Operation of a double phase pure argon Large Electron Multiplier Time Projection Chamber A. Badertscher, L. Knecht, D. Lussi, A. Marchionni, G. Natterer, P. Otiougova, F. Resnati, A. Rubbia, T. Viant Institute for Particle Physics, ETH Zurich, Switzerland 11th Pisa meeting on advanced detectors - Isola d’Elba 26 May 2009 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 Introduction Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions The detector presented in this talk is a liquid argon based Time Projection Chamber capable of charge multiplication. Possible applications are: Giant detector for neutrino physics, proton decay and DM search A. Rubbia, arXiv:hep-ph/0402110, 2003 Dark Matter imaging detector - A. Rubbia, J. Phys. Conf. Ser. 39 (2006) 129 Recent articles: A. Badertscher et al., arXiv:0811.3384, 2008 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

Double phase pure Ar LEM-TPC Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Double phase pure argon LEM-TPC is a tracking and a calorimetric device that allows the amplification and the readout of charge signals from an Ar TPC working in double phase conditions. Anode Free e- drift in LAr towards liquid-vapour interface. e- are extracted to the vapour via extraction grids (Eliq ≈ 3kV/cm). e- undergo multiplication in double stage LEM. Multiplied charge induces signals on the segmented electrodes of top LEM and anode. LEM2 LEM1 LAr level Extraction Grids Cathode 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 LEM working principle Electron drift lines in double phase argon LEM-TPC Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Gain ~1000, 2x = 2mm:  = 35 cm-1 From MAGBOLTZ: E ≈ 31 kV/cm Anode LEM2 x LEM1 e- are driven into the first LEM holes. Townsend multiplication mechanism (G = ex,  = Ape-Bp/E). Double stage of multiplication: increase the gain maintaining low fields in each LEM. Both LEMs were operating at the same voltage difference: G = GLEM1GLEM2 = GLEM2 = e2x. 3D view and energy measurement. Grids Cathode 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 Setup overview Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Input purification cartridge Purification circuit Detector HV supply External bath Readout electronics Vacuum pumps 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 LEM-TPC in detail HV connector Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Level meters Signal cable Signal plane 30 kV feedthrough TPB coated 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

Double stage LEM with anode Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Anode LEM2 10x10 cm2 6 mm strips Produced by standard PCB methods. Double-sided copper-clad FR4 plates. Precision holes by drilling. Thickness: 1.6 mm. Amplification hole diameter: 500 m. Distance between centers of neighbouring holes: 800 m. Segmented anode and LEM2 top plane: 2x16 strips 6 mm wide. 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 Argon purification Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Two purification stages Input LAr purification: Custom made cartridge for LAr purification at detector input. GAr purification circuit: Heating resistors evaporate LAr in the detector. A metal bellow pump pushes GAr into a flow meter and SAES getter (~48h to recirculate 1 volume). Purified GAr condensates into the detector volume. Filling procedure: The detector vessel is evacuated to 10-6 mbar. The detector is filled with pure GAr (99.9999%) @ 1 bar. The external bath is filled, the detector cooled down while recirculating GAr through SAES getter. The detector is filled with LAr through custom made cartridge. 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 Readout electronics Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Custom made front-end charge preamp + shaper 2 channel per chip rise time 0.6 s, fall time 2 s Inspired from C. Boiano et al. IEEE Trans. Nucl. Sci. 52 (2004) 1931 In collaboration with CAEN, ADC and DAQ system development 12 bit 2.5 MS/s flash ADC. Programmable FPGA. Channel-by-channel trigger and global “trigger alert”. 256 channel crate. Chainable optical link. 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

Operation in pure gas argon Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Pure argon gas operation, room temperature, 1.2 bar 55Fe and 109Cd sources positioned below the cathode grid 55Fe (full peak) ~5.9 keV 6.9 kBq 29.3% FWHM Deposited energy is proportional to the sum of the involved strips Both anode and LEM signals can be used for the energy evaluation 55Fe (escape peak) ~2.9 keV 6.9 kBq 42% FWHM 109Cd ~22.3 keV 0.5 kBq 24.7% FWHM The gain is measured from 109Cd peak. The electric field is calculated as the ratio of V across the LEM and the LEM thickness. 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

Operation in pure gas argon Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Pure GAr (Ar-60) Room temperature 1.2 bar Gain ~1000 LEM electrodes Anode electrodes LEM electrodes Anode electrodes E (V/cm) Anode LEM2 760 LEM2 ~14 103 LEM2 LEM1 590 LEM1 Drift 420 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

Operation with LEMs in liquid Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions LEM-TPC can be operated with the LEMs completely immersed in LAr without charge amplification. LAr level can be maintained between the two LEMs allowing the multiplication only in the second LEM. Proof of LEMs transparency Gain = 1 Noise reduction via digital filter S/N ≈ 80/5 Anode electrodes LEM electrodes Anode electrodes LEM electrodes E (kV/cm) Anode LEM2 2.1 LEM2 ~27 LEM2 LEM1 1.7 LEM1 Drift 0.7 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

Operation in double phase Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Charge multiplication occurs in argon vapour: 87 K, 1 bar, ~3.4 denser than at STP LEM electrodes Anode electrodes Radioactive sources were not suitable for cryogenic operation LEM electrodes Anode electrodes Gain ~10 Raw images S/N ≈ 800/10 E (kV/cm) Anode LEM2 2.1 LEM2 ~26 LEM2 LEM1 1.5 LEM1 Drift 0.7 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

Preliminary analysis of cosmic tracks Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions Gauss-convolved Landau function fitted to the dQ/dx distribution (corrected for the free electron lifetime) 3D reconstruction of each cosmic muon track. Energy evaluation from anode electrodes signals. In LAr @ 0.5-1 kV/cm MIP muon releases ~10 fC/cm Gain ≈ 10 Resolution ≈ 12% 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 Argon purity monitor Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions LAr purity is monitored from the time constant of the slow scintillating component (not sensitive if the purity is high) from charge signal of long muon tracks Improvement of the electron lifetime continuously purifying the argon e [O2] = 300 ppb s [O2] ≈ 7 ppb 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 PMT signal Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions PMT (TPB-coated) for monitoring extraction and LAr purity Typical PMT signal from crossing muon Drift time Proportional light Scintillation: primary light due to muon crossing the argon. Proportional: produced by electrons in the high extraction field in the gas phase. Scintillation light 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 Electron velocity Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions From the maximal drift time we evaluated the electron velocity as a function of the drift field: Two different data sets and the empirical function (no fit) W. Walkowiak, Nucl. Instr. and Meth. A 449 (2000) 288 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009

11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009 Conclusions Introduction Double phase pure argon LEM-TPC LEM working principle Setup overview LEM-TPC in detail Double stage LEM Ar purification Electronics Operation in GAr Operation in LAr Operation in double phase PMT signal Conclusions A novel kind of liquid argon TPC was developed and operated: double phase pure argon LEM-TPC acts as an imaging and calorimetric detector capable of higher energy sensitivity than standard LAr-TPC. The detector can operate in pure argon gas as well as in liquid, simulating a standard LAr-TPC. In double phase operation a stable gain of 10 was achieved and cosmic muon tracks observed, higher gains are under study. Outlook: Ongoing further characterization of 3 lt LEM-TPC. Design and construct 1 m2 LEM for 1 ton LEM-TPC for ArDM experiment. This work represents an important milestone in the realization of a very long drift (cost effective) LAr detectors for next generation neutrino physics, proton decay experiments and direct DM search with imaging device. 11th Pisa Meeting on advanced detectors - Isola d’Elba 26 May 2009