Delta undulator magnet: concept and project status Part I: concept and model construction* Alexander Temnykh, CLASSE, Cornell University, Ithaca, New York, USA 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 *Work has been supported by NSF grant DMR 0225180 and PHY-013150 + Supported by DOE Office of Science
Outline Delta undulator magnet concept. Two considerations On-axis vacuum Radiation damage Model construction Magnetic field properties Vacuum Beam test at ATF BNL Conclusion FLS 2010, SLAC March 1-5, 2010 2
Delta undulator magnet concept Two AP (adjustable phase**) undulators assembled in one device. 1. Compact box-like frame: prototype dimension ~150mmx150mm 2. Full polarization control 3. Sqrt(2) stronger field in planar mode and ~2X stronger in helical mode in compare with conventional / Apple II type undulators. 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 FLS 2010, SLAC March 1-5, 2010 3
Delta undulator magnet concept *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 FLS 2010, SLAC March 1-5, 2010 4
Delta undulator magnet concept Historical excurse - similar designs Apple-II (left) and Apple III (right) ** 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. FLS 2010, SLAC March 1-5, 2010 5
On-axis vacuum Four channels from on- axis area to outside. Model in Ref*: 0.5mm wide slit 5mm ID bore B = 0.05cm; L = 1.57cm; L/B = 31.5 a (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: 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 FLS 2010, SLAC March 1-5, 2010 6
Radiation damage consideration Major source of radiation - high energy electrons scattered on the residual gas. Small angle Coulomb scattering cross section : where Z dσ = dω 4Z γ 2 2 r 2 e - nuclear charge, γ - relativistic factor, 1 ( ) ; 2 2 2 θ + θ min re - classical electron radius s x θ dx a High energy electron flux rate though cylindrical surface of radius a as function of residual gas density n gas and distance s: F( s) = I q e e n gas 4π Z 2 γ 2 r 2 e s a 2 2 FLS 2010, SLAC March 1-5, 2010 7
Radiation damage consideration 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: ' 5 D [ rad / sec] = 8.2 10 Ib[ A] P[ nt ] S 2 [ m] Critical dose D c ~ 2Mrad (NbFeB 40SH, 1% demagnetization), see Ref * 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. * A. Temnykh, NIMA, Volume 587, Issue 1, 11 March 2008, Pages 13-19 FLS 2010, SLAC March 1-5, 2010 8
Model construction steps 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 Assembly start Test assembly and dimensions check Magnet field measurement and tuning Model in vacuum vessel Transport from Cornell to BNL FLS 2010, SLAC March 1-5, 2010 9
Model construction: magnetic field tuning B y tuning with Hall probe (1) Conventional setup. For field analysis used B2E software from ESRF (2) 1. Hall probe sensor (HGT-2101) mounted on sliding stage 2. Sliding stage By along magnet Trajectory Optical phase errors, RMS ~2.0deg FLS 2010, SLAC March 1-5, 2010 10
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 90 0 ) Helical mode, right circular polarization (phase between vertical and horizontal pairs -90 0 ) FLS 2010, SLAC March 1-5, 2010 11
Model construction: field properties in planar mode Measured field components Trajectory X-ray Spectra Planar mode, - 45deg linear polarization (phase between vertical and horizontal pairs 180deg) Planar mode, +45deg linear polarization (vertical and horizontal pairs in phase) Note: B1 and B2 two orthogonal field component tilted relative horizontal and vertical axis by 45deg. FLS 2010, SLAC March 1-5, 2010 12
Model construction: vacuum property Assembled model bake out. After 80hrs, 55degC baking P min ~ 40nT Measured pumping speed 7.7litr/sec. Outgassing rate: 2.77e-7 Torr litr/sec H 2 (~89%) RGA spectra H 2 O(5.2%) Nitrogen/CO(5.7%) FLS 2010, SLAC March 1-5, 2010 13
Beam test 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 ATF beam line #2 schematic ATF beam parameters: Energy in range from 52MeV to 72MeV Normalized emittance 1e-6 m*rad Bunch charge ~ 500pC Repetition rate ~ 1.3 pulse/sec Delta undulator installed in BL2 ATF. FLS 2010, SLAC March 1-5, 2010 14
Beam test Optical diagnostics scheme InSb(77K) detector Maximum sensitivity at 4500nm Narrow band pass filters Flat mirror Parabolic mirror Delta undulator Movable Collimator Beam line elements Electron beam FLS 2010, SLAC March 1-5, 2010 15
Beam test Undulator in planar mode. Undulator in helical mode. 4520nm (bottom) and 3600nm (right) wavelength radiations versus beam energy. Both data confirmed 0.93T field amplitude. 5300nm wavelength radiation as function of the electron beam energy. Signal confirmed 1.28T peak field in undulator FLS 2010, SLAC March 1-5, 2010 16
Beam test Undulator in helical mode, 4520nm radiation (fundamental harmonics) 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 Eb = 58MeV 60 MeV 62 MeV 64 MeV 66 MeV FLS 2010, SLAC March 1-5, 2010 17
Beam test Encountered problem: Undulator field focusing effect 1 f = B 2 2 L max ( ) ; 2 Bρ where f is a focal length; max L - undulator length; Bρ - beam stiffness ; B - undulator peak field; For undulator in planar mode and 60MeV beam it gives: f =17cm; focus in one plane For helical mode and 60MeV beam: f = 31cm; focus in both planes Strong focusing in planar mode made beam line optics match very difficult. Higher beam energy would be better. FLS 2010, SLAC March 1-5, 2010 18
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. Acknowledge 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. FLS 2010, SLAC March 1-5, 2010 19