P. Emma FAC Meeting [email protected] 7 Apr. 2005 Low-Charge LCLS Operating Point Including FEL...

P. EmmaP. Emma

FAC MeetingFAC Meeting [email protected]@SLAC.Stanford.edu

7 Apr. 20057 Apr. 2005

Low-Charge LCLS Operating Point Low-Charge LCLS Operating Point Including FEL SimulationsIncluding FEL Simulations

P. EmmaP. Emma11, W. Fawley, W. Fawley22, Z. Huang, Z. Huang11,,C. LimborgC. Limborg11, S. Reiche, S. Reiche33, J. Wu, J. Wu11, M. Zolotorev, M. Zolotorev22

FAC MeetingFAC Meeting April 7, 2005April 7, 2005

LCLSLCLS [1][1] SLACSLAC[2][2] LBNLLBNL[3][3] UCLAUCLA

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

Present Present LCLSLCLS Design Challenges Design ChallengesGun emittance: 1-Gun emittance: 1-m at 1 nC, 100 Am at 1 nC, 100 AResistive wake in undulatorResistive wake in undulatorLSC/CSR micro-bunchingLSC/CSR micro-bunchingTransverse wakes in L2Transverse wakes in L2CSR CSR in BC2 in BC2

too muchtoo muchchargecharge AC resistive wakefieldAC resistive wakefield

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

wakefield-wakefield-induced induced cubic chirp cubic chirp in L2-linacin L2-linac

cubic chirp cubic chirp produces produces current horns current horns after BC2after BC2

much of charge much of charge wasted with only wasted with only 3.0 kA in core3.0 kA in core

NominalNominal1-nC case1-nC case

1-nC, 20-1-nC, 20-m m rms bunch rms bunch length is 6 kA length is 6 kA for a Gaussian for a Gaussian bunchbunch

pre-BC2pre-BC2

post-BC2post-BC2

in FELin FEL

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

Motivation:Motivation:Less charge Less charge less wakeless wakeSame compression factor Same compression factor ~same jitter~same jitterLower gun current Lower gun current lower emittancelower emittance

Chosen Scaling:Chosen Scaling:Charge: Charge: 1 nC1 nC 0.0.2 nC2 nCGun Current: Gun Current: 100100 30 A30 A ( (10 ps10 ps 6.5 ps6.5 ps))Sliced gun emittance: Sliced gun emittance: 1 1 mm 0.8 0.8 mmFinal current:Final current: 3 kA3 kA 2 kA 2 kA (same (same LLsatsat))

Low Charge OptimizationLow Charge Optimization

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

Ming XieMing Xie

87 m87 m

final

slic

efin

al s

lice

= 0

.85

= 0

.85

mm

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

200-pC optimized 200-pC optimized ParmelaParmela output at 64 MeV output at 64 MeV

200k in lcls_200k_02nc_atendl01.dat200k in lcls_200k_02nc_atendl01.datC. LimborgC. Limborg, Oct. 19, 2004, Oct. 19, 2004

thth/r/r = 1 = 1 m/mmm/mm

spot radius = 0.42 mmspot radius = 0.42 mmlaser pulse = 6.5 ps FWHMlaser pulse = 6.5 ps FWHM

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

2 kA2 kA

pre-BC2pre-BC2

post-BC2post-BC2

in FELin FEL

200 pC200 pC

lesslesscubic chirpcubic chirp

spikes reducedspikes reduced 80-fs 80-fs FWHM FWHM X-ray X-ray pulsepulse

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

Much less CSR projected emittance growthMuch less CSR projected emittance growth

0.2 nC0.2 nC

1.0 nC1.0 nC

xx 4 4 mm

xx 1 1 mm

xx

x

yy

yy

BC2BC2

BC2BC2

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

xx ,,

yy (( m

)m

)

xx ,,yy ((

m)

m) 0.2 nC0.2 nC

1.0 nC1.0 nC

Transverse Wakes & Dispersion Errors Transverse Wakes & Dispersion Errors VanishVanish at 0.2 nC at 0.2 nC

Linac Alignment EasedLinac Alignment Eased

300-300-m struct.m struct.200-200-m quadm quad200-200-m BPMm BPMsteer 10 seedssteer 10 seeds

rms errors:rms errors:

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

LSC/CSR Micro-bunching Gain ReducedLSC/CSR Micro-bunching Gain Reduced

1 nC1 nC, , == 1 1££101044, ,

IIpkpk = = 3.4 kA (final 3.4 kA (final

current)current)

1 nC1 nC, , == 1 1££101044, ,

IIpkpk = = 3.4 kA (final 3.4 kA (final

current)current)

200 pC200 pC, , = = 11££101044,,

IIpkpk == 2 kA, 3 kA, & 5 2 kA, 3 kA, & 5

kA, adjusted with L2 kA, adjusted with L2 chirp and laser chirp and laser heater powerheater power

200 pC200 pC, , = = 11££101044,,

IIpkpk == 2 kA, 3 kA, & 5 2 kA, 3 kA, & 5

kA, adjusted with L2 kA, adjusted with L2 chirp and laser chirp and laser heater powerheater power

1-nC nominal1-nC nominal

gain reducedgain reduced

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

L2 L2 RFRF = = 1.61.6ºº 3 kA3 kA::

LLsatsat 87 m at 87 m at 1.15 1.15

mm,, 25 m25 m

L2 L2 RFRF = = 1.61.6ºº 3 kA3 kA::

LLsatsat 87 m at 87 m at 1.15 1.15

mm,, 25 m25 m

200 pC200 pC

3 kA3 kA

(RW-wake and (RW-wake and -bunching OK)-bunching OK)

Compress moreCompress more, until back up to 12% peak-current jitter, until back up to 12% peak-current jitter

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

Cylindrical-Copper Resistive Wakes in UndulatorCylindrical-Copper Resistive Wakes in Undulator

uses K. Bane damped resonator model for AC wakeuses K. Bane damped resonator model for AC wake

1 nC1 nC0.2 nC0.2 nC

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

200-pC FEL Simulations: Cu cyl. pipe (200-pC FEL Simulations: Cu cyl. pipe (rr = 2.5 mm = 2.5 mm))

Data smoothed from raw ~12-as resolution to ~1-fs resolutionData smoothed from raw ~12-as resolution to ~1-fs resolution

Curve represents output power at Curve represents output power at z z = 130 m= 130 m

For 300-kV ext. field + Cu wake case, agreement between codes is For 300-kV ext. field + Cu wake case, agreement between codes is good in overall temporal dependence, with good in overall temporal dependence, with GINGERGINGER showing ~1.5X showing ~1.5X greater power than greater power than GENESISGENESIS

Compared to 1-nC case, lasing occurs over full 200-pC pulseCompared to 1-nC case, lasing occurs over full 200-pC pulse

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

UncompensatedUncompensated 200-pC Cu & Al wake gives lower power ~8-10X 200-pC Cu & Al wake gives lower power ~8-10XGain length increased ~15% but saturation point unaffectedGain length increased ~15% but saturation point unaffectedExternal field of +150 kV/m makes up for wake External field of +150 kV/m makes up for wake Increasing ext. field to +300 kV/m nearly doubles power over no-wake Increasing ext. field to +300 kV/m nearly doubles power over no-wake case, agreeing with Huang/Stupakov modelcase, agreeing with Huang/Stupakov model

UncompensatedUncompensated 200-pC Cu & Al wake gives lower power ~8-10X 200-pC Cu & Al wake gives lower power ~8-10XGain length increased ~15% but saturation point unaffectedGain length increased ~15% but saturation point unaffectedExternal field of +150 kV/m makes up for wake External field of +150 kV/m makes up for wake Increasing ext. field to +300 kV/m nearly doubles power over no-wake Increasing ext. field to +300 kV/m nearly doubles power over no-wake case, agreeing with Huang/Stupakov modelcase, agreeing with Huang/Stupakov model

~10~101212 photons photons

GINGERGINGER Results for 200-pC Pulse Energy vs. Results for 200-pC Pulse Energy vs. ZZ

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

Drive-laser energy Drive-laser energy 1/5 1/5Laser-heater power Laser-heater power 1/4 1/4BC2 CSR BC2 CSR 1/5 1/5Linac quad/BPM align. tol.’s Linac quad/BPM align. tol.’s 22L2 transverse wake L2 transverse wake 1/161/16BC dipole field quality BC dipole field quality 1/2 1/2Peak current jitter Peak current jitter ½ (or X-band ½ (or X-band -tol. -tol. 3)3)Final timing jitter 95 fs (was 120 fs)Final timing jitter 95 fs (was 120 fs)X-ray pulse 85 fs (was 210 fs)X-ray pulse 85 fs (was 210 fs)No undulatorNo undulator RW-wake (even for Cu, AC, cyl.)RW-wake (even for Cu, AC, cyl.)FEL power: 15-20 GW & ~10FEL power: 15-20 GW & ~101212 photons photonsUndulator radiation damage reduced?Undulator radiation damage reduced?Dump power Dump power 1/5 (to 330 W, was 1700 W)1/5 (to 330 W, was 1700 W)Less loading eases multi-bunch operationLess loading eases multi-bunch operation1-nC operation still fully supported option1-nC operation still fully supported option

Advantages for Advantages for LCLSLCLS at Low Charge at Low ChargeDisadvantages:Disadvantages:

Requires 20% smaller gun slice emittance

8-m bunch (z) more

difficult to measure

P. EmmaP. Emma


7 Apr. 20057 Apr. 2005

SummarySummary

LCLSLCLS

The 200-pC configuration is the preferred The 200-pC configuration is the preferred LCLSLCLS operating point (300 pC is similar)operating point (300 pC is similar)Resistive-wall wake, transverse linac wakes, and Resistive-wall wake, transverse linac wakes, and CSR all become ~non-issuesCSR all become ~non-issues1-nC is an alternate configuration with possibly 1-nC is an alternate configuration with possibly more photons, but more challenging on all frontsmore photons, but more challenging on all frontsDiagnostics must emphasize 200-pC rangeDiagnostics must emphasize 200-pC range

P. Emma FAC Meeting [email protected] 7 Apr. 2005 Low-Charge LCLS Operating Point Including FEL...

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