R&D activities on a double phase pure Argon THGEM-TPC A. Badertscher, A. Curioni, L. Knecht, D. Lussi, A. Marchionni, G. Natterer, P. Otiougova, F. Resnati, A. Rubbia, T. Viant Institute for Particle Physics, ETH Zurich CERN, 2 November 2009

Outline Introduction Working principle of a THGEM-TPC 3l test setup The Large Electron Multipliers (THGEMs) Measurements ▫1.6 mm thickness ▫1 mm thickness Conclusion and future plans 2

Introduction Development of a new charge readout technique for pure argon TPC, that allows signal amplification. Applications: Neutrino and proton decay experiments (low rate, gain ≥ 10, good stability, very large area, production). Direct Dark Matter search (very low rate, gain > 100, reasonably reliable). Challenges: High gain in pure argon. Discharge-free operation at lower gain. Large area production. 3

Working principle of a THGEM-TPC 4 Free e - drift in LAr towards liquid-vapour interface Anode Cathode THGEM2 THGEM1 LAr level Multiplied charge induces signals on the segmented electrodes of top THGEM and anode. e - are extracted to the vapour via extraction grids (E liq > 2.5 kV/cm) e - undergo multiplication in double stage THGEM. Extraction grids 4

3l test setup (located at CERN blg182) 5 Signal plane 30 kV feedthrough Signal cable HV connector TPB coated Level meters

Large Electron Multipliers (THGEMs) 6 Produced by standard PCB methods (MULTIPCB Germany) Double-sided copper-cladded (gold-plated) FR4 plates. Precision holes by drilling. Top THGEM2 plane and anode segmented: 2x16 (6 mm) str. Best produced THGEM selected. THGEM1 THGEM2 Anode PCB thicknesses0.8 mm, 1.0 mm, 1.6 mm Hole diameter500 μm Hole pitch800 μm Dielectric rim thickness50 μm holes not centered edges Discharge propagation 6

Double stage 1.6 mm THGEM (I) 7 55 Fe and 109 Cd sources positioned below the cathode grid. Deposited energy is proportional to the sum of the involved strips. Both anode and THGEM signals can be used for the energy evaluation. 55 Fe (full peak) ~5.9 keV 6.9 kBq 29.3% FWHM 55 Fe (escape peak) ~2.9 keV 6.9 kBq 42% FWHM 109 Cd ~22.3 keV 0.5 kBq 24.7% FWHM Operation in pure argon gas: room temperature, 1.2 bar. THGEM electrodes Anode electrodes THGEM electrodes Anode electrodes Typical cosmic muon track effective gain ~ E (kV/cm) Anode THGEM THGEM 2 ~14 THGEM 2 -THGEM THGEM 1 ~14 Drift0.4

Double stage 1.6 mm THGEM (II) 8 Effective gain ~10 Raw images S/N ≈ 800/10 THGEM electrodes Anode electrodes THGEM electrodes Anode electrodes E (kV/cm) Anode THGEM THGEM 2 ~26 THGEM 2 -THGEM THGEM 1 ~26 Drift0.7 Operation double phase (liquid/vapour) pure Argon: 1 bar, 87.3 K

Single stage 1 mm THGEM 9 real data Total mean value = 64 fC/cm gain ~ 6 Operation double phase pure Argon: 1 bar, 87.3 K E (kV/cm) Anode THGEM2 THGEM36 Drift0.5 Measurements done with a THGEM tested in air selection of “good” THGEMs (quality control) cleaning process (could increase voltage after some sparks) configuration:

To Do 1.Adapt setup in order to test new THGEMs efficiently (new anode, allowing readout of two independent coordinates). 2.Optimization of THGEM geometry for high and low gains (rim size, thickness, hole size, pitch, …) 3.Understanding production and quality control procedures. 4. feasibility on producing (many) large size THGEMs (O(1 m 2 ) each). 10

Projective anode 11 pitch600 μ m exposed electrode (w/t)(120 μ m/30 μ m) covered electrode (w/t)(500 μ m/ 30 μ m) kapton layer50 μ m readout pitch3 mm (5 strips connected) Collected charge on the anode is shared between two perpendicular strips Decouple amplification and readout stages. Symmetric X-Y readout. No segmented electrodes on the THGEM No capacitors connected to the THGEM 50% Optimal geometry: 50% of the collected charge on each view Field computations done with COMSOL COMPASS Experiment at CERN

Geometry optimization 12 Important geometry parameters: PCB thickness Hole diameter Dielectric rim Hole pitch (?) Copper thickness (?) Single or double THGEM stage Sensitive parameters to characterize the THGEM behaviour: Electric field configuration Electron diffusion Transparency Gain Maximum field in the vicinity of the electrodes Tools: Comsol Magboltz Garfield

Conclusions 12 We built a 3l pure argon double phase THGEM-TPC. Operated in different configuration: Single / double multiplication stage. Pure argon gas / double phase (liquid-vapour). 1.6 mm thick / 1 mm thick. What we need is: Definition of optimal geometry for our purposes. Standard procedures for production and tests. Extensive tests towards very large area and/or high gain detectors