LCLS-II Undulator Parameters

1 Heinz-Dieter [email protected]

1LCLS Undulator StatusMarch 12, 2010

LCLS-II Undulator Parameters

Heinz-Dieter Nuhn – LCLS Undulator Group LeaderMarch 12, 2010



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.

Segment shortness is required to enable the low beta-functions needed for increased FEL performance.



ExistingExistingPhase-0Phase-0Phase-1Phase-10.75-15 Å 0.75-15 Å

4-14 GeV4-14 GeV

FEE-1Existing 112-m Undulator (1.5-15 Å)

0.75 Å0.75 Å

SHAB30 m

Shortened 74-m Undulator

5 m

FEE-2SXR2 (45 m)

5 m

full polarization full polarization controlcontrol

self-seeding self-seeding optionoption

6-60 6-60 ÅÅadjust. gap adjust. gap

6-60 6-60 ÅÅadjust. gap adjust. gap

SXR1 (45 m)3-7-GeV bypass3-7-GeV bypass

4-GeV SXR and 14-GeV HXR simultaneous op’s with bypass line

2-pulse 2-pulse 2-color2-color

No civil construction. Uses existing beam energy and quality.No civil construction. Uses existing beam energy and quality.


Phase-2Phase-2Phase-3Phase-3

EEHG*?EEHG*?

240 nm 240 nm 6 nm 6 nm

Phased Enhancement Plan for LCLS-II

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

5 m


Shortened (1.5-15 Å)

Larger Gap Undulator(0.75-7.5 Å)

self-seeding self-seeding HXR optionHXR option(2 bunches)(2 bunches)

Large GapLarge Gap (0.5-5 Å)(0.5-5 Å)

Large GapLarge Gap (0.5-5 Å)(0.5-5 Å)



LCLS-I U 1 Enhancement

=

2.8

I pk

= 3

00

0 A

,

xy=

0.6

µm

15 Å 1.5 Å23 Å 1.24 Å

11 Å 0.62 Å

9.6 Å 0.52 Å 130 m

15 GeV3.5 GeV



LCLS-II U 2 FEL Performance Estimatelin

ear

hel

ical

<>

= 5

m,

= 2

.8I pk

= 2

00

0 A

,

xy=

0.6

µm



LCLS-II U 2 Small Period Undulator

<>

= 4

m,

= 2

.8I pk

= 2

00

0 A

,

xy=

0.6

µm

hel

ical

hel

ical



Optimum beta functions at u = 4.0 cmh

elic

alh

elic

al



Beta Function and Undulator Length

Undulator: 1.80 m Break0.70 m

Break0.70 m

Half FODO Length: 2.50 m

Minimum <x,y> = 5 m

ChicaneRF Cavity BPMQuadrupole

The smallest average beta-function achievable with a FODO lattice is

The FODO length is determined by segment length and break length

Breaks 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 FODOL

EXAMPLE:

Be

llow

s



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

r 1.2 6.0 nm

B 203 195 G

x’ 78 175 µrad

xmax 7.6 17 µm

360 360 degXray

x -5.9 -13.2 µm

R56 0.74 3.7 nm



Beta-Function at 6 nm

Smallest practical beta function 4-5 m is above optimum.

Lsat,mag~10.0 m for x,y = 4 m

Lsat,mag~10.8 m for x,y = 5 m

Opt

imum



‘Optimum’ Beta-Function at 6nm

Optimum beta function would reduce saturation length by more than factor 2 but is not accessible.

Lsat,mag~4.3 m for x,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



Undulator TypesA number of different variable field undulator types are under consideration

Parallel-Pole Variable Gap Fixed Linear Polarization

Hybrid or Pure Permanent Magnet

Apple Type Variable Gap Variable Linear/Circular Polarization

Hybrid or Pure Permanent Magnet

Delta Type Variable Phase Variable Linear/Circular Polarization and Intensity

Pure Permanent Magnet

Superconducting Helical Variable Excitation current Fixed Circular Polarization [Substantial R&D required]New Designs …

Key issues arePrecision Hall probe measurementsK stability and settabilityCompact design to mount on movable girders.Gap > 7 mm



Variable Polarization Undulator TypesTwo adjustable phase undulators assembled in one device**.

**A. Temnykh, Phys. Rev. ST Accel. Beams 11, 120702 (2008).

DE

LT

A

*J. Bahrdt, et al., UNDULATORS FOR THE BESSY SOFTX- RAY FEL, Proccedings of the 2004 FEL Conference, pp. 610-613.

Adjustable Phase Undulators

APPLE-II APPLE-III*

Variable Gap

Fixed Gap

Full K range available through row adjustment



The LCLS-I undulator resonance can be shifted to lower wavelengths with moderate loss in xray energy.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.

The LCLS-I undulator resonance can be shifted to lower wavelengths with moderate loss in xray energy.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-II Undulator Parameters

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