BPMs and HOM-BPMs for the XFEL Linac - Desy
BPMs and HOM-BPMs for the XFEL Linac - Desy
BPMs and HOM-BPMs for the XFEL Linac - Desy
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<strong>BPMs</strong> <strong>and</strong> <strong>HOM</strong>-<strong>BPMs</strong><br />
<strong>for</strong> <strong>the</strong> <strong>XFEL</strong> <strong>Linac</strong><br />
N. Baboi<br />
<strong>for</strong> <strong>the</strong> BPM <strong>and</strong> <strong>the</strong> <strong>HOM</strong> teams<br />
(DESY, CEA-Saclay, SLAC, FNAL,<br />
Cockroft/Daresbury)<br />
<strong>XFEL</strong> <strong>Linac</strong> Review Meeting, Mar. 26, 2007<br />
<strong>XFEL</strong> <strong>Linac</strong> Review Meeting, Mar. 26, 2007
• Main parameters<br />
N. Baboi, DESY<br />
N. Baboi, DESY<br />
Cold BPM: ButtonType<br />
charge: 0.1 – 1 nC<br />
bunch spacing: ≥ 200 ns<br />
rep. rate: ≤ 50 Hz<br />
pulse length: ≤ 650 μm<br />
resolution: < 50 μm<br />
position range: ± 20 mm<br />
coupling: < 1 %<br />
interbunch interf.:< 1 %<br />
drift max.: < 10 μm/month<br />
• More info<br />
button diameter: 16 mm<br />
diameter: 78 mm<br />
length: 170 mm<br />
“Update on <strong>the</strong> Cold BPM”<br />
• presentation of Dirk Noelle at <strong>the</strong> <strong>XFEL</strong> meeting on March 21, 2007:<br />
http://xfel.desy.de/projectgroup/meetings/e811<br />
<strong>XFEL</strong>-Wiki<br />
• http://ferrari10/mediawiki/index.php/ColdBPM_EOI<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
•Mechanics<br />
N. Baboi, DESY<br />
N. Baboi, DESY<br />
Cold BPM: Mechanics <strong>and</strong> Cables<br />
fabrication process defined <strong>and</strong> under discussion<br />
3 BPM-prototypes under construction<br />
• <strong>XFEL</strong>-design except feedthroughs (8 mm instead of 16 mm)<br />
• 2 sent out <strong>for</strong> copper plating; one will be built in a cryo-module<br />
<strong>for</strong> <strong>the</strong> test st<strong>and</strong><br />
feedthroughs<br />
• 4 types of feedthroughs from 2 companies under-went cryo-tests<br />
–all were ok<br />
• <strong>XFEL</strong> design <strong>for</strong> feedthroughs under finalization, 16 mm<br />
•Cables<br />
double-shielded Suhner cables (MHF-SL)<br />
• length <strong>and</strong> assembly under discussion<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
• Electronics Concept<br />
N. Baboi, DESY<br />
N. Baboi, DESY<br />
Cold BPM: Electronics<br />
use concept from HERA-e <strong>BPMs</strong><br />
differences to TTF2-type electronics<br />
• use same processing channel <strong>for</strong> all 4 signals ⇒ less drift<br />
• provides also charge measurement<br />
• also <strong>the</strong> monitor is different<br />
integrated test <strong>and</strong> calibration<br />
• can be used between bunch pulses (≥ 200 ns spacing)<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
• Electronics Status<br />
under design<br />
N. Baboi, DESY<br />
N. Baboi, DESY<br />
Cold BPM: Electronics (2)<br />
goal: use similar electronics/<br />
software <strong>for</strong> all <strong>BPMs</strong> (e.g.<br />
‘warm’ <strong>BPMs</strong> from PSI)<br />
• Measurements at TTF<br />
linearity<br />
resolution<br />
q [nC]<br />
1.1<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
charge<br />
Button<br />
29.2<br />
24.6<br />
24.6<br />
23.0<br />
30.7<br />
Re-ent. cav.<br />
5.6<br />
11.8<br />
16.0<br />
23.1<br />
30.1<br />
BPM Response<br />
BPM sum signals<br />
Offset measurement<br />
y<br />
Position Shift calculated from Steerer<br />
x<br />
overdrive ADCs, since<br />
no automatic gain control<br />
Charge measurement<br />
q y<br />
q x<br />
toroid<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
• Dipole modes<br />
excited by off-axis beams<br />
amplitude is proportional to<br />
beam position<br />
⇒ can be used <strong>for</strong> beam<br />
position monitoring, similar to<br />
cavity monitors<br />
• more complicated calibration<br />
• Advantages<br />
no need <strong>for</strong> new design of<br />
vacuum components or extra<br />
beam line space<br />
large proportion of <strong>the</strong> linac is<br />
occupied by <strong>the</strong> acc. cavities<br />
<strong>HOM</strong>-signal already available<br />
N. Baboi, DESY<br />
N. Baboi, DESY<br />
<strong>HOM</strong>-<strong>BPMs</strong> at FLASH<br />
Amplitude [dBm]<br />
−25<br />
−30<br />
−35<br />
−40<br />
−45<br />
−50<br />
−55<br />
−60<br />
Cavity 1, <strong>HOM</strong> coupler 1<br />
Passb<strong>and</strong> 1, mode #6<br />
Pol. 1: 1703.363 MHz<br />
Pol. 2: 1704.223 MHz<br />
<strong>HOM</strong>-couplers (pick-ups)<br />
1.703 1.7035 1.704 1.7045<br />
Frequency [GHz]<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
• Electronics<br />
N. Baboi, DESY<br />
N. Baboi, DESY<br />
<strong>HOM</strong>-<strong>BPMs</strong> at FLASH: Electronics<br />
similar to typical BPM<br />
electronics<br />
filter one dipole mode at<br />
~1.7 GHz (higher kick factor)<br />
out of <strong>HOM</strong> spectrum,<br />
convert to ~20 MHz,<br />
<strong>the</strong>n digitize<br />
installed at both <strong>HOM</strong><br />
coupler of all 40 FLASH<br />
cavities (ACC1-ACC5)<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
N. Baboi, DESY<br />
N. Baboi, DESY<br />
<strong>HOM</strong>-<strong>BPMs</strong> at FLASH: Status<br />
Toroids<br />
<strong>BPMs</strong> up- <strong>and</strong> downstream of each module<br />
<strong>HOM</strong> BPM readouts (average of all enabled cavities)<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
•Calibration<br />
N. Baboi, DESY<br />
N. Baboi, DESY<br />
<strong>HOM</strong>-<strong>BPMs</strong> at FLASH: Status (2)<br />
scan: ~30min <strong>for</strong> all modules<br />
based on SVD<br />
calibration procedure almost automatic<br />
•Resolution<br />
single bunch: 2-10 μm rms measured so far<br />
potential to improve by changes in <strong>the</strong> LO oscillator<br />
•Multi-bunch<br />
capability demonstrated, with worse resolution<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
N. Baboi, DESY<br />
N. Baboi, DESY<br />
<strong>HOM</strong>-<strong>BPMs</strong> at FLASH: Comments<br />
•<strong>XFEL</strong> design<br />
<strong>HOM</strong>-<strong>BPMs</strong> not included yet<br />
•Extra benefits:<br />
can minimize <strong>HOM</strong> signals, i.e. align beam in <strong>the</strong> center<br />
of <strong>the</strong> module ⇒ reduce wakes <strong>and</strong> emittance growth<br />
• e.g. at lower energy<br />
can measure cavity alignment inside module<br />
full modules have to be equipped with electronics<br />
•3.9 GHz<br />
no challenge expected <strong>for</strong> electronics <strong>for</strong> higher freq.<br />
•O<strong>the</strong>r <strong>HOM</strong>-related topic<br />
can use <strong>HOM</strong>-signals to measure RF phase wrt beam<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007<br />
XFEl <strong>Linac</strong> Review, Mar. 26, 2007
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