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Drive beam RF: Klystrons, RF structures, efficiency, modulators, stability of RF systems Erk Jensen, BE-RF with major contributions from: Alexandra Andersson , Alexey Dubrovskiy , Gerard McMonagle , Rolf Wegner. 5th CLIC Advisory Committee (CLIC-ACE) 2-Feb-2010. Outline.

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Drive beam RF: Klystrons, RF structures, efficiency, modulators, stability of RF systemsErk Jensen, BE-RFwith major contributions from: Alexandra Andersson, AlexeyDubrovskiy, Gerard McMonagle, Rolf Wegner

5th CLIC Advisory Committee (CLIC-ACE) 2-Feb-2010

5th CLIC Advisory Committee (CLIC-ACE)

outline
Outline

Power sources:

Klystrons

Modulators

Efficiency (2nd look at IOT’s)

Accelerating structures

Stability/Stabilisation

Measurements at CTF3

Feed-forward

Phase monitor

Globally distributed reference

5th CLIC Advisory Committee (CLIC-ACE)

clic drive beam rf system issues
CLIC Drive Beam RF System – issues:
  • Reminder of the main issues for the Drive Beam RF system:
    • Very large total power (≈23 GW peak, 170 MW average)

What power source? Optimum size of individual power source?

This was addressed in the last ACE.

    • Phase stability (jitter <50 fs)
    • Overall efficiency!
    • Cost!
  • Summary from last ACE: Trends:
    • MBK 10 MW ... 20 MW
      • 10 MW available today (X-FEL, ILC)
      • “smaller” klystrons make reliability and serviceability easier

... remained to be done:

    • Make group delay of acc. structure = length of delay loop
    • Redesign structures to optimize for beam dynamics requirements

5th CLIC Advisory Committee (CLIC-ACE)

klystrons
Klystrons

... not much new, but converging for CDR:

5th CLIC Advisory Committee (CLIC-ACE)

reminder from last year s ace
Reminder: from last year’s ACE

5th CLIC Advisory Committee (CLIC-ACE)

what s new about the klystrons
What’s new about the klystrons?

Questionnaire prepared and sent to klystron manufacturers (CPI, Thales, L3, E2V, Toshiba, Istok, Chinese industry) asking about the feasibility of a 20 MW klystron (4 different scenarios)

So far, only CPI replied:

  • Reasonable to start from ILC/X-FEL klystrons
  • 20 MW, 150 μs, 50 Hz, 65 % ... feasible (≈ 8 beams),
  • design & proto estimate: 2 M$ and 2 years,
  • series cost estimate 1.1 M$ (55 k$/MW),
  • delivery schedule: month 12, 14, 16, ... ARO
  • They tend towards slightly higher voltage (150 kV?)

This sounds reasonable for the conceptual design.

5th CLIC Advisory Committee (CLIC-ACE)

modulators
Modulators

... not much new

5th CLIC Advisory Committee (CLIC-ACE)

reminder from last year s ace1
Reminder: from last year’s ACE

5th CLIC Advisory Committee (CLIC-ACE)

scandinova s k2 system for psi 351kv 416a
ScandiNova’s K2-SYSTEM for PSI; 351kV / 416A !

Achieved pulse to pulse stability: ± 4 10-5

5th CLIC Advisory Committee (CLIC-ACE)

efficiency
Efficiency

... not for CDR, but for later other possibilities should be considered:

5th CLIC Advisory Committee (CLIC-ACE)

iot s a second look
IOT’s – a second look:

According to CPI, IOT’s would be a natural choice for highest efficiencies; CPI’s claims:

  • IOT VHP-8330 reached 930 kW @ 700 MHz.
  • up to 1.5 MW at 1 GHz should be possible,
  • > 80 % efficiency at this power level are possible,
  • IOT’s would be cheaper/MW (!)
  • typical DC voltage range: 35 kV,
  • no modulator necessary → pulses via RF drive!

ηKlystron ηModulator ≈ 60 % would become ηIOT ηpower distribution ≈ 70 %; this would reduce wall plug power quite significantly!

  • no saturation → power regulation with feedback possible.
  • gain ≈ 22 dB (needs 10 kW drive for 1.5 MW)

Disadvantages: less gain, no operational experience, more complex power distribution!

5th CLIC Advisory Committee (CLIC-ACE)

multi beam hom iot s
Multi-beam HOM IOT’s

left: existing VHP-8330

right: planned VKP-8330B

5th CLIC Advisory Committee (CLIC-ACE)

conclusion power sources
Conclusion power sources
  • For the CDR, MBK’s derived from ILC/X-FEL with 15 to 20 MW are realistic.
  • Some of the features of IOT’s make them appear interesting – a more detailed analysis is necessary.
  • At the same time we’re trying to analyze (fellow to start in September 2010) higher η klystrons.

5th CLIC Advisory Committee (CLIC-ACE)

accelerating structures
Accelerating Structures

5th CLIC Advisory Committee (CLIC-ACE)

input power for full beam loading for different cell numbers
Input power for full beam loading for different cell numbers

New interesting region

former “nominal”

≈ 28.3 kW · ncell2

5th CLIC Advisory Committee (CLIC-ACE)

redesign of accelerating structure

Pb

Pb

RBP

Pin

Pout

Redesign of accelerating structure

Rolf Wegner’s work:

SICA -- constant aperture

gapn

Ncells

E0T

Vacc

η= ΔPb/Pin

tfill

mode spectrum

5th CLIC Advisory Committee (CLIC-ACE)

new optimum accelerating structure
New optimum accelerating structure

5th CLIC Advisory Committee (CLIC-ACE)

reminder why 245 ns group delay
Reminder: Why 245 ns group delay?

5th CLIC Advisory Committee (CLIC-ACE)

new structure design r wegner
New structure design (R. Wegner)

Scaled from 3 GHz:

New design:

Outer Ø: 522 mm

Outer Ø: < 300 mm

New idea (A. Grudiev): dampers inside the slots!

This new approach has been verified:

acc. mode Q0= 2.2 ∙104, Qext= 3.7∙107

5th CLIC Advisory Committee (CLIC-ACE)

verification of efficient damping
Verification of efficient damping

5th CLIC Advisory Committee (CLIC-ACE)

conclusion accelerating structures
Conclusion accelerating structures:
  • SICA structures were successfully redesigned and re-optimized for 1 GHz (thanks to Rolf Wegner!).
  • Design includes:
    • Optimum aperture – to be finalized with BD simulations
    • Optimum RF efficiency
    • Optimum group delay (≈ 245 ns)
    • New idea for dipole mode damping verified
    • Moderate outer Ø < 300 mm
    • The coupler design is ongoing.

5th CLIC Advisory Committee (CLIC-ACE)

phase stabilisation
Phase stabilisation

5th CLIC Advisory Committee (CLIC-ACE)

phase stability measurement at ctf3
Phase stability measurement at CTF3

AlexeyDubrovskiy analyzed phase- and amplitude stability of 4 CTF3 klystrons. Example given here: MKS03

  • Result:
  • W/o special measures, the pulse-to-pulse phase jitter is 0.1 ... 0.15°.
  • This is “only” a factor 5 ... 8 away from our specification of 0.02°!
  • Reminder: with feed-forward (see below), we’re probably about OK!
  • This is very encouraging!

phase in deg.

sample #

time

5th CLIC Advisory Committee (CLIC-ACE)

phase measurement and correction scheme
Phase measurement and correction scheme

A. Andersson: CLIC Workshop 14-Oct-09

5th CLIC Advisory Committee (CLIC-ACE)

the phase monitor
The phase monitor
  • Requirement: low impedance, 20 fs resolution
  • Status: Task 9.5 in the Work-package NCLinac of the EuCARD FP7 project (in collaboration with PSI and INFN/LNF), making good progress.
  • Double-mirror concept developed (F. Marcellini)

s21, s31

5th CLIC Advisory Committee (CLIC-ACE)

global vs local timing reference
Global vs. local timing reference

Highly stable globally distributed REF de-magnifies MB jitter dependence

For a more detailed analysis, including influence of feed-forward, see D. Schulte’s presentation

5th CLIC Advisory Committee (CLIC-ACE)

local oscillator
Local Oscillator
  • We need an LO with « 23 fs integrated phase jitter.
  • The beam path provides some noise filtering below 3 kHz
  • The system here seems to come in around ~ 4 fs

noise power density dBc/Hz

O(5k€)

5th CLIC Advisory Committee (CLIC-ACE)

global optical phase stable timing distribution
Global Optical Phase-stable Timing Distribution?
  • Major developments underway in the field, primarily for X-FEL type light-sources.
  • Two relevant presentations at the last CLIC workshop:
    • F. Ömerİlday, BilkentÜniversitesi: Long-distance optical stabilization with femtosecond resolution,

(http://indico.cern.ch/contributionDisplay.py?contribId=96&sessionId=6&confId=45580)

    • Matthias Felber, DESY: Femtosecond Optical Synchronization System for FLASH

(http://indico.cern.ch/contributionDisplay.py?contribId=100&sessionId=6&confId=45580)

  • Still requiresmajorworkand break throughs in order toworkover CLIC distances

5th CLIC Advisory Committee (CLIC-ACE)

timing stabilized fiber links
Timing-stabilized fiber links

PZT-based fiber stretcher

fiber link < 5 km

50:50 coupler

Master Oscillator

isolator

OC

coarse

RF-lock

<20 fs

optical cross-

correlator

ultimately < 1 fs

5th CLIC Advisory Committee (CLIC-ACE)

from mer lday s talk concepts for ref distribution
From Ömerİlday’s talk: Concepts for φ-REF distribution

optic-atomic clock

divide and conquer

Multiple stations with individual master oscillators and mutual links form a chain

Laser frequency combs locked to a precise quantum transition, can be absolutely stable.

Position one at each major point, distribute sync signal locally as before.

Use long links to keep each clock locked to each other (slow corrections).

Distribution of frequencies with 10-14 precision has been demonstrated.

5th CLIC Advisory Committee (CLIC-ACE)

conclusions phase stabilisation
Conclusions phase stabilisation:
  • Phase stability measurements at CTF3 gave encouraging values.
  • A feed-forward, measuring the phase jitter in the drive beam and correcting for it, can significantly relax the requirements (factor 10).
  • The low-impedance, high resolution phase monitor is addressed in FP7/EuCARD and makes correct progress.
  • A stable, globally distributed reference can demagnify the dependence on the main beam jitter further by a factor 7.
  • For global distribution of ultra-stable phase references, strong synergy with the X-FEL community exists.

5th CLIC Advisory Committee (CLIC-ACE)