ESS Phase Reference Signal Distribution Anders svensson, lund University

System Overview Phase reference: Generated by Master Oscillator (MO) For LLRF, BPMs, BSMs, along the whole tunnel In total 155 LLRF stations and 165 BPM stations Optimum solution for whole Linac

Phase reference distribution system Phase reference line: 1-5/8” rigid coaxial line 10 m sections with individual temperature control ±0.1 °C Stub BPM BPM

Phase reference distribution system (cont.) Phase drift main contributors: Phase reference line RF cables from tunnel to gallery LO and Clk generation Overall phase drift requirements: Two adjacent cavities: ±0.1 ° Any cavity to cavity within 100 m: ± 1.0 °

Frequency distribution alternatives LLRF and BPM have opposite frequency needs Alternative LLRF BPM Comment Warm Cold 352 or 704  x2 /2 BPM performance hit All 352 Phase stability of cable over frequency All 704 704 or 352 LLRF performance hit Dual line Expensive 352 & 704 ok Selective filters needed

Gallery to tunnel penetration - Stubs 8 waveguides, each 11.8 m long Total heat dissipation up to 3500 W Water cooling of waveguides RF cables in trays in the roof of the stub Maximum RF cable temperature is +41 °C From cold it will take 2-3 days to reach 90% of final temperature

Reference and LO generation Temperature controlled rack ±1 °C x2 /2

Phase ambiguity Dividers and potentially also PLL’s suffers from phase umbiguity at start-up

Frequency doubler – phase stability Diode based frequency doublers have been characterized minimum 10 dB conversion loss -> amplifier and filter needed Low additive phase noise Fin @ 352 MHz Model Phase stabililty [ps/°C] Conversion loss [dB] Leakage[dBm] Fin 3xFin 5xFin SLX-K5 -0.2 10.2 -25 -40 -15 KC2 -0.8 15.3 -52 -50 -30 AMK -0.1 11.8 -37 -32 -19

Frequency distribution alternatives LLRF and BPM have opposite frequency needs (at least for cold section) Alternative LLRF BPM Comment Warm Cold 352 or 704  x2 /2 BPM performance hit All 352 Phase stability of cable over frequency All 704 704 or 352 LLRF performance hit Dual line Expensive 352 & 704 ok Selective filters needed

Phase stable cables Cables: SCF38-50J-TC from RFS

Phase drift between stations Ref line Tunnel Cavity Stub Multiplier Gallery x2 x2 x2 LLRF LLRF LLRF

Ref line phase drift [°] Different frequencies Total phase drift Assumptions: Phase reference line: DT = 0.2 °C along 10 m (adjacent) DT = 0.2 °C along 100 m Cable pairs in stub, 10 m: same stub: DT : +20 °C to +40 °C between stubs: DT : +20 °C to +40 °C Frequency x2: DT : 2 °C Ref line phase drift [°] Ref line, adjacent Ref line, 100m 352 MHz 0.02 0.16 704 MHz 0.03 0.32 Phase drift [°] Same frequency Different frequencies Cables in Stub 0.02 0.20 X2 multiplication - 0.08

Summary Dual line 352 MHz single frequency Preferred from performance perspective More costly 352 MHz single frequency Phase drift will be higher due to frequency properties of RF cables More studies needed of heliax cables Software compensation being investigated Thanks to the LLRF group at LU and ESS.