Commissioning of LArGe Gas / Liquid A. Gangapshev M. Heisel A. - PowerPoint PPT Presentation

Commissioning of LArGe Gas / Liquid A. Gangapshev M. Heisel A. Klimenko S. Schönert A. Smolnikov G. Zuzel GERDA Collaboration Meeting, 1 LNGS, 1-3 March 2010 GERDA Collaboration Meeting, LNGS, March 2010

Reminder: The LArGe Setup operation of naked HPGe-crystals in LAr using Ar-scintillation light as veto & for background diagnostics: Lock: Can house up to 3 strings (9 detectors) 9 PMTs: For the detec- tion of Ar-scintillation reflector foil & PMT wavelength shifter VM2000 + WLS ~450 nm Cryostat with LAr: Volume: 1000 Ar scintillation 128 nm liter Shield: Cu 15cm, Pb 10cm, Steel 23cm, PE 20cm 2 GERDA Collaboration Meeting, LNGS, March 2010

History Overview Since Last Meeting  last meeting: first scintillation light in GAr presented  light degradation discovered  nov 09: 1st LAr filling of cryostat  light quenched  nov - jan 10: investigations & cryostat modifications  feb 10 2nd LAr filling  light is stable! 3 GERDA Collaboration Meeting, LNGS, March 2010

Light Degradation Measurements in GAr october `09: after last meeting 800 700 600 light yield [a.u.] 500 400 300 GAr at room temperature 200 GAr at room temperature Gd-148 100 source 0 0 1 2 3 4 5 6 time [h] 4 GERDA Collaboration Meeting, LNGS, March 2010

Light Degradation Measurements in GAr october `09: prior to 1st filling with LAr 800 700 600 light yield [a.u.] 500 cold GAr at -73°C to -90°C 400 300 200 GAr at room temperature Gd-148 100 source 0 0 1 2 3 4 5 6 time [h] 5 GERDA Collaboration Meeting, LNGS, March 2010

1st LAr Filling  light yield lower by factor ~60  0.03 pe/keV - measured with Th-228 & Am-241  1.8 pe/keV - in Mini-LArGe  slow component strongly quenched triplet-lifetime: τ trip = 66 ns (lit. τ trip = 1.1 to 1.7 µs)   mass spectrometer measurements:  N 2 : 7 ppm  O 2 : <4 ppm  no other trace contaminations found due to the limited sensitivity of the mass spectrometer 6 GERDA Collaboration Meeting, LNGS, March 2010

Triplet Lifetime (Slow Component) as an Indicator for Impurities pulse shape average over 10000 pulses: clean argon amplitude  contaminated argon time  7 (example from GAr) GERDA Collaboration Meeting, LNGS, March 2010

What is the Origin of the Contamination? Mini-LArGe Investigations… configuration triplet lifetime conclusion LAr 873 ns LAr in LArGe is contaminated, instrumental reasons excluded 112 ns charcoal & PTFE filter 775 ns are clean 733 ns Araldit is no problem stable for 3 days activated charcoal did not remove 74 ns contamination 8 GERDA Collaboration Meeting, LNGS, March 2010

Modifications on LArGe Cryostat jan-feb `10:  cryostat with GAr again  support compensator to allow for pumping the cryostat  degass from air residues by  heating up cryostat (15°C  40°C)  & perform flushing-pumping cycles 9 GERDA Collaboration Meeting, LNGS, March 2010

After Modifications: N 2 and O 2 constant vs. time level of contaminents [a.u.]  time  Ar6.0 reference background 10 GERDA Collaboration Meeting, LNGS, March 2010

Light Degradation Measurements in GAr (2) february `10: triplet lifetime in GAr is much more stable than before 1st filling 4 3.5 3 triplett lifetime [ns] light yield [a.u.] GAr before 2nd filling 2.5 2 1.5 GAr before 1st filling 1 0.5 0 0 2 4 6 8 10 time [h] 11 GERDA Collaboration Meeting, LNGS, March 2010

2nd Filling: Average Pulse Shape in LAr 3 PMTs, 2-fold trigger, no source 12 GERDA Collaboration Meeting, LNGS, March 2010

2nd Filling: Triplett Lifetime Stability in LAr feb-mar `10: triplet lifetime in LAr is stable since 8 days 1400 1200 triplet lifetime [ns] 1000 800 600 400 200 0 0 2 4 6 8 10 time [days] 13 GERDA Collaboration Meeting, LNGS, March 2010

Conclusions & Outlook  LArGe is filled with LAr & the scintillation light is stable since 8 days  the triplet lifetime is  GAr: 3.5 µs @ 950 mbar (ref. 3.2 µs @ 1100 mbar)  LAr: 829 ns (lit. 1.1 to 1.7 µs) Mini-LArGe result: ~790 ns (@LNGS with Ar5.0), 1.2 µs (@MPIK with Ar5.4)  active cooling with LN runs very smooth  good control over pressure & stable LAr filling level  now we can start to study spectral properties of scintillation light in LArGe (light yield, resolution…)  eventually (april?): mount lock and enter BEGe‘s 14 GERDA Collaboration Meeting, LNGS, March 2010