MAC Mtg. DESY, Nov. 2005 Stefan Simrock DESY
Achieving 0.01 deg. Phase Stability
• Short term (within in 1 ms pulse) • medium term (pulse to pulse, several seconds) • long term ( thermal time scale, minutes to hours)
• Sources of cavity field perturbations - Lorentz force detuning - Microphonics - Beam loading - other (electronic noise in field detectors, phase noise and drifts
of phase reference, ripple of klystron power supply, etc.)
PAC 2005, Knoxville Stefan Simrock DESY
RF Regulation TESLA Cavity (Simulation)
Gradient
Detuning
Microphonics
Beam Current
Phase
DetuningLorentz Force
Microphonics
Lorentz Force
Gradient Phase
MAC Mtg. DESY, Nov. 2005 Stefan Simrock DESY
Measured Stability in ACC 2+3
0,2%
0,2%
1 deg.
0.1 deg.
LLRF Regulation Stefan Simrock DESY
Field Regulation at VUV-FEL
ACC1
ACC23
ACC45
LLRF Regulation Stefan Simrock DESY
Field Regulation at the VUV-FEL
ACC1 ACC23
ACC45
LLRF Regulation Stefan Simrock DESY
Field Regulation at VUV-FEL
ERL Workshop 2005 Stefan Simrock DESY
Drift ACC1 (cryomodule before BC) at TTF
1e-3
30 min
1ps
30 min
energy jitter
time jitter
10/31/2005 Holger Schlarb, DESY
Phase stability with pyro-detector
But! This is the phase stability betweenthe beam arrival into the acceleration modulerelative to the RF phase!!!=> Major contribution is likely from laser
MAC Mtg. DESY, Nov. 2005 Stefan Simrock DESY
Error Map
10-1
10-2
10-4
10-3
10-0
10-010-110-210-3
radσA/A LFD=+-f12
mic=0.05*f12
mic=0.05*f12 (on crest)
σI/I=5% (slow)
GoalσI/I=5% (fast)
PS klys.
VS-Calibrationmic. 10 Hz
normalized perturbation
presentperformance
residual ampl.and phase error
MAC Mtg. DESY, Nov. 2005 Stefan Simrock DESY
Improving Cavity Field Regulation
Gain
Error
unstable
lower latency
less noise
70
1*10-4
3*10-4
300
ERL 2005 Stefan Simrock DESY
Control Choices (1)
• Self-excited Loop (SEL) vs Generator Driven System (GDR)
• Vector-sum (VS) vs individual cavity control
• Analog vs Digital Control Design
• Amplitude and Phase (A&P) vs In-phase and Quadrature (I/Q) detector and controller
ERL 2005 Stefan Simrock DESY
Control Choices (2)
KlystronAmplitude Controller
AΦ
PhaseControllerM.O.
Gradient Set Point Cavity
Gradient Detector
Φ
~~
PhaseSetpoint
PhaseDetector
KlystronAmplitude Controller
AΦ
PhaseController
Φ
Gradient Set Point
Limiter
Φ Loop Phase Gradient Detector
CavityM.O.~~
PhaseSetpoint
PhaseDetector
Generator Driven Resonator
Self Excited Loop
ERL 2005 Stefan Simrock DESY
ERL 2005 Stefan Simrock DESY
ERL 2005 Stefan Simrock DESY
Digital I/Q Detection
RF local oscillator (LO)
IF1300 MHz 1300.25 MHz
250 kHz
mixeramplitude
time[µs]
x0
x1
x2
x3
U cos(ωt+∆φ)
1 2 3 40
-
• downconversion of cavity fieldto IF frequency at 250 kHz
• complete phase and amplitudeinformation of the accelerat-ing field is preserved.
• sample IF signal at 1MHz rate
• subsequent samples describereal and imaginary component ofthe cavity field.
ERL 2005 Stefan Simrock DESY
Digital Control at the TTF
DAC
DAC
ReIm
Cavity 32......8x
Cavity 25
klystronvector
modulator masteroscillator
1.3 GHz Cavity 8......8x
Cavity 1
cryomodule 4
...cryomodule 1
. . . .
LO 1.3 GHz + 250 kHz
250 kHz
ADC
f = 1 MHzs
. . . . ...
vector-sumΣ( )ab
a -b
1 8( )ab
a -b
25( )ab
a -b
32( )ab
a -b
DSPsystemsetpoint
tablegaintable
feed
tableforward
++digital
low passfilter
ImRe ImRe ImRe
clock
LO
ADC
LO
ADC
LO
ADC
ImRe
power transmission line
1.3GHzfield probe
Frank Ludwig / 03.12.04
Noise characterization of the LLRF System (TTF2)
n RF digital feedback system (TTF2) :
MHzf 10≈∆Bandwidth for transforming 250kHz squared pulses :
Required regulation bandwidth only :
MHzf 1≈∆
n +I,-I,+Q,-Q detection scheme :
Rotation of the LO-signal in four 90o steps
Re
Im
Phase modulation
(+I,+Q)
(+I,-Q)(-I,-Q)
(-I,+Q)
Frank Ludwig / 03.12.04
n Stability requirements on phase and amplitude of the cavity field vector :
Amplitude stability : 410−<AAd
Phase stability : °< 01.0df
VµUd XFEL 100<(normalized to A=1V)
fSdffSUd Uf
U ∆∆
≈= ∫ )(
rms-voltage noise :
XFELTTF UdmVUd ×=≈ 100.12
n Noise measurement at input of an ADC :
⇓
ACC5, ProbeDCW, AN-36
time100ns/div
voltage2mV/div
Reduce the measuring bandwidth
Low-noise design
Averaging, switched low-pass!
Correlation methods
VµUdUdUdUd externMOIQDWC 100...2222 <++++
Superposition of all noise contributions :
+
-++
and linearity
df
Ad
A
Noise characterization of the LLRF System (TTF2)
ERL 2005 Stefan Simrock DESY
Requirement for CEBAF (JLAB)
ERL Workshop 2005 Stefan Simrock DESY
Performance Measured at JLAB
ERL Workshop 2005 Stefan Simrock DESY
Performance Measure at JLAB
ERL Workshop 2005 Stefan Simrock DESY
Performance at Rossendorf
ERL Workshop 2005 Stefan Simrock DESY
Stability Measured for J-PARC
+-0.08%
+-0.04 deg.
S. Michizono
• AD8347 IQ detectorThe same circuits are also used to detect the incident waveand reflected wave vectors usually described as forwardand reflected power. Examples of the excellent perfor-mance of these detectors are shown in Figure 3. The
ACTUATORS FOR FIELD CONTROLSimilar circuits as used for field detection are also used forthe control of the incident wave. Since analog multiplierscan be also used for control of the amplitude of an rf wavethey can be used in upconverters and for amplitude con-trol. The digital downconversion scheme can also be usedin an upconversion mode where the frequency f1 (discrete
samples) written to the DAC which is clocked at f2 gener-ates a sideband (among many others) of f1+f2 which con-tains the control vector and is filtered and upconverted tothe operating frequency of the cavity. Examples for vectormodulators are:
• RF 2480
• AD8346
• HMC 495 and 497The linearity of a vector modulator is shown in Figure 4.
DIGITAL RF CONTROLThe key elements of a digital feedback system are theADCs for the measurement of the detector signals for thecavity field and forward and reflected power, the DACs
cav 1 cav n
rf switch klystronisolator
Ainc
Aref
ADC
ADC
ADC
DAC
vectormodulator
DAC
ADC
FPGA&
DSP
downconverter
PZTFT
rf power transmission
beam pickup
ADC
waveguidetuner
DAC
timing
clockpiezo tuner drive
rep.rateclock
masteroscillator
HV
digital feedback
local server (VME) main frame (client)network
isolator
Figure 2: Typical configuration of an RF control system using digital feedback control
a) b)
Figure 3: a) Temperature stability of the amplitudedetector AD861 and b) linearity of IQ detector AD8347
Figure 4: Linearity of the vector modulator RF 2480