1. Operational Experience with LCLS RF systems

2. LCLS RF systems RF Gun 23MW 5.75MV, ~115MV/M Laser 30° from crest
Standing Wave structure
OTR screens (7)
YAG screens (7)
Wire scanners (7)
L0A
35MW, 57MV, ~20MV/m
2° nominal (usually on crest)
Dipole magnets (8)
Beam stoppers (2)
S-band RF acc. sections (5)
L0B
60MW, 72MV, ~24MV/m
10° nominal (usually on crest)
L1S
147MV, 20MV/m
25° nominal
Transverse Cavity
2MW, 1.4MV ~4MV/m
180° transverse : diagnostic
250MeV
50%
25%
25%
2-km point in 3-km SLAC linac
L1S
135MeV
BC1
L1X
X-band
~20MW, 20MV, 33MV/M
160° nominal
OTR

3. General RF System Design

4. RF Gun

5. RF Gun System Specifics
Standing wave structure – field probes to measure RF
Contains vacuum sensitive cathode – want to avoid arcs: Hardware RF power interlock.
Hi Q system, needs precise temperature control to stay on resonance.
Gun operates at high peak field – 115MV/M.

6. Gun RF Performance Amplitude Jitter 0.04% Phase Jitter .053°
Spec 0.1%
Phase Jitter .053°
Spec 0.1°
(but same read back as feedback)
Good Reliability

7. RF Gun Issues
Minimal problems
Field probes overheat at high rate, limited to 30 Hz. Re-designed probes to be tested on Gun 2.
Software RF feedback can cause problems with interaction with modulator hardware trips. Software tries to maximize power during hardware RF power ramp.

8. L0A RF System Standard S-band RF system
Noise problems (modulator Thyratron?)
0.2% amplitude
Spec 0.14%
0.16°
Spec 0.14°
System operates with good reliability

9. L0B RF System Standard S-band RF system Good Jitter .024% amplitude
Spec 0.14%
.043° Phase
Spec 0.14°

10. L0B RF System Overall
Excellent jitter (amplitude and phase) performance. Shows how well the S-band Modulator / Klystron can work!
Had some processing problems early in the run (L0B is our highest gradient S-band structure), but seems OK now.
L0B Amplitude normally run in feedback for energy stability. RF long term stability < 1% p-p.

11. Transverse Cavity RF system
Standard S-band RF system
Operates 90° off crest.
Jitter OK, but fliers
.017% amplitude
0.15° phase
Regularly used as a diagnostic

12. L1-S RF System

13. Uses SLED cavity to drive 3 structures
L1S System Specifics
Uses SLED cavity to drive 3 structures
Operates 25° off crest to provide acceleration and energy chirp for compression
147MV, 135MeV energy gain
Phase noise important, off crest operation converts phase noise to bunch length and arrival time error.

14. L1S System Operation Amplitude noise: 0.043% Phase noise 0.10°
Spec is 0.14%
Phase noise 0.10°
Spec is 0.14°
Long term stability from beam feedback (BC1 energy)

15. L1X RF System Uses 60cm X-band structure XL-4 Klystron
Originally developed as part of Next Linear Collider Project.
Operates at ~33MV/M
NLC gradient ~70MV/M
XL-4 Klystron
Operating at 20MW
Design 50MW
X-band operates 160° off crest (net deceleration) to compensate for curvature of energy vs. time from S-band.

16. System reliability has been good
L1X RF System
Amplitude noise 0.62%
Spec is 0.25%
Phase noise 1.2°
Spec is 0.5°
System reliability has been good

17. L1X Transverse Kicks
L1X produces an unexpectedly strong transverse kick on the beam.
Kick is ~50 degrees out of phase with energy gain.
Adjusted timing of RF to eliminate power in couplers during beam passage – did not reduce kick.
Not yet understood
Emittance vs position
Transverse kick
Vs. phase
Energy vs. phase

18. Noise and Stability Issues
Noise measurements shown were performed with the same sensors that are used in feedback.
Not really a fair measurement.
Beam based energy measurements also used in feedback
Just beginning serious measurements of noise and stability: Initial indications are that overall phase noise is < 1°, but doesn’t yet meet the 0.1° requirement.
Low noise on individual stations indicates that the high power components are capable of meeting the spec.

19. Study noise / stability
Near Term Plans
Study noise / stability
Multiple measurements available: Beam phase cavities, beam energy, bunch length monitors etc.
Lack of a single “gold standard” for measuring phase complicates things
Study X-band deflection, wakefields, emittance growth.
May remove the cavity during the down-time (Sept 07) for RF measurements.

20. RF operates with good reliability.
Overall RF Status
RF operates with good reliability.
All systems running at design gradient.
Gun currently at 5.75MV, not 6, but believe we can turn up at any time.
Phase noise needs some work, but high power equipment seems OK
Need to investigate transverse effects in L1X.