G. Hallewell (CERN/CPPM), E. Anderssen (LBNL), D. Bintinger (LBNL),
M. Bosteels (CERN), P. Bouvier (U. Geneva), B. Payne (RAL), R. English (RAL), J. Godlewski (Crackow/CERN), B. Gorski (Crackow), 
S. Grohmann (CERN/Dresden), T. Hayler (RAL), T. Jones (Liverpool),
S. Lindsay (Melbourne), W. Miller (Hytec Inc, N.M.), 
T. Niinikoski (CERN), J. Olszowska (Crackow), A. Pilling (RAL),
M. Olcese (INFN Genoa),
E. Perrin (U. Geneva), H. Sandaker (CERN/Oslo) J. Thadome (Wuppertal),
V. Vacek (CERN/Czech Technical University, Prague)
!!
We report on the development of evaporative fluorocarbon cooling for
the ATLAS Pixel and Semiconductor Tracking  (SCT) detectors. 
The front- end electronics and silicon substrates of these detectors 
collectively dissipate around 50kW of heat, which must be removed 
from the ATLAS inner detector cavity. 

For an operational lifetime of around 10 years in the high radiation
 field close to the LHC beams, the silicon substrates of these 
detectors must operate at a temperature below around -6 deg C, 
with only short warm-up periods each year for maintenance. 
In the case of the pixel B-physics layer, at a radius of 4.5 cm 
from the beams, removal will likely be necessary every year once 
LHC starts full luminosity operation. This layer demands a 
particularly low contribution of dead material, including cooling
 services, to its radiation length.

Our studies are directed to cooling systems presenting the minimal
 possible material contribution in the tracker active volume: 
evaporative fluorocarbon cooling systems have proved preferable 
since they combine high heat transfer coefficients with very 
low circulating coolant mass (in the range 1 - 2 gm/second per 
 100 Watts to evacuate). Liquid refrigerant can be delivered 
directly to the detector in capillaries with inner diameters 
as small as 0.6 mm.  The fluorocarbon refrigerants are furthermore 
non-flammable, non-toxic, non-conductive and have zero ozone 
depletion potential.

We have constructed two evporative recirculators, and will present 
data from studies of  the cooling of representative prototype 
ATLAS Pixel and SCT detector thermo-structures. In some cases,
 these structures employ very high thermal conductivity 
Carbon-Carbon composites. Cooling data were taken with the 
following refrigerants, shown with their chemical formulae and 
saturated vapor pressures at a reference temperature of -15 deg C. 

	Per-fluoro-n-propane 	(C3F8)		2.2 bar (abs)
	Per-fluoro-n-butane	(C4F10)	        450mbar (abs)
	Tri-fluoro-iodo-methane (CF3I)		1.1 Bar (abs)
	Custom mixtures of C3F8 and C4F10 	target: 1  Bar (abs).

A target tube temperature of -15 deg C is chosen to accommodate 
thermal impedance effects between the silicon substrate and the 
flowing coolant. A target tube pressure of 1 bar  (abs) is chosen 
to allow the use of very low mass (typically 0.2 mm wall aluminum 
or CFRP composite) in various cross sections.

Heat transfer coefficients in the range 2000-4000 W/sq.m-Kelvin have 
been measured in a 3.6 mm inner diameter heated tube dissipating the
 full equivalent power (around 110 Watts) of  a barrel SCT detector 
"stave". Data will be presented for a range of power dissipations 
and mass flows in the fluids above. 

For custom fluorocarbon mixtures, thermo-physical  properties 
including enthalpy-pressure relations, vapor pressure, viscosity 
and speed of sound have been calculated with NIST/NBS software, and 
a sonar mixture analyzer has been constructed to aid in mixing.  
Results on mixture analysis and performance will be presented.

Finally, aspects of full scale evaporative cooling circulator design 
for the ATLAS experiment will be discussed, together with plans for
future development.


!!

We report on the development of evaporative fluorocarbon cooling for
the ATLAS Pixel and Semiconductor Tracking  (SCT) detectors from 
which it will be necessary to remove 50kW of heat from the detector 
cavity. 

We will present data from studies of  the cooling of representative 
prototype ATLAS Pixel and SCT detector thermo-structures. Cooling 
data were taken with per-fluoro-n-propane (C3F8), per-fluoro-n-butane
(C4F10), Tri-fluoro-iodo-methane (CF3I) and custom mixtures of C3F8 
and C4F10.

Heat transfer coefficients in the range 2000-4000 W/sq.m-Kelvin have 
been measured in a 3.6 mm inner diameter heated tube dissipating the 
full equivalent power (around 110 Watts) of  a barrel SCT detector
"stave". Data will be presented for a range of power dissipations
and mass flows in the fluids above. 

For custom fluorocarbon mixtures, thermo-physical  properties have 
been calculated, and a sonar mixture analyzer has been constructed 
to aid in mixing.  Aspects of full scale evaporative cooling 
circulator design for the ATLAS experiment will be discussed,
together with plans for future development.

!!