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multi-bunch wake field in ECLOUD

multi-bunch wake field in ECLOUD. in ECLOUD input file :. wakefield switch 2 0.01 0.0 10. ← activate (new) wake field option. ← x offset [m], y offset [m], offset bunch #. ECLOUD output file wake.data:. time, iflag, Ex(0,0), Ex(1,0), Ex(2,0), Ey(0,0), Ey(0,1), Ey(0,2), xstep, ystep.

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multi-bunch wake field in ECLOUD

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  1. multi-bunch wake field in ECLOUD in ECLOUD input file: wakefield switch 2 0.01 0.0 10 ← activate (new) wake field option ← x offset [m], y offset [m], offset bunch # ECLOUD output file wake.data: time, iflag, Ex(0,0), Ex(1,0), Ex(2,0), Ey(0,0), Ey(0,1), Ey(0,2), xstep, ystep (0,0): at the center of the chamber; (1,0): at x=xstep, y=0; (0,2): at x=0, y=2 ystep; etc iflag=1 inside the bunch; otherwise 0; wake is printed each time the e- space charge field is calculated

  2. one has to run the code (at least) two times namely with offset and without offset the (integrated) dipole wake is obtained as difference at the center as follows: small Fortran programm wakediff.f to do this information on higher-order wake fields is contained in the fields at larger amplitudes units = V/C/m multiply by 4p/(Z0c) to get m-2 or cm-2

  3. example with poor statistics LHC dipole field, 50 ns spacing, only 50 macro-e-/bunch, SEY=2.4 x offset of bunch#10 Exfield at different amplitudes

  4. Exfield x offset of bunch#10 no bunch offset

  5. Eyfield x offset of bunch#10 no bunch offset

  6. CB-SB wake field this bunch is offset wake field looks small (?! see next page) cross wake field DFy(Dx) is bigger than proper wake? wake changes sign inside the bunch

  7. zoom at wake field for bunch #15

  8. simulation with 10x better statistics (500 macro-e- / bunch, bunch#15 offset) CB-SB wake field this bunch is offset wake field is larger there is a “wake” for the offset bunch as well

  9. shortest rise time of fastest growing mode for |W|~100 m-2 at injection this gives t~60 s in 1997 the LHC wake field was 104 times bigger, but with 25 ns spacing and at 7 TeV

  10. Comments: Sign of the ECLOUD wake ? an independent check might be good I have got some doubts if the sign of the space charge force in ECLOUD is always correct, e.g. close to a stripe

  11. conclusions • wake-field code seems to be ready • preliminary results need to be consolidated • e-cloud wake must be interpreted; • differences to regular impedance • large cross wake (y wake for x offset) • self wake (affecting offset bunch) • coupled multi-bunch/single-bunch wake • nonlinear (higher-order) wake field

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