Update on the negative ion results Kees Ligtenberg Lepcol meeting - - PowerPoint PPT Presentation

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 Edrift 100 – 500 V/cm Vgrid −380 V 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

Number of hits 20 40 60 80 100 Normalised entries 0.2 0.4 0.6 0.8 1

All chips chip 1 chip 2 chip 3 chip 4

Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 3 / 12

Event display

Run 1070

x position [mm] 10 15 20 25 30 35 y position [mm] 5 10 15 20 25 30 35

1 2 3 4 5 6 7

Drift time [ms]

Timepix hits Laser track Timepix hits Laser track Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 4 / 12

Drift time

Run 1069

Drift time [ms] 1 2 3 4 5 6 7 8 9 Hits 200 400 600 800 1000 1200 1400 1600 1800 4.7 mm 10.7 mm 16.7 mm 22.7 mm 28.7 mm 35.7 mm

Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 5 / 12

Analysis

Global fit: c1 exp (z − µ1)2 2σ2

1

• + f2c1 exp

(z − r2µ1)2 2σ2

2

• + cnoise

(1) fit per run: ratio of Gaussian constants f2) ratio of mobility r2 Per slice: standard deviations σ1 and σ2 mean µ1 constant c1

• ffset cnoise

Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 6 / 12

Drift velocity

Run 1069

drift distance [mm] 5 10 15 20 25 30 35 40 drift time [ms] 2 4 6 8 10

Majority carrier Minority carrier

drift

v 4.18 m/s

drift

E 300 V/cm

Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 7 / 12

Mobility

Run 1065 – 1073

Drift velocity [m/s] 1 2 3 4 5 6 7 8 9 mobility /V/s

2

1.392 cm Drift field [V/cm] 100 200 300 400 500 600 /V/s]

2

Mobility [cm 1.38 1.39 1.4 Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 8 / 12

Diffusion coefficients

Drift field [V/cm] 100 200 300 400 500 ] cm m/ µ Diffusion coefficient [ 50 100 150 200 250 300 350

Transverse diffusion coefficient Longitudinal diffusion coefficient V m/ µ = 2295

drift

E /

T

D V m/ µ = 2594

drift

E /

L

D V m/ µ = 2274

drift

E /

thermal

D Transverse diffusion coefficient Longitudinal diffusion coefficient V m/ µ = 2295

drift

E /

T

D V m/ µ = 2594

drift

E /

L

D V m/ µ = 2274

drift

E /

thermal

D

Dthermal =

• 2kBT

eE , (2)

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: c1 exp

• z2

2(σ2

0 + zD2 L)

• + f2c1 exp
• (zr2)2

2(σ2

0 + zD2 L)

• (3)

With values f2 = 0.9258, r2 = 0.0431, σ0 = 0.159 mm, DL = 119 µm/√cm fixed and fit c1 and z

Kees Ligtenberg (Nikhef) Negative Ion TPC May 18, 2020 10 / 12

Fiducialisation

Run 1073

Residual of reconstructed z-position [mm] 15 − 10 − 5 − 5 10 15 Normalised entries 0.02 0.04 0.06 0.08 0.1 0.12

One laser shot (RMS = 4.78 mm) Superposition of 2 laser shots (RMS = 3.45 mm) Superposition of 4 laser shots (RMS = 2.65 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

driftDistance 5 10 15 20 25 30 35 zReconstructed-driftDistance 5 − 5 10 15 5 10 15 20 25

zReconstructed-driftDistance: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