Chamber with Controlled Atmosphere

(AIRFLY)

Michal Doubrava – CTU PragueVáclav Vacek – CTU Prague

Libor Nožka, Miroslav Hrabovský, Petr Schovánek, Miroslav Palatka, Miroslav Pech, Dušan Mandát – Joint Laboratory of Optics, Olomouc

Martina Boháčová, Jan Řídký – Institute of Physics of Academy of Sciences of the Czech Republic

Purpose of Chamber• Simulation of Earth atmosphere up to about

30 km above its surface

Variables to Handle• Operating pressures from 1010 mbar

(standard atmosphere) to about 0 mbar

• Operating temperatures from normal ambient temperature 20 °C to about -50 °C

• Moisture content of inside atmosphere

The First Prototype• Cooling performance generated by liquid

nitrogen flow through two heat exchangers

• Regulated flow-rate

• Robust, heavy construction

The First Chamber Problems• Chamber started to leak after a few hours of

cooling (as cold penetrates through body)

• Insufficient cooling performance during the last experiment at Van der Graaf accelerator site (too high energy dissipation)

The Second Prototype• Cooling effect realized by dry ice (CO2), that has

melting temperature -79 °C• Standard stainless steel vacuum “cross” should

secure leak-tightness• Temperature controlled through “heating” tape that

is wound round the cylindrical surfaces• Other equipment (PMT`s, etc.) is placed in nitrogen

atmosphere to prevent the condensation of air moisture on it

Overview

Placement of “heating” tape

Initial Tests• May 2006, Prague

• Two runs, each with 5 kg of dry ice

• Packing of dry ice lasts more than 5 hours

• The first run with dry ice only

• The second run with implemented “heating” tape (up to 25 W)

The First Tests Overview

Temperature ProfileNew Chamber Cooling Test

-50

-40

-30

-20

-10

0

10

20

30

0 20 40 60 80 100 120

time [min]

tem

per

atu

re [

C]

First attempt (without heatingtape)

Second attempt (with heatingtape)

25 W

5 W

Further Steps, Improvements• More tests should be performed in order to learn

the behavior of the chamber and to discover possible imperfections of this design

• Difficult to estimate the behavior of chamber when installed on a beam line

• Installation of additional circuit with liquid nitrogen (tube heat exchanger) could assure the cooling power

• N2 flush line recommended – to reduce condensation of moisture on the dry ice crystals

N2 Flush Line• Should prevent the air moisture condensation that

disables dry ice crystals movement• Unmovable crystals create the air-gap around

chamber that decreases the cooling performance

Summary• Two different prototypes available so far

• The first one worked relatively normally in Frascati, so can be used there again (if leakage problem is solved) if necessary

• The second prototype could be acceptable for measurements in States (AWA, Van der Graaf) but needs more testing before its final usage