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POSITRON SOURCES USING CHANNELING FOR ILC & CLIC

POSITRON SOURCES USING CHANNELING FOR ILC & CLIC. R.Chehab, X.Artru, M.Chevallier, IPNL/IN2P3/CNRS, Universite Lyon 1 A.Variola, A.Vivoli, LAL/IN2P3/CNRS, Universite Paris-Sud V.M.Strakhovenko, BINP-Novosibirsk L.Rinolfi, CERN. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC. INTRODUCTION

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POSITRON SOURCES USING CHANNELING FOR ILC & CLIC

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  1. POSITRON SOURCES USINGCHANNELING FOR ILC & CLIC R.Chehab, X.Artru, M.Chevallier, IPNL/IN2P3/CNRS, Universite Lyon 1 A.Variola, A.Vivoli, LAL/IN2P3/CNRS, Universite Paris-Sud V.M.Strakhovenko, BINP-Novosibirsk L.Rinolfi, CERN R.Chehab/Posipol2008/Hiroshima, june 2008

  2. POSITRONSOURCES USING CHANNELING FOR ILC & CLIC • INTRODUCTION • * Necessity to consider conventional-like sources • * Good results and perspectives for crystal sources using electron channeling in axially oriented crystals {experiments at CERNand KEK } • * Studies on energy deposition in crystal and amorphous targets confirm the interest of crystals for the total energy deposited [X.Artru et al PRST-AB 6 (2003)091003] which is less than in an amorphous targets giving the same yield. • * Simulations and experiments showed that an hybrid scheme (crystal radiator + amorphous converter) is advantageous. Such a solution allows a limited energy deposition in the crystal, preserving its qualities (as the available crystal potential decreases with temperature rise). R.Chehab/Posipol2008/Hiroshima, june 2008

  3. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • THE BASIC SCHEME FOR ILC & CLIC “x” meters e+ g e- e+, e-, g e- Crystal Amorphous Radiator Converter Only the photons are impinging on the converter: that limits the energy deposition in the amorphous target. The yield is less than if the particles coming from the crystalwere also impinging on the amorphous target R.Chehab/Posipol2008/Hiroshima, june 2008

  4. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • * THE CRYSTAL : Photons generated by electrons in channeling conditions and above barrier. • * The crystal, axially oriented, may be W, Si, Ge, C(d)… • In our case, we choose W in <111> orientation • * THE AMORPHOUS CONVERTER: it is made of W • * THE DISTANCE RADIATOR-CONVERTER: it is of some meters; here it is 2 meters. It allows the use of sweeping magnet in between. Another possibility is to select also charged particles coming from the radiator (e+, e-) with energy larger than Etresholdto increase the yield e+/e- • * IMPINGING ENERGIES: E- = 3, 4, 5 and 10 GeV R.Chehab/Posipol2008/Hiroshima, june 2008

  5. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC ERL Option e+ e- e-,g e- g e+ crystal Up to 2.4 / 5 GeV superconducting linac with quadrupole focusing Target 3 to 10 GeV superconducting linac Capture Section (AMD, Accelerator, Solenoid) + Bunch Compressor Up to 270 MeV GENERALSCHEME: For CLIC, the preaccelerator may stops at 200 Mev; the DR is at 2.4 GeV R.Chehab/Posipol2008/Hiroshima, june 2008

  6. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • SIMULATIONS • Incident beam: electron beam energy between 3 and 10 GeV and transverse rms radius of 1 and 2.5 mm have been considered • Targets: (a) Crystals of 1, 2 and 4 mm thick: for E-=10GeV • Amorphous target of 8 mm • (b) Crystals of 1.4, 2.4 et 4.4 mm thick for E- =3, 4 • and 5 GeV • Amorphous target of 10 mm thick • Capture system: an Adiabatic Matching Device with a magnetic field decreasing from 6 Teslas to 0.5 Teslas on 50 cms. Iris aperture is ~20mm radius. Accelerating field is 18 MeV/m peak value [SW] • Outputs: Simulations have been carried out corresponding to the general scheme. The yield e+/e-, the transverse emittance as the longitudinal emittance have been determined at the end of the solenoid (270 MeV). The capture efficiency has also been determined. R.Chehab/Posipol2008/Hiroshima, june 2008

  7. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • RESULTS • Selected results are concerning: • 1) An incident energy E- of 10 GeV with 1 and 2.5 mm rms beam radius and a 1 mm thick W crystal on <111> axis. The amorphous target is 8 mm thick [ILC source]. • 2) Incident electron energies of 3, 4 and 5 GeV with 1 and 2.5 mm rms radius and 1.4 mm thick W crystal. The amorphous target is 10 mm thick [CLIC source]. • The results of the simulations are summarized in the table below R.Chehab/Posipol2008/Hiroshima, june 2008

  8. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC TABLE OF SIMULATION RESULTS FOR DIFFERENT ELECTRON ENERGIES R.Chehab/Posipol2008/Hiroshima, june 2008

  9. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • POSITRON YIELD FOR DIFFERENT INCIDENT ENERGIES • Two rms radius values for the incident e- beam: 1 and 2.5 mm Accepted yield The yield values are associated to hybrid sources defined above:10 GeV/1mm crystal & 8mm am. 3, 4, 5 GeV/ 1.4 mm crystal & 10mm am. Incident energy R.Chehab/Posipol2008/Hiroshima, june 2008

  10. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • THE PROBLEM OF PEDD • The local and almost instantaneous energy deposition in a target (for instance during a pulse duration) may be very critical for the target survival. Indeed, due to inhomogeneous energy deposition in the target, thermal gradients causing mechanical stresses lead to target destruction as by shock waves. After the SLC target destruction, analyses showed that a maximum value of 35 J/g (in tungsten) must not be exceeded. So, an accurate simulation of the energy deposited in the target has to be worked out dividing the target in elementary domains (typically, annular disks with radius increments of tenths of mm and thickness of tenths of Xo). The energy deposited in each domain is calculated and comparisons made with the maximum allowed value. The PEDD is strongly depending on the incident beam intensity and energy and on its transversedimensions; it depends also on thethickness of the target. R.Chehab/Posipol2008/Hiroshima, june 2008

  11. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • SOME PEDD VALUES • We give here some values of the PEDD corresponding to one electron in GeV/cm3and will precise later the actual values for precise applications (ILC and CLIC). From X.Artru et al: Polarized and unpolarized positron sources… (NIMB,2008) 10 GeV 5 GeV 10 GeV 5 GeV R.Chehab/Posipol2008/Hiroshima, june 2008

  12. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • SOME PRELIMINARY CONCLUSIONS • * Concerning the positron yield: the highest the incident energy, the highest the yield. The accepted yield is higher with smaller electron beam radii (geometrical acceptance) • * Concerning the PEDD: the larger the incident beam size, the smaller the PEDD • => a compromise is to be worked out to have enough yield with limited PEDD. The choices will be made depending on the particularities of the colliders. R.Chehab/Posipol2008/Hiroshima, june 2008

  13. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC 1-CLIC Hybrid scheme R.Chehab/Posipol2008/Hiroshima, june 2008

  14. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • 1-CLIC: • ACCEPTED POSITRON YIELD • * For an incident e- beam with s = 1 mm => h = 1 e+/e- • * For an incident e- beam with s = 2.5 mm => h = 0.9 e+/e- • PEDD • Assuming an incident e- pulse of 2.34 1012 e-, we have : • CRYSTAL AMORPHOUS • PEDD/e- PEDD/total PEDD/e- PEDD/total • (GeV/cm3/e-) J/g (GeV/cm3/e-) J/g • s=1mm 2 38 2.5 48.5 • s=2.5mm 0.35 6.8 0.8 15.5 • An entirely amorphous target, 9 mm thick, with the same incident e- beam would have provided the same accepted yield and a PEDD of 150 J/g (s=1mm) or 40 J/g (s=2.5 mm). This shows the advantages of an hybrid scheme leading to a unique target with a PEDD < 35 J/g using an e- beam with s= 2.5 mm. R.Chehab/Posipol2008/Hiroshima, june 2008

  15. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • SIMULATION RESULTS AT END OF CLIC PREACCELERATOR Blue: 80% Red: rms ex=10pmmmrad ey=11pmmmrad TRANSVERSE EMITTANCES AT 270 MeV (s -=1mm); for s-=2.5mm, the rms emittance areas are only slightly different, the shapes being the same (see figures below). R.Chehab/Posipol2008/Hiroshima, june 2008

  16. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • TRANSVERSE EMITTANCES FOR CLIC (s -=2.5mm) Blue: 80% Red: rms ex=11p mmmrad ey=12p mmmrad R.Chehab/Posipol2008/Hiroshima, june 2008

  17. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • LONGITUDINAL EMITTANCE AT END OF CLIC PREACCELERATOR • [s -=1mm] Blue: 80% Red: rms ez =9.5pcmMeV For s -=2.5 mm, the emittance shape is very similar and the rms area almost the same R.Chehab/Posipol2008/Hiroshima, june 2008

  18. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • PROPOSED POSITRON TARGET FOR CLIC 2 m e+ e- g e+, e-, g (5 GeV) e- Amorphous Crystal W: 1.4 mm thick W: 10 mm thick With an incident beam of 2.34 1012 e-/pulse, we expect 2.1 1012 e+/pulse at 270 MeV (pulse of 156 ns) Or 6.7 109 e+/bunch R.Chehab/Posipol2008/Hiroshima, june 2008

  19. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • 2-A CRYSTAL SOURCE FOR ILC • At energies of some GeV the electron motion in the axial fields of an aligned crystal may be compared to the electron motion in an helical undulator. However: • * in the crystal the transverse motion is not regular: instead of a • circle we have the so-called rosette motion • * The period of motion in an undulator is that of the undulator • l~ cm. The emitted photon wavelength is L~l/2g2. The period of • motion in a crystal is l’~mm;the photon wavelength is L’~l’/2g2 • There is a factor 10-4 on the wavelengths (L’/l’) and so, a factor 10-2 on • the needed energies. So, instead of an energy of 200 GeV as for the • undulator, we need only some GeV. This system can be tested before the • LC is completed. • * In order to have a high yield, we choose 10 GeV as incident • electron energy. R.Chehab/Posipol2008/Hiroshima, june 2008

  20. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • ILC: what is changed from undulator to crystal e+ target The magnetic undulator is replaced by an atomic undulator /crystal incident electron energy is 20 Times less=> 10 GeV This is not a proposed scheme, but only a presentation of the modifications R.Chehab/Posipol2008/Hiroshima, june 2008

  21. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • INCIDENT BEAM: an incident electron beam of 10 GeV • TARGETS: • CRYSTAL: a 1 mm thick W crystal <111> orientation • AMORPHOUS: a 8 mm thick amorphous target • CAPTURE SYSTEM: AMD with decreasing field from 6 to 0.5 Tesla on 50 cms Accelerating field is 18 MeV/m, peak [SW] • RESULTS:accepted yield: 1.8 e+/e- (s -=1mm) • 1.5 e+/e- (s -= 2.5 mm) • PEDD: assuming an incident e- bunch of 2. 1010 e- • crystal amorphous • PEDD/e- PEDD/bunch PEDD/e- PEDD/bunch • s - =1mm 2 GeV/cm30.33 J/g/bunch 7.5 GeV/cm31.25 J/g/bunch • s - =2.5mm 0.35 GeV/cm3 0.058 J/g/bunch 2 GeV/cm3 0.33 J/g/bunch • It is quite clear that the hybrid target cannot sustain the 2820 bunches and that distributed targets system must be considered. R.Chehab/Posipol2008/Hiroshima, june 2008

  22. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • EMITTANCES AT END OF ILC PREACCELERATOR Transverse emittances at 270 MeV (s -= 1mm) Blue: 80% Red: rms ex,y = 11 p mmmrad rms R.Chehab/Posipol2008/Hiroshima, june 2008

  23. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • TRANSVERSE EMITTANCES AT ILC PREACCELERATOR • (s -=2.5 mm) Blue: 80% Red: rms ex=11p mmmrad ey=12 pmmmrad R.Chehab/Posipol2008/Hiroshima, june 2008

  24. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • EMITTANCES AT THE END OF ILC PREACCELERATOR • LONGITUDINAL EMITTANCE [s -=1mm] Blue: 80% Red: rms ez=9.4pcmMeV (rms) R.Chehab/Posipol2008/Hiroshima, june 2008

  25. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • PROPOSED SCHEME FOR ILC: ONLY IF MULTITARGET 2 meters e+ g e- e+, e-, g e- Amorphous multitarget Crystal multitarget With incident beam of 2.1010 e-/bunch the expected accepted e+ yield is of 3.7 1010 e+/bunch at 270 MeV (s -=1mm). It is of 3.1010 e+/bunch for s -=2.5mm R.Chehab/Posipol2008/Hiroshima, june 2008

  26. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • SUMMARY AND DISCUSSION • * Hybrid schemes using a crystal as a radiator and an amorphous target where only gcoming from the crystal are sent, have been studied for CLIC and ILC as “conventional” solutions. The simulation results showed accepted yields in accordance with the requirements. The emittances at the end of the preaccelerator (270 MeV) can be improved through optimization of the capture section and bunch compression in the longitudinal phase space; energy compression can also been considered in view of efficient stacking in the damping ring. • * One of the main concerns for positron targets is the energy deposited. As demonstrated in recent papers, the total energy deposited is less for a purely cristalline target than for the equivalent (giving the same yield) amorphous target. The Peak Energy Deposition Density (PEDD) is comparable. But using hybrid targets with a separation between the crystal and amorphous parts giving the possibillity of sweeping off part or all the charged particles, allows lowering of the PEDD and henceforth, avoiding multi-target use. That solution can be worked out with CLIC. Concerning ILC, the very intense pulse (> 1013e-) precludes use of a unique hybrid target: both crystal and amorphous systems are multitargets; that makes the crystal solution hard to work out. R.Chehab/Posipol2008/Hiroshima, june 2008

  27. POSITRON SOURCES USING CHANNELING FOR ILC & CLIC • SUMMARY AND DISCUSSION (continued) • * Optimization ? • The optimization of the hybrid scheme concerns the • - the choice of a threshold in energy allowing the charged • particles coming out from the crystal to impinge on the • amorphous target, • - the optimization of the distance between the crystal and the • amorphous target • Both optimizations have consequences not only on the yield but also on the PEDD. • Concerning the incident beam, its energy, intensity as well as its transverse size may be optimized with respect to the yield and PEDD. R.Chehab/Posipol2008/Hiroshima, june 2008

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