Integrated phase reference distribution LLRF and laser synchronization system Gang Huang 1, Jin Yang 1,2, Qiang Du 1, Wenhui Huang 2, Yilun Xu 1,2, Larry Doolittle 1, Russell Wilcox 1, John Byrd 1 1.Lawrence Berkeley National Laboratory 2.Tsinghua University LLRF2015 Shanghai, China

Outline Introduction System design Bench top test Summary

Introduction Femto-second timing for LCLS, Digital LLRF for linac, Short Pulse X-ray for APS-U (canceled,2013). APEX gun and laser control (2013-now)

Introduction Tsinghua Thomson Scattering source. Rev Sci Instrum May;84(5): doi: /

Inverse Compton Scattering to generate X-ray and Gamma ray. – S band Normal conducting Linac upto 400MeV. – fs to ps laser. – Multiple x-ray/Gamma ray energy. New campus at Xi’an, ShannXi, China. DOE approved work for other contract. Tsinghua X-ray Gamma ray Light Source(TXGLS)

Requirement Jitter between scattering Laser and electron. – <250fs rms. Upgradable.

TXGLS timing and synchronization 2 filbers for reference distribution Event distribution Transmission LO distribution TX RX

TXGLS timing and synchronization LO distributed over cable. Reference distributed over fiber. Fiber drift measured by interferometer and feedforward to client. Sync-head located next to the client. Drift between sync-head and receiver chassis measured by calibration signal. – Pulsed LLRF Time division – Laser Frequency division Optics Letters, Vol. 34, Issue 20, pp (2009)

Transmitter CW fiber laser: Koheras Laser. LO/Ref generation: LBL design schematic, HZCY layout/fabricate; Wenzel plate. Modulator: LBL design schematic, YYLabs inc. layout/fabricate. Sender: LBL design schematic, YYLabs inc. layout/fabricate.

Sync-head Located next to the DUC. 3GHz – Amplifier + attenuator EMI shield – On board shielding – Whole board cover with chamber – Macro-circuit Thermal design – Thermal pad – Thermal isolator – TE-cooler

Receiver Chassis 2xLLRF4.6 board Macro-circuit for up/down converter Frequency relationship Prototype chassis DescriptionSymbol Value (MHz) Derivation FPGA and ADC clockF clk 101.2F llrf4.6 /4 DAC clockF dacclk 202.3F llrf4.6 /2 Laser oscillator repetition rateF laser 79.33F clk × 40/51 Laser subharmonicsF sublaser 4.96 F laser /16 = F clk × 5/102 IF frequency FLOdw-FrfF IFdw 23.8F clk × 4/17 IF frequency Frf-FLOupF IFup 158.7F clk × 80/51 IF frequency FLO Cband- FCbandF IFCband 27.8F clk × 14/51

FPGA firmware BIDS library 3 modes – interferoter, pulsed LLRF, laser feedback

Initial bench top demo Hardware test Hardware integration. Firmware functionality Control laser Control cavity ……

Preliminary bench top demo result

Summary We developed an integrated phase reference, LLRF, laser control system for TXGLS. In last August, we run an initial bench top demo in Tsinghua Univ. The control loop functionality are demonstrated. The experiment measured sub-100 fs for our system. We are working with local company on the board and chassis. We will run further experiment with the new hardware and with the high power RF.