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‘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 Content • 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 USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 2 Non-conventional Injection vs. 4 Kicker Bump Conventional layout of BESSY II Storage Ring Injection Two similar injection septa and four separately powered injection kickers in one straight section. 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 *. *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 USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 3 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 USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 4 Mitigation by Series Connection of two Kicker Magnets 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. Difference Mitigation: Idea: The matching of the two pulse currents is ±0.5%. 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. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 5 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 By inside the magnet. Magnetic field distributions: Dipole Quadrupole Sextupole Octupole Non-linear 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. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 6 Non-linear Magnet Concept / Calculation of Induction Concept: Design one single kicker magnet with non-linear field characteristics, zero Bx,y-field in the center and an off-axis maximum, By, which is horizontally displaced by 10-12 mm. Achieve the lowest possible vertical gap height by an in vacuum magnet. Table of Parameters Calculation of Induction By Parameter Value Deflection angle 1 mrad Maximum induction By 25 mT Magnet bore (hor. x ver.) 42 mm x 10 mm Active magnet length 280 mm Length half-sine current pulse 1.5 µs Primary peak current ÎP 1750 A Secondary peak currents ÎS 2 x 700 A K B0 l [ Tm ] [ rad ] p [ GeV c ] 0 .3 [ rad ] p[ GeV c ] B0 [ T ] 0.3 l [ m ] (1) (2) K Kick stregth 1mrad Specified deflectition angle l 0.28m Length of magnet B0 [ T ] 0.001[ rad ] 1.72[ GeV c ] 0.3 0.28[ m ] B0 [ T ] 20 mT 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. B0min = 20 mT, induction required at least By at y = 10 mm Specifications USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 7 Non-linear Kicker Magnet, 2D B-Field Calculations Non-linear refers to the specific characteristics of magnetic Evolution of Design: 4 conductors, 4 coils, with ceramics support and vacuum pipe profile. Induction By. This was to be confirmed by measurement. Desired: 4 currents into one direction The kicker magnet posses mirror symmetry on its horizontal and vertical middle axis. Direction of scalability of design. Measures in [cm] Final design with bore of vacuum pipe and titanized ceramics support. POISSON SUPERFISH, Report No. LA-UR-96-1834, 7 Feb. 2007, Los Alamos National Laboratory Specifications: By max. ≥ 20 mT, depiction in [G], (1 G = 1•10-4 T) By max. at y = 0 and x = +10 mm By min. at y = 0 and x = -10 mm (symmetry condition) Bx = 0 along y = 0 USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 8 Comparison of Different Pulse Circuit Topologies Traveling Wave Circuit Characteristic impedances: 50, 25, 12.5Ω Pro: • Pulser unit in save distance to magnet, therefore no radiation. exposure of power electronics • Small attenuation by cable only. Con: • Impedance matching required. • Small impedance mismatch by load inductance deteriorates slew rate of pulse current. • High charging voltage necessary because of system impedance. Lumped Element Circuit 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. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 9 Circuit Topologies with and without Transducer Lumped Element Pulser - Resonant Circuit Resonant Circuit with Transducer and Cable Idea: add 1:1 transducer! Resonant Circuit + Connection Cable Distance by Insertion of Coaxial Cable Possible? Difficult for short pulses! Resonant Circuit with Cable Inductance Solution: Pulser / Short Cables / Magnet Transducer 1:1, Number of Windings n = 2 Problem: Pulser generates high transient voltages to ground on magnet. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 10 Realization of Magnet and Connections 2D Magnet Model Schematics of Electrical Connections Four Kicker Coils Symmetry axis Sectional View 3D Magnet Model 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). USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 11 Photo of Non-linear Kicker Inner Structure Ceramic support Coils Flange Water cooling pipe Flange USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Laboratory stand Olaf Dreßler 12 Set-up for Magnetic Field Measurements 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 Фmax from oscilloscope for actual position, division by known coil area. • Plot points into digramm. ( t ) v ( t )dt B0 max max A Typical scope picture of B-field measurement Voltage signal in pick-up coil [V] Magnetic flux [Φ] Direction of vertical B-field measurement, Magnet rotated by 90° USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Pulse current [V~A] Olaf Dreßler 13 Magnetic Field Measurement vs. ANSYS Calculation USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 14 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. 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. Turn-by-turn measurement of horizontal and vertical beam oscillations due to kicker schemes. • 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 USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 • 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 Olaf Dreßler 15 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. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 16 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. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 17 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) USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 18 Summary • 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 By-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. USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 19 Outlook • 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? USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 20 Symmetry by Positioning of Coils and Connections Series connection of two coils in upper magnet half USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 21 Schematics of Linear Transducer Conzept: Pulser / Transducer / Magnet Schematics of Linear Transducer Transformation ratio 1:1, only prim. + sec. stray inductance add on M K L1 L2 Transducer in saturation CT2 (1) M - Mutual inductance, K - coupling ratio Scope picture as example for non-linearity and saturation of core material CT1 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 t 1 dI dI I1dt RI1 LS L1 1 M 2 0 C0 dt dt LM L2 dI2 M dI1 0 dt dt LE d 2I1 dI 1 R 1 I1 0 dt dt C LE LS LM L1 1 1 K 2 / 1 L2 (2) (3) (3) in (2) LE - Apparent inductance of pulser circuit, in (4) LL L2 (4) (5) β in (5) (6) α in (6) (7) * 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 USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012 Olaf Dreßler 22