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Beam Dampers for Main Injector and Recycler

Explore the history, design choices, difficulties, and advantages of beam dampers for the Main Injector and Recycler at Fermilab, highlighting the transition to digital signal processing for improved performance and maintenance.

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Beam Dampers for Main Injector and Recycler

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  1. Beam Dampers for Main Injector and Recycler Bill Ashmanskas, Bill Foster, Dave Wildman Warren Schappert, Jim Crisp, Dennis Nicklaus Oct ‘02 MI/RR Dampers - G. W. Foster

  2. Wide Variety of Beam Dampers Required in MI & Recycler • Transverse (X,Y) and Longitudinal • 53 MHz, 2.5 MHz, 7.5 MHz, and DC Beam • Single Bunches, Full Batches, Short Batches • Injection, Ramping, and Stored Beam • Pbar and Proton Directions (different timing) MI/RR Dampers - G. W. Foster

  3. … plus unbunched DC Beam in Recycler… MI/RR Dampers - G. W. Foster

  4. Damper Operating Modes X = Operation c= Commissioning & Tuneup MI/RR Dampers - G. W. Foster

  5. History of Dampers at FNAL • Dampers are essential for maximum performance and forgiving operation. • Over the years, many Beam Dampers have been built at Fermilab. • Essentially all of these fell into disuse. • Some of the most powerful (Superdampers) were deliberately removed from service and not replaced. • In contrast, most other large labs have beam dampers on all coordinates on all machines. MI/RR Dampers - G. W. Foster

  6. Difficulties in Maintaining Beam Dampers • Specialized custom built power amps • e.g. distributed tube amplifier for Superdampers • Limitations of Analog Signal Processing • Crates of specialized custom NIM modules • Few people can understand & maintain system • Many cables, connections to fail • Spares/testing problem with custom analog modules • Unique hardware needed for various machines, various RF bunch structures, etc. Difficult to modify for new RF freq. • Diagnostic signals unavailable in control room. MI/RR Dampers - G. W. Foster

  7. Damper Design Choices for MI / RR • Digital Signal Processing • Commercial electronics, with custom firmware • might change for final implementation • Common Hardware for MI, RR, (& Booster?) • Standard commercial wideband FET power amps (same type used for Recycler RF, Booster (& TeV?) dampers,etc.) MI/RR Dampers - G. W. Foster

  8. Advantages of Digital Filters • Digital filter can also operate at multiple lower frequencies ...simultaneously if desired. • MI will not be blind for 2.5 and 7.5 MHz Beam • Digital filters more reproducible (=>spares!) • Re-use Standard hardware with new FPGA code • or same code with different filter coefficients • Inputs and Outputs clearly defined • filters can be developed & debugged offline MI/RR Dampers - G. W. Foster

  9. Generic Dampertolerating frequency sweep All Logic Inside FPGA FIFO needed due to phase shifts between DAC and ADC clocks as beam accelerates MI/RR Dampers - G. W. Foster

  10. 105 MSPS AD6645 • Prieto, Meyer et. al. evaluating 65MHz DDC for RR BPM upgrade • Asmanskas, Foster, Schappert testing 105 MHz version for RR Dampers Echotek Card Used for Dampers MI/RR Dampers - G. W. Foster

  11. Digital Signal Processing with FPGA’s • Commercial card from Echotek • 8 channels of 14-bit, 106 MHz Digitization • One card does all dampers for one machine • Customized FPGA firmware • Bill Ashmanskas, GW Foster, et. al. • Handles Wide Variety of Bunch Structure MI/RR Dampers - G. W. Foster

  12. All-Coordinate Damper w/ Echotek Card 53 MHz, TCLK, MDAT,... 106 / 212 MHz Stripline Pickup FAST ADC Minimal Analog Filter Monster FPGA(s) 14 Transverse Dampers Identical X & Y FAST ADC Minimal Analog Filter Stripline Kicker Power Amp VME FAST DACs 2-10 > 27 MHz Resistive Wall Monitor FAST ADC Minimal Analog Filter Longi- tudinal (Z) Damper Broadband Cavity Power Amp FAST DACs 2-10 MI/RR Dampers - G. W. Foster

  13. MI Longitudinal Damper(Ashmanskas, Foster) • 80 Bunch-by-Bunch synchrotron oscillations (on Pbar Stacking Cycle) measured with Echotek board & custom firmware BUNCH –BY-BUNCH PHASE (w/offset) Single Bunch Digital Kick  using Digital Velocity Filter implemented in FPGA firmware TURN NUMBER AFTER INJECTION  MI/RR Dampers - G. W. Foster

  14. MI/RR Transverse Dampers(Ashmanskas, Foster) BUNCH–BY–BUNCH BEAM POSITION • Bunch-by-Bunch betatron oscillations (Pbar Stacking Cycle) measured with Echotek board & custom FPGA firmware. • Single board needed for: • Bunch-by-bunch longitudinal & two transverse dampers. • 53MHz, 7.5MHz & 2.5MHz. • Debunched beam, single bunches and bunch trains. TURN NUMBER AFTER INJECTION  MI/RR Dampers - G. W. Foster

  15. “Universal-Damper” Application: Signal Processing Steps (transverse) Echotek Board 1) Bandwidth-Limit input signal to ~53 MHz 2) 14 Bit Digitization at 106 MHz or 212 MHz 3) FIR filter to get single-bunch signal 4) Sum & Difference of plate signals 5) Multi turn difference filter (FIR) w/delay 6) Pickup Mixing for correct Betatron Phase 7) Bunch-by-bunch gain, dead band etc. 8) Timing Corrections for Frequency Sweep 9) Pre-Distortion for Kicker Power Amp 10) Power Amp for Kicker Inside FPGA Buy MI/RR Dampers - G. W. Foster

  16. Damper Priorities in Main Injector & Recycler • Main Injector Longitudinal Dampers • Main Injector Transverse Dampers • Recycler Transverse Injection Dampers • Recycler Longitudinal Dampers • Recycler Broadband (DC Beam) Dampers MI/RR Dampers - G. W. Foster

  17. 1. Longitudinal Damper in Main Injector • Benefits to Bunch Coalescing for Collider • “Dancing Bunches” degrade Proton coalescing and L • Affects Lum directly (hourglass) and indirectly (lifetime) • We are deliberately blowing L in Booster • Benefits for Pbar Stacking Cycles • Bunch Rotation is generally turned off ! (x1.5 stack rate?) • Slip-Stacking etc. (Run IIb) will require stable bunches • Needed for eventual NUMI operation MI/RR Dampers - G. W. Foster

  18. Longitudinal Beam Instability in MI • Occurs with as few as 7 bunches (out of 588) • Prevents low emittance bunch coalescing and efficient Pbar bunch rotation • Driven by cavity wake fields within bunch train • Seeded by Booster & amplified near MI flat top. First Bunch ~ OK 7th Bunch Trashed see Dave Wildman’s Talk MI/RR Dampers - G. W. Foster

  19. Longitudinal Damper Works by Modulating Phase of RF Zero Crossing MI/RR Dampers - G. W. Foster

  20. Damping of Bunch Motion by Modulation of Center of Rotation (RF zero-crossing) on Alternate Half-cycles of Synchrotron Motion MI/RR Dampers - G. W. Foster

  21. Numerical Examples for Longitudinal Dampers Damping can be made faster by raising VDAMPER and/or lowering VRF MI/RR Dampers - G. W. Foster

  22. MI Longitudinal Damper- Inputs(Ashmanskas, Foster) BUNCH –BY-BUNCH PHASE (w/offset) • 80 Bunch-by-Bunch synchrotron oscillations (Pbar Stacking Cycle) measured with Echotek board & custom firmware TURN NUMBER AFTER INJECTION  MI/RR Dampers - G. W. Foster

  23. Longitudinal Damper FPGA Logic +THRESH Synchrotron Motion Velocity Filter Bunch-by- Bunch Digital Phase Detector ResistiveWall Pickup -THRESH +/- KICK to DAMPER Multi-Turn Memory ADC 14 +THRESH Bunch Intensity FIR Filter Individual Bunches are kicked + or – depending on whether they are moving right or left in phase MI/RR Dampers - G. W. Foster

  24. Single-Bunch Phase Signal Single-Bunch Digital Kick (velocity filter) MI Longitudinal Damper Kick Calculated in FPGA Firmware(Ashmanskas, Foster) MI/RR Dampers - G. W. Foster

  25. What ADC Clock Speed is needed? • ~53 MHz Bandwidth limited signal, sampled by 106 MHz ADC, measures eitherin-phase (cosine) orquadrature (sine) component • but not both ==> ADC clock phasing matters! • 212 MHz sampling measures bothin-phaseandquadrature components. Phasing is not critical to determine vector magnitude. • 212 MHz built in phase measurement MI/RR Dampers - G. W. Foster

  26. Bandwidth Limit Signal • Raw signal has high-frequency components which can cause signal to be missed by ADC • “Aliasing” • Bandwidth limited signal (to ~50 MHz) cannot be missed by 106 MHz ADC • Eliminate low-frequency ripple, baseline shifts, etc. with Transformer or AC coupling • Digital Filtering can provide additional rejection MI/RR Dampers - G. W. Foster

  27. Gaussian Filter - Impulse Response • Many implementations, e.g. traversal filter Spreads signal +/-5ns in time so it will not be missed by ADC Reduces ADC Dynamic Range requirement, since spike does not have to be digitized MI/RR Dampers - G. W. Foster

  28. Gaussian Filter - Doublet Response Filtered Output Pulse Shape is insensitive to Bunch Length (for Tb < 10ns) Filtered Signal can be sampled by 100 MHz ADC Digitized Pulsehight is “A - B” MI/RR Dampers - G. W. Foster

  29. Gaussian Filter - Pulse Train Response Filter Output is good sine wave independent of bunch length “A - B” still gives good bunch-by-bunch measurement Can digitally average over many bunches in a batch to get lower noise MI/RR Dampers - G. W. Foster

  30. In-Phase and Quadrature Sampling “A - B” gives bunch-by-bunch “in-phase” signal • This is the argument for sampling at 2x Nyquist “D - (C+E)/2” gives bunch-by-bunch “out-of-phase” or “quadrature” signal Vector Sum sqrt(I**2 +Q**2) is insensitive to clock jitter MI/RR Dampers - G. W. Foster

  31. 2. Transverse Damper in Main Injector • Bunch-by-Bunch 53 MHz Injection Damper • Forgive Pbar injection errors caused by AP3… line drift • Simplify & speed up Shot Setup • Eliminate emittance growth due to waveform defect in Accumulator extraction kicker • Bunch-by-Bunch 2.5 MHz Injection Damper • Eliminate emittance growth in RRMI transfers • Suppress RW instability for NUMI & FT operation • May also be needed for slip-stacking intensities (Run IIb) MI/RR Dampers - G. W. Foster

  32. BUNCH–BY–BUNCH BEAM POSITION TURN NUMBER AFTER INJECTION  MI/RR Transverse Dampers - Inputs(Ashmanskas, Foster) • Bunch-by-Bunch betatron oscillations (Pbar Stacking Cycle) measured with Echotek board & custom FPGA firmware. • FPGA Filter can be reprogrammed for: • 53MHz, 7.5MHz & 2.5MHz. • Debunched beam, single bunches and bunch trains. MI/RR Dampers - G. W. Foster

  33. BUNCH–BY–BUNCH BEAM POSITION TURN NUMBER AFTER INJECTION  Transverse Bunch-By-Bunch Dampers - Results(Ashmanskas, Foster) • Damping active for Bunch #43 …CAN ALSO ANTI-DAMP TO BLOW ANY SELECTED BUNCHES OUT OF THE MACHINE  Anti-Satellite Device MI/RR Dampers - G. W. Foster

  34. BUNCH–BY–BUNCH BEAM POSITION Transverse Bunch-By-Bunch Dampers - Results(Ashmanskas, Foster) Damping kick shared for Bunches #41 - #51 • Pickup Signal from Bunch #43 TURN NUMBER AFTER INJECTION  MI/RR Dampers - G. W. Foster

  35. Three-Turn Filter for Transverse Damper • Damper kick is calculated from single BPM position reading on 3 successive turns. Arbitrary Betatron Phase of Kicker can be accommodated MI/RR Dampers - G. W. Foster

  36. HERA-P Damper uses a 3-turn Digital FIR Filter Klute, Kohaupt et. al. EPAC ‘96 MI/RR Dampers - G. W. Foster

  37. 3 Turn Filter Coefficients • Damper kick is weighted sum of beam positions on the 3 previous turns. • 3 Filter Coefficients Uniquely Determined by: • System Gain • Betatron Phase Desired at Kicker • Constraint that sum of filter coefficients = 0 (so that filter does not respond to DC offsets.) MI/RR Dampers - G. W. Foster

  38. Transverse/ Injection Damper FPGA Logic(single pickup with 3-turn filter) Gain Balance Weighted Sum for Arbitrary Betatron Phase Pickup ADC FIR Filter 1-turn Delay 1-turn Delay 1-turn Delay 14 ADC Standard BPM Processing 3 - Turn Filter Power Amp. Stripline Kicker 106 MHz Optional Pre-compensation Filter for Cable DAC > 27 MHz MI/RR Dampers - G. W. Foster

  39. Narrow band vs. Wide band Dampers • In some cases instabilities only occur with specific frequency and mode patterns in ring • Dealing specifically with those modes lowers the required kicker power and reduces noise. • A wide band (bunch-by-bunch) damper can use digital filtering to provide higher gain for specific mode patterns ( lower power amp.) • Many digital filters can operate simultaneously inside some device -- ADC and DAC are shared The flexibility of Digital Filtering inside the FPGA is a major advantage of this approach. MI/RR Dampers - G. W. Foster

  40. 3. Recycler Transverse Injection Dampers 2.5 MHz Bunch-by-Bunch Injection Damper  Reduces load on Recycler Stochastic Cooling system • Eliminate Emittance Growth from Pbar injection errors caused by AP3 line drift • Eliminate emittance growth due to waveform defect in Accumulator extraction kicker • Simplify & Speed up AccumulatorRR Transfers • Will take place every ~30 mins in Run IIb MI/RR Dampers - G. W. Foster

  41. Differences between Recycler and MI Dampers • RR dampers will track 4 bunches (vs. 588 in MI) • RR signals will have 21 samples/bunch (vs.5) • RR firmware will provide ACNET registers representing the Amplitude, Phase and Bunch length of each of the 4 bunches. • RR firmware will also provide registers for phase and amplitude of stacked DC beam. MI/RR Dampers - G. W. Foster

  42. 106 MHz Digitization of the Recycler signals is overkill, but allows the same hardware to be used in MI & Recycler MI/RR Dampers - G. W. Foster

  43. 4. Recycler Longitudinal Damper • Bunch-by-Bunch 2.5 MHz Injection Damper • Eliminate Emittance Growth from Pbar injection mismatches caused by Phase and Energy errors • Reduces load on Recycler Stochastic Cooling system • Simplify & Speed up AccumulatorRR Transfers • Will take place every ~30 mins in Run IIb THE IMPORTANCE OF THIS DAMPER DEPENDS ON THE PERFORMANCE OF THE RECYCLER STOCHASTIC COOLING MI/RR Dampers - G. W. Foster

  44. 5. Recycler Transverse Dampers • Instability Control Damper to Suppress Possible Transverse Instabilities of Debunched (DC) Beam in Recycler • These instabilities have been seen in Accumulator but not yet in Recycler. • Low-noise pickup w/hybrid & preamp in tunnel • 1-3 Turn Digital delay filter using Echotek board • Kicker amplifier has low power requirement <~20W MI/RR Dampers - G. W. Foster

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