Quasiparticle Diffusion in CRESST Light Detectors Marc W ustrich - - PowerPoint PPT Presentation

▶

quasiparticle diffusion in cresst light detectors

Quasiparticle Diffusion in CRESST Light Detectors Marc W ustrich - - PowerPoint PPT Presentation

Nov 08, 2022 572 likes •872 views

Quasiparticle Diffusion in CRESST Light Detectors Marc W ustrich Max-Planck Institute f. Physics 19.07.2014 Marc W ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 1 / 28 Introduction 1 TES

slide-1

SLIDE 1

Quasiparticle Diffusion in CRESST Light Detectors

Marc W¨ ustrich

Max-Planck Institute f. Physics

19.07.2014

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 1 / 28

slide-2

SLIDE 2

1

Introduction TES and Phonon Collectors Signal evolution in TES systems Phonon Collectors

2

Measurement of the diffusion length in CRESST like light detectors General Setup Simulation of the setup Measurement and Analysis Results

3

Summary

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 2 / 28

slide-3

SLIDE 3

Introduction TES and Phonon Collectors

Transition Edge Sensors

Transition Edge Sensors (TES) common tool to measure precisely energy depositions in a absorber TES are sensitive to tiny temperature changes (Θ(µK)) in the absorber if operated in the mK scale

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 3 / 28

slide-4

SLIDE 4

Introduction TES and Phonon Collectors

Transition Edge Sensors

Transition Edge Sensors (TES) common tool to measure precisely energy depositions in a absorber operated in the mK scale TES are sensitive to tiny temperature changes (Θ(µK)) in the absorber

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 4 / 28

slide-5

SLIDE 5

Introduction TES and Phonon Collectors

Setup for CRESST TES

W layer (100nm-200nm) serving as TES with TC between 15-20mK

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 5 / 28

slide-6

SLIDE 6

Introduction TES and Phonon Collectors

TES setup for CRESST

W layer (100nm-200nm) serving as TES with TC between 15-20mK Au layer serving as thermal link and heater connection

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 6 / 28

slide-7

SLIDE 7

Introduction TES and Phonon Collectors

TES setup for CRESST

W layer (100nm-200nm) serving as TES with TC between 15-20mK Au layer serving as thermal link and heater connection supercunducting Al layer covering most of the W serving as phonon collectors (PC) (proximity effect)

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 7 / 28

slide-8

SLIDE 8

Introduction TES and Phonon Collectors

TES setup for CRESST

W layer (100nm-200nm) serving as TES with TC between 15-20mK Au layer serving as thermal link and heater connection superconducting Al layer covering most of the W serving as phonon collectors (proximity effect) 5-6 days of production

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 8 / 28

slide-9

SLIDE 9

Introduction TES and Phonon Collectors

Signal evolution in TES systems

1

Energy deposition in the absorber => Phonon production and evolution in the absorber

2

Transmission of the phonons from the absorber into the TES/PC

3

Phonon interactions in the TES

4

Phonon interactions in the PC

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 9 / 28

slide-10

SLIDE 10

Introduction Signal evolution in TES systems

Signal evolution in TES systems: Energy deposition in the absorber

recoils produce high frequency optical phonons with a broad frequency distribution (O (10 THz)) within 10 µs the phonons decay rapidly to acoustic phonons with a moderate frequency ( O (0.5 Ghz)) due to surface scatter and crystal inhomogeneities the absorber is completely populated with non-thermal phonons non-thermal phonons have lifetime of some ms and decay very slowly to smaller frequencies

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 10 / 28

slide-11

SLIDE 11

Introduction Signal evolution in TES systems

Signal evolution in TES system: Phonon transmission into the TES

Transmission of the non-thermal phonons into the TES/PC QA→T ∝ 1

2 · E VA · vg,⊥ · α

for the materials used in CRESST LDs the transmission values are between 60%-70% inluence of the absorber volume to the transmission explains CRESST strategy towards smaller crystals to lower energy threshold

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 11 / 28

slide-12

SLIDE 12

Introduction Signal evolution in TES systems

Signal evolution in TES system

Phonon interaction in the TES

interaction of thermal phonons is strongly suppressed due to T5 dependence Absorption of transverse phonons ∝ ν => strongly suppressed Absorption of longitudinal phonons ∝ ν2 => complete absorption ans strong coupling to the electron system strong electron-electron coupling => homogeneous heating of the TES

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 12 / 28

slide-13

SLIDE 13

Introduction Signal evolution in TES systems

Signal composition in a TES

T(t) = Θ(t − t0) · An · (e−t/τn − e−t/tin) + At · (e−t/τt − e−t/tn)

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 13 / 28

slide-14

SLIDE 14

Introduction Phonon Collectors

Phonon collectors

PC are superconducting parts of the TES that reduce the collection time of non-thermal phonons by increasing the collection area The heat capacity is not increased by their addition τcol =

2VA Avg⊥·α

CTES ∝ A

Phonon interaction in the phonon collector

non-thermal phonons break up Cooper Pairs in free electrons (Quasiparticles) as long the energy of the QP is above the band gap, more Cooper Pairs are split up QP diffuse thermally in the PC untill the TES is reached where they can interact with the electron system of the TES

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 14 / 28

slide-15

SLIDE 15

Introduction Phonon Collectors

But:

PCs only influence the TES signal positively if the generated QPs actually reach the TES before their recombination The dimensions of the PC have to be adjusted to the diffusion length of the QPs Measurement

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 15 / 28

slide-16

SLIDE 16

Measurement of the diffusion length in CRESST like light detectors General Setup

General Setup

Rad marked area is illuminated by an Fe55 source Measurement of the correlated particle signals in the right and left W-TES

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 16 / 28

slide-17

SLIDE 17

Measurement of the diffusion length in CRESST like light detectors General Setup

Setup

The number of detected quasiparticles in a detector in a certain distance can be calculated by solving the 1D diffusion equation δn δt − D · δ2n δx 2 + n τqp = 0 (1) The solution for the ratio number of detected quasiparticles in one detector is calctulated to be n1,2(xa) = sinh(α(0.5 ± xa

L )) + βcosh(α(0.5 ± xa L ))

(1 + β2)sinh(α) + 2βcosh(α) (2) with α =

L

√

D·τqp and β = τtr τqp

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 17 / 28

slide-18

SLIDE 18

Measurement of the diffusion length in CRESST like light detectors Simulation of the setup

Simulation of the setup

Simulation of the detector response with a randomly distributed 55Fe spectrum and realistic diffusion parameters

Signal in Detector 1 [eV] 1000 2000 3000 4000 5000 6000 7000 8000 900010000 Signal in Detector 2 [eV] 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Probability postion [mm]

0.25 -0.2 -0.15 -0.1 -0.05

0.05 0.1 0.15 0.2 0.25 Signal in Detector 2 [eV] 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Probability 1 2 3 4 5 6 7 8 Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 18 / 28

slide-19

SLIDE 19

Measurement of the diffusion length in CRESST like light detectors Measurement and Analysis

Measurement

Si substrate equipped with two TES with the same layer properties like CRESST light detectors Setup allows diffusion over a distance of 2mm

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 19 / 28

slide-20

SLIDE 20

Measurement of the diffusion length in CRESST like light detectors Measurement and Analysis

Analysis

raw data

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 20 / 28

slide-21

SLIDE 21

Measurement of the diffusion length in CRESST like light detectors Measurement and Analysis

Analysis

selection of good pulses (removing pile up events, SQUID artefacts,....)

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 21 / 28

slide-22

SLIDE 22

Measurement of the diffusion length in CRESST like light detectors Measurement and Analysis

Analysis

cutted data (all events poluted with measurement artefacts are removed) distinct event classes: substrate hits, PC hits, direct TES hits

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 22 / 28

slide-23

SLIDE 23

Measurement of the diffusion length in CRESST like light detectors Measurement and Analysis

Event selection

energy

Entries 100000 Mean 5596 RMS 1803

energy [eV] 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 counts 2000 4000 6000 8000 10000 12000 energy

Entries 100000 Mean 5596 RMS 1803

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 23 / 28

slide-24

SLIDE 24

Measurement of the diffusion length in CRESST like light detectors Measurement and Analysis

Event discrimination

separation of PC hits and substrate hits necessary =¿ discrimination possible onset difference

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 24 / 28

slide-25

SLIDE 25

Measurement of the diffusion length in CRESST like light detectors Measurement and Analysis

Event discrimination

after isolating the respective particle populations, fit of the data to determine diffusion parameters

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 25 / 28

slide-26

SLIDE 26

Measurement of the diffusion length in CRESST like light detectors Results

Results

4 independent measurements with different substrates reproduced the diffusion parameters the measured diffusion length stays between 1-2mm the diffusion length is strongly dependent on the quality of the Al phonon collectors (RRR) => Diffusion length is much longer than expected

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 26 / 28

slide-27

SLIDE 27

Measurement of the diffusion length in CRESST like light detectors Results

Influence on future CRESST detectors

in future CRESST detectors the size of the PC is increased relative to the TES size first measurements show that 200% more PC area increases the signal height by 30%

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 27 / 28

slide-28

SLIDE 28

Summary

Summary

The efficiency of TES can be increased significantly by the addition of phonon collectors The diffusion parameters of the generated Quasiparticles have to be determined for the respective detector setup The diffusion length is determining the dimensions of the PC => Underestimation of the QP diffusion in CRESST light detectors => Next-generation TES are adjusted to the new results by bigger phonon collectors Thank you!

Marc W¨ ustrich (Max-Planck Institute f. Physics) CP diffusion in CRESST Light detectors 19.07.2014 28 / 28