Daniel S Levin

UM/TAU/IS/ORNL meeting with GE

Sept 27, 2012

University of Michigan

PPS Overview & Experimental Results

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1. Overview of desired PPS attributes2. Basic physics of PPS3. Proof-of-principle experiments & Establishing basic attributes4. Laboratory setups and prototype testing

Hit rates with source and background Signals, pixel capacitance, HV, Pashen potential etc Cosmic Muons Saturation measurement Spatial measurements Test Beam

Outline

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Plasma Panel Detector Overview

Inherits many operational and fabrication principles common to PDPs:

• A dense micro-array of gas discharge cells or pixels

• Pixels bias for gas electrical discharge- Geiger mode operation

• Pixels are enclosed in hermetically-sealed glass panel

• Uses non-reactive, radiation-hard materials:

glass substrates, refractory metal electrodes, inert gas mixtures.

Anticipate eventual device fabrication as low-mass detectors

A high gain and inherently digital device

Potential for:

• < 1 ns response times

• high granularity

• Position resolution < 100 um

• low power consumption

• large area with low cost

• 2D readout

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Plasma Television Display Panel (PDP)

As a detector PPS remove or replace specific elements:

No phosphors

No MgO layer

No dielectric layers

We add a quench resistor to the pixels that terminates the discharge

D.S. Levin University of Michigan

Single pixel: Principles of operation

Muon track

(-) High Voltage

cathode

anode

50-100

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Single pixel: Principles of operation

Muon track

(-) High Voltage

cathodeIonizing particle creates ion pair clusters along trackCluster formation dictated by Poisson statistics

Arfor

barcmclusterspairsionprimaryn

en

nP

i

n

i

30~

/!

)(

Cluster statistics: ni= >1 ion-pair. avg is about 3, with long exponential tail

anode

50-100

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Single pixel: Principles of operation

Muon track

(-) High Voltage

cathode

---------

++++++++++

Electron drift & acceleration in initiates avalancheHigh E –fields lead to streamers & gas breakdown according to Paschen’s Law :

P= pressured= gap sizeV=voltagea,b = gas specific parametersanode

50-100

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Minimum voltage occurs when

Wikipedia: Paschen entry.

A.K. Bhattacharya, GE Company, Nela Park, OH Phys. Rev. A, 13,3 (1975)

Small variations in Penning gas mixtures can dramatically affect breakdown voltage

Paschen discharge potential

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discharge cell: important gas processes

primary ionization

metastable generation

Excitation Penning ionization

Image from: Flat Panel Displays and CRTs (Chapter 10)    L. Tannas, Jr,

photon emission

Metastable ejection

ion ejected electron

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Rquench

Rterm

Cpixel

Electrical description

During discharge cell becomes conductiveThe E field drops, discharge self-terminates

HV Supply

cathode - + anode

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The quench resistance on each pixel (or pixel chain) : 1) impedes E field rise until ions and meta-stables are neutralized2) maintains HV on all other cells so that they are enabled for hits

signal

start with simplified schematic of single PPS discharge cell

{ResNi}

More realistic cell model

Cpixel

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include stray capacitances, line resistance, self inductance (More details in Robert Varner’s presentation)

Proof-of-principle & other tests with modified PDPs

1. Formation of discharge above Paschen potential2. Self-termination3. Response to a source4. Gas hermetic envelope5. Signal characteristics6. Rate from radioactive source vs background7. Discharge spreading8. Response with various gases9. Detection of CR Muons10. Position sensitivity along a one coordinate axis11. Proton beam tests12. Response to multiple, simultaneous sources

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Yiftah Silver talk

Rout

Quench

50 Termination

Discriminator @ 2-4 V

SnO2

Ni

collimator

22 cm

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Lecroy 574Abandwidth 1 GHz

90Sr106Ru

High Voltage

Panel A: Xe @ 650 torr Filled: Aug 2003

Panel B: Ar + CO2 (7%, 1%)

Lab setup

dielectric

Demonstration using Commercial DC-PDPs

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+ + + + + + + + +

- --Discharge gap

glass

Ni anode 800 m

glass

220-340 m

SnO2 280 m cathodes

E field at pixel (COMSOL calculation)

At critical (Paschen) voltage (~700 V) discharges appear in Xe.

O(ns) rise time (for ~ 1 mm dimensions)

Large amplitude indicates discharge of 5-10 pf effective capacitance

Increase voltage amplitude increase & hit rate increase (next slide)

Observed signals are single pulses quenching works

Panel filled and sealed in 2003- gas containment works

Clear response to 90Sr (beta) source

Low discharge spreading: 2% to a single neighbor pixel in open structure

Signal from Xe filled panel

Signal (attenuated) from Ar-CO2 filled panel

proof-of-principle tests

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Rate Measurements using source

Rate increases as expected with HV Response to source is ~100 Hz with very low background

Response to Source vs HV

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Rate Measurements using source

Rate increases as expected with HV and depends on Quench resistanceHigh Rquench (high RC time constant) causes pixel to saturate

Response to source is ~100 Hz with very low background

Rquench

Response to Source vs Rquench

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1/Rquench

Detection Setup of Cosmic Ray Muons

PMT1PMT2

Panel tested with CF4 or SF6 at 600, 200 torr

Events triggered with 3-fold coincidence

Signals collected with DRS-4 fast waveform digitizer

Scaler & waveform digitizer

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Both pure CF4 and SF6 gases shows a signal with a very fast response time.

Arrival time is defined with respect to the hodoscope trigger

Timing jitter is 5 ns

Arrival Time Measurement of Cosmic Ray Muons

20

About 8% of triggers were associated with signal from the panel

This factor represents a convolution of several factors:

Geometric acceptance ion-pair probability intrinsic efficiency

net = Ag AE P(l,p,r) (r) = 8 %

Ag = geometric acceptance of pixel (wrt to trigger area*solid angle)

AE = Pixel area enhancement from fringe E field P(l) = Probability to produce at least one ion-pair at distance R

from anode (r) = efficiency: probability to generate a discharge for ion-pair

created at distance R from anode.

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Detection of Cosmic Ray Muons & Efficiency

D.S. Levin University of Michigan

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Response to two simultaneous sources (setup)

D.S. Levin University of Michigan

Side view

Sr90 top

Ru106 bottom

Top view

HV=815VRO lines

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RO 24

RO 1

HV lines 1 20 100 110 128

Pickoff card100x

attenuation

HV=815VR=400

MΩ

VPA 600 Torr Ar 99%CO21%Filled Feb 15, 2012

Discriminator

-150 mVOR Scalar

Ru106

Sr90

RO lines 3-6

Expectation: rate with two sources = sum of the two rates in single mode until the sources starts (partially) overlapping

Response to two simultaneous sources (setup)

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Response to 2 simultaneous sources (Results)

Result: Panel responds independently to each source until they nearly overlap and saturate a line

Summary

Using off-the-shelf commercial Plasma Panels we have demonstrated

Producing fast, self-terminating, high gain pulse

Sensitivity to charged particles betas (also muon, protons)

Good timing jitter using triggered muons

Sensitivity to independent sources

Spatial resolution commensurate with the high granularity of the electrode pitch (Yiftah’s talk)

Panels sealed with gas in 2003 produce signals 9 years later

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