LCLS-II Bypass Line Design GoalsP. Emma, July 7, 2010

Provide 14-GeV (?) electron bypass line from sector-20 around LCLS-I, feeding new undulators south of LCLS-I at 2 to 4-deg angleUse existing PEP-II 9-GeV line on linac ceiling (2’ above & 2’ south of linac)Sneak line around crowded BSY and BTHWBore new hole in 17-m thick iron m-plug wallPreserve 0.6-mm emittance with up to 3 kA at 14 GeVInclude diagnostics and corrections in design

Bypass-Line ComponentsExtract beam out at 20-5 (use half of sec-20 RF)Rolled x/y bends to existing 9-GeV PEP-II line(Existing PEP-II extraction bends blow up LCLS emittance by factor of 4 – redesigned here)Use 1-km of existing FODO cells (bmax = 400 m)

Also use long FODO as emittance diagnosticRemove 4.6-mrad pitch of linac (as in LCLS-I)Bend south with LCLS bend-cells (four 1-deg cells)Keep beamline at bypass line height (25.5” up)Bore new tunnel in hill 25.5” higher than LCLS-IAdd final wire scanner section & undulator matching (+ room for ECHO seeding)

47”

66”

Inside Linac Vault - Looking Down-Beam

120”

132”

LINAC

25.512”

25.512”

9-GeV17” 3-GeV

(ID-344-013-30)

LCLS-II Bypass Layout

Dx = 25.5”

PLAN VIEW

ELEVATION VIEW

N

Sector 20-517-m thick m-plug wall

17-m thick m-plug wall

Dy = 25.5”

Sector-20(20-5)

m-plug wall

2324 26 28 30

25 27 29existing quads on ceiling

m-plug walleight 0.5-deg bends

LCLS-I Head-House Layout(R. M. Boyce)

South-Side Head-House Port

~5 m

Linac Tunnel Approaching BSY

Bypass Line will pass through

most congested area in BSY

Bypass Line will pass through

most congested area in BSY

LINAC

SIT Lineto PEP-II

Quadrupole magnet here?

problem area

Twiss functions in Elegant

With CSR (uniform temporal dist.) – note that ISR is no problem

gex,y = 0.6 mm

Longitudinal phase space at 13.6 GeV, 3 kA, with CSR(uniform temporal dist.)

Energy spread (green) & bunch length (red) vs. z

QuestionsIs this 2-4-deg option the choice (2 other options exist, but all need a bypass line)?Will we run at 7 GeV/360 Hz, or 14 GeV/120 Hz, or both (assuming both for now)?Can a new hole be bored in the 17-m thick m-plug wall ?Can we tunnel the new undulator hall 25.5” higher in elevation than LCLS-I ?Do we need a jumper line from LCLS-I to LCLS-II, and the reverse?Do we want a horizontal spreader to someday feed 2 undulators in the new hall ?