1 / 31

Bunch length modulation in storage rings

Bunch length modulation in storage rings. C. Biscari LNF – INFN - Frascati. Workshop on “Frontiers of short bunches in storage rings” – Frascati – 7-8 Nov 2005. R 56 = - 0.1. R 56 = 0.3. R 56 = 0.4. R 56 = 0. R 56 = 0.5. R 56 = 0.1. R 56 = 0.2.

decima
Download Presentation

Bunch length modulation in storage rings

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Bunch length modulation in storage rings C. Biscari LNF – INFN - Frascati Workshop on “Frontiers of short bunches in storage rings” – Frascati – 7-8 Nov 2005

  2. R56 = - 0.1 R56 = 0.3 R56 = 0.4 R56 = 0 R56 = 0.5 R56 = 0.1 R56 = 0.2 Bunch length manipulation routinely done in linear systems: linacs, fels, ctf3,…. By using dispersion in dipoles and correlation in the longitudinal phase plane introduced by rf acceleration Bunch length (mm) measurements (2004) CTF3 stretcher - compressor

  3. In storage rings Even if particles follow different paths according to the different energy, their oscillations around the synchronous one are usually within the natural bunch dimensions Large dispersion in dipoles and large rf cavity voltage derivative can force the oscillations to grow and lead to correlation in longitudinal phase plane

  4. Longitudinal plane oscillations in a ring with one rf cavity* One-turn matrix Described by the vector Rf cavity lens Sections with dipoles Drift functions: Momentum compaction *A. Piwinski, “Synchrotron Oscillations in High-Energy Synchrotrons,” NIM 72, pp. 79-81 (1969).

  5. One turn longitudinal matrix – one cavity in the ring Longitudinal Twiss functions Phase advance determined by acL and rf Bunch length can be modulated Energy spread constant along the ring and defined by rf and phase advance

  6. dE/E dl Longitudinal emittance and energy spread* Energy spread defined by eigen values of matrix M, considering radiation damping and energy emission Emittance diverges for m = 0, 180° (Qs = 0, 0.5) *A.W. Chao, “Evaluation of Beam Distribution Parameters in an Electron Storage Ring”, Journal of Applied Physics 50: 595-598, 1979

  7. The idea of squeezing the bunch longitudinally in a limited part of the ring came to Frascati when working in Superfactories studies (A. Hofmann had proposed a similar experiment in LEP) Short bunches at IP + high currents per bunch Low energy: microwave instability dominates the longitudinal bunch dimensions Strong rf focusing

  8. Longitudinal phase space Strong rf focusing – monotonic R1 * High rf voltage + high momentum compaction: High synchrotron tune Ellipse rotates always in the same direction From RF to IP From IP to RF IP RF input RF center RF output Energy spread *A. Gallo, P. Raimondi, M.Zobov ,“The Strong RF Focusing: a Possible Approach to Get Short Bunches at the IP”, e-Print Archive:physics/0404020. Proceedings of the 31th ICFA BD workshop, SLAC 2003 Bunch length

  9. dR1/ds < 0 dR1/ds > 0 Evolution of Strong rf focusing – non monotonic R1* High rf voltage + high derivative of R1 (s): Low synchrotron tune Ellipse rotates on both directions Energy spread Bunch length * C. Biscari - Bunch length modulation in highly dispersive storage rings", PRST–AB, Vol. 8, 091001 (2005)

  10. C = 100 m E = 0.51 GeV frf = 1.3 GHz Vmax = 10 MV Reference ring – DAFNE like acL rf cavity Monotonic R1(s) Non Monotonic R1(s)

  11. Phase advance and minimum beta Longitudinal phase advance as a function of V for different ac Minimum bL as a function of acL for different V

  12. Behavior of bL(s) along the ring ac = 0.001 ac = 0.01 ac = 0.02 ac = 0.03 Monotonic R1(s) Opposite the cavity Non Monotonic R1(s) Near the cavity - - - V = 3MV V = 7.5 MV

  13. Two minima appear in bL(s) if the cavity position is not in the point where R’1(s) changes sign

  14. The energy spread and the emittance increase with the modulation in sL Bunch length in the reference ring for two values of V

  15. Proposal for an experiment on DAFNE: A. Gallo’s talk tomorrow • Needed: • Flexible lattice to tune drift function R1 • O.K. with limits due to dynamic and physical apertures • Powerful RF system (high U) • Extra cavity – 1.3 GHz, 10 MV D. Alesini et al: "Proposal of a Bunch Length Modulation Experiment in DAFNE", LNF-05/4(IR), 22/02/2005 C. Biscari et al , “Proposal of an Experiment on Bunch Length Modulation in DAFNE”, PAC2005, Knoxville, USA - 2005

  16. 6x6 single particle dynamics in SRFF regime Ri: ith element of the ring, including rf cavity D(s) = D’(s) = 0 and the rf cavity effect is neglected R56 (s) is modified by the rf cavity and changes along the ring In a transfer line:

  17. Transverse and longitudinal plane are coupled: Bunch lengthening through emittance and dispersion also outside dipoles

  18. How much does this effect weight on the bunch longitudinal dimensions? • Usually negligible • Can appear in isochronous rings* • with SRFF the effect can be very large due to • Large dispersion, usually associated with large emittance • Large energy spread • Strong rf cavity • In the points where D = D’= 0 => R51 = R52 = 0 • The lengthening does not appear at the IP. *Y. Shoji: Bunch lengthening by a betatron motion in quasi-isochronous storage rings, PRST–AB, Vol. 8, 094001 (2005)

  19. Terms R51, R52, R55, R56, along the ring with MADX* DAFNE Now Frf = 368 MHZ - V = 0.3 MV DAFNE for SRFF – non monotonic Frf = 1.3 GHZ - V = 8 MV *Matrix calculations by C. Milardi

  20. Bunch length with transverse contribution ?? SRFF conditions Usual conditions

  21. D = -1 m D’ > 0 D = D’ = 0 D = - 4 m D’ = 0 2 particles: 1 sx, 1 sp Horizontal phase plane Structure C – 4 MV @1.3GHz D = D’ = 0 D = 2m D’ = 0 D = -2 m D’ >> 0

  22. R51 = R52 = 0 IP1 (long bunch) ? 500 turns- At Long dipole Longitudinal phase plane 2 particles: 1 sx, 1 sp At rf on short at SLM IP2 (short bunch) R51 = R52 = 0

  23. R51 = R52 = 0 IP1 (long bunch) 2000 turns At Long dipole Longitudinal phase plane 2 particles: 1 sx, 1 sp At rf on short at SLM IP2 (short bunch) R51 = R52 = 0

  24. DAFNE with SRFF Bunch lengthening* *L. Falbo, D. Alesini Simulation with distributed impedance along the ring in progress

  25. Possible applications of SRFF Colliders and Light sources Colliders: DAFNE can be used to test the principle Exploiting the regime needs a specially dedicated lattice and optimization of impedance distribution Light sources: Excluding those with field index dipole (large dispersion in dipoles can lead to negative partition numbers)

  26. BESSY II – data by G. Wuestefeld Exercise High momentum compaction e = 1.4 e-03 m rad ac = 7.2 e-04 e = 1.7e-02 m rad ac = 3.8 e-02 Increasing ac increases emittancein low emittance lattices

  27. BESSY II - High momentum compaction E = 0.9 GeV frf = 500 MHz

  28. E = 3 GeV, frf = 1.5 GHz lattice calculations byM. Biagini

  29. PEP II like storage ring - - - - Dashed lines – low ac - non monotonic R1 Full lines – high ac

  30. Two cavities in the ring example Synchrotron tune and energy spread depend on the drift distance between the two cavities

  31. Conclusions Bunch length modulation can be obtained in storage rings in different regimes with high or low synchrotron tune In any case it is associated to increase of natural energy spread Talks on different aspects of the same subject by P. Piminov - Dynamic Aperture of the Strong RF Focusing Storage Ring S. Nikitin - Simulation of Touschek Effect for DAFNE with Strong RF Focusing F.Marcellini - Design of a Multi-Cell, HOM Damped SC for the SRFF Experiment at DAFNE A Gallo - The DAFNE Strong RF Focusing Experiment

More Related