lcls undulators – present status and future upgrades...march 1, 2010 lcls undulator module pole...
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1 Heinz-Dieter [email protected]
1LCLS Undulator StatusMarch 1, 2010
LCLS Undulators –Present Status andFuture Upgrades
Heinz-Dieter Nuhn – LCLS Undulator Group LeaderMarch 1, 2010
2 Heinz-Dieter [email protected]
2LCLS Undulator StatusMarch 1, 2010
Linac Coherent Light Source
INJECTOR
LINAC
UNDULATOR HALL
BEAM TRANSPORT
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Undulator Hall
33 Undulator Segments Installed
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Short Break Section
Quadrupole and horz/vert Correctors
BFWUndulator Segment
Girder
Segment Slider
Girder Mover (cam)
RF Cavity BPM
HLS Sensor
Part of WPM Support
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Quadrupole
Vacuum Chamber
Undulator Segment
RF Cavity BPM
Girder
Fully Assembled Girder (seen from downstream end)
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Quadrupole Undulator Segment with mu-Metal Shield
RF Cavity BPM
Coordinate Measurement Machine Position Sensor
Girder Precision Alignment on CMM
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Quadrupole
BPM
Manual Adjustments
Segment3.400 m
Cam Shaft Movers WPM
HLS
BFW
Sand-Filled, Thermally Isolated
Fixed Supports
Horizontal SlidesNot visible
Vacuum Chamber and
Support
Long Break89.8 cm
Short Break47.0 cm
LCLS Undulator Components
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Vacuum Chamber
Undulator Segment
Magnet Block
Pole Piece
Horizontal Trajectory Shim Holder
Vacuum Chamber Inserted into Gap
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LCLS Undulator Module Pole Canting
• Canting comes from wedged spacers• 4.5 mrad cant angle• Gap can be adjusted by lateral
displacement of wedges• 1 mm shift means 4.5 µm in gap, or
8.2 G • Keff can be adjusted to desired value
Pole canting enables remote K adjustment for fixed gap undulators.
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Neutral; K=3.4881; ∆x= 0.0 mm Neutral; K=3.4881; ∆x= 0.0 mmNeutral; K=3.4881; ∆x= 0.0 mm
Undulator Roll-Away and K Adjustment
First; K=3.5000; ∆x=-4.0 mm Roll-Away; K=0.0000; ∆x=+80.0 mm
Horizontal Slide
Pole Center Line Vacuum Chamber
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unitsNominal Undulator Parameter K 3.5
Undulator Period λu 30 mm
Undulator peak Field, Bpk Bpk 1.249 T
Full Gap Height (fixed) g 6.8 mm
Undulator Type Planar Hybrid Permanent Magnet
Magnet Material Nd2FeB14
Pole Material Vanadium Permendur
Magnet Block Dimensions h×t×w
66×9×56.5 mm3
Pole Dimensions h×t×w
44×6×48 mm3
Periods per Segment 113
Gap Cant Angle α 4.5 mrad
Number of Installed Segments 33
LCLS-I Undulator Parameters
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1. Compensation of spontaneous radiation (linear tapering over 132 m)
2. Compensation of vacuum chamber wakefields (linear tapering over 132 m, for 0.25 nC)
3. Gain enhancement (linear tapering before saturation) [Z. Huang]
4. Enhanced energy extraction (quadratic tapering after saturation) [W. Fawley]
Taper Design Considerations
/ 2E E ρ∆ = −
/ 0.25% E E∆ ≈ −
-152
2
10 ˆ/ 0.633T Vm u
EE E B Ne
λ∆ = − ×
/ E E∆
The ratio between changes in E and K to maintain the resonance condition at a given wavelength is
2
2 1 1.16dK dK
K KdE d KE
γγ
= = + ≈
From Wakefield budget based on S2E Simulations
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K Tapering Requirements
K for segment 33
spontwake
gainpost sat
wakegain
post sat
spont
1.5 Å
15 Å
K for segment 1
±0.
3 %
±0.
3 %
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Figure 3: K Tapering Scenarios (Continuous)Avoid Reliance on Good Field Region at 1.5 Å
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Measured Field Integrals on SN25
( )0 0
', , 'L z
xB dz dzx y z
∫ ∫
( )0 0
', , 'L z
yB dz dzx y z
∫ ∫
( )0
, ,L
xB dzx y z∫
( )0
, ,L
yB dzx y z∫+200 µmy :
+0 µm-200 µm
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Beam Based Measurement: 1st Field Integral SN14
Beam Based Measurements
Horizontal (I1X) and vertical (I1Y) first field integrals measured by fitting a kick to the difference trajectory as function of undulator displacement
Reference Point
MMF Measurement
Req
uire
s 20
nm
BPM
reso
lutio
n
SN14
SN14
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Segmented Undulator Pre-Taper
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CMM Keff Measurements for U33/SN20
K=3.468
K=3.497
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Segmented Undulator K Control
K ADJUSTMENT RANGE(MEASURED)
TEMPERATURE CORRECTED KACT
TAPER REQUEST
K ADJUSTMENT RANGE(MEASURED)
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Tolerance Budget Analysis
Analysis based on time dependent SASE simulations with GENESISEight individual error sources considered:
Beta-Function Mismatch,Launch Position Error,Segment Detuning,Segment Offset in x,Segment Offset in y,Quadrupole Gradient Error,Transverse Quadrupole Offset,Break Length Error.
The ‘observed’ parameter is the average of the FEL power at 90 m (around saturation) and 130 m (undulator exit)The Results are combined into the Error Budget
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Segment K Errors
Module Detuning (Gauss Fit)Location Fit rms Unit090 m 0.042 %130 m 0.060 %Average 0.051 %
Simulation and fit results of Module Detuning analysis. The larger amplitude data occur at the 130-m-point, the smaller amplitude data at the 90-m-point.
/iq K K= ∆
BudgetTolerance
90 m
130 m
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Individual Studies (Example K)Choose a set of ∆Km/K values to be tested, e.g.
{ 0.000%, 0.045%, 0.100%, 0.200%}For each ∆Km/K choose 33 ∆Ks values from a random flat-top distribution with maximum ∆Km.Apply these errors, ∆Ks, to the respective segment Ksvalues and perform a GENESIS FEL simulation.Evaluate the simulation result to extract power levels at the 90 m and 130 m points, P90,m and P130,m, respectively.LoopPlot these results, P90,m and P130,m, versus the rms of the distribution, i.e.
Apply Gaussian fit to obtain rms-dependence.2
220
i
i
q
iP P e σ−
=
112 mK K∆
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Horizontal Segment Misalignment
Horizontal Model Offset (Gauss Fit)Location Fit rms Unit090 m 0782 µm 130 m 1121 µmAverage 0952 µm
Simulation and fit results of Horizontal Module Offset analysis. The larger amplitude data occur at the 130-m-point, the smaller amplitude data at the 90-m-point.
BudgetTolerance
90 m
130 m
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Vertical Segment Misalignment
Vertical Model Offset (Gauss Fit)Location Fit rms Unit090 m 268 µm 130 m 268 µmAverage 268 µm
Simulation and fit results of Vertical Module Offset analysis. The larger amplitude data occur at the 130-m-point, the smaller amplitude data at the 90-m-point.
BudgetTolerance
90 m
130 m
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Tolerance Budget
Gaussian fit yields functional dependence of power reduction on error amplitude:
Assuming that each error is independent on the others other, i.e. each error source causes a given fraction power reduction independent of the presence of the other sources:
22 2
21 1
2 2 2
0
ii i
i
qf fP e e e
Pσ
− − − ∑= = =∏ ∏
tolerance
fitted rms
fi=qi/σi
2
22
0
i
i
q
iP eP
σ−
=
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LCLS Tolerance Budget
Error Source σi fi σi fi Units
@ 130 m (24.2% red.)
Hor/Ver Optics Mismatch (ζ-1)0.5 0.71 0.452 0.32
Hor/Ver Transverse Beam Offset 30 0.176 3.7 µm
Module Detuning ∆K/K 0.060 0.400 0.024 %
Module Offset in x 1121 0.125 140 µm
Module Offset in y 268 0.298 80 µm
Quadrupole Gradient Error 8.8 0.029 0.25 %
Transverse Quadrupole Offset 4.7 0.214 1.0 µm
Break Length Error 20.3 0.049 1.0 mm
ζ < 1.10.64<β/β0<1.56
212
0
ifP eP
− ∑=
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Model Detuning Sub-Budget
MMF K KK K T xα β= + ∆ + ∆
27
Parameter pi Typical Value rms dev. δpi Note
KMMF 3.5 0.0003 ±0.015 % uniform
αK -0.0019 °C-1 0.0001 °C-1 Thermal Coefficient
∆T 0 °C 0.32 °C ±0.56 °C uniform without compensation
βK 0.0023 mm-1 0.00004 mm-1 Canting Coefficient
∆x 1.5 mm 0.05 mm Horizontal Positioning
( )2
2i
i i
KK pp
δ δ ∂
= ∂ ∑
( ) ( ) ( ) ( ) ( )2 2 2 2 2MMF K K K KK K T T x xδ δ δα α δ δβ β δ= + ∆ + ∆ + ∆ + ∆
/ 0.020%K Kδ =
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Beam Based Alignment Tolerance Verification
Random misalignment with flat distribution of widh ±a => rms distribution a/sqrt(3)
Beam Based Measurements
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Beam Based K Tolerance Verification
Beam Based Measurements
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LCLS Undulator Tolerance Budget
Error Source σi fi σi fi Units
@ 130 m (24.2% red.)
Hor/Ver Optics Mismatch (ζ-1)0.5 0.71 0.452 0.32
Hor/Ver Transverse Beam Offset 30 0.176 3.7 µm
Module Detuning ∆K/K 0.060 0.400 0.024 %
Module Offset in x 1121 0.125 140 µm
Module Offset in y 268 0.298 80 µm
Quadrupole Gradient Error 8.8 0.029 0.25 %
Transverse Quadrupole Offset 4.7 0.214 1.0 µm
Break Length Error 20.3 0.049 1.0 mm
212
0
ifP eP
− ∑= Tolerance Budget Components
Module Offset in x @ zSAT 780 µm
BB Verification
0.06
1200
8.8
770
MEASUREMENTS
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LCLS-II
An initial rough evaluation of LCLS-II undulator parameters will be presented.Priority is given to the Soft-Xray line, which is likely to be based on short variable gap undulators.Shortness is required to enable the low beta-functions needed for optimum FEL performance.
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32LCLS Undulator StatusMarch 1, 2010
ExistingPhase-0Phase-10.75-15 Å
4-14 GeV
FEE-1Existing 112-m Undulator (1.5-15 Å)
0.75 Å
SHAB30 mShortened 74-m Undulator
5 m
FEE-2SXR2 (45 m)
5 m
full polarization control
self-seeding option
6-60 Åadjust. gap
6-60 Åadjust. gap
SXR1 (45 m)3-7-GeV bypass
4-GeV SXR and 14-GeV HXR simultaneous op’s with bypass line
2-pulse 2-color
No civil construction. Uses existing beam energy and quality.
full polarization control
Phase-2Phase-3
EEHG*?
240 nm → 6 nm
Phased Enhancement Plan for LCLS-II
* G. Stupakov, Phys. Rev. Lett. 102, 074801 (2009)
5 m
full polarization control
Shortened(1.5-15 Å)
Larger Gap Undulator(0.75-7.5 Å)
self-seeding HXR option(2 bunches)
Large Gap(0.5-5 Å)
Large Gap(0.5-5 Å)
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LCLS-I U 1 Enhancement
σ γ =
2.8
I pk=
3000
A, γ
ε xy=
0.6
µm
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LCLS-II U 2 FEL Performance Estimatelin
ear
helic
al
<β>
= 5
m, σ
γ =
2.8
I pk=
2000
A, γ
ε xy=
0.6
µm
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LCLS-II U 2 FEL Performance Estimatelin
ear
helic
al
<β>
= 5
m, σ
γ =
2.8
I pk=
2000
A, γ
ε xy=
0.6
µm
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Beta-Function at 6 nm
Smallest practical beta function 4-5 m is above optimum.
LG~0.65 m for βx,y = 4 m
LG~0.69 m for βx,y = 5 m
Opt
imum
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‘Optimum’ Beta-Function at 6nm
Optimum beta function would reduce undulator length by more than factor 2 but is not accessible.
LG~0.27 m for βx,y ~ 0.1 m
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Optimum Beta-Function at 0.6 nm
At 0.6 nm beta function of 4-5 m is close to optimum.
Considered Value
Optimum Value
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Beta Function and Undulator Length
Undulator: 1.80 m Break0.70 m
Break0.70 m
Half FODO Length: 2.50 m
Minimum <βx,y> = 5 m
ChicaneRF Cavity BPMQuadrupole
The smallest average beta-function achievable with a FODO lattice isThe FODO length is determined by segment length and break lengthBreaks between segments need to be sufficiently wide to allow space for essential components, such as quadrupole, BPM, Chicane.Smallest practical quadrupole separation is 2.5 m, corresponding to a FODO length of 5 m .
,x y FODOLβ ≥
EXAMPLE:
Bellows
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Multi-Segment variable gap undulators require phase shifters between segments to adjust gap dependent inter-segment phase slippage. An example for such achicane is shown here. Field levels have been kept low to reduce in-tunnel powerrelease.
Example Chicane Dimensions
L = 9 cm
L = 4.5 cm L =4.5 cm
xmax
L = 24 cm
3 cm
E 7.0 3.0 GeV
λr 1.2 6.0 nm
B 203 195 G
x’ 78 175 µrad
xmax 7.6 17 µm
∆φ 360 360 degXray
ηx -5.9 -13.2 µm
R56 0.74 3.7 nm
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Undulator TypesA number of different variable field undulator types are under consideration
Parallel-Pole Variable GapFixed Linear Polarization
Hybrid or Pure Permanent MagnetApple Type Variable Gap
Variable Linear/Circular PolarizationHybrid or Pure Permanent Magnet
Delta Type Variable PhaseVariable Linear/Circular Polarization and Intensity
Pure Permanent MagnetSuperconducting Helical Variable Excitation current
Fixed Circular Polarization [Substantial R&D required]
New Designs …Key issues are
Precision Hall probe measurementsK stability and settabilityCompact design to mount on movable girders.Gap > 7 mm
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The LCLS-I undulators have performed very well during commissioning and first user operation.Initial parameter development for the LCLS-II undulators has started, giving priority to the new soft x-ray line.The goal is a compact variable gap design to cover wavelengths between 6 nm and <0.6 nm at electron energies in the range 3-7 GeV.The low emittance and lower electron energy require beta functions of order 5 m or smaller for best utilization.Low beta-functions require a short FODO length, i.e., short undulator segments of length 1.8 m and compact break sections.The total length of each of the 2 soft x-ray undulator lines is expected to be about 50 m.
Summary