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

bulletAs 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.
bulletCurrent 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 -> negligible gain.
bulletpower cycle without sub-cooling, pdf doc (comment by BW)
bulletcumulative heating without sub-cooling, pdf doc
bulletBW states, that a higher voltage results in a faster ramping, which is again an advantage in power deposition in the magnet.
bulletPT 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.
bulletwe will use only cold vent lines. A warm vent would need a heater, which we intend to avoid.
bulletA 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.
bulletThe 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.
bulletThe 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.
bulletTransfer lines can stand up to 25 bar. The limiting volume in overpressure is the cryostat with a limit of 15 bar.
bulletFH 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.
bulletFH 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.
bulletAn uncontrolled (failure) flush of LN2 could cause vaporized gas equivalent to 500 g/s LN2. Vent has to be designed appropriately.
bulletFH 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.
bulletFH: slides of dewar, DVB, He-transfer lines, He connector
bulletDVB: two are available, but need modifications to be done by an outside contractor.
bulletAt 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 corrugated.
bulletFH asks for discussion on connectors on the solenoid.
bulletA 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.