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Beam dump and positron production studies for CEPC and past CLIC studies

Beam dump and positron production studies for CEPC and past CLIC studies. Armen Apyan Northwestern University Evanston, IL, US. Outline. __________________. Polarized Positron Production Methods CLIC Main Beam Dump Summary. Polarized Positron Production . The Concept.

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Beam dump and positron production studies for CEPC and past CLIC studies

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  1. Beam dump and positron production studies for CEPC and past CLIC studies Armen Apyan Northwestern University Evanston, IL, US FCC-ee Accelerator meeting #6

  2. Outline __________________ • Polarized Positron Production Methods • CLIC Main Beam Dump • Summary FCC-ee Accelerator meeting #6

  3. Polarized Positron Production FCC-ee Accelerator meeting #6

  4. The Concept __________________ + decay of: • naturally existing radioactive isotopes, • short – life isotopes produced by an accelerator Concerning polarization, positrons emitted from beta decays are longitudinally polarized but are subject to a large energy spread, a wide angular distribution, low intensity, etc. e+e- pair production of photons • Positron beam is longitudinally polarized at the upper limit of the e+ energy. FCC-ee Accelerator meeting #6

  5. The Methods of Polarized Positrons Production __________________ • Circularly polarizedgby bremsstrahlung of electrons (longitudinally polarized) in amorphous or crystalline target ande+e-production in converter target. • Circularly polarized gfrom high energy e- (could be unpolarized) beam passing through an helical undulator ande+e- production in converter target. • Circularly polarized gfrom Compton backscattering of circularly polarized laser beam on e- (could be unpolarized) beam and e+e- production in converter target. FCC-ee Accelerator meeting #6

  6. Conventional Scheme based on oriented crystal __________________ Separate amorphous target for e+ production: Separate crystalline target for production of circularly polarized ’s by coherent bremsstrahlung of longitudinally polarized electrons Step-1: Produce Circularly polarized γ Step 2: Convert γ’s to e+ Crystal target Amorphous converter Capture system e+ Crystal increases the yield of the photons, not the polarization High intensity Pol. e- beam Pol. ’s e- Bending Magnet • Apyan, H. Braun, M. Velasco • for CLIC, 2005 To beam dump FCC-ee Accelerator meeting #6

  7. Choice of Crystal Radiator and Converter __________________ Crystal Diamond single crystal 1cm: • Tight lattice (small lattice constant 3.567Å • Low Z=6 Coherent Bremsstrahlung – stable, proven method. High Z amorphous target Tungsten 0.2 mm thick Bremsstrahlung – stable, proven method. Circularly Polarized Photon Sources: Polarized Positron Converter: High Z material Amorphous Tungsten 0.3 mm thick FCC-ee Accelerator meeting #6

  8. __________________ Tungsten was used as a positron converter for both configuratons Number of Photons and Positrons per Incident Electron The crystal scheme provides ~3 times larger photon yield than amorphous configuration with the same beam parameters. Proposed configurations give the following yield of photons Tungsten radiator 0.007 g/e- Diamond single crystal 0.03 g/e- FCC-ee Accelerator meeting #6

  9. Polarized Positron Beam Production Based on Helical Undulator __________________ Circularly polarized gfrom high energy e- beam passing through an helical undulator ande+e- production in converter target. The photons are produced by scattering of virtual photons of a helical undulatorwith period λuoff an electron beam. Converter target Capture system Helical undulator e+ high energy e- beam References: V.E. Balakin, A.A. Mikhailchenko, “The Conversion System for Obtaining High Energy Electrons and Positrons”, Preprinit BINP-79-85, 1979. Pol. ’s e- Bending Magnet To beam dump The electron beam is coaxial with the undulator. The highest energy photons take on the polarization of the undulator field, so that a helical undulator leads to circularly polarized photons. The intensity of undulatorphotons depends on the intensity of the virtual photons of the undulator, and hence on the square of its magnetic field strength. FCC-ee Accelerator meeting #6

  10. Observation of Polarized Positrons from an Undulator-Based Source: E166 Experiment __________________ Electron beam energy 46.6±0.1 GeV Repetition rate of 10 Hz with 1–4x109e/pulse Normalized beam emittances2.2(0.5)X105mrad Transversespot size σxσy35 μm Helical undulator length 1m Undulator aperture 0.9mm The photon beam impinged upon a 0.2-radiation-length tungsten target T1 to produce positrons and electrons which were separated in spectrometer, and the polarization and rate of the positrons were measured in transmission polarimeter TP1. The unconverted photons were monitored in a second transmission polarimeter, TP2. References: G. Alexander et al., Observation of Polarized Positrons from an Undulator-Based Source ,Phys. Rev. Let., 100, 210801 (2008) FCC-ee Accelerator meeting #6

  11. Laser based Polarized Positrons Source __________________ Circularly polarized gfrom Compton backscattering of laser beam on e- beam and e+e- production in converter target. The main advantages of the Compton scheme are that the positron source is imposed independently with respect to the main linac and the required drive electron beam energy is much lower as compared to the undulator scheme CO2 laser Pol. photons Converter target Capture system e+ High intensity e- beam Pol. ’s e- Bending Magnet To beam dump References: T. Omori, “A Polarized Positron Beam for Linear Collider”, KEK Preprints 98-237 and 99-188. FCC-ee Accelerator meeting #6

  12. Compton Source R&D at ATF __________________ A fundamental scheme of polarized positron production. Right-handed polarized laser photons are backscattered off relativistic electrons resulting in production of left handedpolarized rays in the forward direction (in the high-energy part of the spectrum). Pair creation of the rays through a tungsten plate generates left-handed positrons in the high-energy part. Themagnitude of the positron polarization was calculated as 73 ± 15 ±19%, where the first error is a statistical one and the second error is systematic one which comes from the uncertainty in a Monte Carlo simulation. References: T. Omori et al., “Efficient Propagation of Polarization from Laser Photons to Positrons through Compton Scattering and Electron-Positron Pair Creation“. Phys. Rev. Let., 96, 114801, 2006. FCC-ee Accelerator meeting #6

  13. Polarized Positron Source for CEPC __________________ Which scheme of polarized positron production is good for CEPC ? The three concepts have their own problems connected with the cost and technical complexity. Many investigations were done towards the polarized positron production in the last decade. Several existing Monte Carlo codes can help in simulation of the positron production with high accuracy. For example: Laser – electron interaction ------- CAIN, Guinea-Pig Energy deposition, particle interaction ---- GEANT4, FLUKA Magnetization of Iron ----------- POISSON And many other. FCC-ee Accelerator meeting #6

  14. Beam Dump Consideration FCC-ee Accelerator meeting #6

  15. Design Consideration: CLIC post-collision line __________________ • Transport particles of all energies and intensities from IP to dump • Separation of the outgoing beams for diagnostics (luminosity monitoring) • Control beam losses in the magnets • Minimize background in the experiments • Stay clear of the incoming beam FCC-ee Accelerator meeting #6

  16. ILC style water dump intermediate dump carbon based absorbers 1.5m side view C-shape magnets 6m 315m 4m 27.5m window-frame magnets 67m Baseline Design __________________ • Separation of disrupted beam, beamstrahlung photons and coherent pairs • Back-bending region to direct the beam onto the final dump • Allowing non-colliding beam to grow to acceptable size FCC-ee Accelerator meeting #6

  17. Some Numbers __________________ • Uncollided beam: sx = 1.56mm, sy =2.73mm  5.6mm2 • e+e- collision creates disrupted beam • Huge energy spread, large x,y div in outgoing beam  total power of ~10MW • High power divergent beamstrahlung • photons • 2.2 photons/incoming e+e-  2.5 E12 photons/bunch train  total power of~4MW • Coherent e+e- pairs • 5E8 e+e- pairs/bunchX • 170kWopposite charge • Incoherent e+e- pairs • 4.4E5 e+e- pairs/bunchX 78 W Collided 1.5TeV Beam at water dump 315m from IP Right sign coherent beam Beamstrahlung photons Disrupted beam FCC-ee Accelerator meeting #6

  18. __________________ Photons Disrupted beam Coherent beam Particles distribution on the CLIC Main Beam Dump The CLIC post collision line is designed to transport the un-collided beams and the products of the collided beams with a total power of 14MW to the main beam dump. FCC-ee Accelerator meeting #6

  19. Main Beam Dump (History) __________________ • 1966: SLAC beam dump • 2.2 MW average beam power capacity • Power absorption medium is water • 2000: TESLA • 12 MW beam power capacity • Water dump FCC-ee Accelerator meeting #6

  20. Concept of the Water based Beam Dump The basic principle of water dump is to present the incoming beam with a region of cold water. The beam dissipates its energy into water. It is essential that the volume of water exposed to the core of the beam be moved transverse to the momentum vector of the beam to prevent “volume boiling”. To renew the water volume in the central part of the shower, between successive bunch trains, a water flows transverse to the direction of the beam. 2.2 MW beam dump D.R. Walz etal, 1965 This presents the following portion of the incoming beam with fresh cold water. FCC-ee Accelerator meeting #6

  21. Baseline Main Dump Design (CLIC) 2010: CLIC 14 MW water dump Cylindrical vessel Volume: 25m3, Length: 10m Diameter of 1.8m Water pressure at 10bar (boils at 180C) Ti-window, 1mm thick, 60cm diameter  baseline for CLIC 2010 main dump 20.0 mm thick stainless steel vessel 60.0 cm diameter window (Ti) 1.0 mm thick ILC type water dump Diameter 1.8 m Dump axis Length 10.0 m __________________ FCC-ee Accelerator meeting #6

  22. General Parameters of Water Dump __________________ 1.The water beam absorber is a cylindrical vessel with an entrance and exit windows in both sides. 2. Volume of water around 25m3 3. Length of dump around 10 m (sufficient multiple of X0) 4. Diameter of dump about 1.8 m. 5. Pressure of water 10 bar, at which water boils at 1800C. 6. Water flow rate around 1 -1.5 m/s 7. Window made of Tior other material, 1mm thick and 60 cm diameter. FCC-ee Accelerator meeting #6

  23. Longitudinal and Transverse Distributions of Paricles The issue for non-colliding beams are the small beam spot and consequently the high power density on a small point of impact on the dump window and the dump itself. Uncollidedbeam: E=1.5TeV, sx= 1.56mm, sy =2.73mm  5.6mm2 FCC-ee Accelerator meeting #6

  24. Main Beam Dump Issues __________________ • Maximum energy deposition per bunch train: 270 J/cm3 • Remove heat deposited in the dump • Minimum water flow of 25-30 litre/s with v=1.5m/s • Guarantee dump structural integrity • Almost instantaneous heat deposition generate a dynamic pressure wave inside the bath! • Cause overstress on dump wall and window (to be added to 10bar hydrostatic pressure).  dimensioning water tank, window, etc.. • Radiolytical/radiological effects • Hydrogen/oxygen recombiners, handling of 7Be, 3H FCC-ee Accelerator meeting #6

  25. __________________ CAIN Kaoru Yokoya ABEL 1984 Guinea Pig Daniel Schulte PhD Thesis 1996 Simulation Tools These codes are fundamental tools for R&D on future linear colliders. These programs simulate beam-beam interactions in high-energy e+ecolliders and the impact of the beam-beam effect on luminosity and background. FCC-ee Accelerator meeting #6

  26. Beam-beam simulation by Guinea-PIG __________________ TLEP Armen’s simulation 12M (multiplied by 30) CERN simulation 360M HF2012 workshop report, p. 42, Table 8.2 FCC-ee Accelerator meeting #6

  27. CAIN and Guinea-PIG simulations for CEPC and TLEP __________________ FCC-ee Accelerator meeting #6

  28. Conclusion (1) __________________ Polarized or unpolarizede+e- colliders? All mentioned schemes can be used to produce either polarized or unpolarized positron beams. The schemes use different methods for production of circularly polarized gamma beams. The schemes use the same method for converting gamma beam into electron-positron pairs. There are many Monte-Carlo simulation and experimental research devoted to positron polarized production. It is time to think about CEPC positron production scheme. FCC-ee Accelerator meeting #6

  29. Conclusion (2) __________________ Conventional Scheme with crystal • Set of comparatively thin successive targets may increase the yield of photons, positrons and ease heating /stress problems for each target • Small Multiple scattering angle • Well established physics of the processes of interaction of electrons with single crystal • Low cost and the simple technical solution make the conventional method attractive. Low positron yield. Needs to be checked. FCC-ee Accelerator meeting #6

  30. Conclusion (3) __________________ Undulator based Scheme Laser based Scheme High Intensity positron beam. Highly polarized positron beam up to 70%. Ease to switch laser polarization state High intensity positron beam. Highly polarized positronbeam up to 60%. Use electron main linac (150-250 GeV). Long helical undulator 150-220m. Needs to be aligned. Problem on design, construction, commissioning, maintenance. Required high intensity laser. The positrons accepted per one bunch crossing does not fit the high CLIC and ILC requirements. For this reason, stacking of the positron bunches was proposed. The performance of the scheme is complicated. FCC-ee Accelerator meeting #6

  31. Beam Dump __________________ It was seen that the deposited energy through the shower spreads to the whole volume of water dump. Which can cause: Heating of the water. Radiolysis – water molecule is broken up into H+,(OH) and other radicals. The result will be H2O2 and H2. Production of radioactive isotopes – photospallation on oxygen. • Beam dump luminosity monitorbased on detection of high energy muons is considered after the main beam dump • High energy muons escape the main dump nearly unaffected, except for small energy losses due to ionization. • Transverse distribution of muons depends on the offset of primary beams. Each of the two beam dumps of CEPC must be able to dissipate 360 kJ of beam energy in the 0.18 mscirculation time, which equates to a power of 2 GW. FCC-ee Accelerator meeting #6

  32. Beam Dump __________________ It was seen that the deposited energy through the shower spreads to the whole volume of water dump. Which can cause: Heating of the water. Radiolysis – water molecule is broken up into H+,(OH) and other radicals. The result will be H2O2 and H2. Production of radioactive isotopes – photospallation on oxygen. Each of the two beam dumps of CEPC must be able to dissipate 360 kJ of beam energy in the 0.18 mscirculation time, which equates to a power of 2 GW. The luminosity monitoring system is considered at the CLIC beam dump. Luminosity monitor is based on detection of high energy muons High energy muons escape the main dump nearly unaffected, except for small energy losses due to ionization. Transverse distribution of muons depends on the offset of primary beams. FCC-ee Accelerator meeting #6

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