Cryo Pump Limitations Recent operating issues with helium Mick Mann ANSTO – Lucas Heights - Australia

ANTARES LE Beamline

We have a pumping problem! Cryo at injection magnet was regenerated twice in a month because of poor vacuum. HE beamline vacuum LE flange vacuum

We have a pumping problem

What could be causing this? Initial RGA test finds large Xenon peaks even though we have not been using Xenon to strip gas. Ar He N2N2 O2O2 Xe Turn off pelletron chains Terminal turbo dumping gas load into beamline

Helium is the culprit Closing LE flange gate valve results in sharp reduction helium abundance Ar He N2N2 O2O2

ANTARES LE Beamline RGA

Helium is the culprit Scan of LE beamline. Note the dominant He peak. Where is it coming from though??? H2OH2O He N2N2 O2O2 H

Helium is the culprit He N2N2 Unstable helium partial pressure component.

The Source Of Helium? H2OH2O He N2N2 O2O2 H2H2 Ar Closing cryo GV increases gas pressures due to decreased pumping but not in the case of helium RGA

The Source Of Helium? Close manual gate valve H2OH2O He N2N2 O2O2 H2H2 Ar RGA

H2OH2O He N2N2 O2O2 H H2OH2O N2N2 O2O2 H The Source Of Helium? Scan with all cryopumps open to beamline Scan with all cryopumps closed to beamline. Pumped using 2 turbo pumps (520l/s). Helium reduced by a factor of >1000!

What to do now? Since the 15K charcoal array is full of helium Replacement of array on pump is necessary

After changing arrays:

Comparison between Cryopumping speed and turbo pumping speed on different gasses Close then open the cryopump gate valve Close then open the turbopump gate valve H2OH2O He N2N2 O2O2 H2OH2O N2N2 O2O2

After changing arrays: After only 3 weeks we are back to our old problems with the cryo Unknown cause of helium increase Close gate valve Open gate valve H2OH2O He N2N2

Pumping Speed Cryopump – CT8 Turbopump – TMP521 Water4000 l/s300 l/s Hydrogen2500 l/s380 l/s Nitrogen1500 l/s290 l/s Argon1200 l/s260 l/s Helium-400 l/s

What is my effective pumping speed? S eff -1 = L -1 + S -1 L = _ ______ 12.l c.π.d³ Effective Pumping Speed Pump Speed Conductance Gas Velocity Pipe Diameter Pipe Length S eff – S – L – c – d – l – -

What is my effective pumping speed? Conductance based on Ø100mm pipe x 1000mm long

What is my effective pumping speed?

Where to from here? Replace the cryo on alphatross injection line with a turbopump to reduce load of helium from alphatross to the cryo pumps on the LE beamline Monitor helium contamination of LE beamline for change over time More frequent replacement of cryo arrays where necessary

Questions…

Thank You!