minutes collaboration meeting 4.Nov.2004, written AF
present: H.Kirk, P.Titus, R.Bennett, Y.Ivanyushenkov, F.Haug, A.Fabich,
K.McDonald, (J.Lettry, H.Haseroth), J.Sondericker
- As the power supply type Alice/LHCb is capable of delivering up to 950 V
and 7200 A, there is no need for sub-cooling. This saves the use of a heater
and a pump.
- Current baseline is to have an initial cooling to 82 K, which needs a
driving voltage of 704V. The temperature after a cycle is 111 K. With a
voltage of 750 V the final temperature increase would be only 25 K ->
- power cycle without sub-cooling,
- cumulative heating without sub-cooling,
- BW states, that a higher voltage results in a faster ramping, which is
again an advantage in power deposition in the magnet.
- PT states, that the calculated resistance might be pretty close to the
final one, which is only known upon the final testing, whereas the impedance
could be a few percent off. The impact is negligible as there are reserves
in the driving voltage of the power supply.
- we will use only cold vent lines. A warm vent would need a heater, which
we intend to avoid.
- A pulsed flow at the exit of the vent could cause diffusing water to
freeze and block the exit. A one-way valve prevents from water entering the
vent. A permanent flow of warm N2 from bottles could additionally help, but
id thought not to be needed.
- The static pressure head caused by the gas in the vent is a few millibar,
whereas the dynamic pressure head can be a few bar depending on pipe diameter
and flow rate (plot). The plot assumes that the friction
coefficient of corrugated pipes is 30% higher than of straight ones. To be
verified. The static pressure head caused by LN2 in the supply line from the
surface to the solenoid is 1.6 bar. Yury assumes a ratio of 40m straight
piping and 20 m corrugated one. To be confirmed.
- The designed volume of the cryostat is about 300 L. It could be reduced
to 100 L and below by filling the volume partly with fiberglass.
- Transfer lines can stand up to 25 bar. The limiting volume in
overpressure is the cryostat with a limit of 15 bar.
- FH assumes that the pipes available at CERN are corresponding to an
ID=32mm in the plot above. To be verified. Exact numbers should be provided.
- FH and his technician in charge are not in favor of pushing LN2 from the
solenoid back to the dewar. A flow chart with exhausting the LN2 to the free
surface is envisaged.
- An uncontrolled (failure) flush of LN2 could cause vaporized gas
equivalent to 500 g/s LN2. Vent has to be designed appropriately.
- FH presents detailed flow scheme. The drain line and the supplying line
could be united to one line only connected to the drain exit of the
solenoid. This would save one line of about 20m.
- FH: slides of dewar, DVB, He-transfer lines, He connector
- DVB: two are available, but need modifications to be done by an outside
- At CERN transfer lines are something like 600-700 ChF/m. The cryo-system
with LN2 return (flow scheme) to the dewar is about 40kChF (RB) including
installation. In the UK a meter costs about 200 ChF straight and 400 ChF
- FH asks for discussion on connectors on the solenoid.
- A hand-drawing of the flow scheme was produced similar to the one above,
but without instrumentation. A write-up should be produced indicating
flow-scheme, instrumentation together with procedures, operation,
maintenance and safety.