Topic 34,b.3)Helium Mass Flow Meter

The Q0 of Superconducting Radio Frequency (SRF) Accelerator Cavities is a measure accelerator “health”. Increasing Q0 indicates degradation of the accelerator’s ability to work. A real time measurement of cavity Q0, not available now, will flag problems before a cavities become un-usable. A return flow, Helium Mass Flow Meter, to be developed by this SBIR in Phase I makes that measurement. The great public benefit is that DOE sponsored SRF accelerators CEBAF, LCLS, SNS and FRIB may require fewer ~$1,000,000 cryomodule refurbishments - a great savings. Hyperboloid intends to develop and demonstrate a practical, robust Helium Mass Flow Meter, jumpstarting from the successful laboratory scale work of Japanese researchers. The meter has a wire/element made of a superconducting metal that is made cold enough to “switch” to the superconducting state by heat transfer from the flowing 2 K gas flow from the cavities of a cryomodule. This “switch” is a signal that is detected more easily than the change in resistance signal of signal from a meter based on a hot wire. The electronics of the Meter continuously changes a current in a heater wire adjacent to the superconductor element. When the element is driven to “switch” back to the non-superconducting state by the increasing heat from the changing current, the tracked value of current at the “switch” point correlates with Helium Mass Flow at that time. Higher flows need more heater current to do the “switch”. Calibration of the meter’s heater current to helium flow is done in situ using known power from other heaters already adjacent to the cavities of a cryomodule. Phase I tests various configurations of the superconducting element in 2 K helium flow streams and develops the electronics to detect the change in superconducting state and a variable current source to resolve helium mass flow change of about 1/20 g/s. If funds are available, Hyperboloid will design the instrument cartridge that inserts into the return flow U-Tube of Cryomodules at JLab. Hyperboloid intends to install this meter in CEBAF in Phase II and market the meter to the remaining US labs and to labs worldwide in Phase III. Little commercial use is anticipated.