Hamburg, July5, 2 002 P. Colas - Micromegas and w ire TPCs 1 Micromegas TPC and wire TPC Micromegas TPC and wire TPC First measurements in a First measurements in a magnetic field magnetic field • A small-gap wire chamber TPC and a Micromegas A small-gap wire chamber TPC and a Micromegas TPC (both 1cm drift) have been put in 1-2 TPC (both 1cm drift) have been put in 1-2 Tesla magnetic field Tesla magnetic field • Feedback has been measured and progress on Feedback has been measured and progress on simulation has been made. simulation has been made. P. Colas 1 , Y. Giomataris 1 , J. Jeanjean 2 , V. Lepeltier 2 , J. Martin 1 , A. Olivier 1 1) DAPNIA Saclay 2) LAL Orsay
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Micromegas TPC and wire TPC First measurements in a magnetic field
Micromegas TPC and wire TPC First measurements in a magnetic field. P. Colas 1 , Y. Giomataris 1 , J. Jeanjean 2 , V. Lepeltier 2 , J. Martin 1 , A. Olivier 1 1) DAPNIA Saclay 2) LAL Orsay. - PowerPoint PPT Presentation
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Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 1
Micromegas TPC and wire TPCMicromegas TPC and wire TPCFirst measurements in a magnetic fieldFirst measurements in a magnetic field
Micromegas TPC and wire TPCMicromegas TPC and wire TPCFirst measurements in a magnetic fieldFirst measurements in a magnetic field
• A small-gap wire chamber TPC and a Micromegas TPC A small-gap wire chamber TPC and a Micromegas TPC
(both 1cm drift) have been put in 1-2 Tesla magnetic (both 1cm drift) have been put in 1-2 Tesla magnetic
field field
• Feedback has been measured and progress on Feedback has been measured and progress on
simulation has been made.simulation has been made.
P. Colas1, Y. Giomataris1, J. Jeanjean2, V. Lepeltier2, J. Martin1, A. Olivier1
1) DAPNIA Saclay 2) LAL Orsay
Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 2
ExperimentExperimentExperimentExperiment
We ran end of June with a small-gap TPC and a micromegas TPC
The primary ionization was provided by
•an 55Fe source (25 MBq, gain typically 100,000) for the wire chamber
•a 90Sr source (1 GBq, gain a few 100) for the micromegas
The currents from the supplies are monitored, allowing to measure the feedback.
Mainly the results from micromegas are shown here.
The results from the wire chamber are: no significant effect of the magnetic field, though simulation predicts an increase of 50% on the feedback from 0 to 2 T. To be understood.
Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 3
SETUPSETUPSETUPSETUP
Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 4
detector
2T Magnet
High voltage and monitoring
Ar:CH4 90:10
Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 5
55Fe
0 +2KV 0 - 300 V
Cathodegridwires
90Sr
0 -340 V - 640 V
Cathodemeshanode
2mm 2mm 1cm 50 m 1cm
Small-gap wire TPC Micromegas TPC
Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 6
Feedback : theory and simulationFeedback : theory and simulationFeedback : theory and simulationFeedback : theory and simulation
We (Jerôme Martin) carried out simulations with 2D geometry to:
•Understand the feedback
•look at the effect of the magnetic field : predicts 50% increase in the wire chamber, and no effect in micromegas
Ideally, the feedback is given by the inverse field ratio E(drift)/E(amplif)
It is less good (i.e. larger) if the dispersion in the avalanche is small with respect to the hole pitch
The two important quantities are : the dispersion after 50 microns and
l, the pitch. The hole size does not matter when the field ratio is high
Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 7
Theoretical ion feedback
Hypothesis on the avalancheGaussian diffusionPeriodical structure
l 2*sigma
Avalanche Resolution
Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 8
Theoretical ion feedback
CalculationsSum of gaussian diffusions
2D 3D
Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 9