SLIDE 1
Time Projection Chamber
Max Lamparth, 18th November 2016
Time Projection Chamber
2
Outline
- Concept of a TPC
- Underlying theory
- The ALICE TPC
- Variations and outlook
Max Lamparth, 18th November 2016
Time Projection Chamber
Time Projection Chamber Principles of operation and the ALICE - - PowerPoint PPT Presentation
Time Projection Chamber Principles of operation and the ALICE - - PowerPoint PPT Presentation
Time Projection Chamber Master seminar: Particle tracking and identification at high rates Physikalisches Institut Universitt Heidelberg Time Projection Chamber Principles of operation and the ALICE example Max Lamparth, 18 th November 2016
SLIDE 2
SLIDE 3
3
Concept of a TPC
Max Lamparth, 18th November 2016
Time Projection Chamber
SLIDE 4
4
What is a TPC?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
TPC: 3D Reconstruction of charged particle trajectories Invented by David Nygren (1974) for 29 GeV -collisions at SLAC in PEP 4 e
+ / e
- a) LBL-SLAC, 1977, b) history.lbl.gov, c) wikipedia.com, d) Emanuel Pollacco, 2015
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5
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
Produced particles by collision propagate through gas/liquid → deposit energy and ionize gas → E-field to induce drift → detect electrons in end plates
a) O. Schäfer, lctpc.org
e
- ions
SLIDE 6
6
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 7
7
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 8
8
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 9
9
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 10
10
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 11
11
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 12
12
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 13
13
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 14
14
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 15
15
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 16
16
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
a) Magnus Mager, Aug 2016
SLIDE 17
17
How does it work?
Max Lamparth, 18th November 2016
Time Projection Chamber Concept of a TPC
Produced particles by collision propagate through gas/liquid → deposit energy and ionize gas → E-field to induce drift → detect electrons in endplates Detection: → Use principles of Multi-Wire-Proportional-Chamber Combine for full 3D reconstruction → xy-coordinates projected → z-coordinate via drift time ( ) Combinable with e.g. B-field for momentum measurement
a) O. Schäfer, lctpc.org
e
- ions
≈90μs
SLIDE 18
18
Outline
- Concept of a TPC
- Underlying theory
- The ALICE TPC
- Variations and outlook
Max Lamparth, 18th November 2016
Time Projection Chamber
SLIDE 19
19
Underlying theory
- Ionization mechanism
- Wire grids
- Motion in gas
- Amplification and gain
Max Lamparth, 18th November 2016
Time Projection Chamber
SLIDE 20
20
Ionization mechanisms in gas
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
W ⟨ N I⟩ = L⟨ dE dx ⟩ λ = 1/(N σI) Charged particles ( ) propagate through gas → energy loss and ionization
a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008
π, e
- , ...
W : energy, N I : average number of ionization electrons, N : particle density, λ: mean free flight path, σ I: ionization cross section per electron
SLIDE 21
21
Ionization mechanisms in gas
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
W ⟨ N I⟩ = L⟨ dE dx ⟩ λ = 1/(N σI) Charged particles ( ) propagate through gas → energy loss and ionization Different mechanisms:
- primary ionization:
- secondary ionization:
- Intermediate:
π A → π A
+e
- , π A
++e
- e
- ...
e
- A → e
- A
+e
- , e
- A
++e
- e
- ...
π A → π A
* or e
- A → e
- A
*
A
* B → A B +e
- a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008
π, e
- , ...
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22
Ionization mechanisms in gas
Total Energy loss determined by: In TPC: Only measure without retarded ionization Adjusted Bethe-Bloch formula with cut-off at 95% Energy → ignore high energy electrons producing separable tracks (~1 cm restriction)
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
( dE dx )
restricted
=2π N e
4
mc
2
z
2
β
2 [ln √2mc 2 Emaxβγ
I −β
2
2 −δ(β) 2 ]
⟨
dE dx ⟩total = ⟨ dE dx ⟩collision + ⟨ dE dx ⟩Bremsstr
⟨
dE dx ⟩collision
a) Jens Wiechular, 2013 b) “Particle Detection with Drift Chambers”, Blum et al., 2008
z : charge of particle, N : number density of electrons in traversed matter, I : mean excitation energy, δ: correction term
SLIDE 23
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Ionization mechanisms in gas
Total Energy loss determined by: In TPC: Only measure without retarded ionization Adjusted Bethe-Bloch formula with cut-off at 95% Energy → ignore high energy electrons producing separable tracks (~1 cm restriction)
- Average energy loss due to electromagnetic interaction
- For high energies Bethe-Bloch applicable to electrons
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
( dE dx )
restricted
=2π N e
4
mc
2
z
2
β
2 [ln √2mc 2 Emaxβγ
I −β
2
2 −δ(β) 2 ]
⟨
dE dx ⟩total = ⟨ dE dx ⟩collision + ⟨ dE dx ⟩Bremsstr
⟨
dE dx ⟩collision
a) Jens Wiechular, 2013 b) “Particle Detection with Drift Chambers”, Blum et al., 2008
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24
Ionization mechanisms in gas
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
a) ALICE TPC, 2015
( dE dx )
restricted
=2π N e
4
mc
2
z
2
β
2 [ln √2mc 2 Emaxβγ
I −β
2
2 −δ(β) 2 ] Fermi-Plat.
SLIDE 25
25
Ionization mechanisms in gas
More Detail in upcoming talk: “Signal creation, energy loss and dE/dx”
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
a) ALICE TPC, 2015
Fermi-Plat.
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26
Wire grids and fields
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
E-field of a wire & displaced wire in a tube → sagitta due to drift field → affects gain Er = λ 2π ϵo 1 r = U ln(a/b) 1 r (E1)y = − U ln(a/b) d b
2
a) b) c) d) “Particle Detection with Drift Chambers”, Blum et al., 2008
λ: linear charge density, U : voltage, d: displacement from center
SLIDE 27
27
Wire grids and fields
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
E-field of a wire & displaced wire in a tube → sagitta due to drift field → affects gain Use multiple wires to create grid:
- Similar to layer of charge with
Er = λ 2π ϵo 1 r = U ln(a/b) 1 r (E1)y = − U ln(a/b) d b
2
σ = λ/s
a) b) c) d) “Particle Detection with Drift Chambers”, Blum et al., 2008
SLIDE 28
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Wire grids and fields
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
E-Field of a wire grid central electrode Drift region Sensor /acc. region
a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008
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Wire grids and fields
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
E-Field of a wire grid Limited transparency (neutral wire):
a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008
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30
Wire grids and fields
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
Gating grid:
- Additional layer of wires “open”: “closed”:
→ excludes ions/electrons → stops ion back-flow → no space charge → background measurement
a) b) c) “Particle Detection with Drift Chambers”, Blum et al., 2008
SLIDE 31
31
Motion in gas
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
Ions and electrons propagate differently → leads to isotropic scattering → leads to preferred scattering direction In reality: E and B field → B field necessary for momentum measurement Langevin equation: : velocity vector K : frictional force (due to interaction with gas) constant e
- : me ≪ mp
A
+: mA ≈ mp
m du dt = e E + e[u×B] − K u u
a) “Particle Detection with Drift Chambers”, Blum et al., 2008
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32
Motion in gas
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
Solve Langevin equation: → Helix-like propagation Two Cases: (dominant in TPC) (dominant in TRD) ux uz = −ω τ B y+ω
2 τ 2 Bx
(1+ω
2 τ 2)Bz
u y uz = ω τ Bx+ω
2 τ 2 B y
(1+ω
2 τ 2)Bz
|u| = (e/m) τ
√1+ω
2 τ 2|E| = e
m τ|E|cos(Ψ) E∥B E⊥B
a) b) c) “Particle Detection with Drift Chambers”, Blum et al., 2008
ui: velocity component, ω: electron cyclotron frequency, τ=m/K Ψ: E field component in drift direction
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Motion in gas
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
Solve Langevin equation: → Helix-like propagation Two Cases: (dominant in TPC) Other inhomogeneities:
- space-charge accumulation
- effects
(dominant in TRD)
- thermal effects
- electron attachment
ux uz = −ω τ B y+ω
2 τ 2 Bx
(1+ω
2 τ 2)Bz
u y uz = ω τ Bx+ω
2 τ 2 B y
(1+ω
2 τ 2)Bz
|u| = (e/m) τ
√1+ω
2 τ 2|E| = e
m τ|E|cos(Ψ) E∥B E⊥B E×B
a) b) c) “Particle Detection with Drift Chambers”, Blum et al., 2008
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34
Movement in gas
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
Inhomogeneities Example for effects Space-charge accumulation (important) → Upcoming talks: “Diffusion and space point resolution” “Space point distortions”
↓B↓
E×B
a) “Particle Detection with Drift Chambers”, Blum et al., 2008
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35
Amplification and gain
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
Proportional wire E-field accelerates incoming electrons → electron avalanche Limitations: Wire has proportional region Photo-ionization limits stability Lateral extent
a) Jens Wiechular, 2013 b) “Particle Detection with Drift Chambers”, Blum et al., 2008
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Amplification and gain
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
Drift to amplification region: Close vicinity of the wires Calculate gain: for N: number of electrons, ds: path fragment, Townsend coefficient Diethorn formula (for ): With gain , a & b chamber radii, voltage V, minimal ionization field , gas density & normal gas density Gain influenced by: Gas density Sparce charge E-field Ionization energy Geometrical imperfections lnG = ln2 ln(b/a) V ΔV ln V ln(b/a)a Emin(ρ0)(ρ/ρ0) dN = N α ds α: α∝E G=N /N 0 Emin ρ & ρ0
a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008
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Amplification and gain
Max Lamparth, 18th November 2016
Time Projection Chamber Underlying theory
Upcoming talk: Signal creation, energy loss and dE/dx Below: Probability density H of produced ions n (for a weak E-field) Above: Gas gains vs Anode voltage Actual working point: ~ 6k-10k gain
a) Jens Wiechular, 2013 b) “Particle Detection with Drift Chambers”, Blum et al., 2008
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38
Outline
- Concept of a TPC
- Underlying theory
- The ALICE TPC
- Variations and outlook
Max Lamparth, 18th November 2016
Time Projection Chamber
SLIDE 39
39
ALICE TPC
Max Lamparth, 18th November 2016
Time Projection Chamber
SLIDE 40
40
The ALICE collaboration
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
A Large Ion Collider Experiment LHC experiment for heavy-ion (Pb-Pb) collisions Search for non-perturbative aspects of QCD & new physics at high field strengths Up to 20 000 charged particles per collision with → in need of triggering, tracking and identification
√s ≈ 5.5TeV
pt ∈ [100 MeV ,100 GeV]
SLIDE 41
41
The ALICE collaboration
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
a) ALICE Group, 2010
SLIDE 42
42
The ALICE experiment
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
a) Jens Wiechular, 2013
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The ALICE TPC
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Purpose: main tracking detector Largest TPC and largest warm magnet in the world with ITS, TRD & TOF:
- particle identification
- two track separation
- vertex determination
- charged particle momentum measurement
- good dE/dx resolution (for )
TPC vs MWPC stacking?
- MWPCs cannot be stacked as closely → scattering
- MWPC are more expensive (electronics)
pt≈20GeV/c (possibly up to 40) and |η|<0.9
a) Anton Andronic, 2003
510 cm 500 cm
SLIDE 44
44
The ALICE TPC
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Requirements: Hadronic
- two-track resolution
- dE/dx resolution
- track matching
- momentum resolution
Leptonic
- tracking efficiency
- used for electron tagging (with TRD)
- rate capability
SLIDE 45
45
The ALICE TPC – Concept (2000)
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Design objectives: Gas gain / wire amplification
- gain goal: → wire sagitta
Drift field (focus on geometry)
- space-point resolution
Temperature
- drift velocity (required )
Drift gas purity
- electron attachment
(required -content to be ppm) Structure stability 2 x 10
4
a) O. Schäfer, lctpc.org
ΔT =0.1K O2
SLIDE 46
46
The ALICE TPC – After Run 2 (2015)
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Design objectives: Gas gain / wire amplification
- trips! → 1% Pad loss in Run 1
- compromise: S/N vs space-point loss
& hardware stability Drift field
- space-point resolution
→ space-charge dominant!
a) O. Schäfer, lctpc.org
SLIDE 47
47
Field cage
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Provide uniform E-field from central Electrode to end plates Field degrader for homogeneity → Voltage divider Design choices:
- surface smoothness
- low-Z material
- low permeability
- inner/outer containment vessel
b) Jens Wiechular, 2013 a) c) ALICE TPC TDR, 2000
SLIDE 48
48
The ALICE TPC
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Drift field issues due to misalignment of degrader rods: 0.1 mm error will lead to 1mm total error! → Upcoming talk!
a) Marian Ivanov, 2011
SLIDE 49
49
The ALICE TPC
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Drift field issues due to misalignment of central electrode:
a) Marian Ivanov, 2011
SLIDE 50
50
The ALICE TPC – After Run 2 (2015)
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Design objectives: Gas gain / wire amplification
- trips! → 1% Pad loss in Run 1
- compromise: S/N vs space-point loss
& hardware stability Drift field
- space-point resolution
→ space-charge dominant!
a) O. Schäfer, lctpc.org
SLIDE 51
51
Field cage
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Gas choice (by elimination) Nobel gas: Ar (higher Z → multiple scattering, higher M → ion mobility) → Ne Quencher: bad for material, hydrocarbons bad aging → Addition: for better drift velocity Ideal gas equation: Barometric height formula → can measure pressure difference inside chamber → pressure over year pV = n RT P = Pb exp[−g0 M(h−hb) R
*T b
]
a) b) wikipedia.com
N2 CO2 CF4 pb: static pressure T b: standard temperature R
*: universal gas const
M : molar Mass of gas
SLIDE 52
52
Field cage
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Gas choice: Influence of pressure: ( )
a) ALICE TPC, 2010 b) “Particle Detection with Drift Chambers”, Blum et al., 2008
ΔG G ∝ Δ p p
SLIDE 53
53
Readout Chambers
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
All wires in azimuthal direction Inner/Outer ROC → Different wire geometry (track density function of radius) Mounting on end plate to minimise dead space Active area ≈32.5 m
2
a) ALICE TPC, 2010 b) Jens Wiechular, 2013 c) ALICE TPC TDR, 2000
SLIDE 54
54
Readout Chambers
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Pads behind wires for ion detection Copper → ions create mirror charge → total amount: 557 568 pads → needs sophisticated electronics → ALTRO Chip Upcoming talk: “Signal creation, energy loss and dE/dx”
a) “Particle Detection with Drift Chambers”, Blum et al., 2008
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55
Readout Chambers
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Resolution and gas gain
a) ALICE TPC, 2010
SLIDE 56
56
Readout Chambers Upgrade → GEMs
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Gas Electron Multiplier for Run 3 (2020)
- higher luminosity of heavy ions (50k Hz)
- MWPC not continuous readout
→ due to gating → dead time
- GEM continuous readout
→ no dead time → background (ion back flow ~ 1%)
- Disadvantage:
→ S/N smaller
a) Ernst Hellbär, 2015 b) Luciano Musa, 2016
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57
Other TPCs
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Liquid Argon as sensitive medium → high density compared to gas → interaction probability increases by 1000 Usable for low cross section experiments → neutrino searches → dark matter experiments Dual Phase TPCs → explicit for dark matter search → uses liquid and gas as sensitive medium (Further reading: XENON experiment)
a) wikiipedia.org
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Conclusion
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
ALICE TPC Rather simple detector concept, but on a huge scale! → a lot of parameters to control! → success! To reconstruct particle track and momentum → Influence of each parameter has to be known/estimated Brief introduction to some examples, for more detail, please attend:
SLIDE 59
59
Following talks
Max Lamparth, 18th November 2016
Time Projection Chamber ALICE TPC
Diffusion and space point resolution Michael Ciupek Signal creation, energy loss and dE/dx Mihail-Bogdan Blidaru Particle reconstruction Jan Repenning Space point distortions Florian Joerg & Yannik Vetter
a) shapeways.com, 2016