – We decided to replace all the CM2 cavities and magnet to invar rod clamps with the XFEL design clamps. 2

CM2 magnet invar rod clamp did not provide clamping force 3 ~14 mm shift of the magnet package

4 Invar rod clamp was unbolted from the magnet body. Just to assess the clamping force, side screw was tightened as tight as possible and the clamp was able to freely move and rotate around the invar rod. We can conclude that this clamp did not provide any clamping force.

5 Magnet to Cav #8 2-phase pipe bellows as assembled Magnet to Cav #8 2-phase pipe bellows after ~14 mm shift

6 Magnet and the downstream end gate valve was slightly lifted from the bottom with temporary supports. Then we loosened the needle bearing side and top screws in order to adjust the wedged bearings. Then the magnet was moved ~14 mm to its specified axial location.

7 New Invar Rod Clamps Magnet clamp Cavity clamp Fixed point clamp Stainless steel clamps, more bolts, spring washers, 10 Newton/meter torque

New Fixture 8 New Fixture to hold the 2-phase pipe end flanges anchored to the GRHP during vacuum pump down and pressure test. Upstream end Downstream end

Leak Check On July 2, 2-phase helium volume was pumped down in order to leak check and locate the leak. All the Ti bellows, and flanges on the helium volume were thoroughly leak checked. CAF/NML group found that the upstream end CF100 Ti flange has not machined properly and the knife edges are not properly engaging the copper gasket to provide a reliable sealing. The problematic flange was sealed with a rubber cork and the leak check efforts continued. No other leak was found. For a second opinion, we asked IB4 QC dept. leak check technician to conduct leak check on the same volume and he conducted the checks on July 3. No leaks were found. 9 Strings to collapse the convolutions of the bellows during leak check

Pressure Test On August 3, we pressurized the helium volume to 33.5 PSIG design pressure with helium gas in order to locate the potential leak around the questionable bellows and weld. Sniffing with helium detector did not show any leaks. The pressure test was very important to simulate the planned pressure test on the CM2 as a fully assembled cryomodule at NML. Cavity frequency is protected while using the blade tuner to compress the cavity and this is setup before the pressure test. The end forces that will be reacting to the CM2 at NML during the pressure test were simulated with the pressure test setup. A thorough leak check will be done after the pressure test 10

Test Setup on CM1 Known leak introduced upstream: 1E-4 torr l/s Shop-vac drawing air upstream Leak detector connected to 2-phase line downstream Helium sprayed at several locations upstream and downstream of the location where the leak was observed on CM2 Curt Baffes

Test The NML leak test was duplicated using CM1 Leak was created near the upstream 2-phase line flange Leak detector was connected to downstream 2-phase line flange Tarping and vacuum-cleaner-driven air flow similar to CM2 test at NML In order for this hypothesis to be plausible, the CM1 test would need to demonstrate the following characteristics that were displayed by the CM2 leak at NML: A short response time (just a few seconds) from the time helium is sprayed to the response on the leak detector Strong variation in response driven by only small (~6”) variations in location where the helium was sprayed Curt Baffes

Observations and Conclusions Response time to helium sprayed near the downstream end was long: >40s Response time to helium sprayed directly on the upstream leak was ~7s, consistent with diffusion rate rules of thumb This does not match the response time of the CM2 leak at NML, which was nearly instantaneous Response was not very sensitive to longitudinal location where helium was sprayed. For a given duration of helium spray, and with longitudinal location of the spray varied, the response did not vary in the first significant digit. Response was sensitive to the position of the vacuum cleaner relative to the leaking flange. This could change the response magnitude by a factor of 2 (but not the response time). Conclusion: leak simulations using CM1 did not match CM2 observations. The upstream flange is not the culprit. Curt Baffes

What’s next? At the moment, we are trying to pump out the helium out of the 2-phase volume in order to continue with the leak checks. (3 diffusion pumps are pumping for the last 4 days to clean up) As of today 8/13 morning the sensitivity is at 4 x 10^-8 mbar x liter/second Once a reasonable sensitivity (< 5 x 10^-9) is reached on the leak detector, conduct the following leak checks: – A thorough leak check of all the bellows, flange connections, visible weld areas after the pressure test – Cold Shock the questionable bellows and welds, leak check – Heat the questionable bellows and welds with heat gun, leak check – Wiggle the 2-phase pipe downstream end during the leak checks to create motion on the bellows convolutions – Bag the whole cold mass with plastic, isolate the rubber corked pipe ends, fill with helium and leak check. Depending the to the results of these leak checks, meet with the related personnel and decide how to proceed 14