ESS LLRF and Beam Interaction

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

ESS RF system

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.

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.

ESS LLRF installed in Freia

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

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.

LLRF system Summary view

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.

Timing system The LLRF system is triggered by the timing system. The timing system is by MRF (Micro Research Finland), in is clocked at 88.0525 MHz The triggers are distributed on the back-plane of the MTCA-crate.

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

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

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

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

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.

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.

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.

Modulator ripple compensation

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.

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!