1. Hardware considerations about Ar vs. Ne
C. Garabatos

2. 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
with new PS (high background): trips basically gone, but much garbage data due to ‘chamber fighting’
Replace Ne by Ar
with Ar-CO2 (low background): no trips except for two fills
To Ne or not to Ne

3. 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
To Ne or not to Ne

4. 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
To Ne or not to Ne

5. 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 Hz
To Ne or not to Ne

6. BACKUP
To Ne or not to Ne

7. 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
To Ne or not to Ne

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

9. Ar Vs Ne Similar electron transport propertiesVd
(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
To Ne or not to Ne

10. 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
To Ne or not to Ne

11. Status of laser hot spots
To Ne or not to Ne