TRENDS IN BPM SYSTEM DESIGN The ATF Damping Ring BPM Upgrade Nathan Eddy Manfred Wendt Fermilab Low-ε-Ring Workshop 2011 Heraklion, Crete, Greece

Page 2 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Contents Part I (Manfred) –Introduction –BPM Pickup Design  “Button-style” BPM –Read-out Electronics Part II (Nathan) –The ATF DR BPM System

Page 3 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt BPM Building Blocks BPM pickup –RF device, EM field detection, center of charge –Symmetrically arranged electrodes, (or resonant structure) Read-out electronics –Analog signal conditioning –Signal sampling (ADC) –Digital signal processing Analog Signal Conditioning Digital Signal Processing Data Acquisition Trigger, Timing & RF Control Power Supply & Misc. BPM Pickup position data control system (LAN & FB) timing, RF & CLK signals feedback bus (if applicable) –Data acquisition and control system interface  LAN & fast feedback –Trigger, CLK & timing signals

Page 4 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Beam Structure t beam repeats with –t rev in circular accelerators Bunch intensities may vary –Bunch to bunch, within t beam –“Missing” bunches –Or chance with time, e.g.  slowly due to lifetime  fast due to top-up injection Adapt BPM integration time –Single / multi-bunch –TBT, multiturn, narrowband, etc.  System BW: Operation conditions may change –Particle species (e -, e + ) –RF gymnastics, bunch patterns,… t bunch t rev time bunched beam t beam Gaussian bunch:

Page 5 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt BPM Characteristics & Applications Measurement / integration time Position resolution –Resolve an orbit difference (depends on the measurement time). Linearity and accuracy –Absolute error of the reported beam position –BPM offset (zero-order correction coefficient) –BPM tilt (roll) -> x-y coupling Dynamic range –Beam intensity independence (saturation / noise floor). Reproducibility and long term stability –Reference “golden” orbit Variety of applications beyond beam orbit measurements –Injection oscillations, betatron & synchrotron tunes, dispersion & beam energy, x-y coupling, beam optics, magnet alignment and errors, non-linear field effects, etc. –Machine commissioning (intensity).

Page 6 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt BPM Offset & Tilt BPM Read-out (electr. offset) x y BPM offset quad offset beam position reported beam position BPM – quad alignment –Mechanical & “electrical” offsets –E.g. BBA procedure Similar for BPM / quad tilt

Page 7 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Broadband PU: Image Current Model Broadband, e.g. “button” BPM pickup: –Difference and common mode signal components Laplace problem solved for circular and elliptical cross-section –Image current density (cylindrical coordinates, ρ=r/R) –Electrode beam position sensitivity –Two symmetric arranged electrodes Example: –Sensitivity near center for ϕ = > 3.43 dB/mm (R = 10 mm) -> 2.58 dB/mm (R = 20 mm)

Page 8 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt BPM Pickup Position Characteristics Up Down Right (Out) Left (In) UR (Up-Right) Electrode A DR (Down-Right) Electrode D DL (Down-Left) Electrode C UL (Up-Left) Electrode B Solve the Laplace equation numerically for one electrode (2D cross-section) Expansion of ϕ UR by superposition using the symmetry of the pickup, e.g.: UR A B CD

Page 9 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt BPM Pickup Scaling Rearrange horizontal and vertical potential arrays: Fit the 2D polynomials, e.g. of 7 th order (or look-up table) –The coefficients k nn include the scaling of the pickup geometry  k nn ‘s are the same for horizontal and vertical in case of horizontal / vertical symmetry of the BPM pickup electrodes. –As of the symmetry, even terms are ~0.  limit the fit to odd terms, e.g. ϕ, ϕ 3, ϕ 5, ϕ 7. –k 00 is ~0, but reflects the monitor offset, i.e. found e.g. by BBA, and is usually different in horizontal and vertical plane. –k 01 is the “monitor constant”, slope at the origin BPM pickup scaling and non-linear field correction: –Iterate a few times:

Page 10 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Button BPM Commercial UHV RF button feedthroughs, made to specs –RF properties (numerical simulation) –Environmental requirements Compact construction Installation, tolerances, cabling Other button load impedance, than R load = 50 Ω?

Page 11 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Coupling Impedance Longitudinal coupling impedance –Additional effects due to the annual button-ground gap TE 11 gap waveguide resonance at: Try to minimize wake potential: –Reduce r button –Minimize w gap

Page 12 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Read-out Electronics ADCADC 90 0 CICFIR Σ NCO I-Channel Q-Channel same as I NB WB raw A B C D BPF Att BPFLPF Coordinate Transformation A-Electrode Analog Signal Conditioning B, C, D Analog same as A Ctrl LO CLK & Timing A Data Typical BPM read-out scheme –Pipeline ADC & FPGA  bit, MSPS, >70 dB S/N –Separate analog signal processing for the channels –Analog down-converter if undersampling is not applicable.

Page 13 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Some Remarks Analog down-converter / signal conditioning –Defines the TD waveform / frequency band to be digitized. –May need to be located close to the BPM pickup (e.g. pickup input frequencies in the microwave range) –Analog down-conversion vs. undersampling!?  CLK jitter requirements –Linearity / dynamic range extension (attenuator / gain switching) –Needs calibration & gain correction system Digital signal processing –FPGA vs. CPU processing?! –I-Q is only required if ADC CLK is not phase locked to f RF –Down-conversion to base-band, low frequency but not DC  Crawling phase –Coordinate transformation √I 2 +Q 2 vs. rotation to I’?! Key elements: Dynamic range (linearity) & statistics (sample-rate)! Practical considerations, e.g. cabling, VME, xTCA, pizza-box, etc. t jitter A error signal

Page 14 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Typical Performance BSP-100 module (APS ANL) Libera Brilliance ANL) courtesy G. Decker

Page 15 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt BPM Resolution vs. Beam Current ----: Bergoz system resolution  : libera slow acquisition mode  : Libera turn by turn mode  : Libera turn by turn mode (decimated) courtesy C. Milardi Observed at DA ϕ NE (INFN-LNF) –Libera and Bergoz BPM read-out electronics –Each point is averaged over 100 orbits

Page 16 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Automatic Gain Correction Use calibration tone(s) –714+ε MHz, 714-ε MHz –Reflected and/or thru BPM calibration signal –Inside analog pass-band –Separate DDC in NB mode –Error & correction signals: Advice: –Two calibration tones need separate DDCs, or a “ping-pong” calibration tone workaround

Page 17 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Libera Crossbar Switch CAL Scheme Schematics of crossbar switch based BPM electronics from Istrumentation Technologies. Pat. No.: US2004/ A1

Page 18 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt The ATF Damping Ring Machine and Beam Parameters beam energy E=1.28 GeV beam intensity, single bunch≈~1.6 nC ≡ e - (≡ I bunch ≈ 3.46 mA) beam intensity, multibunch (20)≈~22.4 nC ≡ 20 x e - (≡ I beam ≈ 48.5 mA) accelerating frequency f RF =714 MHz revolution frequency f rev =f RF / 330 = MHz (≡ t rev = nsec) bunch spacing t bunch =t RF / 2 = nsec batch spacing t batch =t rev / 3 = nsec horizontal betatron tune≈ (≡ f h ≈ 441 kHz) vertical betatron tune≈8.462 (≡ f v ≈ 1000 kHz) synchrotron tune≈ (≡ f s ≈ 9.7 kHz) repetition frequency f rep =1.56 /3.12 Hz (≡ t rep = 640 / 320 msec) beam time t beam =~460 / ~240 msec t rev t bunch

Page 19 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt BPM Hardware Overview BPF LPF INJ Down Mix Cal (~ 714) Timing (VME) LO (729) CLK (64.9) TRG Digital Receiver (VME) VME µP Motorola 5500 Q I beam position 4 button BPM pickup IF (15) beam VME BUS LAN PLL 4 ATT 4 CAN CTRL

Page 20 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Analog Signal Processing 4-ch. Analog downmixer –IN: 714, LO: 729.1, IF: 15.1 MHz –CAN-bus controlled gain, attenuator & cal system –Gain switchable, low-noise, high IP3 input gain stage –Image rejection (SSB) mixer –~30 dB gain, ultralinear IF stage MHz BPF ATT LNA BPF LNA LPF SSB Mixer LO 0°0° 90 ° LNA LPF Directional Coupler IN 714MHz CF: 714MHz BW: 10MHz G: 14/-2 dB NF: 1dB dB 4 dB steps 1.6 dB loss MHz CF: 15.1 MHz BW: 4MHz G: 18 dBBW: 40 MHz OUT BW: 800 MHz G: 15 dB NF: 1dB Cal Tone Signal

Page 21 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt 8-Ch,14-bit, 125 MS/s VME Digitizer BLOCK DIAGRAM FPGA Altera Cyclone III VME Drivers 4x32M DDR2 SDRAM JTAG EPCS4 Interface VME bus Oscillator CLK IN CLK OUT GATE TRIGGER TCLK SYNC IN SYNC OUT Generic Digitizer External Control Clock Driver (PLL & DIV) ADCADC ADCADC AC passive 8 Analog Inputs 4 Channels per Chip 125 MSPS, 500 MHz BW 4-ch serial ADC chips 8-ch, AC passive (or DC active) PLL/VCO CLK distribution SNR > 72 dB MHz) Ch-Ch xTalk > 80 dB

Page 22 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt ATF FPGA Block Diagram ADC Input 14 Bits 71.4 MHz NB Filter 1.4kHz output 16 Bits/ch 32 ch / NB Gate WB Gate(s) DDR RAM NB Data TBT Data Raw Data Σ 50Hz VME NB Data VME Raw Data TBT Filter VME TBT Data 8 ch / Trigger DAQ SM Ch delays (clocks) Gates in Turns WB Gate(s) NB Gate 32 Registers VME NB Sums VME IRQ resetlatch reset latch 8 ch /

Page 23 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt ATF Narrowband Signal Processing Process 8 ADC channels in parallel up to FIR filter Digitally Downconvert each channel into I,Q then filter I,Q independently CIC Filters operating in parallel at 71.4MHz  Decimate by 17KSPS to 4.2KSPS output rate 1 Serial FIR Filter processes all 32 CIC Filter outputs  80 tap FIR (400 Hz BW, 500 Hz Stop, -100 db stopband) -> 1KHz effective BW  Decimate by 3 to 1.4 KSPS output rate -> ability to easily filter 50Hz Calculate Magnitude from I,Q at 1.4KHz  Both Magnitude and I,Q are written to RAM  Also able to write I,Q output from CIC to RAM upon request ADC Input 14 Bits 69 MHz X NCO (sin, cos) 24 Bits Phase (~1 Hz) I Q 16 Bits CIC 5 Stages R=17001 DDC 24 Bits 4.2 KSPS FIR (80 taps) LPF 500Hz Decimate 3 Bit Shift Select Significant Bits 20 Bits 4.2 KSPS 16 Bits 1.4 KSPS I Q - Denotes Peak Detectors to optimize scaling Calculate Magnitude

Page 24 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt ATF Standard Operation Data Trigger before beam injection (injection rep rate is ~1.5 Hz) –Beam in machine for ~1e6 turns (~450 msec) –Bunch RF is 714MHz with h=330, ADC clock 71.4MHz -> 33 ADC samples/turn –Gates specified in turns (need to account for filter delay/decimation for NB) –Data in digitizer boards is overwritten on each trigger –Note for WB readback (diagnostic and some TBT data) it will be necessary to use “snapshot” which insures synchronization & stores all data in snapshot buffer Trigger Beam NB Gate WB Gate(s) Reset Latch IRQ Readout IRQ CAL

Page 25 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt ATF TBT Study Data Trigger before beam injection (injection rep rate is ~1.5 Hz) –Beam in machine for ~1e6 turns (~450 msec) –Bunch RF is 714MHz with h=330, ADC clock 71.4MHz -> 33 ADC samples/turn –Gates specified in turns (need to account for filter delay/decimation for NB) –Data in digitizer boards is overwritten on each trigger –Note for TBT readback it is necessary to use “snapshot” which insures synchronization & stores all data in snapshot buffer Trigger Beam No NB Gate WB Gate Reset Latch ReadoutIRQ

Page 26 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt ATF Software Components VME ECAN-2 PMC (1x) VME Timing K-TGF (1x) VME Digitizer (12x) CLK (64.9) TRG (Gate) A B C D INJ (BIS) 729 CAN Class ADC Interrupt I/Q Data Configure Class KTGF Bucket Delay Turn Data Sample Count Class CALBox Control Status Class ATFBPM Class ATFBPM CAL Control Status Sample Control Interrupt Control Pos/ Int Data EPICS IOC Control Status Flash WB / NB Single/Multi-turn Diag. Mode Bucket Delay Turn Delay Diagnostic Flash Orbit Multi-turn VME HardwareMotorola 5500 µP Software (VxWorks) Ethernet

Page 27 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt TBT Inj.: Dispersion Measurement Dispersion, horizontalDispersion, vertical Use TBT data to fit the dispersion functions –Use nominal D x to find the amplitude and phase start values, which best fit x_TBT. –Subtract the synchrotron oscillation from x_TBT, to find the actual dispersion function.

Page 28 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Dispersion Measurement (RF) Dispersion measurement using a frequency shift –Perform closed orbit measurements with Δf = -10 kHz  Reference orbit: average 50 data sets RF shifted orbit: average 15 data sets  Particle are now on the dispersion orbit ~ D dp/p, with dp/p ~ df/f * *note: in the green line just connects the measurement points

Page 29 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Dispersion Analysis (cont.) Compare RF and TBT inj. dispersion measurements –Good agreement in the horizontal plane  BPMs 73 and 85 where disconnected –Still fair agreement in the vertical plane, having only little dispersion perturbation. ΔD x ΔD y

Page 30 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt TBT Phase Analysis Beam phase motion (synchrotron oscillation) results in an error on each button magnitude Observed on the intensity (button sum) and varies bpm to bpm In the ideal case where each channel is sampled at the same phase, this would not affect the position Simulated beam signals with expected synchrotron oscillation (200 turn period) We are looking into ways to minimize this effect – cable trims, fit correction

Page 31 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Narrowband Results (preliminary) 250 Orbit measurements recorded over an 8 hour shift Resolution estimated with split signal BPM and by SVD technique –0.650 μm with split signal –1.25 μm (6 SVD modes) –0.660 μm (20 SVD modes) Measurements where performed in low gain –Expect ~3 improvement Need more investigations!

Page 32 October 5, 2011 – LER 2011 – N. Eddy & M. Wendt Summary & Final Remarks Trend to digital signal processing, plus some analog electronics with integrated calibration / drift correction scheme. –Complex processing / math in the digital domain. –Very flexible by FPGA re-programming, however labor intensive! ATF BPM system has been implemented using this scheme –Custom analog downmix module  Tailored to machine parameters  Integrated gain control and calibration –Custom digitizer  ADC locked to machine RF  Can customize signal processing to specific needs –CO, TBT, FFT, etc –EPICs software interface ATF Installation complete at the end of 2010 –Initial commissioning successful –Beam studies to continue – BBA, Tilt -> low emmittance operation!