Phase Reference Distribution System Research Articles

Application of a drift compensation low-level radio frequency system based on time-multiplexing pick-up/reference signals.

The high accuracy, low drift low-level radio frequency (LLRF) system is essential for the long-term stability of the accelerator RF and the acquirement of low emittance, high intensity electron beams. A time-multiplexing pick-up/reference signal based LLRF system is proposed to deal with the component temperature related phase drift and has been deployed and applied at the Xi'an Gamma-ray Light Source (XGLS) injector. The long term dual-receiver out-of-loop stability experiments with a continuous wave laser based phase reference distribution system (PRDS) show that the LLRF system can achieve ∼40 fs Root-Mean-Square (rms) phase accuracy and 51 fs/52 fs peak-peak drift (in 7 days/17 h with the high power RF system, respectively) while the reference phase varies both ∼30 ps. An ∼4 h beam-based experiment has also been conducted to evaluate the overall performance of the whole XGLS timing and synchronization system, which shows that the PRDS, LLRF system, high power RF system, and laser oscillator laser-RF synchronization system can keep long-term phase stability.

An active coaxial line phase reference distribution system

The phase reference distribution system (PRDS) provides high accuracy and low drift reference signals for other subsystems in particle accelerators. We proposed an active coaxial line phase reference distribution method to relax the requirements of the RF components. A low jitter reference signal is transmitted over the coaxial line as the forward signal; at the far end, an asymmetric double sideband suppressed carrier signal (DSB-SC) is generated and phase locked to the forward signal as ”reflected” signal. A demo system with 7 clients distributed in ∼30 meters line was developed in Tsinghua Thomson Scattering Source (TTX). The test results show 54fs RMS jitter and 82fs/158fs peak–peak drift (in 24 h/7 days) while the external reference phase drifts ∼80ps.

Towards the LISA backlink: experiment design for comparing optical phase reference distribution systems

LISA is a proposed space-based laser interferometer detecting gravitational waves by measuring distances between free-floating test masses housed in three satellites in a triangular constellation with laser links in-between. Each satellite contains two optical benches that are articulated by moving optical subassemblies for compensating the breathing angle in the constellation. The phase reference distribution system, also known as backlink, forms an optical bi-directional path between the intra-satellite benches.In this work we discuss phase reference implementations with a target non-reciprocity of at most μrad , equivalent to 1 pm for a wavelength of 1064 nm in the frequency band from 0.1 mHz to 1 Hz. One phase reference uses a steered free beam connection, the other one a fiber together with additional laser frequencies. The noise characteristics of these implementations will be compared in a single interferometric set-up with a previously successfully tested direct fiber connection. We show the design of this interferometer created by optical simulations including ghost beam analysis, component alignment and noise estimation. First experimental results of a free beam laser link between two optical set-ups that are co-rotating by ±1° are presented. This experiment demonstrates sufficient thermal stability during rotation of less than 10−4 K at 1 mHz and operation of the free beam steering mirror control over more than 1 week.

Development of sub-100 femtosecond timing and synchronization system.

The precise timing and synchronization system is an essential part for the ultra-fast electron and X-ray sources based on the photocathode injector where strict synchronization among RF, laser, and beams are required. In this paper, we present an integrated sub-100 femtosecond timing and synchronization system developed and demonstrated recently in Tsinghua University based on the collaboration with Lawrence Berkeley National Lab. The timing and synchronization system includes the fiber-based CW carrier phase reference distribution system for delivering stabilized RF phase reference to multiple receiver clients, the Low Level RF (LLRF) control system to monitor and generate the phase and amplitude controllable pulse RF signal, and the laser-RF synchronization system for high precision synchronization between optical and RF signals. Each subsystem is characterized by its blocking structure and is also expansible. A novel asymmetric calibration sideband signal method was proposed for eliminating the non-linear distortion in the optical synchronization process. According to offline and online tests, the system can deliver a stable signal to each client and suppress the drift and jitter of the RF signal for the accelerator and the laser oscillator to less than 100 fs RMS (∼0.1° in 2856 MHz frequency). Moreover, a demo system with a LLRF client and a laser-RF synchronization client is deployed and operated successfully at the Tsinghua Thomson scattering X-ray source. The beam-based jitter measurement experiments have been conducted to evaluate the overall performance of the system, and the jitter sources are discussed.

The Temporal Drift Due to Polarization Noise in a Photonic Phase Reference Distribution System

The temporal drift due to the polarization noise in an ultralow temporal drift photonic phase reference distribution system is analyzed. The temporal drift is shown to be associated with the polarization changes, the differential group delay of the subsequent parts, and, the state of polarization dispersion of the photonic local oscillator signal. Such temporal drift cannot be corrected by line length correction schemes. As an example, polarization changes from a fiber stretcher are presented, discussed, and identified as one of the major contributors to the system temporal drift. A numerical model is developed. The magnitude and statistical distribution (based on random coupling) of the temporal drift excited by the polarization change of the fiber stretcher are investigated. Experimental work demonstrates that reduction in the polarization change successfully reduces the temporal drift, as predicted by the theory and simulation.