# Presentation: 692717

## AP2 line BPM systemBill Ashmanskas, Sten Hansen, Terry Kiper, Dave Peterson, 2005-09-21

## Background

- AP2 line  275 m long, travels from target to Debuncher
- p/p  4% (at end of line)
- Particles per pulse ~ 1010 at end of line, ~ 1011 earlier in line
- ~ 108 antiprotons reach Debuncher every ~ 2 seconds
-  1.5 s bunch train, bunched at 53.1 MHz
- before amplification, signals while stacking range from about     -19 dBm (30 mV) upstream to about -35 dBm (4 mV) dnstream
- so we amplify downstream signals 20dB in tunnel
- Reverse proton signals range from -50 dBm (1 mV) upstream to -23 dBm (20 mV) downstream (before downstream amplifiers)
- maybe we should have amplified upstream, too?

## Motivation

- Simulations by V. Lebedev et al. indicate that ~ 50% more flux into Debuncher may be possible with well understood optics
- Would like to use AP2 line BPMs
- to measure optics vs. p/p for reverse protons
- to correct orbit using reverse protons
- to monitor orbit drift and intensities while stacking

## History

- Legacy AP2 BPM readout did not provide useful data:
- signals much smaller than other beamlines’ 53 MHz signals
- crosstalk from Debuncher injection kicker
- Kicker crosstalk looked pretty severe on oscilloscope
- see    http://www-bd.fnal.gov/cgi-mach/machlog.pl?nb=pbar03&page=318
- But scope data looked OK offline with narrowband processing
- Added BPF before scope to reduce dynamic range needed
- (Re)connected existing 20 dB amplifiers to make interfering kicker signal less important
- Got ~ 1 mm resolution with scopes – good enough to be useful
- Decided to build boards that do signal processing equivalent to what we did with scopes – less clutter, easier readout, less costly

## Blue = envelope read from new BPM board

- Red = raw BPM signal (scope)
- Green = BPM signal after bandpass filter (scope)

## We built something different from the echotek solution because ...

- Modest demands — only 53 MHz needed
- We wanted to control the details, since we weren’t sure how much tinkering would be needed to make the system work
- Didn’t have legacy system already working, to help specify upgrade
- I spent enough time with CDF trigger to learn to hate VxWorks
- Substantially reduced infrastructure cost appealed to us
- Gives us a toolkit for other ad-hoc projects
**It was much more fun to do it this way**
- Anyway, the resolution is  100 m in the lab.
- We think, some rainy day, we ought to be able to push it to < 50 m

## Slide 7

## Simplified block diagram

- 65 MHz LPF

- BPM
- signal

- 53.1 MHz
- quadrature
- demodulator

- RF

- LO

- I

- Q

- 5 MHz LPF

- 5 MHz LPF

- 10 bit
- dual ADC
- 26.5 MHz

- FPGA

- TI MSP430

- TCP/IP

- Java OAC

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## Misc features

- NIM module, 4 type N inputs, 2 BPMs
- Can lock to external RF or 10 MHz – or not
- 10 bit sampling of IF I and Q waveforms
- 44dB adjustable gain in demodulator chip
- Diagnostic DAC can drive (via analog switches) each input up to about 1⁄4 full scale (at maximum input gain); also drives FP lemo
- 32 MB SDRAM available (e.g. data capture), but not used now
- Debug/test via USB console or telnet
- MSP430F149, programmed in C, provides command interface
- WIZnet 1” x 2” daughtercard provides TCP/IP stack
- Nearly all processing done in Altera Cyclone 1C6Q240 FPGA
- Remote FPGA + CPU update has been demonstrated (but not yet fully implemented in the field)
- Single network connection reads out  ~ 10 boards
- Simple I/O protocol for remote register access (see next page)

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## Java program by Jim Budlong (analogous 

- Java program by Jim Budlong (analogous
- to existing Debuncher BPM program)

## N.B. chnl 721 is 

- N.B. chnl 721 is
- broken in tunnel

## Slide 27

## Resolution  beam motion

- Resolution  beam motion

## Resolution  beam motion

- Resolution  beam motion

## Response

- Board has  44 dB variable attenuation in IQ demodulator chip
- At 3⁄4 full scale, max gain, signal  5 mV peak (-36 dBm)
- (84/2) x 384 x 2  32000 counts intensity reading
- (sample 26.5 MHz, +511 counts FS, A+B chnls)
- A+B rms/mean  0.09% (using board’s own DAC as source)
- AB / A+B rms  0.09%  90 (70) m for 100 (75) mm BPM
- Using min gain, 3⁄4 FS, signal  0.5 V peak (+7 dBm)
- A+B rms/mean  0.11%, AB / A+B rms  0.11%

## Slide 31

## Response

- Using AWG in instrumentation area, 24 dB atten, 83% FS,
- A+B rms/mean = 0.65%, A-B / A+B rms = 0.092%
- 69 m for 75 mm BPM (92 m for 100 mm BPM)
- Using another BPM board’s DAC as source (clocks not synchronized), still at 3⁄4 FS,
- A+B rms/mean  0.4%, AB / A+B rms  0.13%
- Would be interesting to understand why this does worse than AWG

## Slide 33

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## These plots are 1 entry per channel per board

- Relative gain settings (ask for -6dB, what do you get) vary 1.5% (rms/mean)
- Absolute channel gains vary 10% (rms/mean)
-  CPU corrects each “B” signal for gain ratio between “A” and “B”

## Slide 38

## This sort of effect – I vs. Q gains, pedestals, etc. – is likely part of our “excess” resolution

- We already subtract separate I,Q pedestals, but perhaps we could do better

## To-do list

- Remote software update needs to be finished
- Better debug handles, e.g. waveform readout (partially exists)
- Make lots of debug info accessible without creating a dozen new ACNET devices per BPM
- Streamlined (automatic) handling of stacking vs. studies settings
- Simple application to manage calibration constants, gain settings, timing offsets, etc.
- More comprehensive set of bench measurements may be nice
- Try mixing down with  52 MHz, not 53.1, followed by digital downconversion in FPGA?  Better resolution??
- Implement “fast” fast time plots (as done for damper board)??
- Use SDRAM for circular buffer
- Decode TCLK, MIBS directly

## Other applications?

- MI SBD trigger module (Nathan Eddy, Bob Flora): done
- DRF2 AWG: in place (but needs ACNET hooks)
- Very similar boards do various Debuncher LLRF functions
- D to A line (boards in place; need better tunnel electronics)
- Debuncher 53 MHz BPM orbits while stacking (likely)
- Already use one BPM as intensity monitor: switch SA for BPM board?
- Downconvert 75 / 79 MHz diagnostic schottky signals?
- Phase meter for MI injection??
- Could do bunch length, too, if modified for 106 or 159 MHz operation
- Could potentially replace many “turn-by-turn” oscilloscope setups (pickup + RF + mixer + LPF + scope + console app)

## http://pbardebuncher.fnal.gov/wja/docs/ap2bpm/