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Feasibility Study and Pilot TestingFeasibility Study and Pilot TestingFeasibility Study and Pilot TestingFeasibility Study and Pilot Testingof the Evaporative Cooling Circuit for TOTEM Experimentof the Evaporative Cooling Circuit for TOTEM Experimentof the Evaporative Cooling Circuit for TOTEM Experimentof the Evaporative Cooling Circuit for TOTEM Experiment
V. Vacek, V. Vinš, M.Doubrava, M.Galuška, [email protected], [email protected], [email protected], [email protected], [email protected]
CTU, Faculty of Mechanical Engineering, Department of Physics
Technická 4, 16607 Prague 6
©2007V. Vacek & V. Vinš & M. Doubrava & M. Galuška & R. Marek
This research has been supported by GA ČR No.: 1P04LA211 (ČVUT FS - 5404003)
•The applied inner structure demonstrated excellent heat removal capabilities.
•The designed vapor cooling structure proved to be applicable for mass production.
•The thermal bridge on the new contact surfaces between the inner structure and the case
of the ROMAN POT has negligible effect
•A leak of the refrigerant in the ROMAN POT has a greater effect to the cooling
capabilities than a leak of air.
Summary:
TOTEM (TOTal Elastic and diffractive cross section Measurement) is one of six experiments
being installed along the Large Hadron Collider (LHC) built at the international laboratory for
nuclear research, CERN. Main objective of the TOTEM is to measure the size of the proton and to
monitor the LHC's luminosity. It is a minor yet important experiment complementing the results
obtained by the huge experiments such as ATLAS, ALICE, LHCb or CMS. Its particle detectors
are housed inside special vacuum chambers called “ROMAN POTs'”. Twenty four ROMAN
POTs in total, mounted in 8 basic units (Fig.1.), will be installed along the beam pipes of the LHC
near the collision point of the CMS experiment.
As part of the CTU collaboration with CERN, the Department of Physics at Faculty of Mechanical
Engineering has been invited to prepare a prototype design and initial verification measurements
of the ROMAN POTs' cooling system. Since 2006 we perform measurements on prototypes of
continuously developing design.
Fig.1. TOTEM Total Cross Section Detector
Early version of the main structure (2005)
Fig.2. TOTEM ROMAN POT
Thermo prototype internals
Fig.3. Trimming installation Fig.4. Coiled capillaries for ROMAN POTS
Fig.5. Modified prototype of the ROMAN POT connected into the cooling circuit
Each ROMAN POT houses 10 detector planes called “Siliciums”. These are seated in 10
supporting hybrid boards made of a processed capton film laminated on a high thermal
conductivity substrate with a thickness of 0.5 mm. These boards containing the readout
electronics are compactly stacked together making a solid block with high thermal conductivity
and with total power load of 20 W. Through this block there comes two evaporators of two
parallel cooling circuits. To fulfill all specific demands such as dielectric behavior, radiation and
magnetic field resistance, chemical stability etc., a special vapor cooling circuit working with
fluorinert refrigerant R218 was proposed. To allow operation after high irradiation the silicon
detectors have to operate at -15 °C or lower. The structure is spring-loaded to be able to seat in
the exact place in the lid. The position has to be precise. The specially selected capillaries with
nominal inner diameter of 0.55 mm and two connecting pipes were coiled to effectively bypass
the elastic gap.
Capillaries for the experiment were trimmed to match its characteristics with the reference
sample that has been successfully tested. The comparative trimming procedure run on a simple
circuit designed specially for this application (see Fig.3.). New uncoiled capillaries were trimmed
getting the required pressure drop at a length of about 1.7 m. The trimming performed on coiled
capillaries (Fig.4.) had different results. The coiled capillaries showed slightly higher pressure
drop. The reason for this behavior hasn’t been proven yet. During the trimming procedure we have
monitored an average mass flow through the capillary for 8, 9 and 11 bars pressure drop.
The thermo-mechanical prototype of the ROMAN POT (Fig.2.) for the measurement is adapted
to simulate heat sources and is equipped with a number of temperature and pressure sensors inside
and outside its case. We had put together a DAQ system with two ELMBs and a CANbus
interface for 50 temperature and 16 pressure signals. Behavior in various conditions had been
tested, different heat output, pressure and type of the internal atmosphere, different ambient
temperature and settings of the cooling circuit. The measurement also confirmed a negligible
thermal effect of the newly added contacting surfaces between the inner structure and the case.
The ROMAN POT had been connected to our testing cooling circuit in the laboratory at CERN-
Meyrin site. The circuit is based upon a two stage compressor-condenser unit with a number of
added extensions and control devices bringing up the versatility of the system to the highest
possible level.
Fig.6.Two stage compressor-condenser installation
AC
Temperature
control
Condenser
AC
CORI
flow
AC
Safety
valve
16 bar
T
IST
Flowmeter
T
T
T
T
T
T
T
T
Membrane
Compressor
HAUG
Compressor
Schlumberger
Flowmeter
Water 30 °C
Chiller
DATE
Welded Plates
Superheater
KEY
Pressure sensor
Pressure gauge
Peep hole - for monitoring quality
and flow of the coolant
Inlet / outlet to the system - for filling
or emptying the system of the coolant
T Temperature sensor
End cap
Filter
Roman POT
Water 30 °C
Liquid line
Cold Vapor
Hot Vapor
T T
Vacuum pump
Vacuum pump
Bypass for faster vacuming
W1
W2
W5W4
W3
B1
B2
B3 R2
R1
R3
R4
R5
C1
C2
C3
C4
L1L2
L3
L4
L5
L6
L7
L8 L9
P2
P1P3
P4
TT T
T
V1
V2
Cooling Circuit, CERN Prevessin, Fall 2007
N2
Fig.7.Two stage testing cooling circuit scheme
INTRODUCTION PROTOTYPE TESTING
DESCRIPTION OF THE COOLING CIRCUIT FOR SINGLE POT
CAPILLARY VERIFICATION