achieving 0.01 deg. phase stability · 2005-11-21 · guide tuner dac timing clock piezo tuner...

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


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


Field Regulation at the VUV-FEL

ACC1 ACC23

ACC45


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


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


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


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


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.


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)


Requirement for CEBAF (JLAB)


Performance Measured at JLAB


Performance Measure at JLAB


Performance at Rossendorf


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

achieving 0.01 deg. phase stability · 2005-11-21 · guide tuner dac timing clock piezo tuner...

Documents