Cooling detectors in particle physics
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Transcript of Cooling detectors in particle physics
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Cooling detectors in particle physicsGavin Leithall
CCLRC Rutherford Appleton Laboratory
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Gavin Leithall, RAL Placement Conference 2006 2
CCLRC Rutherford Appleton Laboratory
• Government funded central research laboratory which supports a wide range of university research activities
• Located in Oxfordshire• I work in the Particle
Physics Department on the vertex detector for the International Linear Collider
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Gavin Leithall, RAL Placement Conference 2006 3
The International Linear Collider
• Will collide beams of electrons and positrons with energies from 91 - 500 GeV (upgrade to 1000 GeV)
• Scheduled to begin operation in 2015
• Will have a total length of about 30 km
• Intended to complement the Large Hadron Collider by being a more precise measuring tool
• Together they are hoped to discover new particles and test theories (e.g. the Higgs Boson and Supersymmetry)
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Gavin Leithall, RAL Placement Conference 2006 4
What is a vertex detector?
• Collisions produce a spray of high energy particles
• A large detector is built around the beam pipe to work out what happened in the collision
• The vertex detector is the one closest to the collision point
• Used to reconstruct particle tracks to determine their production point (vertex)
• Required to have little material to minimise scattering
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Gavin Leithall, RAL Placement Conference 2006 5
Linear Collider Flavour Identification
• LCFI (my project group) is designing the vertex detector for the ILC
• The detecting elements called ladders are layered in concentric barrels
• The ‘hits’ generated when a particle passes through enable track reconstruction
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Gavin Leithall, RAL Placement Conference 2006 6
Detector Technology
• The main technology being developed by LCFI is the Column Parallel Charge Coupled Device (CPCCD)
• These are composed of tiny pixels which accumulate charge when particles pass through
• Similar to the CCDs in digital cameras, but with a much faster readout
• The readout chips are placed at the end of the ladders
“Classic CCD”Readout time NM/Fout
N
M
N
Column Parallel CCDReadout time = N/Fout
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Gavin Leithall, RAL Placement Conference 2006 7
Detector Cooling
• The vertex detector will produce heat which will need to be removed.
• It will also need to be maintained at a constant operating temperature (possibly as low as -70 deg C)
• It therefore needs a cooling system to meet these requirements
• Conventional cooling systems would add material to the detector volume, so are not ideal
• Blowing cold gas from the ends of the detector is a possible solution
• My project is to investigate the effectiveness of this
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Gavin Leithall, RAL Placement Conference 2006 8
Cooling Test Rig• Built a system to produce a controlled nitrogen gas flow with
– Variable temperatures (-100oC to 20oC)– Variable flow rates (0-20 litres / min)
• Built a system to read temperatures from platinum resistors• Designed programs to enable remote control of both of these
systems
Gas Massflow
controller
Heat exchangerFilter
Regulator
HeaterThermocouple
Liquid nitrogen
ControlBox
To
Computer
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Gavin Leithall, RAL Placement Conference 2006 9
Detector model
• A quarter barrel model was decided upon because it would be easier to build than a full barrel, while maintaining all the essential physics.
• It has:– Stainless steel ladders and aluminium end-plates– Resistors in the place of the readout chips to simulate
heating– Platinum resistors at various positions within the
quarter barrel
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Gavin Leithall, RAL Placement Conference 2006 10
Quarter barrel construction
End plate
Inlet Outlet
Side view of quarter barrelResistors
Ladders
End plates
GasIn
GasOut
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Gavin Leithall, RAL Placement Conference 2006 11
The Physics
Quarter barrel
Temperature = Tq
Gas In
Temperature = Ti
Flow rate = v
Gas Out
Temperature = To
Flow rate = v
Heating power = Pi
Power lost to surroundings = Ps
Surrounding temperature = Ts
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Gavin Leithall, RAL Placement Conference 2006 12
Formulation of the problem
• Pg (power gain of gas) can be calculated by
Pg = cv (To – Ti) (c = specific heat capacity)
• Using energy conservationPi = Ps + Pg
• Using Newton’s Law of CoolingPs = L (Tq – Ts) (L = thermal loss coefficient)
• A graph of (Pi - Pg) against Tq should– Be a straight line with gradient L
– Pass through Pi – Pg = 0 when Tq = Ts
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Gavin Leithall, RAL Placement Conference 2006 13
• This graph
– Is a straight line with a gradient giving L ~ 0.26 W / deg C
– Suggests a room temperature of Ts ~ 19 deg C
(P i - P g ) against T q (5 litres / min)
y = 0.26x - 4.97
-4
-2
0
2
4
6
8
10
10 20 30 40 50
T q (deg C)
(Pi
- P
g)
(W)
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Gavin Leithall, RAL Placement Conference 2006 14
A hypothesis
• I can make a hypothesis about the form of Pg:
Pg = hv (Tq – Ti)
– h is the heat transfer coefficient, assumed constant, but could be a function of v, Tq, Ti
• This can be tested by plotting graphs of Pg against the other variables
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Gavin Leithall, RAL Placement Conference 2006 15
P g against (T q - T i )
-2
0
2
4
6
-5 0 5 10 15 20 25
(T q - T i ) (deg C)
Pg (
W)
20 litres / min17.5 litres / min15 litres / min12.5 litres / min10 litres / min7.5 litres / min5 litres / min
• This graph gives strong support to the hypothesis that Pg is proportional to (Tq – Ti)
• By plotting the gradient (i.e. Pg / (Tq – Ti)) of each line against its flow rate, the hypothesis can be tested further
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• This graph supports the hypothesis that Pg / (Tq – Ti) is proportional to v
• The gradient of this graph gives h ~ 0.022 W / deg C / (litre/min)
(P g /(T q - T i )) against v
y = 0.022x - 0.015
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0 5 10 15 20
v (litres / min)
Pg
/(T
q -
Ti)
(W
/de
g C
)
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Gavin Leithall, RAL Placement Conference 2006 17
Conclusions
• Thermal loss coefficientL ~ 0.26 W / deg C
• The form of Pg is
Pg = hv (Tq – Ti)• Heat transfer coefficient
h ~ 0.022 W / deg C / (litre / min)• Maximum Pg ~ 5 W when v = 20 litres /
min and (To – Ti) ~ 11 deg C
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Gavin Leithall, RAL Placement Conference 2006 18
Summary
• Testing the effectiveness of gaseous cooling for the vertex detector for the International Linear Collider
• Results so far show behaviour that is consistent with predictions
• Move on to investigate new configurations– More inlets, and with different positions– Different sizes and angles of inlets
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Gavin Leithall, RAL Placement Conference 2006 19
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Gavin Leithall, RAL Placement Conference 2006 20
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• Plotting the value of Pg predicted by the hypothesis against the value obtained by the earlier measurement provides a useful crosscheck
• This yields a graph which provides good support for the hypothesis
Predicted value of P g against its measured value
y = 1.00x + 0.02
-2
-1
0
1
2
3
4
5
-2 -1 0 1 2 3 4 5
Predicted value of P g (W)
Mea
sure
d v
alu
e o
f Pg
(W)