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External Cryogenics for CMS
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The External Cryogenics Group of the LHC division is in charge of the
procurement of the cryogenic refrigeration system for the CMS superconducting
solenoid.
This page is dedicated to information on all aspects of the refrigerator
project. In the following you will find:
Equipment Installation
CMS and the Refrigerator Project - an Overview
The Compact Muon Solenoid (CMS)
experiment is one of the experiments which are being built for the analysis
of the collision products at the four collision points of the Large Hadron
Collider (LHC)accelerator.
The CMS experiment will comprise four different detectors:a muon system, a electromagnetic
calorimeter, a central tracking and ahadron calorimeter. For a high resolution of the
detectors, a very highmagnetic field is essential.
The magnetic field inside the CMS
experiment will be as high as 4T,it will be provided by the largest superconducting
solenoid coil in theworld measuring 12.4m in length and 6.9m in diameter.
The solenoid coil cold mass will weigh 220t. The cooling system forthe cold mass
is divided up into two subsystems: The Internal and the External Cryogenics.
The Internal Cryogenics comprise the complex thermosiphon cooling circuits,
the thermal shield of the cold mass and a valvebox for the control of the cooling circuits.
The Internal Cryogenics will be supplied by CEA-Saclay.
The External Cryogenics comprise the refrigerator, the intermediate cryostat and all
transferlines, i.e. all components required to supply the valvebox of the Internal
Cryogenics with refrigeration power and liquid helium.
The Refrigeration Requirements for the CMS Solenoid
The refrigeration system will have to fulfill the following tasks:
- Cool-down
- Cool-down of the solenoid (220t cold mass) to the operation temperature of 4.45K
in about 26 days
- Operation
- Supply of refrigeration power at 4.45K for the thermosiphon cooling system of
the solenoid
- Supply of liquid helium to the current feedthroughs of the solenoid
- Supply of refrigeration power in between 60K and 80K for the thermal radiation shield of the solenoid
- Fast Energy Dump (Quench of the solenoid)
- Recovery of the evaporated helium
- Refrigerator Failure
- Backup supply of the solenoid from the intermediate cryostat for at least5 hours in order to allow a slow discharge
- Helium recovery by the recovery compressor
The Description of the CMS-Refrigerator
The CMS refrigerator process is based on the Claude principle. The heliumis compressed at ambient temperature by two screw compressors in seriesup to 18 bar absolute. After having passed through the gas coolers andthe oil removal system, the helium enters the cold box where it is cooleddown in several stages.
In the first stage, cold helium returning from the cold box is usedto cool the helium stream down to about 70K. If necessary, additional coolingin this stage can be provided by a liquid nitrogen cooled hea t exchanger.
In the second stage, the helium stream is split and a part of the helium gas flow
is expanded in two turbines down to about 14K. This gas is then used together with the
return gas from the intermediate cryostat to cool the main gas stream by the means of
two heat exchangers.
In the last stage, the main gas stream is expanded in a third turbine and a
Joule-Thomson valve. It is thereby cooled to 4.45K and partly liquefied.The liquid fraction
is collected in the intermediate cryostat. The gaseous fraction is returned together with
the boil off from the intermediate cryostat via the heat exchangers of stage two and one
to the compressors.
The CMS-refrigerator hardware comprises three main components:
The compressor system which comprises the compressors and their auxilliary systems as
well as the oil removal systems will be housed in a special compressor building named SH5.
The coldbox which contains all the components required for the cool-down of the helium
will be temporarily installed in an alcove of the SX5 assembly hall in order to test the
solenoid at ground level. Once the tests are completed the coldbox will be removed and
reinstalled in the service cavern USC55.
The intermediate cryostat which collects and stores the liquefied helium will be
installed onto the steelwork structure of the CMS-detector, first in the assembly hall SX5
and then in the experiment cavern UXC55.
Technical Data as specified:
- maker - Air Liquide - DTA
- refrigeration power - 800W at 4.45K and 4500W between 60K and 80K and 4g/s liquefaction
(or in total an equivalent of 1.45kW at 4.4K)
- power consumption - 850kW
- main compressors - 2 screw compressors
- atmospheric compressor - throughput 207g/s, suction pressure 1bar, discharge
pressure 4.6bar
- second stage compressor - through put 207g/s, suction pressure 4.4bar, discharge
pressure 18.4bar
- second stage compressor if used as recovery compressor - throughput 44g/s,suction
pressure 1bar, discharge pressure 18.4bar
- liquid helium storage capacity - 6000l
Page responsible G. Perinic/Th.Dupont - Last revision January'2003
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