diego gonzález-díaz (zaragoza university and tsinghua university), stony brook, 04-oct-2012 1
TRANSCRIPT
Diego González-Díaz (Zaragoza University
and Tsinghua University), Stony Brook, 04-Oct-2012
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TPCs for rare event searches
CAST (axion searches)
NEXT-100 (neutrino-less double beta decay)
T-REX (directional dark matter)ArgonDM (dark matter)……….
XENON (dark matter)
EXO-200 (neutrino-less double beta decay) 2
Microbulk Micromegas technology
x [μm]
y [μ
m]
50 μm
5 μm
115 μm50 μm
Main characteristics:
• Simple and robust all-in-one kapton-clad 2-copper sandwich structure.
• Very low outgassing and high radiopurity (<30 μBq/cm2 for 235U, 238U, 232Th chains).
• Multiplication takes place in ‘cells’. Geometrical UV-photon quenching seems to provide an improved stability at high pressures.
• Granularity demands are easily scalable.
copper
copper
kapton
Comsol simulation for a typical field configuration at high electron transparency: Edrift/Eamp~0.01
Very high quality of pattern!
Hector Mirallas
S. Cebrian et al, Radiopurity of Micromegas readout planes, Astropart. Phys. 34 (2011) 354-359
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A sensible application for next-generation TPC experiments: ββ0-decay
Inverted mass ordering
Normal mass ordering
present ββ0-bounds constrained by ν-oscillations
cosm
olog
ical
con
stra
ints
A relevant figure of merit. Sensitivity to mββ: upper mass limit that can be claimed at 90%CL by a negative result in the next generation ββ0 experiments, as a function of their exposure.
end of inverted mass ordering landscape
Klapdor’s claim
4J. J. Cadenas et al., Sense and sensitivity of double beta decay experiments, JCAP(2011)
Why NEXT-100?
It covers a ‘technological gap’, providing simultaneously:
• Good topological information.
• Good energy resolution down to 0.5-1%FWHM@Qββ.
• Good prospects for scalability to 1Ton.
Canfranc
Underground Lab
2-blob ββ0 event at Qββ
background eventat Qββ
V. Alvarez et al., NEXT-100 Technical design report (TDR). Executive summary, 2012JINST 7 T06001 5
Why microbulk Micromegas?
• Flexibility for large area coverage.
• Possibly the only affordable technological concept that allows simultaneously for energy resolution and virtually unlimited tracking capabilities at high pressure and large areas (1-5m2).
Assets that will be surely useful for 1Ton experiments .
• Extremely radio-pure. .
• Not sensitive to the to signal .
• A priori compatible with electroluminescence .
Can improve resolution down to Fano factor.
Recover sensitivity to to.
work-line 1(this talk)
work-line 2(work in progress)
Why Xe-TMA?
1. They are known to form a Penning mixture, that is a desirable for energy resolution and maximum gain of gaseous detectors.
2. It increases drift velocity and reduces diffussion, recombination and attachment, enhancing the topological signatures.
• Not mature enough, specially for operation at high pressures.
work-line 1(this talk)
work-line 3(Dave Nygren et alat Berkeley)
1. Penning mixtures are known to reduce the Fano factor by 1/2-1/3.
2. If TMA fluoresces in the visible region one might expect to keep sensitivity to to and still being able to create electroluminescence (!).
J. Phys. Conf Ser. 309(2011)012006
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General purpose chamber for R&D studies
Main characteristics:
• Fully stainless-steel vessel, h=10cm, ϕ=16cm.• Designed for standing pressures in the range 0-15bar.• Mini-TPC with microbulk Micromegas as anode.• Bake out system + turbo pump, allowing for vacuum down to 10-6mbar
after full TPC assembly.• Outgassing below 5x10-5 mbar l/s before gas filling.• Gas recirculation through SAES FaciliTorr + Messer Oxysorb
getters.• Characterization of system composition with a Pfeiffer OmniStar mass
spectrometer.• O2 and H2O impurities estimated (indirectly) to be below 30ppms in
running conditions. O2 and H2O –meters will be incorporated soon.• Acquisition with:
1) Canberra 2004/2022 amplifying chain + multichannel analyzer Amptek MCA 8000A.2) Oscilloscope.
3.5cm
10 cm
Micromegas(50μm gap, 50μm holes, 115 μm pitch)
Field cage: h= 1-6cm
10MΩ/resistors
radioactive sourcegoes here
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Operation of Micromegas in Xe+TMA mixtures.General properties.
Good transparency even at 10bar. Only achievable through continuous gas purification.
Xe/TMA at ~98.5/1.5
Xe/TMA at ~98.5/1.5P = 8bar
Good description and good 1/√E scaling.
Diana C. Herrera
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Used for this study.
S. Cebrian et al., Micromegas operation at high pressures in Xenon-Trimethylamine, arXiv
Find these results at:
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too little too little
too little too little
too much too much
too much
too much
Penning at work-IDiana C. Herrera
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Penning at work-II
Necessary increase of the field is much weaker than E/p mainly due to:• Scaling of α = αo p/po
• To a smaller extent to the dynamics of the Penning effect.
Drastic increase in gain at constant field with increasing concentration of TMA!
-> Presumably due to the activation of Penning-type energy-transfer mechanisms
Field for a gain=300 1.5-2.5% (optimal range is extremely narrow!)
Diana C. Herrera
up to x30-50 increaseat constant field
< x3
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Strong exponential drop of the maximum achievable gain at high pressures.
-> Possibly due to the increased space charge at constant gain for high pressure. Is it possible to further improve?. Where is the limit?.
Xe/TMA at ~98.5/1.5
Xe/TMA at ~98.5/1.5
Energy resolution degrading at high pressure:
-> Operation at a much reduced E/p (down to 1/3-1/4) cools the electron swarm at high pressures.
22.1 keV
Pressure scan for Penning-optimized Xe/TMA mixtures (~97.5/2.5)
x400
Diana C. Herrera
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pure Xe, C. Balan et al., 2011 JINST 6, P02P006
pure Xe, T. Dafni et al., J. Phys.: Conf. Ser. 309 (2011) 012009 (similar setup)
Xe/TMA, these measurements
𝜎𝑄𝑋𝑒𝛽𝛽 0
𝑄𝑋𝑒 𝛽𝛽0(2.48𝑀𝑒𝑉 )=0.9 % FWHM
Diana C. Herrera
within a factor x3 of the Fano factor limit for pure Xenon (0.27%FWHM)
Best energy resolutions for Penning-optimizedXe/TMA mixtures (~97.5/2.5)
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pure Xenon
E [V/cm/bar]
v d [
cm/μ
s]Francisco IguazPreliminary modeling and scope
for large area TPCs
Preliminary comparison with TMA rather reasonable(despite TMA it is rated 3* in Magboltz at the moment)
241Amα
γ
Si-diode for triggering (to)
MM
drift region can be imaged
Region of maximum transparency in Xe/TMA mixtures
pushing the Magboltz-truth a step further…
x 4-5
E [V/cm/bar]
pure Xenon
DT
[μm
/cm
1/2 b
ar1
/2]
x 10!
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Preliminary results with a medium size TPC
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time-line
arrival pumping and bake-out system
field-cage
0.8cmx0.8cm pixelized microbulk Micro-Megas
T2K electronics (based on AFTER chip)
35cm30cm
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First results for 1/4th of the readout plane (proof of principle)
57Co
241Am
Xe/TMA 96.3/3.7
Edrift = 170 V/cm,Eamp = 54 kV/cm,P = 1 bar
Unfortunately connectivity not yet perfect:~10/270 pixels are not properly connected.
We have recovered from a design problem by means of a tedious capacitive procedure that ensures a high (yet not perfect) connectivity. Work in progress.
Laura Segui
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𝜎𝑄𝑋𝑒𝛽𝛽 0
𝑄𝑋𝑒 𝛽𝛽0(2.48𝑀𝑒𝑉 )=3 % FWHM
Next steps:
• Channel equalization
• Optimization of pedestal subtraction.
• Event filtering (for instance, sudden noise explosions).
• Improved fiducialization.
• Specially, development of an adequate analysis for this new stage.
Energy resolutionLaura Segui
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some events at around 60keV Laura Segui
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some events at around 90keV
x-ray candidate
Laura Segui
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some events at around 120keV
x-ray candidate
x-ray candidate
Laura Segui
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Conclusions
• Microbulk micromegas in Xe-TMA mixtures is an appealing technological option for rare event searches.
• The Penning transfer mechanisms seem to be optimally active within a mild 1-3% TMA concentration range, therein virtually un-affecting the experiment exposure (Xenon).
• Operation at a gain x400 and at 0.9%FWHM@Qββ,Xe at 10bar is possible.
• We would like to study the mixture more systematically with a new batch, specially the maximum gain, reproducibility and stability.
• Preliminary comparisons with Magboltz (TMA rated 3*) suggest that a dramatic factor x10 reduction of the transverse diffusion is within reach. Further studies resorting to event topology are required to validate this estimate.
• In order to make this option competitive, we are considering various approaches to determine the t o (an obvious one being TMA-fluorescence)
• Proof of principle demonstrated for a medium size ϕ=30cm, h=35cm TPC. Tracks can be clearly reconstructed, albeit a crude value for the energy resolution is about a factor x3 worse than for the case of un-segmented readout in small chambers.
• However, a large effort is still needed in order to achieve competitive results for the complete medium-size TPC at 10bar.
stay tuned!21
The team
• Igor Irastorza• Hector Gomez• Asuncion Rodriguez• Juan Castel• Hector Mirallas• Alicia Diago• Laura Segui• Theopisti Dafni• Diego Gonzalez-Diaz• Diana Carolina Herrera• Susana Cebrian• Gloria Luzon• Alfredo Tomas• Esther Ferrer-Ribas (CEA-Saclay)• Iannis Giomataris (CEA-
Saclay)
and
Rui Oliveira (CERN)Antonio Teixeira (CERN)
and the support of the CERN workshop
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BACKUP
Status of NEXT-I(MM) on the last collaboration meeting (Nov11)
In a nut-shell
• Bake-out and pumping systems fully installed:
Gas tightness: <1mbar/day (T-corrected) at 11bar during 10daysVacuum: ~10-6 mbar after bake-out Out-gassing: <10-5 mbar l/s
• The HV for the 35cm-long drift region proved to be Paschen-tight up to 7kV@1bar and 26kV@8bar in pure Ar. Common wisdom suggests that for Xe it should be usually better.
• Mass-spectrometer working steadily. Calibration factors in Xe-TMA mixtures obtained.
• Re-circulation system installed. Not commissioned.
• T2K electronics connected. Not thoroughly tested. Analysis software still in early stage.
• Four pixelized μ-bulk MicroMegas (Φ=28cm) installed.
Status of NEXT-I(MM) todayFinal system pressure
Levels down to Pf=6x10-6 mbar achieved in the present system after ~72h heating time at 130deg.
However, x10-100 worse vacuum levels were used during most of measurements presented here.
Status of NEXT-I(MM) todayOut-gassing
Levels below Og=3x10-4 mbar l/s achieved in the present system.
From experience it will be much better after bake-out. Unfortunately it was not measured.
Gas tightness
After correcting for temperature variations: Previously: ΔP<1mbar/day at 11bar for 10 days (limited by pressure-meter).Presently: ΔP<3mbar/day at 1bar for 3 days (limited by pressure-meter).
No concern regarding gas leakage but more systematic measurements will come.
Jan-2010
Status of NEXT-I(MM) today
Electrical insulation
Xe-TMA mixtures much less Paschen-tight than pure Ar (Penning effect at work!), by~ x2.
The drift fields are still comfortable and transparency seems to be achievable.
Strong limitation for systematic study of attachment. An extra factor x3 will be handy
Status of NEXT-I(MM) today
If it is Paschen-tight for Xe-TMA, possibly ok for most practical mixtures.
From D. C. Herrera
~x2
really?? 0%TMA2%TMA
Chamber operation (I) Status of NEXT-I(MM) today
After grounding optimization and soft RC-filtering, signal is visible at Edrift= 160 V/cm/bar, and EMM = 58kV/cm (Xe-TMA ~ 98/2) with the following parameters:
• Mesh signal with single amplifying stage (CANBERRA-2004, tfall~50μs for δ-impulse excitation):
Eth~30keV, rmsEnoise~10keV (fairly stable)
• Mesh signal with double amplifying stage (CANBERRA-2004 + spectroscopic amplifier, gaussian response tshaping=8μs):
Eth~10keV, rmsEnoise~3keV (fairly stable)
• Pixel signals with T2K electronics (tshaping=2μs):
Eth~1.5keV, rmsEnoise~0.75keV (unstable)very seldom, even cosmic-ray triggered events can be directly seen from the mesh
external trigger signal
mesh signal
180 μs
System problems galore: -> cross-talk-> noise-> HV in 2 MMs unproperly applied-> dead pixels-> un-perfect cable-connector contact
Micro-bulk MicroMegas produces
nice signals in the scope.
electronics situation