Design and Performance of CSNS Linac Digital LLRF Control System

1. Design and Performance of CSNS Linac Digital LLRF Control System Zhencheng Mu CSNS Linac RF System

2. Introduction of CSNS Linac RF System The Digital Field Control System Common Faults of LLRF The Tunner Loop The High Power Protection System Outline 1 2 3 4 5

3. IHEP, Beijing China Spallation Neutron Source(CSNS)

4. Introduction of CSNS Linac RF System

5. Overview of the CSNS Linac • Main machine and beam parameters • Freq. RF: 324MHz • Type of particle accelerated: H-ions • Output energy: 80 MeV • repetition rate: 25Hz • Beam pulse length: 250 µs at present • Mean pulse current: 5 mA

6. Linac RF Power Sources • RFQ & DTL: Klystron Power Sources • Klystron: CPI&Toshiba triode klystron • 400Hz serial resonant power supply of klystron • Ignitron Crowbar • Solid state switch modulator

7. Linac RF Power Sources • Three Solid State Amplifiers for Two MEBT Buncher Cavities, One LRBT Debuncher Cavity. Each solid state RF amplifier can output 25kW, redundancy design. Table: Performance of the 25kW Solid State Amplifier

8. Digital LLRF Control System

9. 324MHz Reference Line • The reference line located in sub-tunnel, frequency 324MHz. the Andrew phase stable cable is wrapped in a constant temperature water jacket, the variation range of the water temperature limited within ±0.1°.

10. Overview of LLRF • Duties of the LLRF system: • ±1% amplitude of the cavity field • ±1°phase of the cavity field • Cavity resonant frequency control • High Power protection HMI IPC Anolog Module Synchronizing Pulse Distribution Digital Control and High Power Protection Modules

11. Analog Module • The analog module consisits of two units : • The analog up-down conversion unit: RF 324MHz, LO 360MHz, IF 36MHz. 4×down conversion channels 2×up conversion channels • The clock generation unit: 144MHz, 36MHz, 72MHz all the analog modules in the thermostat chamber, the temperature within ±0.1℃ of the setpoint. 324MHz Reference Signal 324MHz Cavity Pick-up 36MHz Clock ╳1 360MHz LO Signal 72MHz Clock ╳2 360MHz LO Signal 144MHz Clock 36MHz IF ╳4

12. The Digital Field Control System • Hardware • 1×FPGA: Altera Stratix II family EP2S90F1020 • 2×ADCs with 4 sampling channels: Linear LTC2156, 170Msps 14-bit, DDR LVDS output to FPGA. • 2×DSPs: TI C6713 • ADCs Sampling frequency 144MHz, IF 36MHz, quadruple frequency sampling gets I, Q, -I, -Q…… • 3 IF signals are sampled by ADCs: cavity field, forward , previous cavity field. • Phase difference between the forward signal and the cavity field is used in the tuning system. • Previous cavity field is used to recover the working point if something changed in the previous RF system.

13. The Digital Field Control System • Software: IQ Demodulation → Feedback PI Controller → Feedforward Table → Numerically Controlled Oscillator (NCO). • Feedback Loop: Suppress various disturbances (power sources noises, high voltage drop, beam loading, etc). • Feedforward: It compensates the beam loading, triggered by beam gate, fixed value table. • NCO: Output 36MHz IF, digital frequency conversion technology. Setpoint point Feedback set Feedforward set

14. ±0.4% in amplitude and ±0.5° in phase during the RFQ beam commissioning, the pulse width of the RF is 700µs, beam width 500µs, beam intensity 10mA. • ±0.3% in amplitude and ±0.3° in phase of the DTL1 now, the pulse width of the RF is 650µs, beam width 250µs, beam intensity 5mA.

15. The Digital Frequency Conversion Technology • Digital Frequency Conversion Technology • Target: the power source output frequency automatically tracks cold cavity resonant frequency, less reflected power. • Actuator: NCO • Two mode can be selected • Manual mode • Auto mode: the detuning frequency from the operating frequency of the cavity by the phase curve of the cavity field during the field decay. .

16. The Tunner Loop • The detuning frequency of DTLs is less than 2k during operation. • Two methods to judge whether the cavity is close to resonant state or not. • The phase difference between the cavity input and output signal. • The detuning frequency which is directly calculated from the phase curve of the cavity field during the field decay. • Actuator • RFQ: Cooling water, regulate the input cooling water valve • Buncher/Debuncher cavities and DTL: Tunner, • The servo motor moves to maintain the cavity resonant. • Displacement sensor sends tunner displacement information to IPC using TCP/IP protocol. Servomotor Servomotor&Tunner of DTL Displacement sensor

17. 460ns The High Power Protection • Power monitor • Eight channels ADCs • VSWR, count the VSWR protection number. • Test result shows the RF shutdown time is less than 460ns once VSWR protection. • AFT ARC sensor and the sentry. • Klystron output window, Circulator, Cavities, etc… • Count ARC number

18. Pizza Box Type LLRF Chassis Digital Field Control Module Power Detector Array Power Monitor and VSWR Protection Module

19. Common Faults of LLRF • Thermostat chamber faults are mainly from two parts. • Semiconductor Refrigeration unit • The fans. • The contact problems of the power plugs in PCB boards. Target Power Running Chart • Operator on duty found the target power exception in April this year. Phase Hop

20. LLRF Update Plans • The CSNS II update will employ superconducting cavities, so the LLRF should satisfy the superconducting requirements. • We want to choose an adaptive platform, maybe MTCA. DWC8VM1: 8 Channel Down Converters and 1 Vector Modulator (DWC) SIS8300-KU: Digitizer and LLRF Controller (ADC&FPGA)

21. Thank You For Your Attention!!