2. SPS 200 MHz LLRF upgrade Part 2: Implementation Philippe Baudrenghien, Grégoire Hagmann, 24.09.2015

3. 200MHz Cavity controller Cavity Controller: Amplitude & phase loops (designed begin 1970s) 1-Turn Feedback (upgraded late 1990s) Feedforward (late 1990s) Long-Damper (late 1990s) Currently in NIM platform (not PPM) Only electronics for 4 cavities (6 cavities installed after LS2) No remote control/diagnostic Mostly analog Long damper not designed for pLHC Q26 Improvements required for LIU-SPS: 2.5E11 p/bunch (25 ns), ions,… Fig1: Current 200MHz feedbacks

4. 200MHz Cavity controller Fig2: TWC200 Cavity Controller

5. 200MHz Cavity controller RF generation Locally (Cavity-loops module) Need continuous clean f RF (clock) : f RF average Voltage modulation possible with Frev marker, used for: Frev marker based on f RF average (h=4620) pLHC : Voltage reduction in a 2µs portion of the circumference, with fall-time < 225 ns, for capture of incoming batch. Required RF power being studied. pFT : Voltage reduction in ½ ring for the incoming batch at injection ions : AM modulation at 4·f REV : on/off for Fixed Frequency Acceleration (FFA) Momentum slip stacking : 1 clock distributor per system => independant f RF Bunch rotation (at flat top) Phase setpoint function Voltage setpoint Fig3: Voltage & Phase setpoint

6. 200MHz Cavity controller IQ demod, Signal processing, IQ Mod PLL : K=2, M=7, N=8 Frf 200 = 199.55 MHz -> 200.395 MHz ∆Frf 200 = 845 kHz LO = M/N * Frf 200 ≈ 175 MHz ADCLK = F RF 200 / K ≈ 100 MHz IF = F RF 200 / 8 ≈ 25 MHz Fig6: Digital signal processing chain Fig5: Clock distribution

7. 200MHz Cavity controller Synchrotron frequencies (fs) 0 to 2.5kHz (ions) Triple or quintuple comb filters (like TWC800) Functions for filter parameters (pre-calculated fs) Longitudinal damper Fast serial link (Gbits) from the Beam control (as it was forseen for TWC800) Correction added to the voltage setpoint Alignement of 200-800MHz phase (+/-5deg @ 800 MHz) with a better 200MHz & 800MHz beam loading compensation. Required gain/bandwidth being studied Long. Damper Filter coeffs variables Fig7: Long Damper

8. 200MHz Cavity controller Fast phase modulation Bunch rotation (unstable phase) <1µs response time Changes applied to the voltage setpoint (phase) Functions for Bunch rotation at flat top (unstable phase) Fast phase modulation Batch per batch blow-up <1µs response time Changes applied to the voltage setpoint (phase) Noise table played synchronously to Frev + timing NoiseFunctions Fig8: Phase modulation

9. 200MHz Cavity controller Fixed frequency acceleration (FFA) f RF average as clock Demodulation of the F RF FSK Modulation applied to the voltage setpoint (phase) Phase: Triangular shape Compensation of transient beam loading would work correctly with fixed frequency acceleration as it depends on the revolution period only F RF FSK (ions) Fig10: FSK generate Phase modulation Fig9: Clock distri for FSK F RF AVG (ions)

10. 200MHz Cavity controller Momentum slip stacking (ions): 1 RF clock distributor per system => independant f RF Phase: Sawtooth shape F RF1 or F RF2 Fig11: Slip stacking generate phase modulation < 1kHz

11. 200MHz Cavity controller Reduction of impedance ½ Required gain/bandwidth being studied 1-Turn Feedback at fundamental and Beam loading TWC800 Comb filters gain: 26 dB (high BW) achieved in prototype system on cavity 1 + add gain at f RF (low BW) Feedforward (~10dB) ↕ 3dB/div ↔ 0.5kHz/div ↕ 10dB/div ↔ 5kHz/div Fig12: TWC800 Comb filters 36dB k·Frev k·Frev+fsk·Frev-fs

12. 200MHz Cavity controller Polar loop TX noise reduction Automatic adjustment of OL phase & gain (less sensitive to intervention on Power plant) Ease the setting-up of the 1-Turn feedback Polar loop Fig13: Polar loop

13. Beam Control Fig14: Current Beam Control systems

14. Beam Control Two control loops Beam phase loop (damping of beam phase oscillation – common mode) Radial or synchro loop (keeps the beam in the center of the vaccuum chamber) Radial loop used for crossing transition Synchro loop used for bunch into bucket transfer (LHC and Awake) Frequency program Generate the RF freq Keeps the beam on desired orbit (including radial steering) Derived from dipole field measured in reference magnet Master RF VCO or DDS generating the Master RF used as ref Clock for Cavity Controllers used for beam-based measurements (phase & radial loop)

15. Beam Control Slip stacking and cavity control 2 sets of cavities must be driven with different Master RF Current Slave DDS to be upgraded to triple slave DDS Fig15: Beam control – synchro loop DF

16. Beam Control Simplifications to be study Transmission of f RF FSK & f RF AVG to Cavity Controller over Gbits links => Avoid generating good RF signal => Avoid having good demodulator Same DDS for ions & protons Filtering VCO for p coast?