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

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 Ground (MΩ) Resistance along strip 2 5 0.5 (MΩ/cm)

Types of Measurements  Properties  Gain  Transparency  Response to cosmics  Charge-up  High rate behavior  Tools  5 keV 55 Fe source  8 keV X-ray gun at various rates  120 GeV pion test beam

Gain & Transparency Measurement – Set up Gas out Protective cover with holes Read out connectors 55 Fe tablet HV Drift HV Mesh Gas in

18 mm  Each read-out connector connected to 72 strips  Covers a cross-section of 18 mm  Strips that are not read out are grounded

Example Spectrum 55 Fe (5.9 keV) Peak Ar escape peak (3 keV lower)

 Peak of 55 Fe taken in arbitrary units from spectrum  Rate, counts, live time, start time also displayed  Converted to gain via calibration signal  Calibration pulse = 10 4 gain  Gain measurements taken for:  R11, 93% Ar 7% CO 2  R12, 93% Ar 7% CO 2  R12, 85% Ar 15% CO 2  R13, 93% Ar 7% CO 2  R13, 85% Ar 15% CO 2

Gain Measurements - Results

Transparency Measurements  Transparency = (# of e – that make it to the amplification field) (Total # of e – produced)  Transparency measurements taken for:  R12, 93% Ar 7% CO 2  R12, 85% Ar 15% CO 2  R13, 93% Ar 7% CO 2  R13, 85% Ar 15% CO 2

Transparency Measurements – Set up  Measured gain as a function of E amplification /E drift  Kept V mesh constant  Varied V drift  E=V/d, where V is the voltage difference and d is the distance  E drift = (V mesh -V drift )/d ≈ 300V/5mm ≈ 600 V/cm  E amplification = (V mesh -V ground )/d ≈ 500V/.128mm ≈ 40 kV/cm  Normalized highest gain = 1

Cosmic Measurements – Set up  Stacked R11, R12, R13 with 15mm spacers  Used R11 and R13 to trigger, R12 to acquire

R11 HV Mesh top Top HV Drift R12 HV Mesh middle MCA R13 HV Mesh bottom Bottom

Cosmics – Logic Top Threshold NIM  Gate TTL for MCA Bottom Threshold

Cosmics - Results

Cosmic most probable value 55 Fe (5.9 keV) Peak 55 Fe 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 CO 2

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

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

 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  E amplification decreases

 Charge deposited per second:  Rate = 200 Hz  (200 Hz) × (225 e – per photon) × (10 4 gain) × (1.6 × 10 -19 ) ≈ .06 nA  Rate = 20k Hz  (20000 Hz) × (225 e – per photon) × (10 4 gain) × (1.6 × 10 -19 ) ≈ 6 nA  Δ Voltage (very rough estimations of what to expect)  In resistor  Low rate: V = IR = .06 nA × 10 8 Ω = .006 V  High rate: V = IR = 6 nA × 10 8 Ω = .6 V  In insulator  Low rate: V = IR = .06 nA × 10 10 Ω = .6 V  High rate: V = IR = 6 nA × 10 10 Ω = 60 V

Δgain≈1600  Gain decreases due to decrease in E mesh

Δgain≈2000 Δgain≈1000

Δgain≈5000 Δvoltage≈15V

Conclusions  Gain  All chambers reach gain of ≈30k  With 93:7 Ar:CO 2, the chambers can be operated at a HV 40V lower than for 85:15 Ar:CO 2  R12 has highest gain, R11 has lowest  Transparency  For good transparency, E amp /E drift > 80  85:15 Ar:CO 2 rises faster, but shows similar behavior to 93:7 Ar:CO 2 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)

This has been an amazing summer! Thank you to everyone who has guided me in this experience!!!