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, R.Marekvaclav.vacek@cern.ch, vaclav.vins@cern.ch, michal.doubrava@cern.ch, michal.galuska@cern.ch, rene.marek@cern.ch

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