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 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

The Buffer Gas Trap

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 3 35

Set of electrodes F igure: 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) 4 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 Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements 5 35

Potential in the trap Positrons accumulation in the second stage 140 Stage 1 Stage 2 Stage 3 120 100 Potential (V) 80 60 40 20 0 0 200 400 600 800 z (mm) F igure: Potential used in the first second stages to accumulate positrons. 6 35

Equation d N ( t ) = N τ + R (1) d t N ( t ) = R τ ( 1 − e − t (2) τ ) N : e + number τ : lifetime R : incoming flux into the trap CSi → s ( t ) = kN ( t ) ⇒ we have to calibrate 7 35

Result Accumulation in the second stage 0.150 data fit 0.125 CsI signal (Arb.) 0.100 0.075 0.050 0.025 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 time (s) F igure: CSi detector signal for different accumulation times in the second stage. LINAC frequency: 100Hz. Fit with s ( t ) = R τ ( 1 − e − t /τ ) + c , τ = 0 . 628 ± 0 . 03 s, R = 0 . 170 ± 0 . 011 s − 1 , c = 0 . 022 ± 0 . 003. 8 35

Electrons effect 0.8 0V -100V 0.7 -200V -400V 0.6 -600V CsI signal (Arb.) -800V 0.5 0.4 0.3 0.2 0.1 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 time(s) F igure: Effect of different potentials on a plate at the BGT entrance with a hole to repel the electrons. 9 35

Electrons effect 1.4 1.1 1.0 1.2 0.9 1.0 1 ) (s) 0.8 R (s 0.8 0.7 0.6 0.6 0.5 0.4 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 Potential (V) Potential (V) F igure: Impact on the lifetime and the incoming flux. 10 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 Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements 11 35

Potential in the trap Compression in the second stage and transfert to the thrid stage 140 Stage 1 Stage 2 Stage 3 120 100 Potential (V) Before compression 80 After compression 60 40 20 0 0 200 400 600 800 z (mm) F igure: Potential used in the second stage to accumulate positrons. After 100 ms of accumulation, the cloud is compressed and transferred into the third stage. 12 35

Result Decay in the third stage 0.8 data fit 0.6 CsI signal (Arb.) 0.4 0.2 0.0 0 5 10 15 20 25 time (s) F igure: CSi detector signal for different storages times in the third stage. Fit with s ( t ) = R τ e − t /τ + c , τ = 14 . 30 ± 0 . 96, R = 0 . 050 ± 0 . 002 s − 1 , c = 0 ± 0 . 029. 13 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 Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements 14 35

Energy distribution of the straight trough beam Energy distribution for a straight through beam data 0.6 fit Energy distribution 0.5 CsI signal (Arb.) 0.4 0.3 0.2 0.1 0.0 0 20 40 60 80 100 Potential barrier (V) F igure: CSi signal for different potential barriers for a straight through beam. Fit with s ( V ) = A � � , V 0 = 44 . 90 ± 0 . 11, V − V 0 2 erfc √ 2 σ A = 0 . 566 ± 0 . 006, σ = 5 . 83 ± 0 . 15, c = 0 . 005 ± 0 . 005. 15 35

Energy distribution after the second stage Energy distribution after the second stage data 0.8 fit Energy distribution CsI signal (Arb.) 0.6 0.4 0.2 0.0 15.0 17.5 20.0 22.5 25.0 27.5 30.0 32.5 Potential barrier (V) F igure: CSi signal for different potential barriers after the second stage. Fit with s ( V ) = A � � , V 0 = 23 . 30 ± 0 . 02, A = 0 . 760 ± 0 . 003, V − V 0 2 erfc √ 2 σ σ = 1 . 040 ± 0 . 027, c = 0 . 063 ± 0 . 002. 16 35

Energy distribution after the third stage Energy distribution after the third stage data 0.7 fit 0.6 Energy distribution CsI signal (Arb.) 0.5 0.4 0.3 0.2 0.1 0.0 21.0 21.5 22.0 22.5 23.0 Potential barrier (V) F igure: CSi signal for different potential barriers for a straight through beam. Fit with s ( V ) = A � � , V 0 = 22 . 10 ± 0 . 01, V − V 0 2 erfc √ 2 σ A = 0 . 639 ± 0 . 003, σ = 0 . 126 ± 0 . 007, c = 0 . 025 ± 0 . 002. 17 35

Positrons cooling Positrons cooling in the Buffer Gas Trap (x 3) without trapping, V 0 = 44.9 after 2nd stage, V 0 = 23.3 0.4 (x 0.15) after 3rd stage, V 0 = 22.1 energy distributions 0.3 0.2 0.1 0.0 10 5 0 5 10 recentered potential barriers (V) 18 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 Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements 19 35

Potential in the trap Compression in the second stage and transfert to the thrid stage 140 Stage 1 Stage 2 Stage 3 120 100 Potential (V) Before compression 80 After compression 60 40 20 0 0 200 400 600 800 z (mm) F igure: Potential used in the second stage to accumulate positrons. After 100 ms of accumulation, the cloud is compressed and transferred into the third stage. 20 35

Stacking in the third stage 3.0 data linear fit 2.5 linear limit CsI signal (Arb.) 2.0 1.5 1.0 0.5 0.0 0 2 4 6 8 10 12 14 16 n° stacks F igure: 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. 21 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 Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements 22 35

BGT efficiency C sI signal Cross 1 : 0 . 27 V CsI signal Cross 3 : 0 . 12 V after 100ms accumulation (10 pulses) 0 . 12 e = 10 × 0 . 27 ∼ 5 % 23 35

Transfert to the Riken Trap Compression in the third stage and transfert to the riken trap 140 Stage 1 Stage 2 Stage 3 120 100 Potential (V) Before compression 80 After compression 60 40 20 0 0 200 400 600 800 z (mm) F igure: Potential used in the second stage to accumulate positrons. After 100 ms of accumulation, the cloud is compressed and transferred in the third stage. 24 35

The Riken Trap

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 25 35

Brief description of the RT R W 26 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 Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements 27 35

Potential in the trap Potential in the Riken Trap 140 120 100 Potential 80 60 40 20 0 700 750 800 850 900 950 1000 z(mm) F igure: Potential used in the Riken Trap. 28 35

Result 0.25 CsI signal (Arb.) 0.20 0.15 0.10 data 0.05 linear fit linear limit 0.00 0 25 50 75 100 125 150 175 200 n° stacks F igure: Stacking in the Riken Trap. Max: ∼ 40 stacks. Fit with s ( n ) = an + b , a = 0 . 00547 ± 0 . 00026 , b = 0 . 0133 ± 0 . 004. 29 35

Potential in the trap Potential in the Riken Trap 140 120 100 Potential 80 60 40 20 0 700 750 800 850 900 950 1000 z(mm) F igure: Potential used in the Riken Trap. 30 35

Result 0.5 data linear fit linear limit 0.4 CsI signal (Arb.) 0.3 0.2 0.1 0.0 0 25 50 75 100 125 150 175 200 n° stacks F igure: Stacking in the Riken Trap. Max: ∼ 100 stacks. Fit with s ( n ) = an + b , a = 0 . 00473 ± 0 . 00079 , b = 0 . 0235 ± 0 . 0034. 31 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 Stacking in the third stage BGT efficiency 2 The Riken Trap Brief description of the RT Stacking in the RT Ways of improvements 32 35