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

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.

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ESS LLRF installed in Freia

FPGA/ADC

PZFPGA

RF/VM

CPU

Timing

Timing

MCH

EPICS, Supervision

Modulator V Modulator IVectormodulator out

Piezo 1Piezo 2HV

Phase referenseCavity PickupVM outPreAmp OutPowerAmp outPowerAmp ReflCavity InCavity Refl

Fan Tray x 2

PSU x 2

Interlock

352.21 MHz MTCA.4 Spoke LLRF crate for ESSCB control on backplaneTiming triggersMCH supervisionExternal I/OEthernet on backplane

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 systemSummary 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

Tunnel

Cavity

Gallery

Master Oscillator

LLRFTiming Generator

Phase Reference Line

Cavity

LLRF

BeamSource

ESS Cavity and Amplifier typesCavity type Number Amplifier

technologyRFQ 1 KlystronBuncher 3 Solid stateDTL 5 KlystronSpoke 26 TetrodeMedium Beta 36 KlystronHigh Beta 84 IOT

ESS Cavity and Amplifier typesCavity type

Number Frequency(MHz)

Amplifier technology

RFQ 1 352.21 KlystronBuncher 3 352.21 Solid stateDTL 5 352.21 KlystronSpoke 26 352.21 TetrodeMedium Beta

36 704.42 Klystron

High Beta 84 704.42 IOT

ESS Cavity and Amplifier typesCavity type Number Temp. Amplifier

technologyRFQ 1 ”Room” KlystronBuncher 3 ”Room” Solid stateDTL 5 ”Room” KlystronSpoke 26 2 K TetrodeMedium Beta

36 2 K Klystron

High Beta 84 2 K 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 extensionsBeam current

• Measurement and feed-forward of the beam current measurements along the linac to minimize the influence of the variations.

Ion Source LEBT RFQ MEBT DTL Etc.

LLRF

LLRF ExtensionsInner 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

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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!