Silvia Zorzetti

1. Digital Signal Processing and Generation for a DC Current Transformer for Particle Accelerators Silvia Zorzetti

2. Contents • Introduction • Fermilab • Direct-current current transformer principles • Direct Current Current Transformer (DCCT) • Simulink Model • Specifications and Parameters • Hardware • Digital implementation • Open loop test • Closed loop test

3. Introduction • This activity was supported and accomplished at Fermilab, in the Instrumentation Department of the Accelerator Division

4. Circular Accelerators at Fermilab Main Injector (MI) Rapid cycling synchrotron 150 GeV as Injector for the Tevatron High intensity protons for fixed target and neutrino physics Recycler Permanent Magnetics 8 GeV Antiproton cooling before the injection into the Tevatron Proton storage Tevatron Superconducting synchrotron 980 GeV

5. Differenttypes of DCCTs at FNAL • An analog, homebrew version was developed at FNAL in the 80’s. • Installed in all the machines, except for the Recycler • Bandwidth: 2 MHz • A commercial DCCT, designed by K. Unser (Bergoz) • Entire system, i.e. pickup, electronics, cables, etc. • Only DC signal detection (narrow band). • In 2004 the system failed due to an asymmetry of permeability between the toroids. • Temporary replaced with another commercial DCCT from Bergoz, will finally be replaced by the “digital” DCCT that is now under development.

6. DCCT Introduction • The DCCT is a diagnostics instrument, used to observe the beam current. • Detection of DC and low frequency components of the beam current • Non-Distructive instrument • For the detection of high frequency components the classical AC transformer is used.

7. Principle of Operation -AC Transformer • The classical AC transformer can be used to identify the high frequency components of the beam current

8. Principle of Operation of the DCCT – Single Toroid • The modulator winding drives the toroid into saturation. • The total magnetic flux is shifted proportionally to the DC current • The measured DC current is proportional to the amplitude of the 2nd harmonic detected by the detector winding

9. Principle of Operation of the DCCT – Double Toroids

10. PrincipleofOperationof the DCCT – DoubleToroids

11. Beam • DCCT • Modulator • 400Hz digitally supplied • SecondHarmonic detector • AM demodulator on FPGA • AC Transformer • Sum and Feedback • Output Complete System

12. SecondHarmonic Detector • Input: The input signal can be viewed as a low frequency signalmodulated (in amplitude) with 800Hz

13. SecondHarmonic Detector • CIC1: Perform the first decimation of the signalsamplingfrequency • From 62.5MHz to 500kHz

14. SecondHarmonic Detector • NCO: • Supplies in-phase and quadrature-phasesignals of same amplitude and frequency (800Hz), for downconversion to baseband

15. SecondHarmonic Detector • CIC2: Performs a seconddecimation of the samplingfrequency, allows a more efficient FIR filter • From 500kHz to 2kHz

16. SecondHarmonic Detector • FIR: Defines the overallsystembandwidthatbaseband • DC to 100Hz

17. SecondHarmonic Detector • Some mathematics to format the signal, and adjust gain and phase • There is no phase detector required, because the signalissufficiently slow, thus a signum detector isimplemented.

18. DCCT Model • Analytic study of the DCCT functionality • Simulink Model of the complete system (AC+DC) • Toroids behaviour simulation • Filter Design • Feedback

19. Simulink Model

20. Simulink Model – Flux at Ib=0 (a.u.)

21. Simulink Model – Output Voltage at Ib=0

22. Simulink Model – FluxatIb=1 (a.u.)

23. Simulink Model – Voltage Output atIb=1

24. Simulink Model – AC + DC Closed Loop

25. RequiredSpecifications and Parameters • Number of turns per winding • Current and Voltage to saturate the toroids • DCCT Bandwidth • AC Bandwidth

26. Parameter Space • Toroids Saturation • Isat<3A , Vsat=36V, • Nm=22 • AC and DC Sensor windings • BDC=100Hz • BAC=1MHz • Ns_DC=100 • Ns_AC=200

27. Test Setup for ToroidMeasurements

28. Output Voltage from the pick-up windings of the toroids • Thereis a mismatchbetween the voltageoutputs from the twotoroids. • Poormatching of the core material

29. Complete System

30. VHDL Implementation – CIC • M: Differential Delay • ρ: Decimation factor • N: Filter Order • A: Gain • Notchat:

31. CIC Filter– VHDL Model • The firmware issynchronizedwith a single clock • Integration Section • CombSection • Gain • Number of bits:

32. Filters – Test Setup

33. VHDL Implementation and Test– CIC1 • fs=62.5MHz, • fd=500kHz, • M=1 • ρ=125 • N=2 • f1=500kHz • A= 15625

34. VHDL Implementation and Test– CIC2 • fs=500kHz, • fd=2kHz, • M=2 • ρ=250 • N=2 • f1=1kHz • A= 250000

35. VHDL Implementation and Test– FIR • bi: filter coefficients • N: filter order (127)

36. FIR Filter- VHDL Model • The firmware issynchronized with a single clock • Counter • ROM • Serial Function • Number of bits

37. VHDL Implementation and Test- FIR • fs=2kHz, • fc=100Hz, • N=127

38. VHDL Impelementation and Test – AM Demodulator • With a waveform generator a low frequencysignal, modulated at 800Hz isgenerated and digitized by the ADC • The resulting output signalisobserved on an oscilloscope, connected to the DAC.

39. VHDL Implementation and Test- Demodulator • Input: • Output:

40. Open Loop Test Measurement Setup

41. DC Dectector - Output signalBefore the Transition Board - Ib=0.4A • The signal is supplied by the DCCT DC Sense • Before the transition board • There are both odd and even harmonics

42. DC Detector - Output Signal After the Transition Board - Ib=0.4A • The signal is supplied by the DCCT DC Sense • Passed by the Transition Board • Has only the 2nd harmonic (800 Hz), the 1st harmonic is suppressed.

43. Open LoopResult

44. Closed Loop Test Measurement Setup

45. Closed Loop Results

46. Conclusions • At this stage a preliminaryimplementation and test of the DCCT has beensuccessfullyrealized. • P control • τ=0.05s • Resolution 0.01A • Nextsteps • Implementation of the AC section • Fasterloop control

47. Thankyou for yourattention Silvia Zorzetti

48. Backup Slides Silvia Zorzetti