Update on the negative ion results Kees Ligtenberg Lepcol meeting May 18, 2020 Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 1 / 12
Run parameters Number of runs 9 Run duration 17 minutes 100 – 500 V / cm E drift − 380 V V grid Threshold 515 e − Temperature 295.9 – 297.0 K Pressure 1030 – 1029 mbar Oxygen concentration 654 – 1133 ppm Water vapor concentration ∼ 4000 ppm Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 2 / 12
Number of hits Run 1069 Normalised entries All chips chip 1 chip 2 chip 3 1 chip 4 0.8 0.6 0.4 0.2 0 0 20 40 60 80 100 Number of hits Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 3 / 12
Event display Run 1070 Timepix hits Timepix hits y position [mm] 35 Laser track Laser track 7 30 6 25 5 20 Drift time [ms] 4 15 3 10 2 5 1 0 0 10 15 20 25 30 35 x position [mm] Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 4 / 12
Drift time Run 1069 Hits 4.7 mm 1800 1600 10.7 mm 1400 16.7 mm 1200 22.7 mm 28.7 mm 1000 35.7 mm 800 600 400 200 0 1 2 3 4 5 6 7 8 9 Drift time [ms] Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 5 / 12
Analysis Global fit: � ( z − µ 1 ) 2 � ( z − r 2 µ 1 ) 2 � � c 1 exp + f 2 c 1 exp + c noise (1) 2 σ 2 2 σ 2 1 2 fit per run: ratio of Gaussian constants f 2 ) ratio of mobility r 2 Per slice: standard deviations σ 1 and σ 2 mean µ 1 constant c 1 offset c noise Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 6 / 12
Drift velocity Run 1069 drift time [ms] Majority carrier Minority carrier 10 8 6 4 v 4.18 m/s drift 2 E 300 V/cm drift 0 0 5 10 15 20 25 30 35 40 drift distance [mm] Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 7 / 12
Mobility Run 1065 – 1073 9 Drift velocity [m/s] 8 7 6 5 4 3 mobility 2 1.392 cm /V/s 2 1 0 /V/s] 1.4 2 Mobility [cm 1.39 1.38 0 100 200 300 400 500 600 Drift field [V/cm] Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 8 / 12
Diffusion coefficients 350 ] cm Transverse diffusion coefficient Transverse diffusion coefficient m/ 300 Longitudinal diffusion coefficient Longitudinal diffusion coefficient µ Diffusion coefficient [ µ µ D D / / E E = 2295 = 2295 m/ m/ V V T T drift drift 250 µ µ D D / / E E = 2594 = 2594 m/ m/ V V L L drift drift µ µ D D / / E E = 2274 = 2274 m/ m/ V V thermal thermal drift drift 200 150 100 50 0 0 100 200 300 400 500 Drift field [V/cm] � 2 k B T D thermal = , (2) eE Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 9 / 12
Fiducialisation 4.3% of the hits in second peak at 500 V / cm Perform maximum likelihood fit using: z 2 ( zr 2 ) 2 � � � � c 1 exp + f 2 c 1 exp (3) 2( σ 2 0 + zD 2 2( σ 2 0 + zD 2 L ) L ) With values f 2 = 0 . 9258, r 2 = 0 . 0431, σ 0 = 0 . 159 mm, D L = 119 µ m / √ cm fixed and fit c 1 and z Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 10 / 12
Fiducialisation Run 1073 Normalised entries One laser shot (RMS = 4.78 mm) 0.12 Superposition of 2 laser shots (RMS = 3.45 mm) Superposition of 4 laser shots (RMS = 2.65 mm) 0.1 0.08 0.06 0.04 0.02 0 − − − 15 10 5 0 5 10 15 Residual of reconstructed z-position [mm] Reconstructed z resolution depends on the number of hits Clear bias which needs to be investigated Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 11 / 12
Fiducialisation Run 1073 zReconstructed-driftDistance:driftDistance zReconstructed-driftDistance 15 25 10 20 5 15 10 0 5 − 5 0 5 10 15 20 25 30 35 driftDistance Resolution is poorer for the shortest drift drift distance of 5 mm because the peaks overlap Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 12 / 12
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