1. ESS Phase Reference Signal Distribution
Anders svensson, lund University

2. 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

3. 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

4. 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 °

5. 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

6. 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

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

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

9. Frequency doubler – phase stability
Diode based frequency doublers have been characterized
minimum 10 dB conversion loss -> amplifier and filter needed
Low additive phase noise
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

10. 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

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

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

13. 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

14. 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.