1. ‘Development and Commissioning of a Single Non-linear Kicker Magnet System for the BESSY II Storage Ring Injection’ O. Dressler, P. Kuske - USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012

2. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 2 Content 2 Non-conventional Injection vs. 4 Kicker Bump - Improvement Matching of Conventional 4 Kicker Bump Undisturbed Injection in Top-Up-Mode Non-linear Magnet Development and Laboratory Test - Concept, Evolution of Design, 2D Magnetic Field Calculations - Comparison of Different Pulse Circuit Topologies - Realization of Magnet and Connections with good Symmetry - Laboratory Tests for Magnetic Field Measurements Non-Linear Kicker Commissioning and Design Improvements - Mitigation of RF Power Losses - Commissioning of Non-linear Kicker as Storage Ring Injection - Measured Beam Excitation with Kicker Magnet Summary and Outlook Extra: Principle of Kicker Circuit, Linear Transducer

3. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 3 3 Non-conventional Injection vs. 4 Kicker Bump *PHYSICAL REVIEW SPECIAL TOPICS - ACCELERATORS AND BEAMS 10, 123501 (2007), New injection scheme using a pulsed quadrupole magnet in electron storage rings, Kentaro Harada, Yukinori Kobayashi, Tsukasa Miyajima, and Shinya Nagahashi, Photon Factory Non-conventional injection with one single non-linear kicker Application of the two injection septa and one single pulsed non-linear kicker magnet outside the injection straight for special injection procedure in top-up-mode *. Conventional layout of BESSY II Storage Ring Injection Two similar injection septa and four separately powered injection kickers in one straight section. Oscillation from injection point to non-linear kicker

4. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 4 4 Improvement Matching of Conventional 4 Kicker Bump Exercise: Changing the intrinsic pulser circuit impedance improves the matching of the four different current pulse shapes. Result: Adjustment of circuit inductances achieves better matching of the injection kicker pulses than before. Problem: The adjustment could only be preserved within ±2% in the long term (month). The inherent timing jitters and drifts of the four single thyratron driven kicker pulsers units cause transverse beam excitations still, and therefore, reduce injection efficiency. O. Dressler, J.-O. Kuszynski, ‘Matching Pulse Shapes of the BESSY II Storage Ring Injection Kicker System / High Precision Pulse Measurements’, PPC05, Monterey, CA, U.S.A., 2005

5. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 5 5 Mitigation by Series Connection of two Kicker Magnets Mitigation: The matching of the two pulse currents is ±0.5%. Result: The injection became much less sensitive to timing adjustments and jitters of the two pulsers. The sensitivity to trigger timings decreased from ±35ns before to about ±350ns now. Idea: Move septum magnet to the beam axis by 1/3. Reduce kicker pulse current from 6.8 kA to 4.5 kA. Relaxing injection geometry. Series connection of two kicker magnets on one pulser unit each side of septum magnet. Maintained only two independent pulse current shapes and timings equal. Problem: Applied pulse currents between both pulser units differ by 30% for lowest beam excitation. Difference

6. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 6 6 Undisturbed Injection in Top-Up-Mode Aims: For the ‘Top-Up’ operation mode of the BESSY II storage ring an electron beam current of 300mA must be maintained constant for a long time period. The loss of electrons will be compensated continuously by a new injection every 30s, ideally without any excitations resulting in transversal oscillations of the already stored beam. Therefore a pulsed non-linear kicker was inserted into the accelerator at a suitable position. At this point the injected electron beam is deflected closer to the already stored electron beam, and so, will be accumulated. The term ‘non-linear’ refers to the characteristic magnetic field distribution of induction B y inside the magnet. Tasks for single non-linear kicker magnet system development: Beam optics calculations, magnet system concept, magnetic field calculations, rf estimations, mechanical design, power electronics, control electronics, integration, etc. Magnetic field distributions: Dipole QuadrupoleSextupoleOctupoleNon-linear

7. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 7 7 Non-linear Magnet Concept / Calculation of Induction Table of ParametersCalculation of Induction B y ParameterValue Deflection angle1 mrad Maximum induction B y 25 mT Magnet bore (hor. x ver.)42 mm x 10 mm Active magnet length280 mm Length half-sine current pulse1.5 µs Primary peak current Î P 1750 A Secondary peak currents Î S 2 x 700 A (2) (1) B 0min = 20 mT, induction required at least B y at y = 10 mm Concept: Design one single kicker magnet with non-linear field characteristics, zero B x,y -field in the center and an off-axis maximum, B y, which is horizontally displaced by 10-12 mm. Achieve the lowest possible vertical gap height by an in vacuum magnet. Specifications Values of pulse currents are stated for current design solution, after all iterations. Two coils of top and bottom magnet halfs are in series, both are connected in parallel to the pulser unit.

8. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 8 Measures in [cm] Desired: 4 currents into one direction The kicker magnet posses mirror symmetry on its horizontal and vertical middle axis. Direction of scalability of design. Final design with bore of vacuum pipe and titanized ceramics support. Specifications: B y max. ≥ 20 mT, depiction in [G], (1 G = 110 -4 T) B y max. at y = 0 and x = +10 mm B y min. at y = 0 and x = -10 mm (symmetry condition) B x = 0 along y = 0 Non-linear refers to the specific characteristics of magnetic Induction B y. This was to be confirmed by measurement. Evolution of Design: 4 conductors, with ceramics supportand vacuum pipe profile. Non-linear Kicker Magnet, 2D B-Field Calculations POISSON SUPERFISH, Report No. LA-UR-96-1834, 7 Feb. 2007, Los Alamos National Laboratory 4 coils,

9. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 9 Pro: High currents on small load impedance. High accuracy possible. Low ripple on pulse top. Con: Small distance to magnet. Foot width vs. pulse top of half-sine pulse current. Lumped Element Circuit Traveling Wave Circuit Comparison of Different Pulse Circuit Topologies Pro: Pulser unit in save distance to magnet, therefore no radiation. exposure of power electronics Small attenuation by cable only. Characteristic impedances: 50, 25, 12.5Ω Con: Impedance matching required. Small impedance mismatch by load inductance deteriorates slew rate of pulse current. High charging voltage necessary because of system impedance.

10. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 10 Lumped Element Pulser - Resonant Circuit Resonant Circuit + Connection Cable Resonant Circuit with Cable Inductance Resonant Circuit with Transducer and Cable Distance by Insertion of Coaxial Cable Possible? Solution: Pulser / Short Cables / Magnet Transducer 1:1, Number of Windings n = 2 Idea: add 1:1 transducer! Problem: Pulser generates high transient voltages to ground on magnet. Difficult for short pulses! Circuit Topologies with and without Transducer

11. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 11 Four Kicker Coils Realization of Magnet and Connections Symmetry axis 2D Magnet Model Sectional View 3D Magnet Model Schematics of Electrical Connections Options for Coil Interconnections 2 coils in parallel on 1 transducer (top/bottom), 2 circuits in parallel. 2 top and 2 bottom coils in series using 1 transducer respectively (installed). 4 coils in series on 1 transducer (future).

12. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 12 Photo of Non-linear Kicker Inner Structure Flange Coils Laboratory stand Water cooling pipe Ceramic support

13. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 13 Procedure for Magnetic Field Measurements: Measurement of in long straight coil induced voltage v(t) at succeding horizontal positions. Instantaneous calculation of magnetic flux φ (t) out of voltage trace with the storage oscilloscope. Readout of max. value Ф max from oscilloscope for actual position, division by known coil area. Plot points into digramm. Typical scope picture of B-field measurement Voltage signal in pick-up coil [V] Magnetic flux [Φ] Pulse current [V~A] Direction of vertical B-field measurement, Magnet rotated by 90° Set-up for Magnetic Field Measurements

14. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 14 Magnetic Field Measurement vs. ANSYS Calculation

15. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 15 Conventional vs. Non-linear Kicker Injection Local Orbit Bump Injection Neighboring kicker magnets (K1 + K2 and K3 + K4) are powered in pairs to form a local pulsed orbit bump for beam accumulation. 4-kicker injection bump optimized for small orbit perturbation. Injection efficiency ~ 80% rms orbit perturbation horizontal ~ 1.000mm vertical ~ 0.500mm Standard injection, beam current 300mA Significant perturbation of the stored beam in both planes, horizontal and vertical Turn-by-turn measurement of horizontal and vertical beam oscillations due to kicker schemes. Single non-linear kicker injection, not yet completely optimized. Injection efficiency ~ 80% rms orbit perturbation horizontal ~ 0.060mm vertical ~ 0.015mm Injection up to a beam current of 300mA possible Second design was cured from rf warming Non-linear Kicker Magnet Injection One pulsed non-linear kicker magnet located outside the injection straight at an effective phase advance of 45° in reference to the injection point.

16. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 16 Commissioning of Non-linear Kicker magnet (1) Methodology of Measurements: The kicker magnet was excited by its nominal current (4 x 700A). The kicker timing relative to the storage ring injection was changed stepwise [µs]. The kick strength [kick/µrad] into either horizontal or vertical direction, measured at a particular horizontal / vertical geometric position (x / y [mm]) of the beam in the vacuum pipe, is shown in the plots. Set-up: All 4 magnet coils were powered in parallel, on 2 transducers for upper and lower magnet half respectively (previous schematic). Maximal efforts for tuning of current symmetry had been done.

17. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 17 Commissioning of Non-linear Kicker magnet (2) Set-up: The 2 magnet coils magnet coils of top and bottom magnet half were connected in series, on 2 transducers for upper and lower magnet half respectively, and tuned for best current, and hence, magnetic field symmetry. Result: In both coil set-ups a minimum of beam excitation in horizontal direction can be detected. While in the first case as minimum for vertical beam perturbations is far away from the horizontal minimum, in the second case one finds much better agreement with the theory. Supposition that only a series connection of all four kicker coils will achieve horizontal and vertical minima at the same x / y position.

18. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 18 Acknowledgement We would like to acknowledge the determined and very successful collaboration of the HZB project team: Scientific project leader: P. Kuske Power electronics and magnet concept: O. Dressler Mechanics and magnet design: M. Dirsat Magnetic field calculations: T. Atkinson RF design: H. Rast (TU Dortmund)

19. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 19 Integration of magnet system; timing, control & power electronics are effectively working. Successful tests of non-linear kicker magnet in BESSY II storage ring for beam injection is achieved. Beam injection and accumulation were easily attained. RF warming of 1st structure was reduced by design changes for 2nd magnet structure by a complete coating of ceramic support surfaces with sufficient titanium thickness. Upper and lower half-coils are currently powered in series to achieve better B y -field symmetry, and at the same time, reduce necessary over all pulse current, and hence, the applied voltage on the structure. Usage of one single pulse power supply in a lumped element circuit has the advantage that current amplitude and amplitude stability are no issue for the functionality as injection kicker system. First studies of beam excitation and injection efficiency show satisfying results. Further studies in top-up mode are ongoing. The series connection of all coils is feasible and may reduce the measured imbalance. Summary

20. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 20 Development efforts are proposed for a 3rd magnet prototype to remove remaining design bugs, to achieve better reliability of the kicker magnet in long term operations. Eddy currents in mechanical support structure near the connections outside the vacuum system cause imbalance of upper and lower half pulse currents. Therefore, adjustment and synchronism of pulse currents in upper and lower kicker magnet half on one pulse power supply must be improved by inductance tuning. The deployment on two synchronized lumped element pulser units for top and bottom half of magnet is feasible. Here timing jitters and pulse current synchronism must be obeyed to avoid excitations of stored beam. The application of one traveling wave kicker system to power the magnet from a distant, radiation protected place by one solid state pulser unit could be studied. How does the change of dynamic apertures by insertion devices in different operation conditions influence the injection efficiency? Outlook

21. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 21 Symmetry axis Symmetry by Positioning of Coils and Connections Series connection of two coils in upper magnet half

22. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012Olaf Dreßler 22 Conzept: Pulser / Transducer / Magnet Transducer in saturation CT1 CT2 Schematics of Linear Transducer Scope picture as example for non-linearity and saturation of core material Properties: Primary and secondary stray inductance of windings and connections Non-complete coupling Eddy current and hysteresis losses in core material, possible saturation Transformation ratio ≠ 1:1 causes transformation (increase) of load impedances and hence longer current pulses * Heinz Knoepfel, S. 143, Physical effects and generation methods concerning pulsed fields up to the megaoersted level, Verlag: North-Holland Publ. Co. (1970), ISBN-10: 0-444-10035-0 (2) (3) (1) (5) (4) (6) (7) (3) in (2) L E - Apparent inductance of pulser circuit, in (4) β in (5) α in (6) Transformation ratio 1:1, only prim. + sec. stray inductance add on M - Mutual inductance, K - coupling ratio Schematics of Linear Transducer