Delta undulator magnet: concept and project status

*Work has been supported by NSF grant DMR 0225180 and PHY-013150+ Supported by DOE Office of Science

Part - II: beam test at ATF in BNL+

M. Babzien, D. Davis, M. Fedurin, K. Kusche, J.Park, V. Yakimenko, Brookhaven National Laboratory, Upton, USA

Alexander Temnykh, CLASSE, Cornell University, Ithaca, New York, USA

Part – I: concept and model construction*

Alexander Temnykh, CLASSE, Cornell University, Ithaca, New York, USA

FLS 2010, SLAC March 1-5, 2010 2

• Delta undulator magnet concept.– Two considerations

• On-axis vacuum• Radiation damage

• Model construction– Magnetic field properties– Vacuum

• Beam test at ATF BNL • Conclusion

Outline

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1. Compact box-like frame: prototype dimension ~150mmx150mm2. Full polarization control3. Sqrt(2) stronger field in planar mode and ~2X stronger in helical mode in compare with

conventional / Apple II type undulators.

Two AP (adjustable phase**) undulators assembled in one device.

Potential applications: ERLs, XFELs , (storage rings?)

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

**Basic theory: Roger Carr, Nucl. Instr. And Meth. A 306(1991) 391-396

Delta undulator magnet concept

FLS 2010, SLAC March 1-5, 2010 4

*See Ref: P. Elleaume, et al., Design considerations for a 1 A SASE undulator, NIMA, 455(2000) 503-523

25m long Delta and 25m long APS U33 undulator structures comparison

Delta undulator magnet concept

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Historical excurse - similar designs

Pavel Vobly, HELICAL UNDULATOR FOR PRODUCINGCIRCULARLY POLARIZED PHOTONS, In proccedings of the workshop on new kinds of positron sources for linear collider, March 4-7, 1997. SLAC-R-502, CONF-970374, pp. 429-430

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

Apple-II (left) and Apple –III (right) **

Delta undulator magnet concept

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Four channels from on- axis area to outside. Model in Ref*:

B = 0.05cm; L = 1.57cm; L/B = 31.5a (transmission probability) = 0.12*

Molecular conductance for 4 channels:C [L/s] = 4 x 11.6 x a x B [cm] / per 1cm of length

Ni plated PM blocks outgassing rate (after 48hrs, 120degC baking) has been measured in Ref **: R~4 x 10^-12Torr/L/sec/cm^2 or less **

The pressure differential between on-axis and outside will be:

5mm IDbore

0.5mm wide slit

15.7mm

dP = Q / C = 3.1415*0.5*4e-12/(4*11.6*0.12*0.05) = 2.3e-11Torr (0.02nTorr!)

*John F. O'Hanlon, A Users Guide to Vacuum Technology, Second Edition, pp.33 – 37 ** Yulin Li, ADC In-Vacuum Undulator Magnet Material Out-gassing Test Report Feb. 20, 2008

On-axis vacuum

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Radiation damage consideration

radiuselectron classical - factor, icrelativist - charge,nuclear - where erZ

Major source of radiation - high energy electrons scattered on the residual gas.

x

a

dx

s

Small angle Coulomb scattering cross section :

High energy electron flux rate though cylindrical surface of radius “a” as function of residual gas density ngas and distance s:

2

22

2

24)(

a

sr

Zn

q

IsF egas

e

e

;14

22min

2

22

2

erZ

d

d

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Radiation damage consideration

][][][102.8sec]/[ 25' mSnTPAIradD b

Critical dose Dc ~ 2Mrad (NbFeB 40SH, 1% demagnetization), see Ref *

Assuming Z=7.5 (worst case), 5mm bore, 5GeV beam energy and that all scattered electrons deposit energy into ~5mm layer around bore (required simulation) we can estimate the rate of the dose accumulation as:

* A. Temnykh, NIMA, Volume 587, Issue 1, 11 March 2008, Pages 13-19

Estimated life time for 5 and 25m undulators as function of on-axis residual gas pressure.

As a life time criteria we used ~1% demagnetization of undulator “downstream” end.

The undulator temperature lowering will•Decries out-gassing, lower pressure•Increase radiation resistivity.

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Model construction steps

Assembly start Test assembly and dimensions check

Model in vacuum vessel Transport from Cornell to BNLMagnet field measurement and tuning

Model parameters

•PPM structure•NbFeB (40SH) Br =1.25T, Hci > 20Koe•Period 24mm•Length ~ 30cm•Bmax (designed) in helical mode ~1.0T•Bmax (designed) in planar ~ 1.4T

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Model construction: magnetic field tuning

Conventional setup. For field analysis used B2E software from ESRF

1. Hall probe sensor (HGT-2101) mounted on sliding stage

2. Sliding stage

By along magnet TrajectoryOptical phase errors,

RMS ~2.0deg

“By” tuning with Hall probe

(1)

(2)

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Model construction: field properties in helical mode

Measured field components Trajectory X-ray Spectra

Helical mode, left circular polarization (phase between vertical and horizontal pairs 900)

Helical mode, right circular polarization (phase between vertical and horizontal pairs -900)

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Planar mode, - 45deg linear polarization (phase between vertical and horizontal pairs 180deg)

Model construction: field properties in planar mode

Planar mode, +45deg linear polarization (vertical and horizontal pairs in phase)

Measured field components Trajectory X-ray Spectra

Note: B1 and B2 two orthogonal field component tilted relative horizontal and vertical axis by 45deg.

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Model construction: vacuum property

RGA spectraH2 (~89%)

H2O(5.2%) Nitrogen/CO(5.7%)

Assembled model bake out.

After 80hrs, 55degC baking Pmin ~ 40nTMeasured pumping speed 7.7litr/sec.

Outgassing rate: 2.77e-7 Torr litr/sec

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Beam test

ATF beam parameters:Energy in range from 52MeV to 72MeVNormalized emittance 1e-6 m*radBunch charge ~ 500pCRepetition rate ~ 1.3 pulse/sec

Two major goals:1. Get experience in transportation, installation, test mechanics.

(No problems with transportation and installation, mechanics work OK)2. Characterize (verify) undulator radiation properties

Delta undulator installed in BL2 ATF.

ATF beam line #2 schematic

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Delta undulator

Flat mirror

InSb(77K) detectorMaximum sensitivity at 4500nm

Narrow band pass filters

Beam line elements

Electron beam

Movable Collimator

Parabolic mirror

Optical diagnostics scheme

Beam test

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Undulator in planar mode.

5300nm wavelength radiation as function of the electron beam energy.

Signal confirmed 1.28T peak field in undulator

Undulator in helical mode.

4520nm (bottom) and 3600nm (right) wavelength radiations versus beam energy. Both data confirmed 0.93T field amplitude.

Beam test

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60 MeVEb = 58MeV

66 MeV64 MeV62 MeV

Radiation cone spatial distribution as function of beam energy measured with collimator 2D scan.

Scanning range: -20+20mm, -23+27mm, Step: 5mm Collimator: 12.7mm diameter

Undulator in helical mode, 4520nm radiation (fundamental harmonics)

Beam test

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Encountered problem:

Undulator field focusing effect

;

2

12

2max

BLB

f

; stiffness beam - length;undulator -

field;peak undulator - length; focal a is where max

BL

Bf

For undulator in planar mode and 60MeV beam it gives:

plane onein focus ;17cmf

For helical mode and 60MeV beam:

planesboth in focus ;31cmf

Strong focusing in planar mode made beam line optics match very difficult. Higher beam energy would be better.

Beam test

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Conclusion

1. We developed concept and built short model of “Delta” undulator magnet.

2. Mechanical, magnetic and vacuum properties of the magnet have been tested.

3. The beam test confirmed the basic characteristics of the magnetic field: 0.93T in helical mode and 1.27T in planar.

4. Future plans – under consideration.

I would like to thank David Rice, Sol Gruner, Donald Bilderback and Maury Tigner for support. My special thanks to Yulin Li and Karl Smolensky as well as vacuum group for useful discussions and help in the model construction.

Acknowledge