ctf3 stability, twts and gun
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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
10
20
30
40
50
60
70
80pulse-to-pulse phase stability
Pulse-to-pulse phase difference
coun
t
-5 -4 -3 -2 -1 0 1 2 3 4 5
x 10-3
0
10
20
30
40
50
60
70
80
90
100pulse-to-pulse amplitude stability
Normalized pulse-to-pulse amplitude difference
coun
t
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
0.998
0.999
1
1.001
1.002
1.003Stability over time, amplitude and phase, SHB1, SHB2
norm
aliz
ed a
mpl
itude
time, hours
0 1 2 3 4 5 620
21
22
23
24
25
phas
e, d
egre
es
time, hours
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
400 450 500 550 600 650 700 750 800
1
1.005
1.01
1.015
1.02
shb1 amplitude across pulse
time, arbitrary units
norm
aliz
ed a
mpl
itude
400 450 500 550 600 650 700 750 800
89.8
90
90.2
90.4
90.6
90.8
91
91.2
91.4
91.6
91.8
time, arbitrary units
phas
e, d
egre
es
shb1 phase across pulse
Quality of the flat-top TWT1
≈6‰
≈1.2°
≈2.5‰
Quality of the flat-top TWT2
400 450 500 550 600 650 700 750
1
1.005
1.01
1.015
1.02
shb2 amplitude across pulse
time, arbitrary units
norm
aliz
ed a
mpl
itude
400 450 500 550 600 650 700 75020
21
22
23
24
25
26
27
shb2 phase across pulse
time, arbitrary units
phas
e, d
egre
es
≈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
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