Possible TOF improvements

1. On the previous shift quitea strong “noise” ~1-3 sec in TOF measurements was observed

2. A series of checks was suggested:- Check beam timing on the ISIS exit - Crosscheck TOF given by the discriminator and TDC with the scope- Effect of the beam acceleration and acquisition conditions on TOF noise and accuracy

Signal from ISIS Time jitter < 10-20ns

- Measurements were done at three values of radius.- Good stability and low jitter were observed- Rise time of the pulse ~1.2µsec

Radius: 147 ‘’ 212’’ 309’’

Jitter, ns: <30 <40 <50

On the other hand a two-peaktime structure was observeddepending on- Probe radius- Beam phase width (flags)- Center beam phase

Second peak was jittering a lot

R=147”

R=212”

R=309”

Tim

e of

Flig

ht

R=147”

R=212”

R=309”

Noi

se s

pect

rum

Variation in time of flight may becaused by -variation in energy gain per turn: rf amplitude, phase and frequency-betatron oscillations

~10-4 is a good stability

Spikes are removed

Averaging may help in reducing random noise. Mike Mouat looksinto problems related to controls

Quantization minimum 43nsec is natural for this system

1. Acquisition electronics likely behaves reasonably good2. Most of the noise comes likely from beam fluctuations but small when the beam quality is good3. Let’s look at TOF (R)

1. Convert R to E2. Following Larry Root split TOF in LMS linear fit and “fast” varying

part: Tof(E) = aE+b + V(E)3. Apply smoothing to V(E)4. Differentiate V(E)5. Find Vcos

-R to E conversion is not perfect? -Betatron oscillations reproducible on tof- Spikes nature ?- Noise at reasonable level

Cubic Spline smoothing minimizes

Advantage: one later differentiate a continuous function

dxdx

sdpxsyp

iii

2

22 1

Normal conditions Flags inserted

Flags out, bunchers off Data from 04/07/13

04/07/27

04/07/13

Conclusions

• TOF noise observed in the previous run was not detected, but almost for sure came from the beam itself.

• Electronics behaves reasonably well. If further increase in resolution is needed the whole thing is to be redesigned : impedance match, amplifiers, constant fraction discriminator, TDC, higher rf harmonics but this may not reduce noise

• Instead, averaging may reduce it• Mystery spikes but can be easily smoothed out but one can may

look at origins• Some kind of smoothing is unavoidable before differentiating.• Spline smoothing helps in reduction of Vcos noise.

Near-future plans

• Piece of electronics for TOF at BM1A• Constant fraction discriminator test• RF harmonics test• Spike hunting• Phase capacitive probe reanimation (money for cables)• Wide band head for HE3. It is planned for winter shutdown.