1. ESS LLRF and Beam Interaction

2. ESS RF system From the wall plug to the coupler Controlled over EPICS
Connected to the global Machine Protection System (MPS)
Includes the master oscillator and the phase reference line
No electronics in the tunnel

3. ESS RF system

4. LLRF at ESS LLRF: Low-Level Radio Frequency
Controls the phase and amplitude of the field in the cavities.
Starts at cavity field pickup connector on cavity/cryomodule.
Ends at input to the pre-amplifier.
Controls the fast piezo tuners.
Controls the slow stepper motor tuners.

5. Design concept Digital implementation of fast control in FPGA
Slow updates of feed foeward and similar in software
Modular design for simple maintenace
Modular design for large volume procurement
Redundant design for availability
The RF signals are downconverted to an IF-signal, AD-converted, processed in an FPGA, and DA-converted and finally upconverted in a vector-modulator.

6. ESS LLRF installed in Freia

7. 352.21 MHz MTCA.4 Spoke LLRF crate for ESS
CB control on backplane
Timing triggers
MCH supervision
External I/O
Ethernet on backplane
CPU
Phase referense
Cavity Pickup
VM out
PreAmp Out
PowerAmp out
PowerAmp Refl
Cavity In
Cavity Refl
Timing
Timing
FPGA/ADC
RF/VM
Interlock
Modulator V
Modulator I
Vectormodulator out
FPGA PZ
Piezo 1
Piezo 2 HV
MCH
Fan Tray x 2
EPICS, Supervision
PSU x 2
230 V AC

8. LLRF control
The RF signals controlled by two PI-controllers, one for each of the I- and Q-signal.
A precalculated FeedForward correction is added to the output.
Corrections are added to the output to compensate for imperfections in ADC, vector modulator etc.

9. LLRF system Summary view

10. Phase reference distribution
Phase reference is distributed in the tunnel.
The phases at the taps, one for each cavity or cryomodule, are kept constant by temperature control.
LLRF picks up the reference in parallell with the cavity signal, and the two signals are transferred in identical cables next to each other to the Gallery.

11. Timing system The LLRF system is triggered by the timing system.
The timing system is by MRF (Micro Research Finland), in is clocked at MHz
The triggers are distributed on the back-plane of the MTCA-crate.

12. Phase reference and timing distribution
Gallery
Master Oscillator
Timing Generator
LLRF
LLRF
Tunnel
Beam
Source
Cavity
Cavity
Phase Reference Line

13. ESS Cavity and Amplifier types
Cavity type
Number
Amplifier technology
RFQ 1
Klystron
Buncher 3
Solid state
DTL 5
Spoke 26
Tetrode
Medium Beta 36
High Beta 84
IOT

14. ESS Cavity and Amplifier types
Cavity type
Number
Frequency
(MHz)
Amplifier technology
RFQ 1
352.21
Klystron
Buncher 3
Solid state
DTL 5
Spoke 26
Tetrode
Medium Beta 36
704.42
High Beta 84
IOT

15. ESS Cavity and Amplifier types
Cavity type
Number
Temp.
Amplifier technology
RFQ 1
”Room”
Klystron
Buncher 3
Solid state
DTL 5
Spoke 26
2 K
Tetrode
Medium Beta 36
High Beta 84
IOT

16. ESS Beam 62.5 mA Proton Beam 2.86 ms pulse length
14 Hz pulse repetition frequency
The pulse to pulse current variation is <3.5 %
The intra-pulse current variation is <2 %
Averaged over 200 us.

17. LLRF extensions Beam current
Measurement and feed-forward of the beam current measurements along the linac to minimize the influence of the variations.
LLRF
Ion Source
RFQ
DTL
LEBT
MEBT
Etc.

18. LLRF Extensions Inner closed loop / HV measurements
Two strategies to reduce the influence of the HV ripple are investigated
Measuring the HV ripple and feeding it forward to the LLRF system.
Closing the loop around the Klystron with a separate PI-loop.

19. Modulator ripple compensation

20. Lorenz Force Compensation
The LLRF system will calcalute and update the excitation waveforms used to combat the lorenz force detuning.
Long pulse – 2.86 ms.
Same order of magnitude as the mechanical modes of the cavities.

21. LLRF – Beam Dynamics
Balance demands on stability with technology of different sections along the linac.
Include system wide aspects on the design – balance the requirements on different Linac components, i.e. source, modulator, LLRF.
This workshop!