nanoBPM Progress January 12, 2005 Steve Smith

nanoBPMs at ATF Steve Smith ATF2 Workshop January 6, 2005 SLAC

Cavity BPMs C-Band Cavities Livermore Spaceframe Dual Downconversion: Hexapods flexure legs Dual Downconversion: First IF at 476 MHz Second IF at 25 MHz Digitize at 100 MSamples/sec

Algorithm Digital Downconversion: Multiply digital waveform by complex “local oscillator” eiwt Low-pass filter (currently 2.5 MHz B/W) Sample complex amplitude of position cavity at “peak” Divide by complex amplitude from reference cavity Scale by calibration constants Refine calibration with linear least-squares fit to other BPM measurements Removes rotations, calibration errors.

Data: Raw & Demodulated

Calibration Move BPM more than beam jitters Estimate scale, phase Doesn’t use information from other BPMs

Does calibration work in presence of beam jitter? Look at same calibration data Use other BPMs to remove beam jitter

Fits to Calibration Data, All BPMs

Measurement Predict Y2 Linear least-squares fit to (x, y, x’, y’) at BPMs 1&3

Preliminary Resolution s ~ 20 nm Individual BPM resolution is better, this is measurement – prediction from 2 other BPMs Calibration scale is clearly off by ~20%

Move BPM in 1 mm Steps

X Resolution

Anticipated Improvements Analysis improvements Adjust cavity parameters Frequency Decay constant Optimize algorithm Filter bandwidth may be reduced => improve statistical power Optimize measurement sample time Investigate handling of saturated pulses Is saturation handled properly in this algorithm? Are there non-linearities apparent at large amplitudes? Potential Physical improvements Lock Local Oscillators to accelerator RF Improve understanding, operation of movers

Exercise BPM Movers Y2 is a little low Move Y2 up 1 mm Oops, wrong way Go up 2 mm What happens during the move? 40 mm excursions(!) in process of making 1 mm move Why is resolution worse after the move? s=40 nm, was 20nm BPM rotated during move? No

Conclusions Resolution is not difficult ~20 nm, should get better with optimized analysis Demonstrating resolution is hard Must beat beam jitter, drifts Stability looks good, but is poorly studied so far. Implemented system should be able to prove BPM capabilities Redundancy? Movers?

End ATF2 Talk

Progress This Week Parameters Saturation Stability

Anticipated Improvements Analysis improvements Adjust cavity parameters Frequency Done, but makes no difference Decay constant Optimize algorithm Filter bandwidth may be reduced => improve statistical power Optimize measurement sample time Investigate handling of saturated pulses No improvement, essentially no saturation in runs I’ve been evaluating. Is saturation handled properly in this algorithm? Can’t tell yet Are there non-linearities apparent at large amplitudes? Potential Physical improvements Lock Local Oscillators to accelerator RF Improve understanding, operation of movers

Stability Calibrate using Dec-16 calibration runs Examine all runs in \14-Dec-2004_19_55\ Refine calibration using a single run (Run9) Regressed y2 against (y1, y3, x1, x3, y1’, y3’) i.e. left out x2, y2’, x’s Plot mean & rms of (y2-y2est) ~ 2min /run -- for ~20 minutes stable to +- 15 nm! Sometimes things move!

Stability (cont) Now examine all runs in \14-Dec-2004_21_4\ Using same calibration-regression Plot mean & rms of (y2-y2est) Only run1 looks like previous runs!!! Is all lost?

Stability (cont) Look at earlier data \14-Dec-2004_17_30\ Using same calibration-regression \14-Dec-2004_19_55\Run9 <100 nm motion in 1 hr!

To Do Investigate handling of saturation Understand Calibration Calibrate tilts Understand scales Understand regression What part is helping? How much? What’s it hiding? How stable are coefficients? What do they mean? Should we establish DST files? what format?

Minimal Regression Regress against Y1, X2, Y3 Y2 = 10mm + Different choices of regression variables yield different direction of motion beyond data set regressed!

Drift < 50 nm over 1 hr !!

Stability Must be careful about regression variables Drifts look small (at least for a data set selected for small drifts)