Report on Measurements in the Lab with R11, R12, R13 Alexandra - - PowerPoint PPT Presentation

▶

Jun 12, 2023 217 likes •536 views

Report on Measurements in the Lab with R11, R12, R13 Alexandra Moskaleva What is a resistive chamber? Non-resistive Micromegas Resistive Micromegas (R11, R12, R13) Resistive Characteristics CHAMBER R11 R12 R13 Resistance to 15 45 20

SLIDE 1

Report on Measurements in the Lab with R11, R12, R13

Alexandra Moskaleva

SLIDE 2

What is a resistive chamber?

Non-resistive Micromegas Resistive Micromegas (R11, R12, R13)

SLIDE 3

Resistive Characteristics

CHAMBER

R11 R12 R13

Resistance to Ground (MΩ) 15 45 20 Resistance along strip (MΩ/cm) 2 5 0.5

SLIDE 4

Types of Measurements

 Properties

 Gain  Transparency  Response to cosmics  Charge-up  High rate behavior

 Tools

 5 keV 55Fe source  8 keV X-ray gun at various rates  120 GeV pion test beam

SLIDE 5

Gain & Transparency Measurement – Set up

HV Drift HV Mesh Gas in Gas out

55Fe tablet

Read out connectors Protective cover with holes

SLIDE 6

 Each read-out connector connected to 72 strips

 Covers a cross-section of 18 mm

 Strips that are not read out are grounded

18 mm

SLIDE 7

SLIDE 8

Example Spectrum

55Fe (5.9 keV) Peak

Ar escape peak (3 keV lower)

SLIDE 9

 Peak of 55Fe taken in arbitrary units from spectrum

 Rate, counts, live time, start time also displayed

 Converted to gain via calibration signal

 Calibration pulse = 104 gain

 Gain measurements taken for:

 R11, 93% Ar 7% CO2  R12, 93% Ar 7% CO2  R12, 85% Ar 15% CO2  R13, 93% Ar 7% CO2  R13, 85% Ar 15% CO2

SLIDE 10

Gain Measurements - Results

SLIDE 11

SLIDE 12

SLIDE 13

Transparency Measurements

 Transparency =

(# of e– that make it to the amplification field) (Total # of e– produced)

 Transparency measurements taken for:

 R12, 93% Ar 7% CO2  R12, 85% Ar 15% CO2  R13, 93% Ar 7% CO2  R13, 85% Ar 15% CO2

SLIDE 14

Transparency Measurements – Set up

 Measured gain as a function of Eamplification/Edrift

 Kept Vmesh constant  Varied Vdrift  E=V/d, where V is the voltage difference and d is the

distance  Edrift = (Vmesh-Vdrift)/d ≈ 300V/5mm ≈ 600 V/cm  Eamplification = (Vmesh-Vground)/d ≈ 500V/.128mm ≈ 40 kV/cm

 Normalized highest gain = 1

SLIDE 15

SLIDE 16

SLIDE 17

Cosmic Measurements – Set up

 Stacked R11, R12, R13 with 15mm spacers  Used R11 and R13 to trigger, R12 to acquire

SLIDE 18

HV Drift R11 R12 R13

Top

HV Mesh top

Bottom

HV Mesh bottom HV Mesh middle

MCA

SLIDE 19

Top Threshold NIM  TTL Gate for MCA Bottom Threshold

Cosmics – Logic

SLIDE 20

Cosmics - Results

SLIDE 21

55Fe (5.9 keV) Peak

Cosmic most probable value



55Fe produces 225 e– in drift region, with a peak ≈ 420



Cosmics produce a peak ≈ 100 (a factor of ¼)



Therefore, cosmics produce ≈ 50 e– in 5mm drift region



Agrees with 90 e–/cm for Ar and for CO2

SLIDE 22

Charge Up – Theory

 Charge is deposited on the detector in <2mm radius for

every photon  Due to dispersion in electron avalanche

 Some charge deposits on resistive strips

 Runs to ground due to relatively low resistance

 Some charge deposits on insulative area

 Cannot drain away as quickly  builds up an excess of

negative charge

 No longer at ground

SLIDE 23

 Charge is deposited on resistive and insulative strips  Footprint of roughly 2mm in diameter

≈2mm

SLIDE 24

 Charge leaks away through the resistive strips  Takes much longer to leak away charge from insulative

portion

 If the rate of deposition >> rate of discharge, then there

is a buildup of charge

 Eamplification decreases

SLIDE 25

 Charge deposited per second:  Rate = 200 Hz

 (200 Hz) × (225 e– per photon) × (104 gain) × (1.6 × 10-19)

≈ .06 nA

 Rate = 20k Hz

 (20000 Hz) × (225 e– per photon) × (104 gain) × (1.6 × 10-19)

≈ 6 nA

 Δ Voltage (very rough estimations of what to expect)

 In resistor

 Low rate: V = IR = .06 nA × 108 Ω = .006 V  High rate: V = IR = 6 nA × 108 Ω = .6 V

 In insulator

 Low rate: V = IR = .06 nA × 1010 Ω = .6 V  High rate: V = IR = 6 nA × 1010 Ω = 60 V

SLIDE 26

 Gain decreases due to decrease in Emesh

Δgain≈1600

SLIDE 27

Δgain≈2000 Δgain≈1000

SLIDE 28

Δgain≈5000 Δvoltage≈15V

SLIDE 29

Conclusions

 Gain

 All chambers reach gain of ≈30k  With 93:7 Ar:CO2, the chambers can be operated at a HV 40V lower than

for 85:15 Ar:CO2

 R12 has highest gain, R11 has lowest

 Transparency

 For good transparency, Eamp/Edrift > 80  85:15 Ar:CO2 rises faster, but shows similar behavior to 93:7 Ar:CO2 in

steady state

 Cosmics

 Cosmic measurements show good results (Landau curve) with most

probable value showing creation of 50 e– in 5mm drift region, as expected

 Charge up

 Charge up is observed

 As function of rate (reducing gain by 10% at 200 Hz, 20% at 20 kHz)

SLIDE 30