Speaker
Description
Precise phase regulation in LLRF systems relies on a phase-stable RF reference, making reference distribution an integral part of achievable field-control performance*. We present an actively stabilized RF-over-fiber link for distribution of a 1.3 GHz reference.
The system measures optical round-trip delay and compensates fiber-induced fluctuations through feedback to a fast optical delay actuator with 2.4 ns control range. By directly stabilizing the optical propagation delay rather than correcting the RF phase, the approach provides reciprocal delay compensation and avoids residual errors associated with non-reciprocal RF phase correction. The optical delay actuator enables fast cold start and response without the long warm-up times and limited control bandwidth of thermally controlled fiber spools.
Out-of-loop measurements demonstrate 6.6 fs RMS jitter for [1Hz – 1MHz] and 19.2 fs RMS drift over 8 h with 2 Hz sampling, corresponding to only ~20 fs RMS over the full bandwidth of [35uHz – 1MHz]. Residual frequency stability is 8.6E-15 at 1 s, reaching 1E-17 at 2000 s. These results demonstrate femtosecond-stable RF reference distribution for demanding accelerator LLRF systems.
| Abstract Classification | Control Architecture and Strategies |
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