Frequency Control through Pulse Width Modulation for NRF Cavities. As example at FLASH RF GUN Sven Pfeiffer for the LLRF team LLRF Workshop 2015 Shanghai,

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 2 Content > Introduction > Water Regulation > LLRF Controls > Cascaded Control Scheme

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 3 Introduction Cooling water regulation LLRF control How: Variation of input signal P IN > RF-field control  LLRF control  GOAL: Maintain constant acceleration field in amplitude and phase for virtual probe signal (combination of forward and reflected signal) Disturbance for water circuit

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 4 > Cooling water regulation  GOAL: Constant cooling, i.e. keep geometry and reflected signal constant Introduction Cooling water regulation LLRF control How: Variation of input signal P IN Disturbance for water circuit > RF-field control  LLRF control  GOAL: Maintain constant acceleration field in amplitude and phase for virtual probe signal (combination of forward and reflected signal) How: Variation of input water temperature T IN Disturbance for LLRF regulation

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 5 > Cooling water regulation  GOAL: Constant cooling, i.e. keep geometry and reflected signal constant Introduction Cooling water regulation LLRF control How: Variation of input signal P IN Disturbance for water circuit > RF-field control  LLRF control  GOAL: Maintain constant acceleration field in amplitude and phase for virtual probe signal (combination of forward and reflected signal) How: Variation of input water temperature T IN Disturbance for LLRF regulation Separation of both feedback loops is impossible for precision regulation

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 6 Content > Introduction > Water Regulation > LLRF Controls > Cascaded Control Scheme

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 7 Water Regulation by Water from GUN Water to GUN Cold water and valve position to be controlled Warm water, pump, heater, tank > Mixing valves are controlled via PLC with PI control scheme  Keep water input temperature constant for given RF power  Keep RF GUN (IRIS) temperature constant, e.g. on-resonance

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 8 Water Regulation by > Mixing valves are controlled via PLC with PI control scheme Long term error ± 1 (16 bit ADC) of 0.02 K – 0.03 K

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 9 Content > Introduction > Water Regulation > LLRF Controls > Cascaded Control Scheme 1.3 GHz SWS, Pulsed 10 Hz, Pulse length up to 800 μs

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 10 LLRF – Single Cavity Regulation Scheme GOAL: dA/A < 0.01% dφ < 0.01 deg. (rms) Talk: M. Hoffmann (Friday morning) PI –like feedback controller

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 11 LLRF – Single Cavity Regulation Scheme PI –like feedback controller 0.01% 0.01deg. x3-4 improvement necessary MTCA.4 (9MHz  1MHz) VME (1MHz) GOAL: dA/A < 0.01% dφ < 0.01 deg. (rms) Talk: M. Hoffmann (Friday morning) x6 x2 x8

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 12 Content > Introduction > Water Regulation > LLRF Controls > Cascaded Control Scheme

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 13 Cascaded Control Scheme Goal: Fast compensation of temperature drifts  Fast and precise temperature information  Fast Actuator 2 Concepts > LLRF Controls (MHz – Hz loop)  MIMO feedback controller  Sensor: Virtual probe (V forw and V refl )  Actuator: Input to vector modulator > Water regulation (Hz loop)  PI feedback controller (PLC)  Sensor: IRIS Temp.  Actuator: Cold water valve  Cascaded feedback loop

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 14 Cascaded Control Scheme Idea: Usage of LLRF Signals > Delayed T IRIS (9s) and T IN (5s) information  Transition from cavity body to sensor  Low pass behavior of temp. sensor FLASH RF GUN data Temp. sensor (16 bit ADC)

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 15 Cascaded Control Scheme Idea: Usage of LLRF Signals > Delayed T IRIS (9s) and T IN (5s) information > Temperature estimation using LLRF signals is almost without time delay and suitable for feedback loop > Use pulse length variation to heat/cool gun body within pre-defined limits

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 16 Cascaded Control Scheme - Result > RF GUN phase at 1 st beam position (700μs) for 50 minutes > Without and with modulation (each 25min)  Pulse to pulse compensation (10 Hz) > Factor 3 improvement (dφ = 53mdeg.  16 mdeg.) > Converges towards pre-defined limiter  additional loop to adjust IRIS set-point required Blue: single pulse, Red: mean 100 pulses * Under Physical Review Special Topics - Accelerators and Beams

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 17 Cascaded Control Scheme – Long Term Run (5h) Temperature feedback loop > σ(ΔT) = 3mK  σ(Δf) = 63Hz  With K = 21kHz/K > σ(T IRIS ) = 1.4mK 9 MHz RF field full res. > σ(dA/A)(700 μs) = 1.7 ⋅ > σ(dφ)(700 μs) = deg. 100 kHz RF field GUN (filtered by cavity bandwidth) > σ(dA/A)(700 μs) = 4.8 ⋅ > σ(dφ)(700 μs) = deg. Successful in operation at FLASH GUN and PITZ GUN * Under Physical Review Special Topics - Accelerators and Beams

Sven Pfeiffer | Frequency Control through Pulse Width Modulation for NRF Cavities | | Page 18 Cascaded Control Scheme – Long Term Run (5h) Temperature feedback loop > σ(ΔT) = 3mK  σ(Δf) = 63Hz  With K = 21kHz/K > σ(T IRIS ) = 1.4mK 9 MHz RF field full res. > σ(dA/A)(700 μs) = 1.7 ⋅ > σ(dφ)(700 μs) = deg. 100 kHz RF field GUN (filtered by cavity bandwidth) > σ(dA/A)(700 μs) = 4.8 ⋅ > σ(dφ)(700 μs) = deg. Successful in operation at FLASH GUN and PITZ GUN Thank you for your attention! * Under Physical Review Special Topics - Accelerators and Beams