Hardware considerations about Ar vs. Ne C. Garabatos

History 2010 with Ne-CO2-N2: many trips with damage to electronics remove HV capacitors, remove N2 2011 with Ne-CO2 (high background): still trips, but no damage to electronics replace HV power supplies: include ‘time to trip’ feature 2012-2013 with new PS (high background): trips basically gone, but much garbage data due to ‘chamber fighting’ Replace Ne by Ar 2015-2016 with Ar-CO2 (low background): no trips except for two fills 20.05.2016 To Ne or not to Ne

History of signal and voltages Danilo History of signal and voltages Charge estimated from Kr83 42 keV peak Ar scaled by a factor 0.72 to account for X-ray yield and a factor 2 to account for MIP yield 20.05.2016 To Ne or not to Ne

If we switch to Ne… Distortions decreased by 40% GG closing time –and minimum busy time- could be adjusted accordingly Primary ionisation reduced by factor 2 Not clear what the stability would be: past instabilities were most probably due to beam quality and were enhanced by capacitors and HV PS Machinery for TPC calibration for Ne exists; details being worked out Gas system ready for the switch 20.05.2016 To Ne or not to Ne

Further special runs Extend HV scan to lower voltages 1 run at <50% gain in IROCs Extend trigger rate scan to lower rates 1 run at 50-100 Hz 20.05.2016 To Ne or not to Ne

BACKUP 20.05.2016 To Ne or not to Ne

Gas An incident with the gas system happened on 4.07.2017 the coil of an electrovalve burned no contact between this coil and the gas High luminosity runs followed this incident, and distortions were observed also dramatic gain drop, which took many weeks to recover No high luminosity runs before incident Laser hot spots were not there before incident No pollutant was found through Gas Chromatography analyses Gas completely replaced end of March 2016 20.05.2016 To Ne or not to Ne

Ne-CO2 Vs Ne-CO2-N2 N2 provides stability at no penalty 20.05.2016 To Ne or not to Ne

Ar Vs Ne Similar electron transport properties Vd (cm/ms) sl (cm-1/2) st wt Nt mion (cm2/Vs) Co (m) Ne-CO2 (90-10) 2.73 0.0231 0.0208 0.34 36.8 4.08 345 Ar-CO2 (90-10) 3.31 0.0262 0.0221 0.43 74.8 1.52 118 Similar electron transport properties Ar provides factor 2 more primary electrons higher space-charge for full protection with GG (no IBF) allows for factor 2 lower gain and 40% smaller gain fluctuations Ion mobility in Ar 1.7 times lower that in Ne Ar has 3 times shorter radiation length, but this does not affect momentum resolution at any pT 20.05.2016 To Ne or not to Ne

Momentum resolution M. Kowalski The shorter radiation length of Ar does not affect the resolution at low pT At high pT Ar performs better, as expected 20.05.2016 To Ne or not to Ne

Status of laser hot spots 20.05.2016 To Ne or not to Ne