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

Results

1500 lpi (sigma/l=0.75)1000 lpi (sigma/l=0.5)500 lpi (sigma/l=0.25)

5.2_

_ ratiofield

feedbackion 03.1_

_ ratiofield

feedbackion 1_

_ ratiofield

feedbackion

Theoretical ion feedback

Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 10

Theoretical ion feedback

0

0,05

0,1

0,15

0,2

0,25

0,3

0,2 0,3 0,4 0,5 0,6 0,7 0,8

sigma/l

ion

fee

db

ack

Field ratio

Feedback 2D

Feedback 3D

Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 11

Hamburg, July5, 2002 P. Colas - Micromegas and wire TPCs 12