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LHC RF Feedback. Donat Stellfeld John Molendijk Philippe Baudrenghien Pierre Maesen Urs Wehrle. SM18 tests, Aug-Sept 2005. Reported by P. Baudrenghien. Open Loop. 56 kV, 7.8 A. Q 20000 -> 180000. DC coupled Analog Fdbk (Digital Fdbk OFF). RF feedback Theory. - PowerPoint PPT Presentation
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Dec. 15, 2005 SM18 tests Aug-Sept 05 1
LHC RF FeedbackSM18 tests, Aug-Sept 2005
Reported by P. Baudrenghien
Donat StellfeldJohn MolendijkPhilippe BaudrenghienPierre MaesenUrs Wehrle
Dec. 15, 2005 SM18 tests Aug-Sept 05 2
Cavity Servo Controller.Simplified Block Diagram
Technology:DSP
CPLD or FPGA (40 or 80 MHz)Analog RF
Signals: Digital:
Analog:
Digital I/Q pair:
Analog I/Q pair:
X
DigitalIQ
Demod
SUM
TunerProcessor
X
DigitalIQ
Demod
Dir.Coupler
Single-CellSuperconducting
Cavity
Fwd
Rev
X
DigitalIQ
Demod
DAC
Digital RF feedback (FPGA or DSP)
1 kHz
60 dB
From long.Damper
Voltagefct
I0
Q0
dpdV
Set PointGeneration
DA
C
PhaseEqualizer
ADCDAC
DIFF
Vcav
DIFF
SUM
Analog RF feedback
1 kHz
20 dB40 dB
1-Turn FeedforwardWideband
PUDAC ADC
An
alo
g IQ
Dem
od
ula
tor
Ic fwd
X
DigitalIQ
Demod
Ic rev
Master F RF
TUNER LOOP
SETPOINT
RF FEEDBACK
Dual Var GainIF Ampifier
An
alo
g IQ
Mo
du
lato
r
RFPhase Shifter
RF MODULATOR300 kW Klystron
Circ
Ig fwd
An
alo
g IQ
De
mo
du
lato
rQ
I
ANALOGDEMOD
KlystronPolar Loop(1 kHz BW)
AD
C
PhaseShift
Gain CntrlSUM
BasebandNetworkAnalyzer
DA
C
noise
X
DigitalIQ
Demod
X
DigitalIQ
Demod
1-Turn Feedback
Tuner Control
Ic fwd
CONDITIONING DDS SWITCH/PROTECTION
SWITCH
Dec. 15, 2005 SM18 tests Aug-Sept 05 3
Open LoopSynthesizer
SPre-
driverDriver Klystron
Cavity
Attn
Coupler
NLP5504
way
Demod
Fdbk
Fdbk
Mod
NLP550
Network Analyzer
Hol
CW @ 400.8 MHz
Freq sweep
I
Q
S
Beam loading test
circ
7/8" cable200 ns
7/8" cable200 ns
56 kV, 7.8 A
Q 20000 -> 180000
DC coupled Analog Fdbk (Digital Fdbk OFF)
Dec. 15, 2005 SM18 tests Aug-Sept 05 4
RF feedback Theory
• RF Feedback theory [1],[2]– Minimal cavity impedance (with
feedback) scales linearly with T (600 ns)
– Achieved for a gain value proportional to Q
– Achievable fdbk BW inversely proportional to T
TQ
RR 0min
2
T
3.1=ωΔ
assumed single-cell
Tω
Q≈G
oopt
690 kz 2-sided BW
43.2 k
Q Gopt20000 13.560000 39.8
180000 119.4
Dec. 15, 2005 SM18 tests Aug-Sept 05 5
Effect of coupling
cavitycirc
Pin Pout
1
• Transmission Loss Pout/Pin [3]:
• At resonance we get:
• So Vout/Vin is proportional to sqrt[QL]
21
0L
0
220
221
21
in
out
β+β+1
Q=Q
ω
ω-ω=δ
δQ4+)β+β+1(
ββ4=
P
P=)ω(T
20
L
1
20 β
Q
Q4=
β
β4=)ω(T
Dec. 15, 2005 SM18 tests Aug-Sept 05 6
RF Feedback Module (eda-586.v2)Notch to damp the resonance of the second klystron cavity (404.8-405.45 MHz) + phase advance to increase closed loop BW.
400.8 MHz
10 MHz
klystronloop amplifier
Dec. 15, 2005 SM18 tests Aug-Sept 05 7
O.L. vs. Notch position
• Left: notch well adjusted• Right: Notch at min and max positions (~800 kHz range)
Dec. 15, 2005 SM18 tests Aug-Sept 05 8
Stability. Open Loop:What we expected…
• Nyquist Plot using measurement of real klystron• Q=20000, real klystron, loop delay 450 ns (excluding klystron)• Low Level: Notch plus Phase Advance
2 4 6 8 10 12
-6
-4
-2
2
4
6
Nyquist : RF fbk
-1 -0.75 -0.5 -0.25 0.25 0.5 0.75 1
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1Nyquist : RF fbk
10 dB gain marginOpen Loop gain = 13
Dec. 15, 2005 SM18 tests Aug-Sept 05 9
O.L. Stability vs. CW power
• Positive Fdbk -> unstable point = (+1,0)• 50 kW vs 200 kW• Gain drops by 2 dB• Phase does not change
50 kW CW 200 kW CW
Q=20000O.L. gain = 20(26 dB)
Dec. 15, 2005 SM18 tests Aug-Sept 05 10
O.L. stability vs. Q
• All meas, 50 kW CW• To keep same gain margin, LL
gain varies as SQRT(Q)• No significant phase change
Q=20000Q=60000, LL gain x 1.7
Q=180000, LL gain x 3
O.L. gain =20
O.L. gain =60
O.L. gain =180
Dec. 15, 2005 SM18 tests Aug-Sept 05 11
O.L. stability vs. detuning
• Q=60000, 50 kW CW• No change in gain neither phase• Detuning has no effect on stability
Cavity detuned by 10 kHzCavity on tune
Dec. 15, 2005 SM18 tests Aug-Sept 05 12
O.L. stability vs. Klystron HV
MHz400@reesdeg840=
UUΔ
φΔ RF
• Q=60000,• Change HV 56 kV to 54 kV• Thomson TH2089 measurements:
• But Cathode current does not change RF phase. But changes gain.
Dec. 15, 2005 SM18 tests Aug-Sept 05 13
Closed Loop
• Closes OK on first trial
• Tracks Iref,Qref OK
• But when large step in Iref, remains stuck with strong pure CW
Synthesizer
SPre-
driverDriver Klystron
Cavity
Attn
Coupler
NLP5504
way
DemodMod
NLP550
Hol/(1-Hol)
CW @ 400.8 MHz
I
Q
S
Beam loading test
NetworkAnalyzer
-20 dB
-10 dB
Iref
Qref
Dec. 15, 2005 SM18 tests Aug-Sept 05 14
Overdriving the Modulator
• AD8345 wants IF levels max +-0.3 V offset by 0.7 V DC
• Driven by AD8138 single-ended to differential• Adding clamping diodes HSMS-2820 (RF
Schottky diodes) on input of AD8138 cured problem
Dec. 15, 2005 SM18 tests Aug-Sept 05 15
Closed Loop. LL output noise
• Pre-driver -20 dB out TP• Noise varies linearly with Low Level gain -> it is a
Measurement noise: Analog Demodulator noise• High HF gain due to Phase Advance• Probably no effect on beam… but…
All spectra with phase advance, Q20000, 130 kW, 1MVaccO.L. gain 20 O.L. gain 10
O.L. gain 5
Dec. 15, 2005 SM18 tests Aug-Sept 05 16
Phase Advance and LL output noise
• Pre-driver -20 dB out TP• Phase Advance network boosts noise by 5 linear at +-1 MHz offset• Probably no effect on beam… but…
With phase advance No phase advance
Both spectra loop closed, O.L. gain 20 linear, Q20000, 130 kW, 1MVacc
Dec. 15, 2005 SM18 tests Aug-Sept 05 17
Closed Loop:What we expected…
• Mathematica using measurement of real klystron• Q=20000, real klystron, loop delay 450 ns (excluding klystron)• Low Level: Notch, no Phase Advance. Gain set for 10 dB margin
2-sided -3 dB BW = 600 kHz
-2106
-1106
1106
2106
Freq .Hz
-25
-20
-15
-10
-5
Gain
-210 6 -110 6 110 6 210 6Freq .Hz
-150
-100
-50
50
100
150
Phase
linear phase response in <1 MHz band
Dec. 15, 2005 SM18 tests Aug-Sept 05 18
C.L. vs. LL gain
• No Phase Advance Network• Q=20000, 1MVacc, 135 kW• O.L. gain = 20 linear for 10 dB gain margin
O.L. gain 20 O.L. gain 28
Group delay compensated
Dec. 15, 2005 SM18 tests Aug-Sept 05 19
C.L. vs. CW power
• No Phase Advance Network• Q=20000• O.L. gain = 20 linear for 10 dB gain margin
50 kW CW (0.62 MVacc)
135 kW CW (1 MVacc)
Dec. 15, 2005 SM18 tests Aug-Sept 05 20
C.L. vs. Q
• No Phase Advance Network
• O.L. gain = proportional to Q (keep 10 dB gain margin)
• Low Level gain = proportional to Sqrt[Q]
• Significant change in phase distortion
Q200001 MVacc (135 kW)
Q1800002 MVacc (60 kW)
Dec. 15, 2005 SM18 tests Aug-Sept 05 21
C.L. with/without Phase Advance
• Q=20000, O.L. gain set to keep 10 dB gain margin, 135 kW CW -> 1 MVacc• Phase Advance
– increases gain outside 3 dB BW
– reduces non-linear phase distortion
No Phase Advance With Phase Advance
Dec. 15, 2005 SM18 tests Aug-Sept 05 22
Impedance ReductionSynthesizer
SPre-
driverDriver Klystron
Cavity
Attn
Coupler
NLP5504
way
DemodMod
NLP550
1/(1-Hol)
CW @ 400.8 MHz
I
Q
S
Beam loading test
NetworkAnalyzer
-20 dB
-10 dB
Iref
Qref
• First calibrate with Feedback Off• Then measure response
Dec. 15, 2005 SM18 tests Aug-Sept 05 23
Impedance Reduction:What we expected…
• Mathematica using measurement of real klystron• Q=20000, real klystron, loop delay 450 ns (excluding klystron)• Low Level: Notch, no Phase Advance. Gain set to 13 (linear) for 10
dB margin
-110 6 -500000 500000 110 6Freq .Hz
-40
-30
-20
-10
ZeffRdB Reduction by 13 linear at the tune
Reduction in a 300 kHz band (2-sided)
Increase
Dec. 15, 2005 SM18 tests Aug-Sept 05 24
Impedance Reduction vs. LL gain
• Q=60000, zero CW. No Phase Advance • 10 dB margin is the “best”• Modulus of Z is reduced in a +- 150 kHz band
Gain set to 10 dB margin
Gain set to 7 dB margin
Dec. 15, 2005 SM18 tests Aug-Sept 05 25
Impedance Reduction vs. CW power
• Q=60000. No Phase Advance• Marginal effect of CW power.
Zero CW
2 MVacc (190 kW)
Dec. 15, 2005 SM18 tests Aug-Sept 05 26
Klystron ripples reduction
• Using vector voltmeter 8508A Analog Out on high Z (1 kHz BW)• Q=20000, 1 MVacc, 130 kW, with phase advance, O.L. gain = 20 linear• Data in..\..\Modules\RFfeedback\Tests\SM18\Week35\PhaseNoise.xls
Phase noise Vacc: 10 mV/dg
-0.003
-0.0025
-0.002
-0.0015
-0.001
-0.0005
0
0.0005
0.001
-2.50E-02
-2.00E-02
-1.50E-02
-1.00E-02
-5.00E-03
0.00E+00
5.00E-03
1.00E-02
1.50E-02
2.00E-02
2.50E-02
time (s)vo
ltag
e (V
)
Series1
Cavity field phase ripples at 50 Hz and 600 HzFdbk OFF. ~3 degrees pkpkFdbk ON. ~ 0.2 degree pkpk Enlargment Fdbk ON. ~0.2 degrees pkpk
Phase noise Vacc: 10 mV/dg
-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
-2.50E-02
-2.00E-02
-1.50E-02
-1.00E-02
-5.00E-03
0.00E+00
5.00E-03
1.00E-02
1.50E-02
2.00E-02
2.50E-02
time (s)
volt
age
(V)
FBoff
FBon
Dec. 15, 2005 SM18 tests Aug-Sept 05 27
Klystron ripples reduction
• Using HP423A X-tal detector plus 100 kHx LPF on high Z Analog Out on high Z • Q=20000, 1 MVacc, 130 kW, with phase advance, O.L. gain = 20 linear• Data in..\..\Modules\RFfeedback\Tests\SM18\Week35\AmplNoise.xls
Cavity field amplitude ripples at 50 Hz and 600 HzFdbk OFF. ~25 kVacc pkpk Fdbk ON. ~15 kVacc pkpk
Amplitude noise Vacc: 10 kVacc / mV
-0.0015
-0.001
-0.0005
0
0.0005
0.001
0.0015
-6.00E-02 -4.00E-02 -2.00E-02 0.00E+00 2.00E-02 4.00E-02 6.00E-02
time (s)
volt
age
(V)
Series1
Amplitude noise Vacc: 10 kVacc/mV
-0.0015
-0.001
-0.0005
0
0.0005
0.001
0.0015
-6.00E-02 -4.00E-02 -2.00E-02 0.00E+00 2.00E-02 4.00E-02 6.00E-02
Time (s)
Vo
ltag
e (V
)
Series1
Left with 50 Hz measurement noise ?
Dec. 15, 2005 SM18 tests Aug-Sept 05 28
Klystron ripples reduction
-3
-2
-1
0
1
2
3
-3.00E-02
-2.00E-02
-1.00E-02
0.00E+00
1.00E-02
2.00E-02
3.00E-02
Time (s)
Ph
as
e (
de
gre
e)
FDBK OPEN
gain 3
gain 10
gain 40
• Using ZLW-1W mixer plus SLP-100 onto 50 ohm• Q=60000, 2 MVacc, 170 kW, no phase advance• Data in..\..\Modules\RFfeedback\Tests\SM18\Week37\PhaseNoise.xls
Cavity field phase ripples at 50 Hz and 600 Hz
Gain Phase NoiseO.L. 4 degrees pkpk
3 1.4 dg pkpk10 0.4 dg pkpk20 0.2 dg pkpk40 0.2 dg pkpk
Dec. 15, 2005 SM18 tests Aug-Sept 05 29
Cavity field noise
• Using Independent Analog I/Q demodulator plus 20 MHz LPF (1 mV-> 6.6 kVacc)• Q=60000, 2 MVacc, no phase advance, O.L. gain = 40• Data in..\..\Modules\RFfeedback\Tests\SM18\Week39\IndepNoiseMeas.xls
AC coupled Vcav I and Q vs time
Vcav Q DC 20 MHz BW
0
0.05
0.1
0.15
0.2
0.25
-0.25 -0.2 -0.15 -0.1 -0.05 0
Vcav Q DC 20 MHz BW
Vcav on I/Q plot
Noise ~ 13 kVacc pkpk around 2 MVacc (0.4 degrees pkpk, 0.65 % pkpk)
-0.003
-0.0025
-0.002
-0.0015
-0.001
-0.0005
0
0.0005
0.001
0.0015
-1.50E-02
-1.00E-02
-5.00E-03
0.00E+00
5.00E-03
1.00E-02
1.50E-02
Vcav I AC
Vcav Q AC
Dec. 15, 2005 SM18 tests Aug-Sept 05 30
Beam Loading Test50 kV step in quadrature with 1 MVacc
• 400 MHz rectangular burst on Beam Loading Test input. (see page 22)• Measure Voltage error signal, that is RF feedback I/Q inputs• After transient, beam loading perturbation reduced by O.L. gain• Q=20000, 1 MVacc in I, 130 kW, with phase advance, O.L. gain = 20• Data in..\..\Modules\RFfeedback\Tests\SM18\Week35\BeamLoading.xls
50 kV step in 1 s (+ 600 ns delay)
1 s
Beam loading transient
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
-5.00E-06 0.00E+00 5.00E-06 1.00E-05 1.50E-05
time (s)
Vca
v
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
Det
Pw
r Vcav I
Vcav Q
Ic,fwd Det
Beam loading transient
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
-2.00E-06
-1.00E-06
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
time (s)
Vca
v
Vcav Q
1 s falltime
600 ns delay
Dec. 15, 2005 SM18 tests Aug-Sept 05 31
Beam Loading Test50 kV step in phase with 1 MVacc
• Very asymmetric• After transient, beam loading perturbation reduced by O.L. gain• Q=20000, 1 MVacc in I, 130 kW, with phase advance, O.L. gain = 20• Data in..\..\Modules\RFfeedback\Tests\SM18\Week35\BeamLoading.xls
50 kV step in 1 s (+ 600 ns delay)
Transient beam loading
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
-1.50E-05 -1.00E-05 -5.00E-06 0.00E+00 5.00E-06
Time (s)
V e
rro
r
-0.25
-0.2
-0.15
-0.1
-0.05
0
Det
Pw
r Vcav I
Vcav Q
Ic,fwd Det
Vcav I
-0.165
-0.16
-0.155
-0.15
-0.145
-0.14
-0.135
-1.50E-05 -1.00E-05 -5.00E-06 0.00E+00 5.00E-06
V e
rro
r
Vcav I
5 s falltime
1 s risetime
Dec. 15, 2005 SM18 tests Aug-Sept 05 32
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
-2.00E-04
-1.50E-04
-1.00E-04
-5.00E-05
0.00E+00
5.00E-05 1.00E-04
Vcav I
VcavQ
Step Response70 kV step in quadrature with 1 MVacc
• Q=20000, 1 MVacc in I, 130 kW, no phase advance, O.L. gain = 20• Data in..\..\Modules\RFfeedback\Tests\SM18\Week39\RefStepVcav.xls
VcavQ
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
0.008
-8.00E-06 -6.00E-06 -4.00E-06 -2.00E-06 0.00E+00 2.00E-06
VcavQ
70 kV step in 1 s -> limit saturation (with 1 MVacc CW)
1 s risetime
Dec. 15, 2005 SM18 tests Aug-Sept 05 33
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
-2.00E-04
-1.50E-04
-1.00E-04
-5.00E-05
0.00E+00
5.00E-05 1.00E-04
VcavI
VcavQ
Step ResponseVcavI
-0.148
-0.146
-0.144
-0.142
-0.14
-0.138
-0.136
-0.134
-8.00E-06 -6.00E-06 -4.00E-06 -2.00E-06 0.00E+00 2.00E-06
VcavI
70 kV step in phase with 1 MVacc
• Q=20000, 1 MVacc in I, 130 kW, no phase advance, O.L. gain = 20• Data in..\..\Modules\RFfeedback\Tests\SM18\Week39\RefStepVcav.xls
saturation when step adds to 1MVacc CW
1 s risetime
VcavI
-0.15
-0.148
-0.146
-0.144
-0.142
-0.14
-0.138
-0.136
-0.134
-0.132
-1.05E-04 -1.03E-04 -1.01E-04 -9.90E-05 -9.70E-05 -9.50E-05
VcavI
5 s falltime
Dec. 15, 2005 SM18 tests Aug-Sept 05 34
-0.2
-0.19
-0.18
-0.17
-0.16
-0.15
-0.14
-0.13
-0.12
-0.11
-0.1
-1.50E-04 -1.00E-04 -5.00E-05 0.00E+00 5.00E-05
0
0.05
0.1
0.15
0.2
0.25
0.3
VcavI
"-Ic,fwd det"
Step Response70 kV step in phase with 1 MVacc
• Q=20000, 1 MVacc in I, 130 kW, no phase advance, O.L. gain = 20• Data in..\..\Modules\RFfeedback\Tests\SM18\Week39\RefStepVcav.xls
saturation at 280 kW when step adds to 1MVacc CW
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
-8.00E-06 -6.00E-06 -4.00E-06 -2.00E-06 0.00E+00 2.00E-06
-0.148
-0.146
-0.144
-0.142
-0.14
-0.138
-0.136
-0.134
-0.132
"-Ic,fwd det"
VcavI
0
0.05
0.1
0.15
0.2
0.25
0.3
-1.05E-04 -1.03E-04 -1.01E-04 -9.90E-05 -9.70E-05 -9.50E-05
-0.15
-0.148
-0.146
-0.144
-0.142
-0.14
-0.138
-0.136
-0.134
-0.132
"-Ic,fwd det"
VcavI
Dec. 15, 2005 SM18 tests Aug-Sept 05 35
Huge Step Response+- 0.5 MV MV step in quadrature with 1 MVacc
• Q=20000, 1 MVacc in I, 130 kW, no phase advance, O.L. gain = 20• During heavily saturated transients, measurements from input coupler do not make sense!!!• Data in..\..\Modules\RFfeedback\Tests\SM18\Week39\RefStepVcav.xls
1 MV step in 10 s -> severe saturation (with 1 MVacc CW)
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
-2.00E-04 -1.50E-04 -1.00E-04 -5.00E-05 0.00E+00 5.00E-05
Vca
v
0
0.05
0.1
0.15
0.2
0.25
0.3
Det
Pw
r Vcav I
Vcav Q
-Ig,det
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
-1.50E-04 -1.00E-04 -5.00E-05 0.00E+00 5.00E-05
Ic, fwd det
Ic,rev det
Dec. 15, 2005 SM18 tests Aug-Sept 05 36
Huge Step Response1 MV step in phase with 1 MVacc (from 0.5 MV to 1.5 MV)
• Q=20000, I from 0.5 MV to 1.5 MV, no phase advance, O.L. gain = 20• During heavily saturated transients, measurements from input coupler do not make sense• Data in..\..\Modules\RFfeedback\Tests\SM18\Week39\RefStepVcav.xls
From 0.5 MV to 1.5 MV in 25 sFrom 1.5 MV to 0.5 MV in <10 s
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
-1.50E-04 -1.00E-04 -5.00E-05 0.00E+00 5.00E-05
Vca
v
-0.5
-0.45
-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0D
et P
wr VcavI
Vcav Q
Ic,fwd det
Dec. 15, 2005 SM18 tests Aug-Sept 05 37
Why we have been lucky…K020 - saturation curve
0
50
100
150
200
250
300
350
0 20 40 60 80 100 120 140 160
drive power (W)
forw
ard
po
we
r (k
W)
• During SM18 tests, the klystron could never go above saturation peak…
Typical klystron curveKlystron used in SM18 tests
Courtesy of Olivier Brunner
Dec. 15, 2005 SM18 tests Aug-Sept 05 38
Overdriving the klystron (ramp)
Courtesy of Janne Holma
Klystron input clamped Klystron over-driven
Dec. 15, 2005 SM18 tests Aug-Sept 05 39
Overdriving the klystron (steps)
Courtesy of Janne Holma
Klystron input clamped Klystron over-driven
Dec. 15, 2005 SM18 tests Aug-Sept 05 40
Conclusions (good)• If the LL gain scales with sqrt[Q] we have
– Closed loop BW 550 kHz, independent of Q and CW power -> Apparent Q < 1000
– Apparent cavity impedance ~45 kohm, independent of Q– Reduction of apparent cavity impedance modulus in a 300
kHz band, independent of Q• Phase advance is not worth it…rid of it in eda586.v3• 1% ripple in HV causes 8.4 degrees phase shift @400.8 MHz.
That is acceptable for stability. (At least in the absence of 1-T fdbk).
• Close Loop phase characteristic OK for 1-T feedback in a 1 MHz band (2-sided)
• Reduction of klystron phase ripples by O.L. gain (as expected)
Dec. 15, 2005 SM18 tests Aug-Sept 05 41
Conclusions (good)• With 1 MVacc, Q=20000, step 70 kV in quadrature in 1 s (OK for
long damper at injection?)• No problem when klystron saturates on transients• Rare trips: Main Coupler Vacuum (always cured by additional
conditioning) and Klystron Body Overheat when running in saturation for long time.
• RF feedback and Tuner Loop fully compatible
Dec. 15, 2005 SM18 tests Aug-Sept 05 42
Conclusions (bad)
• Non-linear phase distortion changes with Q• Without phase advance the phase distortion is bigger• Close Loop phase characteristic NOT OK for 1-T feedback in a >1
MHz band (2-sided). Foresee Phase Equalizer in 1-T feedback?• Reduction of klystron amplitude ripple by less than loop gain
(measurement noise at 50 Hz?)• Measurements from the cavity input coupler do not make sense
during heavily saturated transients• What if the klystron is allowed to go over saturation peak?
Dec. 15, 2005 SM18 tests Aug-Sept 05 43
References
[1] Control of cavities with high beam loading, D. Boussard, IEEE Tr. On N.S. Vol NS 32 No.5, p. 1852, 1985
[2] Low Level RF Systems for Synchrotrons, Part 2, P. Baudrenghien, CERN SL-Note-2001-028 HRF
[3] Microwave Measurements, Edward L. Ginzton, McGraw-Hill Book Company Inc., New-York, 1957, pp 404-405