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Positrons traps Samuel Niang C.E.A. Saclay / GBAR Experiment - - PowerPoint PPT Presentation
Positrons traps Samuel Niang C.E.A. Saclay / GBAR Experiment - - PowerPoint PPT Presentation
Positrons traps Samuel Niang C.E.A. Saclay / GBAR Experiment 28/11/2018 Positrons traps 1 35 Table of contents 1. The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling
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Table of contents
- 1. The Buffer Gas Trap
Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency
- 2. The Riken Trap
Brief description of the RT Stacking in the RT Ways of improvements 2 35
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The Buffer Gas Trap
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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Set of electrodes
Figure: The BGT is made of 3 sets of electrodes. Stage 1 + 2 : accumulation from the LINAC, Stage 3: storage of positrons. (Picture source: A. Maia Leite)
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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Potential in the trap
200 400 600 800 z (mm) 20 40 60 80 100 120 140 Potential (V) Stage 1 Stage 2 Stage 3 Positrons accumulation in the second stage
Figure: Potential used in the first second stages to accumulate positrons.
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Equation
dN(t) dt = N τ + R (1) N(t) = Rτ(1 − e− t
τ )
(2) N: e+ number τ: lifetime R: incoming flux into the trap CSi → s(t) = kN(t) ⇒ we have to calibrate 7 35
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Result
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 time (s) 0.000 0.025 0.050 0.075 0.100 0.125 0.150 CsI signal (Arb.) Accumulation in the second stage data fit
Figure: CSi detector signal for different accumulation times in the second stage. LINAC frequency: 100Hz. Fit with s(t) = Rτ(1 − e−t/τ) + c, τ = 0.628 ± 0.03 s, R = 0.170 ± 0.011 s−1, c = 0.022 ± 0.003.
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Electrons effect
0.0 0.5 1.0 1.5 2.0 2.5 3.0
time(s)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
CsI signal (Arb.)
0V
- 100V
- 200V
- 400V
- 600V
- 800V
Figure: Effect of different potentials on a plate at the BGT entrance with a hole to repel the electrons.
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Electrons effect
100 200 300 400 500 600 700 800
Potential (V)
0.5 0.6 0.7 0.8 0.9 1.0 1.1
(s)
100 200 300 400 500 600 700 800
Potential (V)
0.4 0.6 0.8 1.0 1.2 1.4
R (s
1)
Figure: Impact on the lifetime and the incoming flux.
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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Potential in the trap
200 400 600 800 z (mm) 20 40 60 80 100 120 140 Potential (V) Stage 1 Stage 2 Stage 3 Compression in the second stage and transfert to the thrid stage Before compression After compression
Figure: Potential used in the second stage to accumulate positrons. After 100 ms of accumulation, the cloud is compressed and transferred into the third stage.
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Result
5 10 15 20 25 time (s) 0.0 0.2 0.4 0.6 0.8 CsI signal (Arb.) Decay in the third stage data fit
Figure: CSi detector signal for different storages times in the third stage. Fit with s(t) = Rτe−t/τ + c, τ = 14.30 ± 0.96, R = 0.050 ± 0.002 s−1, c = 0 ± 0.029.
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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Energy distribution of the straight trough beam
20 40 60 80 100 Potential barrier (V) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 CsI signal (Arb.) Energy distribution for a straight through beam data fit Energy distribution
Figure: CSi signal for different potential barriers for a straight through
- beam. Fit with s(V) = A
2erfc
- V−V0
√ 2σ
- , V0 = 44.90 ± 0.11,
A = 0.566 ± 0.006, σ = 5.83 ± 0.15, c = 0.005 ± 0.005.
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Energy distribution after the second stage
15.0 17.5 20.0 22.5 25.0 27.5 30.0 32.5 Potential barrier (V) 0.0 0.2 0.4 0.6 0.8 CsI signal (Arb.) Energy distribution after the second stage data fit Energy distribution
Figure: CSi signal for different potential barriers after the second stage. Fit with s(V) = A
2erfc
- V−V0
√ 2σ
- , V0 = 23.30 ± 0.02, A = 0.760 ± 0.003,
σ = 1.040 ± 0.027, c = 0.063 ± 0.002.
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Energy distribution after the third stage
21.0 21.5 22.0 22.5 23.0 Potential barrier (V) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 CsI signal (Arb.) Energy distribution after the third stage data fit Energy distribution
Figure: CSi signal for different potential barriers for a straight through
- beam. Fit with s(V) = A
2erfc
- V−V0
√ 2σ
- , V0 = 22.10 ± 0.01,
A = 0.639 ± 0.003, σ = 0.126 ± 0.007, c = 0.025 ± 0.002.
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Positrons cooling
10 5 5 10
recentered potential barriers (V)
0.0 0.1 0.2 0.3 0.4
energy distributions Positrons cooling in the Buffer Gas Trap (x 3) without trapping, V0 = 44.9 after 2nd stage, V0 = 23.3 (x 0.15) after 3rd stage, V0 = 22.1
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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Potential in the trap
200 400 600 800 z (mm) 20 40 60 80 100 120 140 Potential (V) Stage 1 Stage 2 Stage 3 Compression in the second stage and transfert to the thrid stage Before compression After compression
Figure: Potential used in the second stage to accumulate positrons. After 100 ms of accumulation, the cloud is compressed and transferred into the third stage.
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Stacking in the third stage
2 4 6 8 10 12 14 16 n° stacks 0.0 0.5 1.0 1.5 2.0 2.5 3.0 CsI signal (Arb.) data linear fit linear limit
Figure: Stacking in the third stage. Linear limit: 8 stacks. Fit with s(n) = an + b, a = 0.246 ± 0.006, b = 0.067 ± 0.028.
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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BGT efficiency
CsI signal Cross 1 : 0.27 V CsI signal Cross 3 : 0.12 V after 100ms accumulation (10 pulses) e = 0.12 10 × 0.27 ∼ 5% 23 35
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Transfert to the Riken Trap
200 400 600 800 z (mm) 20 40 60 80 100 120 140 Potential (V) Stage 1 Stage 2 Stage 3 Compression in the third stage and transfert to the riken trap Before compression After compression
Figure: Potential used in the second stage to accumulate positrons. After 100 ms of accumulation, the cloud is compressed and transferred in the third stage.
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The Riken Trap
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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Brief description of the RT
R W
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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Potential in the trap
700 750 800 850 900 950 1000
z(mm)
20 40 60 80 100 120 140
Potential Potential in the Riken Trap
Figure: Potential used in the Riken Trap.
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Result
25 50 75 100 125 150 175 200 n° stacks 0.00 0.05 0.10 0.15 0.20 0.25 CsI signal (Arb.) data linear fit linear limit
Figure: Stacking in the Riken Trap. Max: ∼ 40 stacks. Fit with s(n) = an + b, a = 0.00547 ± 0.00026, b = 0.0133 ± 0.004.
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Potential in the trap
700 750 800 850 900 950 1000
z(mm)
20 40 60 80 100 120 140
Potential Potential in the Riken Trap
Figure: Potential used in the Riken Trap.
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Result
25 50 75 100 125 150 175 200 n° stacks 0.0 0.1 0.2 0.3 0.4 0.5 CsI signal (Arb.) data linear fit linear limit
Figure: Stacking in the Riken Trap. Max: ∼ 100 stacks. Fit with s(n) = an + b, a = 0.00473 ± 0.00079, b = 0.0235 ± 0.0034.
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Table of contents
1 The Buffer Gas Trap Brief description of the BGT Lifetime in the second stage Lifetime in the third stage Positrons cooling Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements
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Ways of improvements
find a better potential well rotating wall do a real calibration (for now ∼ 107 − 108 positrons for 100 stacks, we want 1010). 33 35
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Conclusion
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Conclusion
Lifetimes in the different stages:
◮ 2nd stage: τ = 0.6 s ◮ 3rd stage: τ = 14 s ◮ RT: τ → ∞
Positrons cooling (energy spread):
◮ linac: σ = 6 eV ◮ 2nd stage: σ = 1 eV ◮ 3rd stage: σ = 0.1 eV
∼ 108e+ stored in the Riken Trap (in 100 s) 34 35
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