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CLIC RF manipulation for positron at CLIC Scenarios studies on hybrid source

tarik-hanson avatar
tarik-hanson
20 diapositives · 326 Views · Nov 11, 2014

This document presents an overview of ongoing studies on hybrid sources for positron production in the Compact Linear Collider (CLIC) scenarios, focusing on Compton sources and hybrid sources. The efficiency of positron capture and acceleration techniques is analyzed using 2 GHz Traveling Wave (TW) tanks. Results indicate significant improvements in efficiency with updates to the tank structures, emphasizing both deceleration strategies and the effects of space charge on positron yield. The primary objective is to enhance the performance of the positron sources in reaching higher energy levels.

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CLIC RF manipulation for positron at CLIC Scenarios studies on hybrid source
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  1. CLIC RF manipulation for positron at CLICScenarios studies on hybrid source Freddy Poirier 12/08/2010

  2. Compton source HB source e+ Efficiency snapshot Up to Target Results here with old aperture structures On the way to be updated Efficiency (here): Nb e+ /nb e- at 200 MeV, E>165 MeV polarisation Global ACS only No polarisation As of 4 weeks ago Compton 1.3 GeV Compton 3 GeV Hybrid Source 5 GeV Single 5 ip • Sources scenarios (pol. and non-pol. ) being studied: • - Hybrid source (CLIC baseline) • - Compton source (see talks from I.Chaikoska) Up to Target ACS only e- g

  3. HB source e-/g Target (crystal) Primary beam Linac for e- g/e+ Target Pre-injector Linac for e+ 5 GeV 200 MeV e- 2 GHz AMD 2 GHz Hybrid Source Scenario (Baseline) • 5 GeV • 2 m between crystal and target • 10 mm target thickness • Positron Bunch length at target exit= 500 mm Focus of the present study

  4. Present Studies • Capture and acceleration using Travelling Wave (TW) tanks. • 84 accelerating cells tanks + 2 couplers i.e. long cavity • Prior studies have used Standing Wave (SW) 6 cells cavities (see talk of A.Vivoli) • For Hybrid source (HB) • Scenarios with modification phase of first TW • Space charge limits • Additional Scenarios • Solenoid field (1T) • Cavity within AMD

  5. HB source 2 GHz TW tanks Typical cells dimension for the TW tanks • 2 GHz • 84 accelerating cells constitute the TW tanks • Note: 84 cells + 2 half cells for couplers within ASTRA • 2p/3 operating mode • 4.36 m long • 15 MV/m • Up to 5 tanks are used to accelerate e+ up to 200 MeV Case with 4 cells 15 mm Typical electric field for the 4 cells cavity 2p/3 First optimisation done on 15 mm iris (radius aperture) tanks but final results with 20 mm iris tanks

  6. HB source e+ g/e+ target AMD Solenoid TW tanks Capture Strategy Capture strategy of the first tank? Other tanks: full acceleration • Acceleration: Phase of the first tank tuned for use of maximum accelerating gradient for the first tank • 4 tanks are needed to reach ~200 MeV • Deceleration: adapt the phase and gradient of the first tank to capture a maximum of positrons • 5 tanks are needed to reach ~200 MeV

  7. HB source Transverse distribution Population X (m) Acceleration Acceleration case at 18.12 m (to reach ~200MeV) E (MeV) Z (m) Population Z (m) • 2388 positrons With cut at emin=165 MeV E (MeV) Total Efficiency(200MeV,emin) 2388/6000= 0.398

  8. HB source Deceleration • First tank Phase = 280o • Choice of gradient: Values at 22.63 m (at ~200 MeV) More positrons in the higher tail but tail further in z 7Mv/m E (MeV) 6Mv/m 5Mv/m More positrons in lower tail but tail lower in energy Z (m) Z (m)

  9. HB source 1317 e+ 691 e+ At 200 MeV Acceleration case Deceleration case • For the deceleration case the efficiency* at 200 MeV is higher than for the acceleration case • For further information: The value in red gives the number of positrons within the red dashed box Energy (MeV) Energy (MeV) Z (m) Z (m) Eff 200MeV = 0.40 Eff 200MeV = 0.53 *Eff 200 MeV: Nb of particles entering target/ Nb of particles at exit of tank with energy greater than 165 MeV

  10. HB source 20 mm aperture New 2 GHz cavity and field provided by P.Lepercq Acceleration scenario Deceleration scenario Total yield=0.9 Total yield=0.95 Efficiency >165MeV=4621/6000= 0.77 (was 0.4 for 15 mm aperture) Efficiency >165MeV=5335/6000= 0.89 (was 0.53 for 15 mm aperture) This is the big advantage of the deceleration technique

  11. HB source HB: Acceleration scenario Impact of space charge At 200 MeV No space charge -10% level Negligible space charge effect to be expected Charge per macro-particles (nC): Cmp=Ne+i x qe+ / ( 1e-9 x Ne+s Ne+i: initial nb of e+ Ne+s: simulated nb of e+ Charge x 250 In order to have a 10% level impact on the result, the e- charge has to be multiplied by 250. We are far from this with the present CLIC values. 3.75 10 37.5 375 x109 e- Expected level of charge for HB

  12. HB source Impact of space charge • Acceleration scenario: • The use of space charge imply -3.6% e+ at 200 MeV. • With the present e- charge, we are at ~2.5 102 lower than a 10% effect • Deceleration scenario: • The impact is -4.6%. • With the present e- charge, we are at 102 lower than a 10% effect The impact of space charge is here of the order of less than 5% The difference from acceleration to deceleration is noticeable but the level is not detrimental in both case

  13. e+ g/e+ target AMD 4 cells cavity Solenoid TW tanks Additional Studies on the capture with hybrid source • Additional scenario: • 1) An accelerating field within the Adiabatic Matching Device (AMD) • 2) Increase of the magnetic field surrounding the TW Accelerating section. Traditionally it is fixed at 0.5 T. e- g

  14. HB source Additional Scenarios Acceleration scenarios 20 mm nominal case Case (AMD 6T  0.5 T and no cavity inside the AMD, but AMD inner radius=15 mm) e+ g/e+ target AMD 4 cells cavity Solenoid TW tanks

  15. HB source Conclusion • 2 scenarios studied: • Acceleration and deceleration • Very interesting scenario is deceleration • Further optimisation (on lattice) for capture can be done • No major impact from space charge foreseen in both scenarios • Additional scenarios are also studied (booster within the AMD and higher solenoid field) which shows good potentials Perspectives • What about power consumption (TW/SW)? • The choice of TW/SW is not done yet. It will highly depends on the power consumption. • Though if TW are in use for acceleration between 200 MeV up to DR then it is an attractive choice. • Review of dimension should be done (2 GHz  1 GHz?) • The results need to be sent to the bunch compressor and check the effective yield there

  16. More Slides

  17. Compton source Compton Scenario target e- e+ Laser Pulse length=1.5 mm Laser pulse energy=0.1 J ll=1064 um x 5 1.3 GeV e- sze-=600 mm sz = 600 mm szl>sze- 2o

  18. Compton source Distributions at ~200 MeV Acceleration case (18.12 m) Deceleration case (22.63 m) 1255 e+ 2138 e+ This value is used for the efficiency calculation 1.3 GeV, 5 IP Red box: de=10 MeV, dz=5 mm

  19. HB source Impact of space charge • The space charge is considered traditionally low because: • Large transverse size of the beam at exit of AMD • High enough energy (The positrons have an average energy > 5 MeV so quite relativistic) • Previous studies with Parmela simulation have shown an impact of space charge of the order of 1 % on the result • Are we far from any effect due to Space charge? • What is the limit wrt to the charge of the bunch. i.e. if we increase the charge of the bunch at the exit of the AMD will there be a noticeable impact? • What happen to the space charge limit if we do deceleration?

  20. HB source The CLIC CDR yield hypothesis Target e+/e- Pre-accelerator PDR 10 109 e- Yield e+/e- = 0.7 7 109 e+ CDR values We are simulating 6000 e- (macro-particles), representing 10 109 e- i.e. the charge per simulated particle is 2.7 10-4 nC. PDR: Pre-Damping Ring