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Micromegas-TPC development for rare event detection Leila Ounalli Neuchâtel University 3 rd symposium on Large TPCs for low energy rare event detection,

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Presentation on theme: "Micromegas-TPC development for rare event detection Leila Ounalli Neuchâtel University 3 rd symposium on Large TPCs for low energy rare event detection,"— Presentation transcript:

1 Micromegas-TPC development for rare event detection Leila Ounalli Neuchâtel University 3 rd symposium on Large TPCs for low energy rare event detection, Paris, December 2006.

2 Restrictive conditions for rare event detection Big detector mass (high pressure), Radioactive background as low as possible (underground laboratory + radio- pure components), Good energy resolution (FWHM), High gas gain (collected charge / initial charge).

3 Cones Sticks Optic nerve Brain (analyze, classify, memorize) The eye and the retina Light

4 Micromegas « Compact » The TPC and Micromegas 1mm spacers Woven wires (gamma, RX, UV …) Cathode Grid Amplification (> 50 m) Micromesh E d ~ 200V/cm E a ~ kV/cm Anode Conversion + Drift e- analyze, classify, memorize. Dave Nygren (1970)

5 The Neuchâtel mini-TPC miniTPC(10X20cm) The source position. max of d C-g =18cm E drift The drift electric field choice: E d = 200 V.cm -1.bar -1 The gap dimension (d grille-anode ): ( µm) High pressure + low voltages The quencher choice and %: - Xe + (CF 4, isobutene): double beta decay - CF 4 + (Xe, Ar): low E

6 Why we replace the MWPC by the Micromegas micro-pattern?

7 Contours of V near the amplification gap x10 -3 Y-Axis[cm] X-Axis[cm] x Comparison with MWPCs Y-Axis[cm] X-Axis[cm] rectilinear: E uniform: // of electrons. (R E + ξ ) good 6keV with 1 bar of CF 4 ) Circular form: Charge deviation from their trajectories. (R E + ξ ) bad 6 keV)

8 The increase of the gap amplification permits a good charge collection at high pressure C G Amplification (75, 250) m Micromesh A Conversion + Drift How to operate the Micromegas- TPC at higher pressures?

9 Why we choose a gap of 250 µm? 10 4 bar 75 µm 250 µm

10 How to improve the charge collection in Xe? A small CF4 addition is sufficient

11 increases the electron drift velocity in Xe. CF 4 is the best additive for Xe CF 4 addition: reduces longitudinal and transversal diffusions. improves the charge collection. P: 1.00 atm, E d =200 V.cm -1.atm -1, Gap: 100 µm Xe-CF 4 (2, 5, 10, 50%) Xe-isobutene (2%)

12 Optimal parameters E d = 200 V.cm -1.atm -1. E d = 200 V.cm -1.atm -1. Gap: 250 µm. Gap: 250 µm. Gas: Xe(98)CF 4 (2) Gas: Xe(98)CF 4 (2) Make preliminary tests in the mini-TPC of Neuchâtel ( 241 Am). Make preliminary tests in the mini-TPC of Neuchâtel ( 241 Am).

13 The Xe(98)CF 4 (2) gain and the energy 60 keV at different pressures 1.05 atm 2.01 atm 3.00 atm 4.00 atm Gas: Xe(98)CF 4 (2) E d = 200V.cm -1.atm -1 Source: 241 Am (37kBq) 8.05 keV Cu-K α keV Xe-K α 10 3

14 Pulse height spectra of 241 Am source in Xe(98)CF 4 (2) with a Micromegas-TPC 8 keV G keV G keV G keV G 1340 Cu-K α Xe-K α Pulser 1 bar 3 bar

15 Radio-pure and radio-active components

16 The Germanium detector : gamma spectrometry Ge (400 cm 3 ) Vue-des-Alpes

17 Kevlar Resin-epoxy 2614 x10 4 Lead. Copper (TPC+rings+cathode). Glue (araldite). Grid (Stainless steel). insulators (delrin, teflon) Radio-pure Printed-circuit (resin-epoxy). Resistances (ceramic). Solder ( 210 Pb) Radio-active

18 Gotthard results

19 The Gotthard TPC TPC (60X70cm) - Find the sources of noise: Measure the radioactivity of components using a Ge detector Vue-des-Alpes. Estimate the radioactive background of the TPC. Gotthard-TPC low energies ( 241 Am, 133 Ba). diameter: 50 cm Gap: 250 µm Micromegas

20 The compact Micromegas is tested before being installed

21 Micromegas (50 cm of diameter): (Am and Ba) sources effect 60 keV ( 241 Am) 81 keV ( 133 Ba) The Compton plateau ( 133 Ba) 60 keV ( 241 Am)

22 The behavior of the background registered in the Gotthard TPC 1 bar of P10 gas 3 bar of P10 gas 46 keV

23 Conclusions We improve the energy resolution when we replace the MWPC with a Micromegas. Xe(98)CF 4 (2): ideal for double beta search: high gains, good efficiency, good (energy, spatial and time) resolutions. Increase the gap (amplification): permits a good charge collection in Xe and go up at higher pressures. Micromegas in compact: (50 cm) showed high efficiency and good energy resolution.


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