recirculation: looking from inside
DESCRIPTION
Recirculation: looking from inside. Igor, Alessandro and Alexey Special thanks to Erik. 12 GHz PETS testing at CLEX, CERN ( as it was shown in 2008 ). To the Load. Variable Splitter (coupling: 0 1). Variable phase shifter. PETS output. CTF3. PETS input. #1. Drive beam. DL. CR. - PowerPoint PPT PresentationTRANSCRIPT
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Recirculation: looking from inside
Igor, Alessandro and AlexeySpecial thanks to Erik
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12 GHz PETS testing at CLEX, CERN (as it was shown in 2008)
Operation mode #1 #2 #3 CLIC
Current, A <30 14 4 101
Pulse length, ns 140 <240
<1200
240
Bunch Frequency, GHz 12 12 3 12
PETS power (12 GHz), MW
<280
61 5 135
DBACRDL
TBTSCLEX
CTF3
CTF2
#1
#2
#3
• Different scenarios of the drive beam generation in the CTF3
• To compensate for the lack of current, the active TBTS PETS length was significantly increased: from the original 0.215 m to 1 m.
• In order to demonstrate the nominal CLIC power level and pulse length, it was decided to implement a different PETS configuration – PETS with external re-circulation.
Variable Splitter (coupling: 01)Variable
phase shifter
To the Load
PETS output
Drivebeam
PETS input
Round trip efficiency: 76%Round trip delay: 25 ns
0 100 200 300 4000
50
100
150
Time,ns
Pow
er, M
W
P 0.9
Calculated output RF pulse envelops in PETS with re-circulation. Circles – mode 2, diamonds – mode 3, boxes – the CLIC pulse by design. Solid line – PETS output, dashed line – to the load.
<30A
14 A
4 A
0 500 1000 15000
100
200
300
Time,ns
Pow
er, M
W
#1. The coupling and pulse length optimized to provide pulsed parameters comparable to the CLIC nominal values.
#2. Full re-circulation (coupling=1) and full pulse length for the mode 3.
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Network analyzer
Rec. loop RF check configuration
#2 #1
#3
Measured transmission and reflection for the case of the full recirculation
PETS
Measured transmission and reflection for the case with NO recirculation
S12
S13
Transmissions:
Pis
tons
pos
ition
Pis
tons
pos
ition
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b
nn
rc N
n
atjnN
kb
jk etAFFweSFFtFFwFFttU00
12 ))(()()(
PETS single bunch response (GDFIDL)
Measured spectrum of the recycling loop transmission
artificial RF phase delay
Number of round trips
The complete system single bunch response spectrum Multi-bunch part
Number of bunches
Distance between bunches (~RF phase)
Bunch amplitude (~q and F)
PETS with recirculation operational analysis
The method allows for the detailed reconstruction of re-circulation including: The tuning of the loop phase length (if needed) Manipulation of the current amplitude and RF phase along the bunch train Provides direct calculation of the reflection in the loop and the power extraction to accelerating structure
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Analyzing the spectrum of the signal, we can add artificially an extra RF phase delay () to the original measurements and tune the total recirculation phase:
Resonant extraction
=0
=180
TBTS PETS single bunch responseGDFIDL simulation
Direct power productionPower build up in 49 bunches
single bunch signal circulating in a loop(full re-circulation)
Power build up for the full (200 ns) beam and full recirculation
Destructive extraction
forward reflected
Example of the full recirculation & rect. 200 ns DB current pulse
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Full recirculation and RF phase errors vs. simple model (used by Erik Adli)
g=sgrt(0.752)t=25 ns As measured
=0
=/2
=
Excellent agreement!
Off regime for the On/Off mechanism
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When we switch-off recirculation, the RF phase is needed to be shifted by /2 compared to the best phase advance used for the full recirculation. If not then residual recirculation will occur:
single bunch signal circulating in a loop
=/2I=10A
From the PETS
=0
NO recirculation
To the structure
Losses in attenuator ~ 10%
Back to the PETS
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Power split=(1-S)Att
TP=S Att
g2 = S Loop =TP Loop/ Att
Measured:Loop=0.76Att=0.9
In 2010 we have measured Tp (blue).In 2011 we measured g2 and Power split (red).
Reference plane
Power balance (2011)
zoom
(1+S)-S1-S = Power split / 0.9S = g2 / 0.76
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g2,
Pow
er s
plit
Following theory, both curves can be nicely fitted with cosine/sine functions:
2
2
5.1029.10cos76.0)(
xxg
2
5.1029.10sin9.0
xPowersplit
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DB: 10 A x 250nsAtt: 16.6 mm
The attenuator settings s=16.55 mm (g22011 = 0.334). The recirculation is tuned in phase with rectangular dB pulse
PETS output
To structure
gr
gb
QV
L
L
V
QRFLIP
2
,)exp(1
4
/
0
2
0222
With measured DB current pulse (FF2=1)
Power production in the PETS (normalization):
1 A drive beam produces 0.306 MW RF power
R/Q= 2290 OhmBeta= 0.453 CQ= 7200L= 1 m
Vs. simple model
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F2=0.415=3.73 mm
Simulated power (s=16.55 mm) scaled to the measured (s=16.60mm):
Fitted phase error for recirculation is 1.80
From PETS(#707)
F2=0.56=3.03 mm
F2=0.415
Power split(#701)
F2=0.415
F2=1.8
Reflected from 2nd attenuator
The whole system signals analysis. The measured spectra of the 2nd attenuator and accelerating structure were used
From PETS(#707)
(#710)
707
701
702
708
F2=0.415=3.73 mm
All signals tracking
These simulations allow to conclude on the relative calibration errors.For example, if one believe that #707 is properly calibrated, then power level in #701 is overestimated by 35% and in #710 by factor 4.3.
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Spectral analysis vs. Adli’s model
g2 = 0.334measured
g2 = 0.355fitted
=1.80
F=1
The two approaches show a good agreement. The difference in recirculation gain is ~3%
10%
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Rise time 20 nsFall time 30 ns
The drive beam BPM bandwidth issues
Drive beam amplitudeAnalysis stage by stage
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20 degrees RF phase jump
+ frequency detuning by 1.1 MHz
Drive beam phase and frequency
The residual discrepancy of the pulses shapes can came from: Variation of the bunches form factor linearity of the detector
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Relative single bunch form factor
0.19
‘simple’ sine-type modulation
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707 701 710
702706
Fitted form-factor 0.906
X 0.6
X 3.9
All signals tracking
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-50dB Directional coupler re-calibration