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Space charge effects in rings (not only ) at FAIR

Oliver Boine-Frankenheim Beam physics department, GSI, Darmstadt and Computational electromagnetics laboratory, TU Darmstadt. Space charge effects in rings (not only ) at FAIR. Contents Space charge effects at FAIR Space charge: Protons vs. Heavy- Ions

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Space charge effects in rings (not only ) at FAIR

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  1. Oliver Boine-Frankenheim Beam physics department, GSI, Darmstadt and Computational electromagnetics laboratory, TU Darmstadt Space chargeeffects in rings (not only) at FAIR • Contents • Space charge effects at FAIR • Space charge: Protons vs. Heavy-Ions • Simulation codes for space charge effects used at GSI • Beam diagnostics: How accurate (and fast) can we measure space charge ? • Conclusions

  2. The FAIR accelerator facility L=1080 m Existing facility UNILAC/SIS-18 GSI facility: provides ion-beam source and injector for FAIR 100 m SIS-100/300 p-linac L=216 m SIS-18 UNILAC Radioactive Ion Production Target For Uranium beams: 50 kW beam power 50 kJ total energy HESR Super FRS Anti-Proton Production Target CR FLAIR Talk by Peter Spiller on Tuesday RESR NESR Protons from SIS-100: 29 GeV, 4x1013, 1 bunch, 0.2 Hz 2

  3. Space charge @ FAIR General: Intense heavy ions at low-medium energies. Injection: Injectors: - low energy transport - UNILAC/p-linac SIS-100 Extraction (short bunch): p-linac SIS-18 UNILAC SIS 100 cycle SIS-18 multi-turn injection: - Final momentum spread determined by space charge - Injection efficiency vs. tune -> talk by S. Appel 4x1011 U28+ Interplay of space charge with resonances, impedances, cooling, IBS, …. HESR SIS 18 SIS-100 bunch compression: emittance growth + beam loss modification of the dispersion -> talk by S. Aumon SIS-100 accumulation + acceleration: - ‘space charge limit’, beam loss - modification of coherent instability thresholds -> talks by G. Franchetti, V. Kornilov (1 s accumulation time) CR RESR NESR

  4. Initial longitudinal beam quality in SIS-18 Debunching of UNILAC micro-bunches with space charge 36 MHz ≈ 20 turn injection no rf: debunching SIS-18 Measured momentum spread of the coasting beam Micro-bunch in longitudinal phase space Longitudinal space charge field: Momentum spread after debunching (dc beam): b/a=2 zm/a=5 Minimum momentum spread of the coasting beam: S. Appel, O. Boine-Frankenheim, Phys. Rev. ST-AB (2012)

  5. Space charge: Protons vs. Heavy Ions FAIR: Operation with intermediate charge state ions (e.g. U28+) to reduce space charge effects Lifetime of intermediate charge state heavy-ions in rings - Large cross sections for electron stripping/capture - (stable) residual gas pressure of the order of 10-12 mbar required for sufficient lifetime - Beam loss causes dynamic pressure instabilities. -> at present beam intensities are limited by lifetime and not by space charge. Production of intermediate charge state ions - Performance of ion sources compared to proton sources. - Stripping efficiency of heavy-ions at low energies. - Conventionally ‘Liouvillian’ multi-turn injection into rings. Beam diagnostics in rings: - Profile measurements: Wire scanners vs. residual gas monitors (RGMs). -> for energetic heavy-ion beams RGMs have to be used (more complex). Other intensity effects in rings: - Intra-beam scattering induced diffusion:

  6. Simulation codes (not only) for space charge effects used at GSI • MICROMAP (G. Franchetti): • 3D particle tracking with error multipoles, • 2D self-consistent, 3D adaptable space charge. • G. Franchetti et al., Experiment on space charge • driven nonlinear resonance crossing in an ion • synchrotron, PRST-AB 2010 • PATRIC (O. Boine-F., S. Appel, V. Kornilov, et al.): • 3D particle tracking with self-consistent 2.5D space charge solver and wake fields • MADX maps, arbitrary rf bucket forms • Implemented for multi-core CPUs using MPI. • V. Kornilov, O. Boine-F., Head-tail instability and Landau damping in bunches with space charge, PRST-AB 2010 • pyorbit(A. Shishlo, S. Cousineau, J. Holmes, et al.) • https://code.google.com/p/py-orbit/ • Teapot tracking • 2D/3D space charge • MPI • LOBO (O. Boine-F.): • Longitudinal dynamics with space charge, impedances, cooling, IBS, internal targets • direct Vlasov-Fokker-Planck solveror PIC • O. Boine-F., rf barrier compression with space charge, • PRST-AB 2010 • Al-khateeb et al, Longitudinal collective echoes in coasting particle beams, PRST-AB 2003 S. Appel, this workshop VORPAL (Tech-X) 3D EM PIC O. Boine-F., E. Gjonaj, F. Petrov, F. Yaman, T. Weiland, G. Rumolo, Energy loss and longitudinal wakefield of short proton bunches in electron clouds, PRST-AB 2012 Used also for studies of laser ion acceleration at GSI

  7. PArticleTRackIng Code: PATRIC 2D space charge field for each slice: (3D interpolation) (fast 2.5D Poisson solver) sm: position in the lattice z: longitudinal position in the bunch y M(sm|sm+1) ∆sm << betatron wave length s Sliced bunch The transfer maps Mare ‘sector maps’ taken from MADX. z GPU implementation: -> talk by JuttaFitzek slice-length: ∆z≠∆s (N macro-slices for MPI parallelization) x MPI send/receive to neighbor slices ghost layers 2D grids macro- slice 3D Grid-> Particle / Particle->Grid interpolation Space charge and PIC: Birdsall, Langdon (2005),…….

  8. PATRIC: Matched 3D bunch distribution (in a dual rf bucket) - The bunch distribution can be matched to arbitrary rf bucket forms (Hofmann-Pedersen 1979) - Transverse matching with space charge (Venturini, Reiser, PRL 1998) Bunch distribution (longitudinal-horizontal) Tune footprint with space charge (SIS18) Current profile Local dipole (offset) moment (‘noise’) A. Luccio, N. D’Imperio, Eigenvalues of the one-turn matrix, BNL (2003) -> FFT-> tune spectra

  9. Measurement of transverse space charge in rings Why: - to characterize the beam and understand the (space charge) intensity limit - set machine parameters (feed-forward) according to the space charge tune shift. How: Beam profiles for heavy-ions from RGM A. Parfenova (2010) (rms beam radius) P. Forck et al. (rmsemittance) Integration time - presently: msecs - future: μsec Error bar ?

  10. Transverse beam offset signals Schottky signals: Using a pick-up + spectrum analyzer (SA) BTFs: Using exciter/pick-up + network analyzer (NA)

  11. Transverse offset oscillations of coasting beams Space charge force cancels: The transverse space charge force does not act on the beam center (in contrast to image forces): Oscillationof a beam inside a pipe. Er (beam center) (Transverse equation of motion) Bθ Ex Ex x (beam center equation of motion) a b x -> Measurement of the beam offset fluctuations. -> This does not hold for head-tail modes in bunches ! a b Space charge field

  12. Transverse Schottky spectrum with space charge SIS-18 experiments with coasting beams Space charge parameter: Fit to a measured, modified Schottky band: Measurement time: ≈ 100 msecs Beam parameter: Ar18+, 11.4 MeV/u f0=215 kHz from RGM profiles Space charge tune shift from Schottky/BTF is systematically (factor 2) larger than the one from RGM profiles. S. Paret, O.Boine-Frankenheim, V.Kornilov, T Weiland, Phys. Rev. ST-AB (2010)

  13. Tune spectra for bunched beams (Head-tail modes) space charge parameter: or Weak space charge: Shift of synchrotron satellites (synchrotron tune Qs): SIS-18/100: qsc=10-20 CERN PSB/PS: qsc ≥100 positive k Strong space charge or positive k: negative k negative k: strongly damped Blaskiewicz, Phys. Rev. ST Accel. Beams (1998) Boine-F., Kornilov, Phys. Rev. ST Accel. Beams (2009), Burov (2009), Balbekov (2009)

  14. Transverse tune spectra measured in the SIS18 Tune spectra TOPAS: Tune, Orbit, Position, Measurement System (Forck, Singh, et al. ) Intensity Head-tail tune shifts Weak space charge: Width of lines caused by nonlinear synchrotron motion. Moderate space charge: Width of the lines caused by nonlinear space charge Integration time: ≈ 100 msecs R.Singh, O. Boine-F., O.Chorniy, P. Forck, P. Kowina, et al., Phys. Rev. ST-AB (2013)

  15. Space tune shifts: RGM vs. tune spectra R.Singh, O. Boine-F., O.Chorniy, P. Forck, P. Kowina, et al., Phys. Rev. ST-AB (2013) Space charge tune shift from tune spectra is lower (factor 1.5) than the one from RGMprofiles. from tune spectra from RGM profiles

  16. Computer tune spectraPATRIC simulations with self-consistent space charge • Good agreement with measurements (Positions and widths !) • Self-consistent space charge model is required ! • Image charges can suppress the head-tail modes (k≥0)! • -> see talk by V.Kornilov • -> tune spectra: not very useful for space charge measurement

  17. Quadrupolar tune spectra PATRIC simulation: Damping of an initial transverse mismatch oscillation in a bunch with a transverse KV distribution. Quadrupolar Pickup (QPU) Shift of the quadrupole mode: Measurement time: < msec Problem: Strong damping of the quadrupolar mode for transverse Gaussian distributions. M. Chanel, Proc. EPAC 1996 R. Bär, I. Hofmann, NIMA 1998

  18. Conclusions • The FAIR design intensities for protons and heavy ions are determined by the ‘space charge limit’. • - For (intermediate charge state) heavy ions there at present other intensity limitations (lifetime). • For heavy ions the default measurement of space charge tune shift relies on RGM profiles. • - Issues: Error bars. Integration time. • Schottky and tune spectra provide an independent alternative for dc and bunched beams. • - Long integration times needed. Does not work for strong space charge. • - In the SIS18: discrepancies with RGM measurement (not understood so far). • Transverse quadrupolar lines provide a direct link to the incoherent space charge tune shift. • - Successful measurements in dc beams at CERN and GSI. • - Simulations indicate well pronounced quadrupolar tune lines also in intense bunches. • - Dedicated quadrupolarpickup (and exciter) needed ! • For the optimization of the GSI and FAIR rings, including the important interplay of incoherent • and coherent collective effects, different simulations codes are employed, in combination • with dedicated beam physics experiments in the GSI SIS-18 and in the CERN PSB/PS.

  19. Additional material (not part of the presentation)

  20. Octupoles as a cure for transverse coherent instabilities in SIS-100coasting beams at SIS-100 injection Resistive wall instability: Incoherent tune: V. Kornilovet al., PRST-AB (2007) nonlinear space charge octupoles chromaticity stability boundary with octupoles stability boundary with nooctupoles For K3=50: DA lower by 20 % SIS-100 injection -> unstable nonlinear space charge Octupoles in combination with space charge can be used for the stabilization of dc and head-tail instabilities in SIS-100.

  21. Tune spectra: Effect of image currents Image impedance

  22. Measured SIS-18 tune spectra (noise excitation) 11.4 MeV/u (injection energy) 0.1-1.0 x 109 U73+ Bunching factor: 0.35 : from beam profile measurement (IPM) : from longitudinal Schottky signal noise excited tune spectrum R. Singh, P.Forck, P. Kowina, O. Boine-F., et al., Interpretation of tune spectra for high intensity, to be published -> see presentation by OleksandrChorniy

  23. Intrinsic Landau damping of head tail modes A. Burov, Phys. Rev ST-AB (2009) V. Kornilov, O. Boine-F., Phys. Rev. ST-AB (2010) V. Balbekov, Phys. Rev. ST-AB (2009) Damping rate of head-tail modes from PATRIC Landau damping of head-tail modes for: and with -space charge can suppress head tail instabilities! - image currents/charges increase the damping rate. -damping depends crucially on bunch tails.

  24. ‘Space charge limit’ in SIS-18 (and SIS-100) We presently assume that the maximum beam intensities in SIS-18 and SIS-100 are ‘space charge limited’. High current working point: A. Parfenova, G. Franchetti, GSI (2011) Space charge tune spread: ‘Cures’: flattened bunch profiles + resonance compensation ‘Space charge limit’: : bunching factor εx,y: transverse emittances N: number of particles in the ring

  25. Multi-stream instability during debunching Longitudinal space charge impedance: Normalized space charge impedance: Δp/p Δp/p Δp/p Time needed to form M filaments: Critical number of streams/filaments: Time Length Length Length I. Hofmann, Part. Accel. (1990) S. Appel, O. Boine-Frankenheim, Phys. Rev. ST-AB (2012)

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