rf break-down studies in the ctf3 tbts
DESCRIPTION
RF break-down studies in the CTF3 TBTS. Accurate measurements on TBTS. The newly installed structures. Germana Riddone. Since September 2012. Franck Peauger - IRFU. New setup with 2 accelerating structures. 2 phase shifters 1 variable splitter. 7 BPMs on PB. 1 FCU. Andrea’s talk. - PowerPoint PPT PresentationTRANSCRIPT
RF Break-Down Studies in the CTF3 TBTS 1
RF break-down studies in the CTF3 TBTS
Accurate measurements on TBTS
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 2
The newly installed structures
29 Jan. 2013 Wilfrid Farabolini
Franck Peauger - IRFU
Germana Riddone
• Since September 2012
RF Break-Down Studies in the CTF3 TBTS 3
New setup with 2 accelerating structures
Roger Ruber
2 phase shifters 1 variable splitter
15 RF channels(Diodes and IQ)
7 BPMs on PB
2 screens 1 Flash box
Thermal probes and flow rate
3 PMTs16 WFMs channelsFranck’s talk
1 FCU
Alexey’s talk
Andrea’s talk
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 4
Accurate Energy measurement
• It is no longer possible with the energy gained with 2 ACS to track simultaneously on the same spectrum line screen both accelerated and non accelerated beams (dipole strength change is required)
• Califes beam energy fluctuates by +/- 2 MeV with a period around 150 s (temperature ?)• A fit with a sinusoidal function is valid at least for a duration up to 30 minutes
Ener
gy [M
W]
Time
29 Jan. 2013 Wilfrid Farabolini
For stabilization see Tobias Persson talk, Wednesday
RF Break-Down Studies in the CTF3 TBTS 5
Procedure to determine the maximum energy gain
• Extrapolated Califes energy is subtracted to measured accelerated beam energy gain.
• During RF power cut magnet is set to measure Califes energy and check extrapolation
• RF powers from couplers is logged as well
• Califes / Drive beam phase is scanned over 360 deg of 12 GHz
• Upstream / downstream phase was previously adjusted to identical phase vs. beam
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 6
Upstream / downstream phase optimization
• Inter-structures phase shifter is moved up to the point where no acceleration is measured whatever the Drive Beam / Califes phase. At this phase the 2 structures act oppositely.
• From this point we move the phase by 180 deg in order to place the 2 structures at the same phase vs. the probe beam.
• Due to this phase shifter lack of repeatability no systematic scan was performed after this setting
Califes phase scan with ACS’s phase set in oppositionconstant energy = Califes energy (195 MeV)
Input phases when ACSs in opposition
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 7
Energy gain as function of RF power
• Since both the ACS measured power are not equal, an averaged value is computed for the RF power coordinate.
• With this representation the maximum measured acceleration constantly failed to reach its nominal value by 4 MeV approx.
Energy gain versus root mean power during two records of phase scan
Phase scan
Power fluctuations
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS
Structure tuning frequency check
LO = 11994.2 MHz LO = 11994.2 + 1 MHzLO = 11994.2 - 2 MHz
• Down mixing the RF output signal produced by a short probe beam pulse (6 bunches) allows to measure the ACS resonant frequency. Very well tuned (better than 1 MHz).
• The RF produced last 65 ns (structure filling time)
RF output frequency is now forced by the probe beam pulse frequency • RF output rising time = ACS filling time (65 ns)• RF output rising time + sustain time = pulse length• RF output falling time = ACS filling time (65 ns)
Short pulse: 4 ns
LO = 11894.2 MHz
Long pulse: 150 ns
Long pulse: 194 ns
LO = 11994.2 MHz
Alexandra Andersson
29 Jan. 2013 Wilfrid Farabolini 8
RF Break-Down Studies in the CTF3 TBTS 9
Water temperature method to derive the deposited mean RF power
Upstream Downstream
File Date time start time stopmoy time start
moy time stop Power RF Power Temp Ratio Temp in Temp out Power RF Power Temp Ratio Temp in Temp out
2012_11_29 01 00 07 00 03 00 03 10 6.25 4.4 1.42 29.27 29.07 5.66 5 1.13 29.65 29.49
2012_11_30 17 00 23 00 21 45 22 10 5.89 4.37 1.35 29.23 29.02 5.23 4.91 1.06 29.6 29.45
18 10 18 20 5.84 4.29 1.36 5.21 4.79 1.09
2012_11_30_a 10 00 16 40 11 40 12 10 5.67 4.57 1.24 29.26 29.06 5.11 4.92 1.04 29.65 29.47flow rate change
2012_12_04 19 20 21 40 20 50 21 00 5.99 4.52 1.32 29.25 29.06 5.34 4.99 1.07 29.65 29.48
2012_12_04 19 20 21 40 20 17 20 22 6.4 4.81 1.33 29.24 29.05 5.71 5.28 1.08 29.62 29.46
2012_12_05 14 00 23 00 20 45 20 55 7.59 5.66 1.34 29.24 29.07 5.76 6.41 1.05 29.58 29.45
2012_12_06 00 00 23 00 01 20 01 30 7.35 5.09 1.45 29.21 29.02 6.45 5.94 1.09 29.57 29.42
Average : 1.35 1.08
• From thermal method and averaging on a lot of runs, it appears that the RF power is overestimated by a factor 1.35 for the Upstream ACS and 1.08 for the Downstream ACS
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 10
Energy gain vs. power after recalibration
• Applying the correction factor derived by the thermal method allows to plot an acceleration vs. power chart much closer to the nominal ACS performances.
• However, an accurate recalibration of the RF couplers lines as well as the diodes crates has been done during this winter shutdown and sensitivity has been improved.
• The correction factors computed by integrating power cannot reveal the diode calibration linearity default (automatic calibration procedure installed)
Energy gain versus root mean corrected power
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 11
Energy spread vs. accelerating phase
• Energy spread (s of Gaussian fit and FWHM) is maximum when energy gain is null
• And is minimum when energy gain is extreme (pos. or neg.)
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 12
Energy spread and bunch length measurement• An efficient method of deriving bunch
length and even slice energy…• 12 GHz = 83.3 ps: fast slope and high
accelerating field• Ex. sESmin = 1.1 MeV, sESmax = 9.05 MeV, Ds = 8.98 MeV
-> slength = Asin( /Ds Egain max) = 16.2 deg -> slength = 3.7 ps -> FWHMgauss = 8.7 ps
Resolution approx. 0.8 ps FWHM • A model should be developed taking into
account the energy and charge distribution within the bunch
• Sinus fit period should be ¼ T3GHZ for energy gain and 1/8 T3GHZ for energy spread. Phase shifter linearity seems poor on its lower range.
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 13
RF and BDs detection signal monitoring
Pulses main parameters are continuously data logged6 hours
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 14
Accurate BD detection• Two criteria used: Reflected Power
and Missing Energy Miss = Enerin – Enerout x attenuation
• Data are post processed with adapted thresholds.Thresholds = mean + 3.72 s
[ PGauss(X>3.72s) = 10-4]
• Compromise between Detection prob. and False Alarm prob.
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 15
BD count evolution and BD rate
What to do with the periods of high activity ?(clusters)
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 16
BDR as function of RF PowerBut conditioning is still under progress• previous structure: 3 106 RF pulses
• theses structures:6 105 RF pulses ?
• 1 day of Stand alone Test Stand:4.3 106 RF pulses
29 Jan. 2013 Wilfrid Farabolini
Date Mean power [MW]
sigma power [MW]
Pulse number
BD ACS up
BD ACS down
2012_11_16 29.2 2.2 14807 3 22012_11_19 30.3 1 36955 5 152012_11_23 29 2.1 10932 1 12012_11_29 37.2 2.6 45535 102 602012_12_04 38.4 2.9 10174 12 142012_12_05 46.1 1.8 13394 16 202012_12_06 46.5 2.1 21622 27 82012_12_07 36.2 3 9311 3 6
RF Break-Down Studies in the CTF3 TBTS 17
BDR as function of Power (2)
• Fitting the Power distribution when BD by a power law of the power distribution of all pulses provide an exponent between 12 and 18.
RF power density of Probability of all RF pulses (blue), of RF pulse with BD (red) and power law fit of BD probability (green)
Previous ACS Upstream new ACS
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 18
BD location inside the structuresReflected
rising edgeTransmitted falling edge
1st method (transmission): looking at BD position when BD strikes
Input falling edge
Reflected falling edge
4th method (echo): looking at BD position when RF pulse stops
Reflected rising edge
2nd and 3rd methods (combining previous signals
with FCU):
Transmitted falling edge
FCU edge
29 Jan. 2013 Wilfrid Farabolini
First 3 methods give consistent results, method 4 seems to show a BD drift toward the structure input coupler
BD with precursor
BD w/o precursor
RF Break-Down Studies in the CTF3 TBTS 19
Hot spot at cell #6 in the previous structure
29 Jan. 2013 Wilfrid Farabolini
Previous ACS compilation
RF Break-Down Studies in the CTF3 TBTS 20
No hot spot in the 2 present structures
29 Jan. 2013 Wilfrid Farabolini
Present ACSs compilation
RF Break-Down Studies in the CTF3 TBTS 21
Summary
• New ACSs are still in conditioning (not yet at 100 MV/m).• Accurate procedures have been developed to assess their
characteristics (energy gain, RF power, BD detection).• Energy spread at zero crossing allows to measure the bunch
length.• BDR are presently on the same curve than for the previous
structure.• BD locations show no hot spot for whatever structures.
29 Jan. 2013 Wilfrid Farabolini
RF Break-Down Studies in the CTF3 TBTS 22
Back-up slides
29 Jan. 2013 Wilfrid Farabolini
CTF3 days - 11 October 2012 23
FCU and PMFCU signals reliability
• When RF transmitted power is low (early BD), BD produced electrons are not likely to reach the FCU (not accelerated towards the FCU)
• Also when RF reflected power is low FCU signal is often weak (why ?)
OTR light seen on FCU mirror surface is current and energy dependent but not saturated. (Blue dots correspond to low reflected power)
Alexandra A.
W. Farabolini
FCU
max
out
put [
V]
PM o
n FC
U m
ax o
utpu
t [V]
Max Transmitted Power [MW]
Max Reflected Power [MW]Max Transmitted Power [MW]
RF Break-Down Studies in the CTF3 TBTS 24
Coupled BDs
29 Jan. 2013 Wilfrid Farabolini
Reflected power
Transmitted power
Input power