The Restoration of Magnetic Cores in Multi-Pulse Burst Mode

1. The Restoration of Magnetic Cores in Multi-Pulse Burst Mode Huang Ziping Institute of Fluid Physics, CAEP, China

2. What kind of pulses we want in the Multi-pulse Burst Mode? • Numbers: 2~10 pulses • Voltage: > 200kV • Pulse Width (FWHM): about 100ns • Interval: < 1000ns • Rising time : <25ns • Flat top: >60ns (voltage difference < 1%) RPIA 2006 in Japan

3. How to generate such burst multi-pulse string? • Solid-state modulator • The pulse voltage is not high enough (MOSFET) • The rise time of pulse is more than 100ns (IGBT) • Cable delay • Only fit for double pulses • Several parallel PFLs isolated by diodes • Several PFLs in series RPIA 2006 in Japan

4. (1) (2) What’s the difficult to restore the magnetic cores in such mode ? The accelerate voltage of a inductive accelerate cavity can be figure out by Faraday electromagnetic induce theorem In pulse condition, has constant voltage V0 and duration tp, then • To insure the magnetic cores have enough flux change range (ΔB ) after restoration for the next exciting pulse: • Restoring pulse should have same volt-second with the exciting pulse • The restoring voltage should be high enough for the interval is very short • The exciting pulses and restoring pulses should not interrupt each other RPIA 2006 in Japan

5. How to Restore The Cores in Multi-Pulse Burst Mode • Overlap restoration of the cores between multi-pulses • Restore the cores between multi-pulses by cable short reflection • Use new magnetic material of lower remanence and higher self-restore speed RPIA 2006 in Japan

6. Overlap restoration • By covering the exciting pulses over a long inverted voltage pulse can form an inverted pulse between every two exciting pulses • For the length of the interval is 5~10 times to the duration of each exciting pulse, to restore the magnetic cores from each exciting pulse, the voltage of the long restoring pulse only need to be 1/10~1/5 of the exciting pulse. RPIA 2006 in Japan

7. power system reset system load Circuit diagram of the ferrite cores restoration between double-pulses 1: restoring current without exciting; 2: restoring and exciting current; 3 restoring and exciting voltage Overlap restoration experiments RPIA 2006 in Japan

8. Double-pulse waveforms with restoring between exciting Overlap restoration experiment • In this experiment, we use three ferrite cores: • the total cross-sectional area S=103.25cm2 • the maximum change of the flux densityΔB =0.78T • V0×tp = ΔB ×S => for single pulse, when tp=90ns, V0 <90kV • With overlap restoration, those cores inducted two 80kV pulses with 700ns interval. RPIA 2006 in Japan

9. Cable short reflection • A full invert reflection will happen when a pulse transmit to a short end of a cable • If we add a coaxial-cable as a parallel load with the cores, after the exciting pulse, the reflected pulse will restore the cores RPIA 2006 in Japan

10. Delay cable A MARX Generator Reflective cable Blumlein PFL Diode isolation network + cable short reflection RPIA 2006 in Japan

11. Result Cable delay 100ns,single pulse Cable delay 600ns RPIA 2006 in Japan

12. series PFL+ cable short reflection Switch 3 Switch 2 Switch 1 Delay cable Reflective cable Match resistor RPIA 2006 in Japan

13. Result Cable delay 100ns Cable delay 600ns RPIA 2006 in Japan

14. self-restore • If we want more pulses in the burst… • Longer restoring pulse (Overlap restoration) • Longer delay cable (Cable short reflection) • Can we find another restoration method which can ignore the pulse number? • The magnetic cores with follow characteristic will solve the problem: • Higher saturation flux density Bs ( compare with ferrite cores) • Lower remanence Br ( be close to Zero) • After exciting, the flux density B can return to Br in 500ns • Can generate the inductive pulse with fast rising time (<25ns) RPIA 2006 in Japan

15. The experiment in lower voltage (<1kV) • Use MOSFET to generate burst multi-pulse string • Test some low remanence ferrite and Amorphous cores RPIA 2006 in Japan

16. Typical hysteresis curve of low remanence core in 50Hz Amorphous cores (1) 1k107 (2) 1k104 RPIA 2006 in Japan

17. Single pulse test of ferrite and amorphous cores V V Low Br Ferrite Amorphous (1) I I V • Ferrite: Spend about 5us to Br • Amorphous (1): about 2us to Br • Amorphous (2): about 200ns to Br Amorphous (2) I RPIA 2006 in Japan

18. The magnetization curve of amorphous (2) Pulse width：150ns，voltage：200、400、600、700、800V； Magnetization curve permeability curve RPIA 2006 in Japan

19. Multi-pulse test of amorphous (2) Interval 120ns Amorphous (2) RPIA 2006 in Japan

20. Thanks RPIA 2006 in Japan

21. Double pulses by cable delay • The pulse transmitted by long cable will be delayed • Each cable is the load of another cable RPIA 2006 in Japan

22. Parallel PFLs by isolation network RPIA 2006 in Japan

23. square-wave injected into the delay The cell voltage Series PFLs Come from Neutrino Factory Feasibility Study (USA) Pulsed Power System layout Pulsed Simulation RPIA 2006 in Japan