lcls undulators – present status and future upgrades...march 1, 2010 lcls undulator module pole...

1 Heinz-Dieter Nuhnnuhn@slac.stanford.edu

1LCLS Undulator StatusMarch 1, 2010

LCLS Undulators –Present Status andFuture Upgrades

Heinz-Dieter Nuhn – LCLS Undulator Group LeaderMarch 1, 2010

Linac Coherent Light Source

INJECTOR

UNDULATOR HALL

BEAM TRANSPORT

Undulator Hall

33 Undulator Segments Installed

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

Quadrupole

Vacuum Chamber

Undulator Segment

RF Cavity BPM

Girder

Fully Assembled Girder (seen from downstream end)

Quadrupole Undulator Segment with mu-Metal Shield

RF Cavity BPM

Coordinate Measurement Machine Position Sensor

Girder Precision Alignment on CMM

Quadrupole

Manual Adjustments

Segment3.400 m

Cam Shaft Movers WPM

Sand-Filled, Thermally Isolated

Fixed Supports

Horizontal SlidesNot visible

Vacuum Chamber and

Support

Long Break89.8 cm

Short Break47.0 cm

LCLS Undulator Components

Vacuum Chamber

Undulator Segment

Magnet Block

Pole Piece

Horizontal Trajectory Shim Holder

Vacuum Chamber Inserted into Gap

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.

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

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

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∆ ≈ −

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 1 1.16dK dK

K KdE d KE

= = + ≈

From Wakefield budget based on S2E Simulations

K Tapering Requirements

K for segment 33

spontwake

gainpost sat

wakegain

post sat

1.5 Å

K for segment 1

Figure 3: K Tapering Scenarios (Continuous)Avoid Reliance on Good Field Region at 1.5 Å

Measured Field Integrals on SN25

( )0 0

', , 'L z

xB dz dzx y z

∫ ∫

( )0 0

', , 'L z

yB dz dzx y z

∫ ∫

xB dzx y z∫

yB dzx y z∫+200 µmy :

+0 µm-200 µm

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

Segmented Undulator Pre-Taper

CMM Keff Measurements for U33/SN20

K=3.468

K=3.497

Segmented Undulator K Control

K ADJUSTMENT RANGE(MEASURED)

TEMPERATURE CORRECTED KACT

TAPER REQUEST

K ADJUSTMENT RANGE(MEASURED)

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

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

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

iP P e σ−

112 mK K∆

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

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

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:

qf fP e e e

− − − ∑= = =∏ ∏

tolerance

fitted rms

fi=qi/σi

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

ifP eP

− ∑=

Model Detuning Sub-Budget

MMF K KK K T xα β= + ∆ + ∆

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

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 =

Beam Based Alignment Tolerance Verification

Random misalignment with flat distribution of widh ±a => rms distribution a/sqrt(3)

Beam Based K Tolerance Verification

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

ifP eP

− ∑= Tolerance Budget Components

Module Offset in x @ zSAT 780 µm

BB Verification

MEASUREMENTS

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.

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

FEE-2SXR2 (45 m)

full polarization control

self-seeding option

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.

Phase-2Phase-3

EEHG*?

240 nm → 6 nm

Phased Enhancement Plan for LCLS-II

* G. Stupakov, Phys. Rev. Lett. 102, 074801 (2009)

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)

LCLS-I U 1 Enhancement

σ γ =

ε xy=

LCLS-II U 2 FEL Performance Estimatelin

ε xy=

LCLS-II U 2 FEL Performance Estimatelin

ε xy=

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

‘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

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

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

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

L = 24 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

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

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

End of Presentation

lcls undulators – present status and future upgrades...march 1, 2010 lcls undulator module pole...

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