Recent Developments of Variably Polarizing Undulators at the APS. By Mark Jaski

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1 Recent Developments of Variably Polarizing Undulators at the APS By Mark Jaski

2 Outline What is an Undulator IEX device Analysis Prototypes Final device EMVPU Device Analysis Prototypes Final device 2

3 What is an Undulator An undulator is and insertion device (ID). It is typically used in an electron storage ring or free electron laser to create x-rays. Scientist use these x-rays to study matter on an atomic scale. An ID consist of a set of dipole magnets arranged in a periodic alternating northsouth field pattern (see figure). The figure shows a vertical field ID. This device undulates the electron beam horizontally (planar). A circular polarizing undulator has both vertical and horizontal poles offset by ¼ period. This device undulates the electron beam both horizontally and vertically in a spiral (circular) shape. 3

4 The IEX undulator IEX stand for Intermediate Energy X-ray The IEX device is an Electromagnetic Variably Polarizing Quasi-periodic Undulator or Just The IEX Undulator [1]. IEX can be a circular polarizing undulator, planar undulator or any combination in between. Electromagnetic allows for adjustment of the field strength (change the photon energy). Quasi-periodic is a method of changing the field strength at certain locations in order to phase out undesirable harmonics. 4

5 Full Period Periodic Model (lower jaw)

6 Half Period Periodic Model Test the mesh size then use the coarse mesh to optimize [2] the pole shapes (maximize the field). Thousands of models were solved using the OPTIMIZER. Use the tight mesh to check the final model. Coarse Mesh 476,134 linear elements 1 hour to run (3 hours with quadratic elements) Results are within 5% of tight mesh Tight Mesh 1,450,435 Quadratic elements 24 hours to run

7 4 period model with end poles and coils The final device will be 76 periods but only a 4 period model was used as a design model.

8 Jaw Half Model The poles shall be made of Vanadium Permendur The back legs shall be made of 1008 steel The poles are accurately located with dowel pins The coils are vacuum impregnated with epoxy The coil conductor is 11 GA square solid copper coated with HPT (polyimide enamel) and double polyester glass

9 IEX Coil design - See reference [3]

10 IEX Four Period Prototype #1

11 Tesla Bx Effective OPERA/measured / Tesla (-8.1%) Compair OPERA Data to Measured Data Bx-OPERA 0 0 Bx meas OPERA Ix -8.1% compare delta z (mm)

12 Tesla By Effective OPERA/measured / Tesla (-3.7%) Compare OPERA Data to Measured Data By By meas z (mm)

13 Why Less Field 5 micron nickel plating causes 10 micron gaps between the pole joints. OPERA model has no bolt holes. Adding bolt holes reduces the field. Vanadium Permendur The vanadium permendur (VP) poles were incorrectly heat treated. Poor heat treating could caused the B-H curve to shift. This lead to development of a new B-H curve [2].

14 OPERA 4 Period Model For Prototype #2 No Coils Flux Bridge 14

15 OPERA 4 Period Model For Prototype #2 Add the Coils Typically end coils are ~¼ - ¾ - 1 turns Actual Turns Bx By

16 OPERA 4 Period Model For Prototype #2 Add Trim Coils For Beam Steering And Multipole Correction 16

17 Field plots with end poles and coils Bx By 5 Period Device

18 Trajectory - Bx End Poles and Coils By adjusting the pole tip lengths on the end poles can steer the electron beam. Hundreds of models were solved to obtain the best configuration.

19 Trajectory - Bx End Poles and Coils Several Iterations

20 Trajectory - Bx Downstream End Poles and Coils

21 Trajectory - Bx Downstream End Poles and Coils Several Iterations

22 A look at the trajectory in the z direction

23 2nd prototype Model 23

24 Prototype General Assembly Exploded View Vanadium permendur poles By Coils Bx Coils Indirect water cooling of coils Steel Core 24

25 Main coil leads Trim coil leads Trim coil winding Main coil winding Trim Coils Two windings per coil Main coil winding Trim coil winding 25

26 Second Prototype on the magnet measurement test stand Everything tested and worked as predicted. 26

27 Full Size IEX Device Selected Parameters General By Field 2 Bx Field 2 Period 12.5 cm Gap 10.5 mm Periods per device (including end poles) 38 Periods Length 4.8 m Max Achievable Vertical Effective Field 4599 Gauss Peak field Gauss Current A Number of By coils 112 Each Number of By Quasi-periodic coils 40 Each Total Power of By Coils Watts Total Power of By Quasi-periodic coils Watts Max Achievable Horizontal Effective Field 3362 Gauss Peak field Gauss Current A Number of Bx coils 224 Each Number of Bx Quasi-periodic coils 80 Each Total Power of Bx Coils Watts Total Power of Bx Quasi-periodic coils Watts 17 Power Supplies Peak Current 5.87 A Total Power at Peak Current 40 Watts Bx Trim Coils 4 upstream Each 8 Number of Bx trim coils 4 downstream Each Peak Current 5.53 A Total Power at Peak Current 45 Watts By Trim Coils 2 upstream Each 4 Number of By trim coils 2 downstream Each DS Skew Dipole 9,021 G-cm DS Normal Dipole 13,153 G-cm DS Skew Quadrupole 4,251 G DS Normal Quadrupole 15,158 G Maximum DS Normal Sextupole 10,236 G/cm Achievable DS Skew Octupole 346 G/cm 2 Multipole US Skew Dipole 8,043 G-cm Corrections US Normal Dipole 13,054 G-cm US Skew Quadrupole 4,569 G US Normal Quadrupole 15,144 G US Normal Sextupole 10,140 G/cm US Skew Octupole 375 G/cm 2 Integrated Field Per Ampere 490 Gauss-cm/A Earth Field Peak Current 8 A Corrector1 Total Power at Peak Current 4.5 Watts Maximum Temperature of Coils 100 C 1 At the Max Achievable Effective Field All fields listed above are calculated values 27

28 IEX OPERA Model 38 periods long 11 million nodes 39 million elements 456 coils (468 windings) 14 days to solve 28

29 IEX Device Installation in April m long ~14,000 lbs 29

30 IEX Layout Air Exhaust ports each end To the tunnel air handling system (Marvin Kirshenbaum) Welded Aluminum Top Frames Steel Second Frame Steel Bottom Frame 30

31 Electromagnet IEX Device Can Be Periodic or Quasiperiodic Quasi-periodic Field The field is reduced at selected poles 1 Quasi-periodic Electron Trajectory 1 S. Sasaki, Overview of Quasi-periodic Undulators, PAC09 31

32 Quasi-periodicity Suppresses the Higher Harmonics R. Dejus et al., Coil Energizing Patterns for an Electromagnetic Variably Polarizing Undulator, PAC11 Flux in linear horizontal polarization mode at 250-eV first-harmonic energy for two different QP patterns with reduced magnetic field at the QP poles (85% of regular field). The higher harmonics are shifted to lower energies with the QP turned on. The energy shift is smaller for the 16-pole pattern (blue dashed curve). The flux of the third harmonic is reduced to ~ 8% and the second harmonic is reduced to less than 50% for both patterns. The first harmonic is reduced by ~ 20%. 32

33 Assembly 33

34 IEX at the magnet measurement bench. 34

35 EMVPU Outline Introduction One period test model Four period test model Further information can be found in reference [4]. 35

36 ElectroMagnetic Variably Polarizing Undulator (EMVPU) Strong scientific demand to increase the sensitivity of the x-ray magnetic circular dichroism to the record level of 10-5 Bohr magneton per atom drives the development of this unique undulator. The photon energy range is 400 ev to 2000 ev. 10 Hz switching between leftand right-circular is required for lock-in detection. A 1-period test model will be developed and built to show the fast switching concept. A 4-period test model together with a newly-developed power supply will complete the evaluation. General assembly layout of the 4-period EMVPU test model. The field strength combined with the switching speed and high duty cycle exceeds the capability of any existing undulator at any light source around the world. This device will provide unique technical and scientific capabilities as a part of APS Upgrade. Adv 36 anc

37 One Period Test Model - Opera Model (ELEKTRA) Voltage in/out 37

38 One Period Test Model Vertical field poles One turn By coils are used to minimize inductance for fast switching Horizontal field poles TOSCA/OPTIMIZER was used to optimize the pole tip shape (maximize the field) before ELEKTRA modeling.

39 One Period Test Model Current path for By field 2000 amperes Figure 5: Circuit path for the By coils for a one period test model 39

40 Field(Gauss)-Current(A) Volts Field(Gauss)-Current(A) Volts Current Field - Voltage EMVPU By Effective, Current, Voltage By Eff Current 99.5% Volts per half coil Amperes change from positive to negative field in 8 msec. 10 Hz cycle time. Current has a sinusoidal transient. Eddie currents in the system are responsible for slowing the field change ms current rise 59 V Time (s) EMVPU By Effective, Current, Voltage By Eff Current 99.5% Volts per half coil Time (s) -3

41 One Period Test Model Aluminum vacuum chamber eddy currents

42 Field Animation No vacuum chamber 42

43 One Period Test Model Main Assembly

44 One Period Test Model Selected Parameters EMVPU One Period Prototype Specifications Description Value Units Comments Gap 8.5 mm switching speed 10 Hz 50 ms for a half period By test current 1410 A Provided by old CPU power supply By resistance 154 µω at 27 C By inductance 11 µh By peak Field 3450 Gauss At test current By Power supply current switch time 6 ms Half sine wave By field switch time 10 ms to 99% full field Bx current (max) 50.3 A Thermal load may limit this to a smaller value Bx resistance Ω at 27 C Bx peak field 3750 Gauss at max current

45 One Period Test Model Bus Bar Routing 2000 amperes max operating current

46 One Period Test Model Cooling Water Circuit 46

47 EMVPU One Period Test Model Nonconductive hose for buss bar cooling Fake vacuum chamber Aluminum frame Positive 2000 A terminal Negative 2000 A terminal Deionized cooling water supply and return

48 Solder Test Tin plated copper

49 Lower Jaw

50 Force (N) One Period Test Model Forces By Coil 0 By Coil Forces Fx Fy Fz lbs time (s) 50

51 EMVPU One Period Test Model Measured Results Compare 5 Hz Current and By Field Current from old CPU power supply Field 16 ms 18 ms Shows the field lags behind the current which is expected because of the eddy currents in the system.

52 EMVPU One Period Test Model Compare Bx Field with simulation. Measured Measured 3760 G at 50 A 90 C Simulated 3750 G at 50 A 70 C Simulated Higher temperature was expected because coils were not epoxied to the poles and no blower was used.

53 4 Period Test Model Vector Fields Model 2mm Core gap to magnetically isolate end poles from main poles Laminated Flux Bridge 53

54 4 Period Test Model By coils and cores Apply voltage BC to all these surfaces OFCH one-turn By coils 54

55 4 Period Test Model By Cores (flux path) By end poles are cut back for steering 100% 50% 25% 100% 75% typical Silicon steel laminated By poles Laminated Flux Bridge 55

56 4 Period Test Model Bx Coils and Cores Low carbon steel core Bx end coils are smaller for steering Vanadium Permendur Bx poles Bx end poles are cut back for steering 56

57 4 Period Test Model Steering During Switching 20 microns This is for a 4 period device. A full size device (~18 periods) will mis-steer ~90 microns. 57

58 Slope Field (Gauss) 4 Period Test Model Corrector Magnet Corresponds to 1600 G-cm integrated field Slopes/Field vs. time US_slope_ave DS_slope_end #By time (s) It needs to be shown that the corrector magnet can provide the fields at the speed necessary to correct the mis-steering during switching. 58

59 4 Period Test Model With currents in correctors

60 Final Design 0f the 4 period EMVPU 60

61 Several analyses tools were used OPERA ELEKTRA and TOSCA were the dominant tools. Field profiles Animations Force calculation Multipole calculations Eddy currents evaluated Trajectory calculation Dimensional parameterized comi files Optimizer Thousands of magnetic field analyses were run to obtain results. Thermal analysis (Pro-Mechanica) Stress analysis (Pro-Mechanica)

62 Publications and References IEX Publications [1] M.S. Jaski, M. Abliz, R.J. Dejus, B. Deriy, E. Gluskin, E.R. Moog, I. Vasserman, A. Xiao, An Electromagnetic Variably Polarizing Quasi-Periodic Undulator, PAC13 North American Particle Accelerator Conference, 29 September 4 October, 2013, Pasadena, CA. [2] M.S. Jaski, R.J. Dejus, E.R. Moog, Magnetic Simulation of an Electromagnetic Variably Polarizing Undulator, PAC11 - Particle Accelerator Conference, 28 March - 1 April, 2011, New York, New York. [3] M. Jaski, Design and Fabrication of Magnet Coils MEDSI Mechanical Engineering Design of Synchrotron Radiation Equipment and Instrumentation July, 2010, Oxford, United Kingdom. EMVPU Publications [4] M.S. Jaski, R.J. Dejus, B. Deriy, E. Gluskin, E.R. Moog, I. Vasserman, J. Wang, A. Xiao, Fast-Switching Variably Polarizing Undulator, PAC13 North American Particle Accelerator Conference, 29 September 4 October, 2013, Pasadena, CA. 62