Development of elliptical polarization undulators for TPS

Ting-Yi ChungMagnet group, NSRRC, Taiwan

Outline

2

• Characterizations and status of EPUs in Phase-I at TPS

• Motivation of two collinear EPU48• Heat load issue• Design and construction of EPU48• Performance of EPU48• Dynamic multipole error issue• Conclusion

Characterizations of EPUs

EPU46 EPU48 x2Photon energy* (eV) 270-2000 230-2000Deflection parameter 3.48/2.32 3.72/2.47Period Length (mm) 46 48

Number of effective periods 82 67Total physical length (m) 3.89 3.43

Range of magnet gap (mm) 13.5≦G≦110 13≦G≦120

Maximum field strength (T) By=0.81Bx=0.54

By=0.83Bx=0.55

Remanence NdFeB (T) ≧1.22 ≧1.24* Operating at 3GeV

Two kinds of period and three APPLE-II EPUs total are designed, constructed, andinstalled in Phase-I at TPS. Both EPUs can cover the K-edge absorption of the mostabundant elements on Earth (C, Ni, O, Si) and the L-edge absorption of the importanttransition metal (Fe, Co, Ni, Cu).

3

-7.10 -3.55 0.00 3.55 7.100

5

10

15

20

25

30

35

Betay

Beta

func

tion

(m)

Distance (m)

Double_mini Betay

Betax

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

Dx

e-

EM Phase shifter Corrector

EPU48 EPU48

Motivation of two collinear EPU48High polarization mode : double EPU48 with the same polarization are phase matched using aphase shifter between both EPU48. Interference effect increases the intensity of flux.Rapid change polarization mode : double EPU48 with opposite polarization obtain linear orcircular polarized radiation with any required polarization direction depending on the phase shiftersetting.

4

Spectrum and polarization calculation• Operating in the same polarization modes:− The difference of angular flux density between in phase and out-of phase of double EPU will

be up to 40%-2% (in the energy range of 0.22-1.7 keV). The phase shifter is necessary.− Comparing two collinear EPU48 in double mini beta-y lattice with single 3m long EPU, the

flux density increases by a factor of 2.6.− Operating in opposite circular modes, no heat load issue due to no higher harmonics. The

linear polarization rate decreases to 37%, which is attributed to a long drift space and ID.Operating in a common crossed undulator case, the circular polarization rate reduces to 31%.

210 212 214 216 218 220 222 224 226 228 2300.0

2.0x1017

4.0x1017

6.0x1017

8.0x1017

1.0x1018

1.2x1018

1.4x1018

1.6x1018

1.8x1018

2.0x1018

With energy spread and emittance In phase Out of phase

w/o In phase Out of phase

F.D

ensi

ty (p

h/s/

mr^

2/0.

1%)

Energy (eV)

Both in Horizontal Linear

5

Heat load issue on the straight section vacuum chamber. Upstream bending magnet and insertion device will create large heat load on

downstream chamber, up to 15.3W/m in the vertical direction. Temperature rising of a chamber is less than 0.50C via water cooling(250C).

Heat load of two collinear EPU48

Vertical linear mode

Water cooling

Mechanical consideration of EPU48Design concept:•In order to support strong magnetic force (~34kN in horizontal linear mode), thedesign of a cast support structure, instead of a welded structure, of the EPU48 is tolimit the effect of deflections and rotations of the magnet arrays so that the contributionto the r.m.s. phase error is less than 0.5o, corresponding to a gap variation of ±3um.•Deflection of the strong-back, the bearings, the magnet girders, the magnet holdershave all evaluated with a 50% safety margin.

0 50 100 150

-80

-60

-40

-20

0

20

40

60

80 Gap Var. (μm) 2 4 10 12 30 55 72

Gap

var

iatio

n (u

m)

Pole 0 50 100 150

-20

-10

0

10

20r.m.s. Phase error(o)

0.3 0.66 1.5 1.77 4.43 7.7 10.6

Phas

e er

ror (

degr

ee)

Pole 7

Mechanical performance of EPU48

• After sub-girder shim, gap variation has been flattenedfrom ± 75 to ± 20 um. This is able to improve the r.m.s.phase error from 9.8 to 3.4 degree.

• Repeatability of gap and phase movement is less than2.5 um, which ensures a photon energy deviation is lessthan one-tenth of the width of the fifth harmonic.

• Lateral deformation of magnet blocks is less than ±10um.

0 500 1000 1500 2000 2500 3000

-80

-60

-40

-20

0

20

40

60

80

Gap

var

iatio

n (u

m)

Position (mm)

Before Sub-girder shim After

0 50 100 150

-30

-20

-10

0

10

20

30

Phas

e er

ror (

degr

ee)

Pole (degree)

r.m.s. Phase error (o) 9.8 3.4

8

Magnetic consideration of EPU48

Magnet block sorting strategies :1.Individual blocks are sorted based on Helmholtz coil measurement.Importing the component of magnetization of each magnet into RADIA codeto minimize the phase error in various polarization modes.2.Sub-modules holding 7 or 9 blocks are sorted based on Hall probe scan andstretched wire measurements.To eliminate the influence of inhomogeneity and imperfect of blocks, sub-modules are sorted again based on the simulated annealing (SA).

-0.2 -0.1 0.0 0.1 0.2

-0.2

0.0

0.2

0.4

-3 -2 -1 0 1 2 3 4 5 6

-30

0

30

60

By (T

)

Z (m)

Measurement Simulation

(a)

Iy (G

cm)

X (cm)

(b)

Magnet Block

Sub-module 7The cost function consists of terms for multipole error and phase error, which means it takes into account the major influences on the electron beam and the spectrum.

eFSxdFSycESxbESyaMPE ++++=

E : cost energy, MP : multipole error term, ESy/x : error-storage (ES) with respect to vertical or horizontal direction, FSy/x field storage (FS), and coefficients a … e are weight factors of each term. 9

Magnetic consideration of EPU48

-8-6-4-202468

0 5 10 15 20 25 30 35-4

-2

0

2

4

6

dIx/

Ix (%

)

dIy/

Iy (%

)

Pole

Predict_w/o NonUnit Predict_with NonUnit Measurement

• The distribution of dI/I is not only the superposition of each sub-module data, butconsidering the interaction nearby an interface attributed to the non-unit effect.

• The contribution of the non-unit effect is periodic and up to 100Gcm.• After the sorting, the phase error contributed from magnets is suppressed to that

from mechanical error.

I : field integral of poles

0 50 100

-20

-10

0

10

20

30

Producing from mechanical error Measurement

Gap

var

iatio

n (μ

m)

Pha

se e

rror

(deg

ree)

Pole

Position (mm)0 1000 2000 3000

-20

-10

0

10

20

30 Mechanical error

10

Magnetic consideration of EPU48

Magnetic field shimming algorithm :1.Phase error shimming : To improve straightness of trajectories, phase error, and staticmultipole error in all operation modes using a screw-driven wedge and slide mechanismto move magnet blocks, virtual shimming.

2.Static multipole error shimming : To reduce the residual field integral using magnetchips, located at the extremities of EPU. The best arrangement of chips is achievedbased on the simulated annealing.

Before 2D virtual shimming After 2D virtual shimming

The deviation of field integral in the transverse direction is flattened after the 2D virtual shimming, meaning to reduce the quadrupole error. 11

Magnetic performance of EPU48

-60-50-40-30-20-10

0102030405060708090

-40-35-30-25-20-15-10-505

1015202530354045

-150 0 150

-40-35-30-25-20-15-10-505

1015202530354045

-150 0 150

-40-35-30-25-20-15-10-505

1015202530354045

Hor

izon

tal t

raje

ctor

y (u

m)

(a) Random

(b) After individual block sorting

z (cm)

(c) After submodule sorting

Phase mode ( π ) 1 0.64 0.35 0 -0.35 -0.64 -1

z (cm)

(d) After shimming

Road map (straightness of trajectories) :After the submodule sorting, the straightness has been improved within ±11um. Aftershimming, it has even been improved within ±4um in all operation modes.

12

Magnetic performance of EPU48Road map (Phase error) :• Phase errors for linear/circular mode are better than 2.5/4 degree.• The flux density of linear polarization mode at the fifth harmonic energy and circular

polarization mode in the fundamental harmonic energy are greater than 95% of anideal value.

-1 0 1

2

3

4

5

6

7

8

15

20

25

50 60 70 80 90 100

Random After individual block sorting After submodule sorting After shimming

R

MS

Pha

se E

rror

(Deg

ree)

Phase mode ( π )

Gap 13 mm

n=3

Related flux density (%)

n=1

n=5

13

Magnetic performance of EPU48

100 200 300 400

3

6

9

FERMI_EPUb1~6

BESSYII_UE52

BESSYII_UE46

ELETTRA_EU60

BESSYII_UE56_1&2

TPS_EPU46PETRAIII_UE65

Soleil_HU80

MAXII_EPU46

TPS_EPU48

Polarization mode H/V Linear Cir./Ellip.

RM

S ph

ase

erro

r ( o )

Length / Gap

Position in APPLE-II map: Constructing a longer and smaller gap of a undulator is muchdifficult. Stiff mechanical structures and good quality magnets are essential. Mechanicalarts and magnetic field treatments are equally important for a high performance undulator.

14

Magnetic performance of EPU48

-500

0

500

1000

-2 -1 0 1 2

-500

0

500

1000

Random After submodule sorting After phase error shimming After Magic finger shimming

Ix (G

cm)

Iy (G

cm)

X (cm)

• The static multipole error has beencompensated with magnet chips, calledmagic fingers, based on the simulatedannealing algorithm. The results arewithin ±30Gcm in the range of ±15mm.

• All multipole terms are within the spec.

Gap(mm) Phase mode

Skew NormalDi Quad. Sext. Oct. Di Quad. Sext. Oct.

Gauss.cm (<100)

G(<50)

G/cm(<100)

G/cm2

(<100)Gauss.cm

(<100)G

(<50)G/cm(<100)

G/cm2

(<100)

13

VLP -29 20 4 -12 18 25 -19 -3 LCP -46 -12 7 -1 -10 9 0 4 HLP -14 -6 -3 -3 2 -3 -4 5 RCP 86 40 -22 -22 34 21 -30 -3

3rd order within x= ± 1.5cm

15

Dynamic multipole error

• A horizontal injection scheme makes a tightrequirement of horizontal good field region. APPLE-IItype, however, has a gap between magnet rows and aninherent narrow Bx good field region.

• A shim pad design on magnets can improve roll off ofvertical field By.

• The second order kick is responsible for dynamicmultipole due to narrow Bx good field region.

electron

16

Dynamic multipole error

• The active shim system based on a similar scheme used at BESSYII is adopted tocompensate dynamic multipole error.

• The effect of the ID second order kicks can be compensated by the counteractingfirst order correction with the current strips.

-300

-200

-100

0

100

200

300

-30 -20 -10 0 10 20 30

-3

-2

-1

0

1

2

3

Dyn

amic

Ix (G

cm) Current off

On

Vertical linear mode at Gap13mm

Cur

rent

(A)

Horizontal position (mm)

17

Conclusion

• There is interference between our two collinear EPU48s. The phaseshifter is necessary to phase matching both radiation.

• The EPU48s are designed carefully and constructed completely inNSRRC. Sorting and shimming algorithms are developed based on asequence of magnetic field error analysis, separating the contributionof magnetic material and mechanical parts. The performance ofEPU48 is qualified to achieve the requirements of electron andphoton beams.

• The shim pad design on a magnet can solve the dynamic multipoleissue of vertical field. Constructing the flat wire system forcompensating the dynamic multipole errors of horizontal field isongoing.

Thank for your attention.

EPU48_front view EPU48_back view