Undulator Specifications Heinz-Dieter Nuhn, SLAC / SSRL November 14, 2003. Undulator Overview FEL Performance Assessment Recent Undulator Parameter Changes. Near Hall. Far Hall. Undulator. Linac Coherent Light Source. LCLS Undulator Schematic (Regular Section). 3,410. 406. 863 mm. - PowerPoint PPT Presentation
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Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
SASE FEL theory well developedSASE FEL theory well developed
and verified by simulationsand verified by simulations
FEL radiation starts from noise in FEL radiation starts from noise in spontaneous radiation spontaneous radiation
Transverse radiation electric Transverse radiation electric field modulates the energy and field modulates the energy and bunches the electrons within an bunches the electrons within an optical wavelengthoptical wavelength
Exponential build-up of radiation Exponential build-up of radiation along undulator lengthalong undulator length
SASE FELsSASE FELs
Undulator RegimeUndulator Regime
Exponential Gain Regime
Exponential Gain Regime
Saturation
Saturation
1 % of X-Ray Pulse1 % of X-Ray Pulse
Electron BunchMicro-Bunching
Electron BunchMicro-Bunching
Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Expected PerformanceExpected Performance
Low charge cases are modeled in PARMELALow charge cases are modeled in PARMELAafter the GTF results and then imported into after the GTF results and then imported into ELEGANT/GENESIS for the transportELEGANT/GENESIS for the transportthrough the LCLS beam line. through the LCLS beam line.
The simulations includes:The simulations includes:
Space charge in the gunSpace charge in the gun
Emittance compensationEmittance compensation
Wakefield and CSR effects Wakefield and CSR effects
Optimized beam transport (Jitter)Optimized beam transport (Jitter)
Low charge cases are modeled in PARMELALow charge cases are modeled in PARMELAafter the GTF results and then imported into after the GTF results and then imported into ELEGANT/GENESIS for the transportELEGANT/GENESIS for the transportthrough the LCLS beam line. through the LCLS beam line.
The simulations includes:The simulations includes:
Space charge in the gunSpace charge in the gun
Emittance compensationEmittance compensation
Wakefield and CSR effects Wakefield and CSR effects
Optimized beam transport (Jitter)Optimized beam transport (Jitter)
Preserve transverse overlap between beam and Preserve transverse overlap between beam and radiationradiation => Tolerance for betatron amplitude < 8 => Tolerance for betatron amplitude < 8 m (beam radius m (beam radius
dep.)dep.)
Avoid longitudinal phase shake between beam and Avoid longitudinal phase shake between beam and radiationradiation
=> Tolerance for rms phase shake 10 degrees per module=> Tolerance for rms phase shake 10 degrees per module
=> Equivalent tolerance for rms electron beam straightness 2 => Equivalent tolerance for rms electron beam straightness 2 m m
Preserve transverse overlap between beam and Preserve transverse overlap between beam and radiationradiation => Tolerance for betatron amplitude < 8 => Tolerance for betatron amplitude < 8 m (beam radius m (beam radius
dep.)dep.)
Avoid longitudinal phase shake between beam and Avoid longitudinal phase shake between beam and radiationradiation
=> Tolerance for rms phase shake 10 degrees per module=> Tolerance for rms phase shake 10 degrees per module
=> Equivalent tolerance for rms electron beam straightness 2 => Equivalent tolerance for rms electron beam straightness 2 m m
Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Halbach formula for hybrid undulator is used to Halbach formula for hybrid undulator is used to estimate relation between gap/period and on-axis estimate relation between gap/period and on-axis fieldfield
Measured prototype field 5.3% larger than estimatedMeasured prototype field 5.3% larger than estimated
Halbach formula for hybrid undulator is used to Halbach formula for hybrid undulator is used to estimate relation between gap/period and on-axis estimate relation between gap/period and on-axis fieldfield
Measured prototype field 5.3% larger than estimatedMeasured prototype field 5.3% larger than estimated
Adjusting Estimate of On-Axis Undulator FieldAdjusting Estimate of On-Axis Undulator FieldAdjusting Estimate of On-Axis Undulator FieldAdjusting Estimate of On-Axis Undulator Field
2gap gap
b cperiod periodB a e
3.44 T
5.08
1.54
a
b
c
3 cm1.325 T
6.00 mm
periodB
gap
6.35
3 cm1.325 T
mm
periodB
gap
5.08
1.5
3.6
4
2 Ta
b
c
Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Undulator PeriodUndulator PeriodUndulator PeriodUndulator Period
Present undulator period length of 3 cm is near Present undulator period length of 3 cm is near optimum for shortest gain lengthoptimum for shortest gain length
Change of undulator period length would require more Change of undulator period length would require more man-power and time than available before next reviewman-power and time than available before next review
Undulator period length will be kept at Undulator period length will be kept at
uu = 3.0 cm = 3.0 cm
Present undulator period length of 3 cm is near Present undulator period length of 3 cm is near optimum for shortest gain lengthoptimum for shortest gain length
Change of undulator period length would require more Change of undulator period length would require more man-power and time than available before next reviewman-power and time than available before next review
Undulator period length will be kept at Undulator period length will be kept at
uu = 3.0 cm = 3.0 cm
Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Maximum Available Linac EnergyMaximum Available Linac EnergyMaximum Available Linac EnergyMaximum Available Linac Energy
14.35 GeV has been nominal energy to reach 1.5 Å14.35 GeV has been nominal energy to reach 1.5 Å
Loss of available linac energy due toLoss of available linac energy due to Reduction of available linac sections (incl. Injector Reduction of available linac sections (incl. Injector
relocation)relocation)
Off-crest accelerationOff-crest acceleration
New maximum energy set to 14.1 GeV to restore New maximum energy set to 14.1 GeV to restore operational overheadoperational overhead
Requires change in K valueRequires change in K value
14.35 GeV has been nominal energy to reach 1.5 Å14.35 GeV has been nominal energy to reach 1.5 Å
Loss of available linac energy due toLoss of available linac energy due to Reduction of available linac sections (incl. Injector Reduction of available linac sections (incl. Injector
relocation)relocation)
Off-crest accelerationOff-crest acceleration
New maximum energy set to 14.1 GeV to restore New maximum energy set to 14.1 GeV to restore operational overheadoperational overhead
Requires change in K valueRequires change in K value
Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
New Break LengthsNew Break LengthsNew Break LengthsNew Break Lengths
Separations between undulator modules (breaks) designed to Separations between undulator modules (breaks) designed to produce slippage by integer number of optical wavelength.produce slippage by integer number of optical wavelength.
Break increments for adding slippage of 1 optical wavelength is Break increments for adding slippage of 1 optical wavelength is LLBB==uu (1+K (1+K22/2). /2).
LLBB=23.7 cm (old); 22.8 cm (new)=23.7 cm (old); 22.8 cm (new) Present design uses break pattern 1-1-2 which corresponds to Present design uses break pattern 1-1-2 which corresponds to
the lengths sequence the lengths sequence 18.7 cm – 18.7 cm – 42.1 cm 18.7 cm – 18.7 cm – 42.1 cm
18.7 cm gives not enough space for quads, BPMs, etc.18.7 cm gives not enough space for quads, BPMs, etc. Length needed > 30 cm Length needed > 30 cm 42.1 cm gives not enough space for x-ray diagnostics42.1 cm gives not enough space for x-ray diagnostics Length needed > 70 cm Length needed > 70 cm
New break pattern 2-2-4 corresponding to lengthNew break pattern 2-2-4 corresponding to lengthsequence 40.6 cm – 40.6 cm – 86.3 cmsequence 40.6 cm – 40.6 cm – 86.3 cm
Separations between undulator modules (breaks) designed to Separations between undulator modules (breaks) designed to produce slippage by integer number of optical wavelength.produce slippage by integer number of optical wavelength.
Break increments for adding slippage of 1 optical wavelength is Break increments for adding slippage of 1 optical wavelength is LLBB==uu (1+K (1+K22/2). /2).
LLBB=23.7 cm (old); 22.8 cm (new)=23.7 cm (old); 22.8 cm (new) Present design uses break pattern 1-1-2 which corresponds to Present design uses break pattern 1-1-2 which corresponds to
the lengths sequence the lengths sequence 18.7 cm – 18.7 cm – 42.1 cm 18.7 cm – 18.7 cm – 42.1 cm
18.7 cm gives not enough space for quads, BPMs, etc.18.7 cm gives not enough space for quads, BPMs, etc. Length needed > 30 cm Length needed > 30 cm 42.1 cm gives not enough space for x-ray diagnostics42.1 cm gives not enough space for x-ray diagnostics Length needed > 70 cm Length needed > 70 cm
New break pattern 2-2-4 corresponding to lengthNew break pattern 2-2-4 corresponding to lengthsequence 40.6 cm – 40.6 cm – 86.3 cmsequence 40.6 cm – 40.6 cm – 86.3 cm
Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
LCLS Operating Points for 1 nC Bunch Charge (Old)LCLS Operating Points for 1 nC Bunch Charge (Old)
LCLS Operating Point at LCLS Operating Point at 1.5 Å1.5 ÅLCLS Operating Point at LCLS Operating Point at 1.5 Å1.5 Å LCLS Operating Point at LCLS Operating Point at 15 Å15 ÅLCLS Operating Point at LCLS Operating Point at 15 Å15 Å
Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL
Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
ConclusionsConclusions
Requirements for LCLS undulator are well establishedRequirements for LCLS undulator are well establishedLCLS undulator performance requirements are well understoodLCLS undulator performance requirements are well understoodRisks have been assessed and undulator specifications address the riskRisks have been assessed and undulator specifications address the riskNew parameter values have been chosenNew parameter values have been chosen
Increase in undulator gap, Increase in undulator gap, reduction in maximum electron beam energy, reduction in maximum electron beam energy, longer break length, and longer break length, and reduced quadrupole gradientsreduced quadrupole gradients
Benefits areBenefits aremore room for vacuum chambermore room for vacuum chambermore energy safety marginmore energy safety marginmore space for diagnostics components between undulator modulesmore space for diagnostics components between undulator modulesincrease of accessible wavelength rangeincrease of accessible wavelength range
Requirements for LCLS undulator are well establishedRequirements for LCLS undulator are well establishedLCLS undulator performance requirements are well understoodLCLS undulator performance requirements are well understoodRisks have been assessed and undulator specifications address the riskRisks have been assessed and undulator specifications address the riskNew parameter values have been chosenNew parameter values have been chosen
Increase in undulator gap, Increase in undulator gap, reduction in maximum electron beam energy, reduction in maximum electron beam energy, longer break length, and longer break length, and reduced quadrupole gradientsreduced quadrupole gradients
Benefits areBenefits aremore room for vacuum chambermore room for vacuum chambermore energy safety marginmore energy safety marginmore space for diagnostics components between undulator modulesmore space for diagnostics components between undulator modulesincrease of accessible wavelength rangeincrease of accessible wavelength range
Undulator Parameter Workshop, November 14, 2003Undulator Parameter Workshop, November 14, 2003 Heinz-Dieter Nuhn, SLAC / SSRLHeinz-Dieter Nuhn, SLAC / SSRL