An Experimental Study Using Helium to Produce a Catastrophic Loss of Vacuum in a RHIC Dipole Magnet Cryostat Page: 2 of 18
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AN EXPERIMENTAL STUDY USING HELIUM TO PRODUCE A CATASTROPHIC
LOSS OF VACUUM IN A RHIC DIPOLE MAGNET CRYOSTAT
K. C. Wu, D. P. Brown, J. Sondericker and D. Zantopp
RHIC Project, Brookhaven National Laboratory
Upton, New York 11973-5000
ABSTRACT
A heat load of approximately 10 kilowatts was measured when the insulating vacuum of
a RHIC dipole magnet operating at 4.5 K in MAGCOOL was spoiled by introduction of helium
to the magnet cryostat. This heat input is more than 1000 times the heat load on the cryostat
under good vacuum, but is less than the heat input when air was introduced in a previous
experiment.' The response of the cryogenic system is very fast although slower than in the
previous test with air. The heat transfer mechanism is different for air as compared to helium.
When helium is introduced, the pressure in the insulating space increased rapidly causing the
vacuum tank to become colder and the heat shield warmer as heat is transferred primarily by
conduction. When air is introduced, the air initially is cryopumped on the cold surfaces and the
pressure in the insulating space increases more slowly which inhibits the heat transfer by
conduction between the vacuum envelope and the cold surface. The initial impact on the 4.5
K system by conduction through helium gas is less than that from condensation of air.
However the heat conduction by helium gas eventually becomes larger than that by air. Because
the maximum rate at which heat is introduced to the magnet is greater with air than helium, the
relief system shall be sized for an air leak.
INTRODUCTION
A sudden loss of vacuum experiment using air was performed in October 1992. A heat
load of approximately 20 kilowatts was reported.' In a continuing effort to understand the effect
of loss of vacuum, a study was performed on RHIC dipole DRD-010 in MAGCOOL during
which helium gas at ambient temperature was introduced into the insulating space.
As in the previous test, the RHIC magnet was cooled to 4.5 K and powered to 5000
Amperes prior to the introduction of helium. Since helium gas will not be cryopumped, a small
amount of helium spoils the vacuum.
Parameters of the system including current through the magnet, insulating vacuum,
pressures, temperatures and flow rates for the helium coolant, liquid levels in helium pots,
temperatures on the vacuum tank and the heat shield were recorded as a function of time. The
heat load was found to be about 10 kilowatts from the sum of heat into the magnet and the
helium system, and heat removed by the MAGCOOL cold box and the helium vented from the
cooling system. The results agree well with the rate of the vaporization of liquid in the helium
pots.1
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C., Wu K.; Brown, D.P.; Sondricker, J. & Zantopp, D. An Experimental Study Using Helium to Produce a Catastrophic Loss of Vacuum in a RHIC Dipole Magnet Cryostat, report, February 26, 1993; United States. (https://digital.library.unt.edu/ark:/67531/metadc868589/m1/2/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.