ERL: G-5/e-GunCryogenic & Pressure Safety Committee Review ERL G-5/e-gun Beam Line Vacuum Failure Analysis

April 24, 2009

Cathode isolationValve

Cathode installationassembly

Beam lineisolation valve

Top cover withfacilities feedthru

Cavityassembly

InternalHelium dewar

Adjustable supports

Magnetic and thermalshielding

HOM Load

Powercoupler

Cryomodule Configuration

Beam Line Vacuum Failure

Two vacuum system failure modes• Small leak into beam line and cryopumped by cold

surfaces of SRF cavity.- Vacuum instrumentation will show abnormally high

pressure in advance of cavity pumping sufficient air to go positive on warm up.

• Catastrophic venting of beam line while cold resulting in significant solid air formation on the cold surfaces of the SRF cavity.

- Heat transfer to solid air insufficient will not result in a flow rate higher than burst disk.

Pressure and Time to Reach Atm as a Function of Air Leak Rate

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01

Leak Rate (Torr l/sec)

P (

To

rr)

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

Tim

e to

S

TD

AT

M (

hrs

)

Pressure at warm end (Torr)

time to reach STD ATM (hours)

Flow rate of singe burst disk/vent line @ 6 psig internal217

Heat Load (Watts)

RT Flow Rate vs Heat Load

Impulse Force on Vent Piping (5-cell)

The potential reaction force from the impulse of released cold gas was calculated using the method presented in API-RP520 (American Petroleum Institute).F = W ((kT/(k+1)m)1/2 / 366) +A0P2 Where: W = Discharge flow, 5940 lbs/hr (0.75 Kg/sec)

k (helium) = 1.66T = temperature, 9.6° R (5°K)M (helium) = 4A0 = 12.6 in2P2 = 0 (flow velocity in the vent pipe is subsonic)

In this case, the impulse force is 20 lbs. ASME B31.1 Power Piping Code recommends using a dynamic load factor of 2.0 to allow for the instantaneous force at the time the relief valve opens. Depending on the final configuration of the vent header pipe run, the maximum force imposed on the string assembly or any other portion of the vent header is 40 lbs.

5-cell Burst Disk to Vent Header

BS&B leak tests 10% with a minimum of two per production run.

Minimum net flow area for the device is 1.496 sq in. (area of 1.5” tube).

Over 50 units in service with no reported failures.

Trapped Helium in Warm Bore

Sector Valves

Helium vapor enters warm injection line from catastrophic failure and is trapped when isolation valves close.

• Sector valves take ~3 seconds to close which can allow sufficient helium vapor/liquid to enter warm space that would result in a positive pressure when warm.

- Volume of injection line and components- ~1.5 cu. ft.- Requires ~50cc of liquid to go positive on warm up.

Warm bore spaces will have burst disks installed to relieve.• Can release up to 5000 cu ft and still maintain 16% oxygen in cave.

- Assume entire warm bore volume is 100% LHe- 750x expansion results in 1125 cu ft.

Will release helium into cave and not be plumbed into vent header.• Will use the commercially available UD certified 11.5 psi device.

Certified Burst Disk for Warm Bore UD certified Available from MDC On order