CTF3 stability, TWTs and Gun

Alexandra Andersson, CERN

TWTs -- Measurement Setup

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.30

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80pulse-to-pulse phase stability

Pulse-to-pulse phase difference

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-5 -4 -3 -2 -1 0 1 2 3 4 5

x 10-3

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100pulse-to-pulse amplitude stability

Normalized pulse-to-pulse amplitude difference

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The pulse-to-pulse difference in average value of the flat-top of the RF pulse from the TWTs was around 1‰ in amplitude and 0.1° in phase. The distributions were roughly Gaussian.

Pulse-to-pulse stability

0 1 2 3 4 5 60.997

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1.003Stability over time, amplitude and phase, SHB1, SHB2

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0 1 2 3 4 5 620

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SHB1

SHB2

Long term stability

•The two TWTs drift together in phase•There was almost no drift at all on the third channel, mixing LO with itself•Probably some temperature effect

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1.005

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shb1 amplitude across pulse

time, arbitrary units

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shb1 phase across pulse

Quality of the flat-top TWT1

≈6‰

≈1.2°

≈2.5‰

Quality of the flat-top TWT2

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shb2 amplitude across pulse

time, arbitrary units

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shb2 phase across pulse

time, arbitrary units

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≈8‰ ≈3.5°≈2.5‰

TWT phase flip programming

•Currently the IQ modulation input remains unused •On the drive to the TWT we observe disturbances of ≈6°, lasting some 40ns, after each phase flip•Some attempts where made to cure this by modifying the signal path•Some amplitude difference was observed on the TWT output, but not on the drive•As these effects are constant pulse-to-pulse, one could attempt to run a slow feedback via the IQ, which was foreseen for this purpose

Gun current stability

• At the moment, not much is known about this due to a lack of availability of measurements on the gun deck

• Some elements will shortly be added to the gun setup in order to address this issue

• Further, devices have been added to shape the current pulse exiting the gun, i.e. the possibility to add modulation on top of the pulse

Gun pulser - upgrade

Gun pulser - upgrade• Current modulation:

– ±5% modulation, 10kHz - 50 MHz bandwidth– Looking into boosting modulation strength to ±10%– Can be used with gun current measurements, or potentially some

BPM further downstream to correct the beam current in the linac.• Current measurements:

– One resister divider on the gun connector– One dI/dt current pickup coil followed by integrator– Two measurements since the cathode is a rather non-linear

device, thus knowing both current and voltage values could be useful.

• So far, only tests in the lab has been performed

Digitizer

•2 Channels•13-bit vertical resolution•250MS/s or 500MS/s interleaved•250MHz Analog bandwidth•0.5‰ resolution at full bandwidth•Ethernet connection

Should be adequate for all the measurements we might wish to do on gun deck.

Conclusions

• Measurements of TWT indicate that they have decent stability.

• There is a slow phase drift that is probably due to temperature

• Gun will be equipped to have stability measurements done

• A modulation input has been upgraded to allow for an arbitrary modulating waveform