Single Nonlinear Kicker Magnet System at BESSY II

‘Single Non-linear Kicker Magnet System at BESSY II’ O. Dressler - Topical Workshop on Injection and Injection Systems, Berlin, Germany, 28 – 30 th August 2017

Bibliography • H. Kaden, ‘Wirbelströme und Schirmung in der Nachrichtentechnik’, Springer-Verlag Berlin Heidelberg Gmb. H, 1959, • Heinz Knoepfel, ‘Physical effects and generation methods concerning pulsed fields up to the megaoersted level’, North-Holland Publ. Co. , 1970, p. 143, • D. Goldberg, G. Lambertson, ‘Dynamic Devices, A primer on Pickups and Kickers’, AIP Conf. Proc. , p. 249, 1992, • S. H. Kim, ‘Calculation of Pulsed Kicker Magnetic Field Attenuation Inside Beam Chambers’, APS technical note, January 8, 2001. • K. Harada et al. , ‘New injection scheme using a pulsed quadrupole magnet in electron storage rings’, Phys. Rev. ST Accel. Beams 10, 123501, 2007, • S. C. Leemann, ‘Pulsed Sextupole Injection for the MAX IV Storage Rings’, MAX-lab, Lund University, S-22363 Lund, Sweden, July 7, 2011. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 2

Content • Non-conventional Injection vs. 4 Kicker Bump - Improvement Matching of Conventional 4 Kicker Bump - Concept of Non-conventional Injection • Non-linear Magnet Development - Specification, Evolution of Design, 2 D Magnetic Field Calculations - Principle of Kicker Circuit with Linear Transducer - Realization of Magnet and Connections with good Symmetry - Magnetic Field Measurements in Laboratory Environment • Non-Linear Kicker Commissioning - Commissioning of Non-linear Kicker as Storage Ring Injection - Measured Beam Excitation with Kicker Magnet • Discussion, Summary and Outlook Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 3

Non-conventional Injection vs. 4 Kicker Bump Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 4

Non-conventional Injection vs. 4 Kicker Bump Conventional layout of BESSY II Storage Ring Injection Two similar injection septa and four injection kickers in one (long) straight section, were two kicker magnets are powered in series by one pulse power supply respectively. 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 *. rom ion f t to t a l l i Osc on poin r e ti injec ear kick n i l non *Phys. Rev. ST Accel. Beams 10, 123501, ‘New injection scheme using a pulsed quadrupole magnet in electron storage rings’, K. Harada, Y. Kobayashi, T. Miyajima, S. Nagahashi, Photon Factory, 2007. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 5

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. Challenge: 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 et al. , ‘Matching Pulse Shapes of the BESSY II Storage Ring Injection Kicker System / High Precision Pulse Measurements’, PPC 05, Monterey, CA, U. S. A. , 2005 Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 6

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 ± 35 ns before to about ± 350 ns now. Mitigation: The matching of the two pulse currents is ± 0. 5%. Difference Idea: Move septum magnet to the beam axis by 1/3. Reduce kicker pulse current from 6. 8 k. A to 4. 5 k. A. • 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. Observation: Applied pulse currents on both pulser units differ by 30% for lowest beam excitation. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 7

Pulse Measurements vs. BESSY II Machine Parameters Measurements taken on SR injection septum magnet Strip tool observed parameters: Injection efficiency (%) Pulse current amplitude (V) Pulse current FWHM (ns) Initiated by machine operator: Increase of pulse current amplitude to restore Top-up injection efficiency. Required precision of pulse current parameters must be better than 1 x 10 -3! Malfunction of a magnet system: Inadvertent increase of pulse current and decrease of FWHM, indicating changes in magnet. But in this case no negative effect on top-up injection efficiency observed. Availability of measurement values inside the control system environment enables: • Online shot to shot monitoring of system parameters during pulsed power system operation, • Instantaneous correlation of observed accelerator events with of single component parameters, • Data archive within the control system and long term availability, post mortem failure analysis. • Also, possibility of slow feed-backs to stabilize beam position during injection process, etc. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 8

Non-linear Magnet Development and Laboratory Tests Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 9

Undisturbed Injection in Top-Up-Mode Aims: ‘Top-Up’ operation mode for the BESSY II storage ring, for constant beam current of 300 m. A, with injection shots every 60 s, high accumulation efficiency, without excitations of stored beam. Magnetic field distributions: Dipole Quadrupole Sextupole Octupole Non-linear ‘Non-linear’ refers to the characteristic distribution of induction in the magnet. Advantages: Wide zero field region on axis, reliable zero crossing, flat By-max at certain distance. Tasks for single non-linear kicker magnet system development: Beam optics calculations, magnet system concept, magnetic field calculations, rf power loss estimations, mechanical design, power electronics, control electronics, system integration, etc. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 10

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 has a maximum at a horizontal distance of 10 -12 mm. Achieve the lowest possible vertical gap height by an in vacuum magnet. Table of Parameters Calculation of Induction By (1) Parameter Value Deflection angle 1 mrad Maximum induction By 25 m. T 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 925 A Secondary peak current ÎS 750 A (2) B 0 min = 20 m. T, Specifications induction required at least By at y = 10 mm Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 11

Non-linear Kicker Magnet, 2 D B-Field Calculations Evolution of Design: 4 conductors, 4 coils, with ceramics support and vacuum pipe profile. Desired: 4 currents into one direction The kicker magnet posses mirror symmetry on its horizontal and vertical middle axis. Direction of scalability of design. Vertical aperture required for storage ring is most limiting factor. 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 m. T, 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 Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 12

Skin Depth with different Metals vs. Frequency δ- Skin depth f σμ 0 μr - Skin depth, el. field strength reduced by 1/e (factor 0, 367) for frequency f Frequency Conductivity Permeability constant vacuum Relative permeability for applied material Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 13

‘Sternvierer’ = NL-Kicker? ! p. 160 - 161 Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 14

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. Lumped Element Circuit Con: • Impedance matching required. • Small impedance mismatch by load inductance deteriorates slew rate of pulse current. • High charging voltage necessary because of system impedance. 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. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 15

Circuit Topologies with and without Transducer Lumped Element Pulser - Resonant Circuit Schematics of Linear Transducer (1) M - Mutual inductance, K - coupling ratio Resonant Circuit with Transducer + Cable (2) (3) in (2) Transformation ratio 1: 1, only prim. + sec. stray inductance add on 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 LE - Apparent inductance of pulser circuit, in (4) (5) β in (5) (6) α in (6) (7) * Heinz Knoepfel, ‘Physical effects and generation methods concerning pulsed fields up to the megaoersted level’, North-Holland Publ. Co. , 1970, p. 143, ISBN-10: 0 -444 -10035 -0 Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 16

Pulsed Voltages and Currents Curves on Kicker Magnet Due to the resistive losses in the transducer and lines, etc. , a charging voltage of UCh = 8, 6 k. V is required to generate a primary pulse current of ÎP = 2465 A to obtain two secondary pulse currents of 1000 A respectively (here upper and lower half of magnet). The curves of the two secondary kicker pulse currents ÎS = 2 x 1000 A are overlapping in the oscilloscope picture (in the ideal case). Voltages on primary side of transducer Pulse currents Primary pulse current ÎP = 2465 A Secondary pulse currents ÎS = 2 x 1000 A 1. 7µs Secondary voltages on upper magnet half coils 232. 0 V 3. 767 k. V -5. 539 k. V -418. 9 V Transient voltages would be critical for magnet structure Moderate Voltage on magnet structure Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 17

Laboratory Set-up for Magnetic Field Measurements Procedure for Magnetic Field Measurements: • Measurement of in long straight coil induced voltage v(t) at succeeding 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 diagram. Typical scope picture of B-field measurement Voltage signal in pick-up coil [V] Direction of vertical B-field measurement, Magnet rotated by 90° Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 Magnetic flux [Φ] Pulse current [V~A] O. Dressler 18

Magnetic Field Measurement vs. ANSYS Calculation Problem: Measurements of B-fields in small bores. • Reliability and precision of measurement, • Positioning of pick-up coil inside gap, • Integrating effect caused by probe width / size, • Coupling capacitance of field probe to structure, • Hazardous HV near measurement equipment, • Discontinuous transition of voltage on probe, • etc. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 19

Pulser Systems at MLS and Diagnostic Kicker Slotted pipe kicker in MLS SR with solid state pulser attached Thyratron pulser system for diagnostic kicker in BESSY SR ÎP = 800 A half sine τ = 2. 3µs fr up to 10 Hz ÎP = 4000 A half sine τ = 1. 5µs fr up to 10 Hz Amplitude stability 0. 1 % References: F. Marhauser, O. Dressler, V. Dürr, J. Feikes, ‘Impedances in Slotted-Pipe Kicker Magnets’, proceedings of the EPAC, Edinburgh, Scotland, 2006. O. Dressler, J. Feikes, ‘Diagnostic Kicker System as a Versatile Tool for Storage Ring Characterizations’, proceedings of the EPAC, Edinburgh, Scotland, 2006. O. Dressler, V. Pickert, C. Rediess, ‘IGBT Driver Circuit in Inductive Adder Technology for Pulsed Power Applications’, proceedings of the PCIM, Nürnberg, 2008. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 20

Symmetry by Positioning of Coils and Connections Sectional View 3 D Magnet Model Picture of open NL Kickermagnet Schematics of Electrical Connections 4 coils in series on 1 transducer Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 21

Non-Linear Kicker Commissioning Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 22

Excitation Pulse Current Length Time Scale for BESSY II Storage Ring with Circumference of 240 m Gap 700 ns 0 Electrons Gap Recirculating from booster 700 ns beam 100 ns 1. 5µs Assume possible pulse current duration (hence pulsed B-field duration) up to 1. 5 µs. Pulser / Transducer / Magnet Measured pulse curve on pulse power supply CT 1 and CT 2. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 23

Conventional vs. Non-linear Kicker Injection Local Orbit Bump Injection Neighboring kicker magnets (K 1 + K 2 and K 3 + K 4) 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 excitation. • Injection efficiency ~ 80% • rms orbit perturbation horizontal ~ 1. 000 mm vertical ~ 0. 500 mm • Standard injection, beam current 300 m. A • Perturbation of the stored beam in both planes • Single non-linear kicker injection, not completely optimized. • Injection efficiency ~ 80% • rms orbit perturbation horizontal ~ 0. 060 mm vertical ~ 0. 015 mm • Injection up to a beam current of 300 m. A possible Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 24

More Non-Linear Kicker Commissioning Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 25

Direct Field Measurements Inside Kicker Magnet Methodology: • Small single bunch current was injected through the NL-kicker onto a screen monitor which is located 5 m behind the magnet, • CCD-camera and image analysis delivers beam position and beam size, • Shift of the beam was monitored when the kicker was fired, • Delay between bunch arrival time and the kicker pulse was varied, • Vary horizontal and vertical position in the kicker. But, measurement uncertainties in the horizontal plane due to 9 pulsed extraction and injection magnets in injector chain. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 26

Temporal Field Distribution (1) Temporal variation of the field at about dx~-11 mm and dy~2 mm Off-axis beam experiences fields dominated by eddy currents at later times. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 27

Temporal Field Distribution (2) Temporal variation of the field at about dx~-11 mm and dy~2 mm For red delay variation of the beam position inside the kicker. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 28

Spatial Field Distribution Inside Kicker Magnet • Flat, zero horizontal and vertical fields close to zero (location of the stored beam), • ‘Flat’ field in the mid-plane ~11 mm off-axis (position of the injected beam), • The off-axis vertical kick contains large eddy current field contributions (polarity change). Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 29

More Realistic Network of Pulsed Power Circuit Simplified pulser circuit Pulser network without transducer to concentrate on magnet properties only. Lm - Magnet inductance Simplified pulser circuit plus secondary loop caused by magnet structure Remember: frame support structure Possible current path, but not under suspicion anymore since no significant asymmetries are noticeable. Effects of eddy currents in to coils adjacent metallic surfaces are investigated because of their excitation current independent, much longer time constant. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 30

Measurement of Small Fields Methodology: • Short bunch train, small beam current, chromaticities set to zero, • Horizontal and vertical closed orbit bumps inside the kicker magnet, • Kicker fired and dipole motion detected turn-by-turn with Libera-Brilliance electronics, • FFT of the data delivers amplitude of beam motion at the tunes: sub m-resolution achieved, • Measurements performed as a function of the kicker timing (for short kicker pulses only). Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 31

Line Scan Close to Smallest Orbit Perturbations Vertical perturbations: can be made vanishingly small in the vertical plane: < 1 m, Horizontal perturbations: ~3 m is the minimum, in a quite small area, Linear dependence could be related to a quadrupolar field component. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 32

Discussion Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 33

Multipole Kicker Magnets - Limitations by Accelerator Multipole Injection Kicker (MIK) development at SOLEIL for MAX VI is succeeding BESSY NL-Kicker design. Advantages of MIK Concept: • Non-disturbed stored beam in top-up injection mode. • Octupole like field distribution with zero field on axis and flat By-field maximum at a certain distance. Only injected beam deflected. Limitations of MIK Concept: • Positioning of the MIK within the storage ring by considering non-linear optics of modern accelerators. Changes in optics may require to move kicker. • Vertical aperture requirements limit positioning of the kicker coils; injected beam at chosen position may not be at By-field maximum of non-linear field distribution. This may require a (dynamic) optic change, e. g. beta function change, for injection in NLK straight section. • Limitation for the excitation pulse length by revolution time; injected beam only kicked once. • Small emittance of injected beam required. xs Better position for injected beam Reference: S. C. Leemann, Phys. Rev. ST Accel. Beams 15, 050705, ‘Pulsed sextupole injection for Sweden’s new light source’ MAX IV, 2012. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 34

Multipole Kicker Magnets - Technological Challenges of MIK Concept: • Precise wire positioning in alumina (2/100 mm). • Sensitive vacuum system with welded flanges to ceramics. • Uniform coating of alumina with titanium for mirror current path and good rf containment. • Low inductance pulse power circuit for required high pulse currents at short pulse duration. Technical details: • Eddy currents in neighboring metallic surfaces cause field distortion, asymmetries and weakening. • Proper contacting of coated surface to avoid rf power loss and temperature rise of component. • Pulsed PS outside the tunnel foreseen, to avoid risk of radiation damage on switching power electronics. • Now cable connections are necessary with ‘pseudo matching’ to keep load impedance low. Reference: P. Lebasque, Magnetic and electric evaluation in transient mode of the Bessy-II MIK design … (collaboration report), March 2013. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 35

Summary and Outlook • Kicker magnet and pulsed PS work fine: No thermal problems and kicker serves as back-up solution for BESSY II, • Injection Efficiency: All kicker (interconnection) configurations have shown 80 % efficiency; without much optimization, could be further improved, (80% with xinj= xkicker, 60% with xinj=2· xkicker), • Orbit perturbations: < 1 m vertically and ~3 m horizontally, • Field distributions: Were determined experimentally with reduced pulse duration, • Investigation of impact of eddy currents will continue. Workshop on Injection and Injection Systems, Berlin, Germany, Aug. 2017 O. Dressler 36