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Status of Malter effect study in MUON MWPC (2014) Dmitrii Mausuzenko , Oleg Maev ( PNPI)

Status of Malter effect study in MUON MWPC (2014) Dmitrii Mausuzenko , Oleg Maev ( PNPI). Status of Malter effect study. From the beginning of operation many of MUON chambers demonstrated multiple HV-trips due the Malter effect manifestation .

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Status of Malter effect study in MUON MWPC (2014) Dmitrii Mausuzenko , Oleg Maev ( PNPI)

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  1. Status of Malter effect study in MUON MWPC (2014) DmitriiMausuzenko, Oleg Maev(PNPI)

  2. Status of Maltereffectstudy. • From the beginning of operation many of MUON chambers demonstrated multiple HV-trips due the Malter effect manifestation. • Most of affected chambers are cured by with working gas mixture at the nominal polarity with beam and at inversed polarity during Technical stops and Winter Shutdowns. But not all of them. • In November 2013 we started the study of curing MUON chambers from Malter effect with using as an option the adding small amount of Oxygen in the nominal gas mixture.

  3. Previousresults. Malter effect was cured successful after ~1h of HV+ & ~2h HV- training with 2% of Oxygen. Malter insulation layer in chamber M4R4#94 was removed after ~ 10 hours of HV+ training with 2% of Oxygen.

  4. Chambers M5R3 from the low irradiation region. Very difficult to ignite the Malter currentduring the Sr90(39MBq)scanning. Were cured successful in nominal mixture by short time Last results. 4

  5. Last results. Strong Malter effect was detected in GAP B , after 6h of training with nominal mixture the chamber failed to cure. Curing with O2 in progress! 5

  6. Studied chambers. M2R4 #41 Cured with Oxygen M4R4 #94 M5R3 10C Cured in nominal mixture M5R3 24B M.E. not detected. large dark currents saved M5R4 #FIR05400037 M.E. presents, no success after 7h of HV training in nominal mixture . In progress with O2! M5R4 (22C) #FIR05400021 M.E. wasn’t detected M4R4 #46

  7. Conclusion Six chambers have been studied up to now and one is in progress. Four chambers cured successful by HV training. Two of them we managed to cure only after HV training with Oxygen addition. Malter effect more difficult to detect in chambers from low irradiation regions. Adding a small amount of oxygen could be useful for chambers with large value of pollutant when the only CF4 (F*) insufficiently. Most of cured chambers are/will be installed back in the detector. 7

  8. Future plans and perspectives • Continue the study this year with chambers suffered with M.E. – there are few chambers available on C-side? • Continue with spare chambers in framework of revision of spares? • Public note about the done work . • Proposal for GIF++ in 2015.

  9. Thanks for Your attention !

  10. BACK SLIDES

  11. Scanning and treatment the CMB M2R4 #41 with radioactive sources Beam in 2012: J~0.1 nA/cm2 Scanning with source Am241 (J~0.3 nA/cm2)not give ignition! Scanning with Sr90- J~70 nA/cm2 ignited the Malter current in two places only in GAP A

  12. CMB M4R4#94 scanning with Sr90 - 39MBq CMB M4R4#94 The Maltereffect manifested on GAP D at low current density J< 0.2 nA/cm2 *The currents in CMB M4R4 was increased more faster than in CMB M2R4 and ignited at lowest current density. Different chambers – different Malter currents behavior

  13. Malter effect Necessary condition for electron emission: a) Localized primary ionization deposit. b) An insulator on the cathode. c) A rate of the charge build up is higher than its removal rate. d) Excessive field cathode gradients help to trigger it. e) To start the effect, it needs an ignition. SOURCES: • Avalanche producing polymers deposits • Some oxides are highly resistive. • Constructions material and gas pollutants. • Insulating deposits left from sparks. • Corona on sharp point on the cathode. • Fingerprints • Etc. Ignition mechanisms: a) Highly ionizing heavy ions. b) X-rays. c) Sparks. d) Sharp points on electrodes causing corona.

  14. HV+ or HV- • Sources of ionization: • HV+ : • External irradiation (Sr90) • Malter current • HV-: • External irradiation (Sr90) • Possible mini avalanches on tips HV-→ small current = less etching particles , but it’s all near the insulating film HV+→ high current = more etching particles

  15. Treatment procedure in brief • Setting the chamber taken from the detector with nominal gas mixture at MUON/OT gas quality check room in the PIT. • Check that the chamber is properly conditioned with HV. It means that CMB has almost zero dark current at HV= +2850V and -2300V. • Scanning the chamber sensitive area with radioactive source at HV=2800V to provoke and localize “Malter currents zone(s)” • Try to remove the insulating film in Malter zone: • Setup the radioactive source over the “Malter zone” • Training the chamber at different polarities HV with admixing a small amount of Oxygen (~2%) to the nominal gas mixture. • Controlling the Malter currents in different places of Malter zone until the moment when it disappeared completely. • Check on nominal gas, that the current in “Malter zone” does not reappear again.

  16. Addition of OXYGEN With ~2% of Oxygen the currents in reference point decreased by ~20% , that corresponds to the Gain calculations in GARFIELD HV =2850V Gain calculations inGARFIELD Oxygen O% Oxygen 2% HV=2600V HV=2600V

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