RF Synchronization Activityat SPARC

A. Gallo

and

D. Alesini, M. Bellaveglia, R. Boni, G. Di Pirro, A. Drago, A.GhigoP. Baldini, L. Cacciotti, M. Scampati, A. Sprecacenere, S. Quaglia

EUROFEL DS3 Meeting, CEA-Saclay May 17th 2005

SPARC PHASE STABILITY SPECIFICATIONS:

• SPARC phase I:

± 3° between the Laser pulse and the Linac RF

(RF gun mainly)

• SPARC phase II:

± 0.5° between the Laser pulse and the Linac RF

(RF gun and RF compressor mainly)

SPARC RF DISTRIBUTION: SCHEMATIC LAYOUT

• All the Linac RF signals will be phase-monitored respect to the RF ref. Line.

• The slow phase phase variations will be sampled at 10 Hz (the Linac rep. rate) and corrected acting on the phase shifters (included those placed in the high power waveguide branches).

• The fast phase variations (i.e. the jitter with spectral components beyond 10 Hz) can be hardly corrected. The possibility of implementing intra-pulse, fast phase lock to correct the fast phase jitter introduced by the RF stations (klystrons + drivers) is under study.

Phase Lock to the RF Reference Line

1 I&Q Demodulator 0.5 k€½ PCI Sampling Board 0.6 k€1 RF Isolator 0.2 k€RF Attenuators 0.1 k€

1.4 k€

1/4 PCI Samp. Board 0.3 k€1 Peak Detector 0.2 k€1 Directional Coup. 0.2 k€RF Attenuators 0.1 k€

0.8 k€

Total cost:

2.2 k€/channel (High Quality)1.4 k€/channel (Standard)

RF Demodulation Channel based on I&Q Detectorpassive, low cost, 4 quadrants, amplitude independent

RF Isolator

CW RF

PulsedRF

PULSAR I&Q DEMODULATORMODEL ID I4-0428 (custom)

PULSAR I&Q DEMODULATORMODEL ID I4-0428 : CALIBRATION

PULSAR ID I4-0428 Long Term Acquisition

PULSAR ID I4-0428 +ADLINK 9810 20 MS/sPCI Sampling Board

Phase Resolution

LASER to RF Line Syncronization

• The phase of the Laser pulse respect to the Linac RF reference line will be continuously monitored and the “slow drifts” (i.e. the phase noise in a frequency band limited to ½ of the Linac rep. rate) will be compensated (shifting the phase of the RF ref. Line seems the simplest way to do it).

• The “fast phase jitter” (i .e. the noise in a band larger than ½ of the rep. rate) of the Laser pulse can’t be compensated and must be kept inside the acceptable limits by specifications (1°nrequested to the manufacturer).

Monitoring the synchronization of the bunch from the Gun and of the laser pulse

HOMDYN Time-of-Flight Simulations

TM010 – 2856 MHzR/Q = 28.5 Q0 = 15000 (Al)

Qext = 30000

Vp (@ 1 nC) = 4 V= 0.5 sftun 10 kHz

TE111 – 2985 MHzR/Q = 0.5 Q0 = 17000 (Al)

Bunch Monitor Cavity

Bench measurements of short pulse synchronization

-30.0n -20.0n -10.0n 0.0 10.0n 20.0n 30.0n

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de S

igna

l [V

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ignal [V]

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Q [V

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plitu

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se [d

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X Axis Title

Results of the bench measurements of short pulse synchronization

KLYSTRON PHASE LOCK

FAST PHASE LOCK FEEDBACK SYSTEMSketch of the Experimental Set-up

“Noisy” RF Station

PULSAR ST-G9-411 Phase Shifter

CALIBRATION

FREQUENCY RESPONSE

Fast Phase Lock Feedback System:Open Loop Gain(amplitude and phase)

Lock Amp:Circuit sketch

10°pp

Open/Closed Loop Phase Pulses

256 frames with 10°pp , 10 kHz phase noise

Single shot phase pulses

DANE LINAC KLYSTRON MEASUREMENTS

The phase jitter at the output of one of the DANE TH2128C Linac klystrons has been measured to figure out the amount of expected noise in the SPARC case and to gain some experience in this subject.

PHASE STABILITY MEASUREMENTS

DAFNE LINAC – STATION BAugust 2003

mixer sensitivity = 5.6 mV/Deg

Long Term

(90 min) phase

variation:

± 2.5°

Short Term

(16 shots) phase

variation:

± 1°

KLYSTRON PHASE NOISE MEASUREMENTS CONCLUSIONS

• The measured phase jitter at the output of the Linac station-B klystron is about ± 2.5° in long term and and ± 1° in short term.

• The main contribution seems to come from the driver amplifiers (planar triode technology). In the SPARC case the driver amplifiers will be of a different and better performing technology (pure class A, solid state) with tight phase jitter specification (1° rms). The expected phase jitter values of the SPARC RF stations are consequently lower.

BENCH MEASUREMENTS OF A FAST INTRA-PULSE PHASE-LOCK CONTROL

An intra-pulse phase-lock system is under study to actively correct the fast phase jitter coming from the RF stations. Since the RF pulse is about 4.5 s long, the rise time of such a system should be of the order of 1 s, corresponding to a bandwidth of about 1 MHz. Consequently a fast phase modulator is needed, while the overall delay of the connections (including the group delay of the RF station) should be limited to 100 ns. The speed of the OpAmps manipulating the signal has also to be adequate.