Hengjie Ma, 1/18/2007, JLab RF Control in SNS Linac Implementation and what has been learned Hengjie Ma 1-2007 O AK R IDGE N ATIONAL L ABORATORY 1
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementation and understanding Outline � SNS LLRF System Overview � Some Observations •Configuration •Lorentz Force detuning. •Phase reference schemes •5/6pi mode excitation. � Issues & Improvements •Mechanical construction � Implementations •Control stability •Chosen controller type •Cavity filling techniques. •Performance analysis •Feed forward control algorithms •Digital implementation � Test & Operation Results •Control bandwidth, error •Linac-wise performance O AK R IDGE N ATIONAL L ABORATORY 2
Hengjie Ma, 1/18/2007, JLab The Spallation Neutron Source 1999 O AK R IDGE N ATIONAL L ABORATORY 3
Hengjie Ma, 1/18/2007, JLab Summary of Beam Parameters Achieved in Commissioning Parameter Baseline/ Achieved Units Design π mm-mrad Linac Transverse Output 0.4 0.3 (H), 0.3 (V) Emittance (rms,norm) CCL1 bunch length 3 4 degrees rms Linac Peak Current 38 > 38 mA Linac Output Energy 1000 952 MeV Linac Average Current 1.6 1.05 (DTL1 run) mA 0.003 (SCL run) 1.3x10 14 (DTL run) 1.6x10 14 Linac H-/pulse Ions/pulse 1.0x10 13 (CCL run) 8.0x10 13 (SCL run) 1.0x10 14 (Ring run) Linac Pulse length/Rep- 1.0/60/6.0 1.0/60/3.8 (DTL1 run) msec/Hz/% rate/Duty Factor .050/1/.005 (CCL run) 0.85/0.2/0.017 (SCL) 1.5x10 14 5x10 13 Extracted protons/pulse Protons/pulse O AK R IDGE N ATIONAL L ABORATORY 4
Hengjie Ma, 1/18/2007, JLab O AK R IDGE N ATIONAL L ABORATORY 5
The SNS utilizes 100 RF systems Hengjie Ma, 1/18/2007, JLab for acceleration and bunching Type Application Frequency Peak Power Vendor Installed Spare Klystron RFQ, DTL 402.5 MHz 2.5 MW E2V & 7 5 Thales Klystron CCL 805 MHz 5 MW Thales 4 5 Klystron SCL 805 MHz 550 kW CPI & 81 14 Thales Triode MEBT 402.5 MHz 20 kW CPI 4 3 Rebunchers Tetrode Accumulator 1 & 2 MHz 100 kW Thales 4 1 Ring O AK R IDGE N ATIONAL L ABORATORY 6
Hengjie Ma, 1/18/2007, JLab SNS HPRF Configuration SNS Linac Layout NC Linac DTL CCL RFQ 1 2 3 4 5 6 1 2 3 4 to SCL K K K K K K K K K K K XMTR XMTR XMTR XMTR XMTR XMTR XMTR XMTR XMTR XMTR XMTR RFQ 1 2 3 4 5 6 1 2 3 4 ME1 ME3 ME5 ME1 ME2 ME3 ME4 Medium Beta SCL High Beta SCL from 1 2 3 4 5 6 7 8 9 10 11 12 CCL XMTR XMTR XMTR XMTR XMTR XMT A B A B A B SCL SCL SCL ME1 ME5 ME9 High Beta SCL 13 14 15 16 17 18 19 20 21 22 23 XMTR XMTR XMTR XMTR XMTR XMTR XMTR XMTR A B A B A B A B SCL SCL SCL SCL ME12 ME15 ME18 ME21 550 kW klystron SCL Klystron HV Tank O AK R IDGE N ATIONAL L ABORATORY 7
Hengjie Ma, 1/18/2007, JLab RFQ, DTL and CCL RF Systems Seven 402.5 MHz, 2.5 MW klystrons power the RFQ and DTL Four 805 MHz, 5 MW klystrons power the CCL O AK R IDGE N ATIONAL L ABORATORY 8
Hengjie Ma, 1/18/2007, JLab SC Linac RF System Layout High Beta 4-Cavity Cryomodule s CAV CAV CAV CAV CAV CAV CAV CAV CAV CAV CAV CAV Tunnel Klystron Gallery Typical SC RF Layout by CIRC HVCM CIRC LLRF Racks LLRF Racks Load Load Transmitter Transmitter Racks Racks Cooling SCR Cooling Manifolds Manifolds HVCM K K K K K K K K K K K K 3 Klystrons per HV Tank 6-1-05 McCarthy O AK R IDGE N ATIONAL L ABORATORY 9
Hengjie Ma, 1/18/2007, JLab Eighty-One 805 MHz, 550 kW klystrons power the superconducting Linac Transmitter racks & LLRF for support of six klystrons. Three klystrons mount to a single oil tank. O AK R IDGE N ATIONAL L ABORATORY 10
Each Rack in the Superconducting Linac Hengjie Ma, 1/18/2007, JLab Contains LLRF Hardware for Two RF Systems Typical LLRF control rack installation in the The VXI crate contains: superconducting Linac. • Input/Output Controller: PowerPC running VxWorks • Utility Module: Decodes events from Real Time Data Link • Timing Module: Generates RF Gate timing signal • Two FCM/HPM pairs O AK R IDGE N ATIONAL L ABORATORY 11
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – system overview System configuration and phase reference scheme R e f e r e n c e L i RF / IF Host (“IOC”) n e Host (“IOC”) RF / IF Host (“IOC”) RF / IF Host (“IOC”) RF / IF Time : Calibration pulse : RF pulse O AK R IDGE N ATIONAL L ABORATORY 12
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – system overview FCM Electrical Specs. I-Q sampling interval:(1+1/4)*2pi • (Fs=40MHz) IF inputs: 2, 50MHz • IF ADC resolution: 14-bit • RF inputs: 2, 805/402.5MHz • Channel analog bandwidth:1MHz • High-speed output DAC:1 • DAC resolution: 14-bit • Output Frequency shift range:+/-645kHz • FPGA: XC2V1500, SDRAM: 128Mb • O AK R IDGE N ATIONAL L ABORATORY 13
The Field Control Module (FCM) consists of a Hengjie Ma, 1/18/2007, JLab motherboard and three daughterboards Digital Front End (DFE) Analog Front End (AFE) RF Output (RFO) Four 14 bit, 40 MHz ADC channels Down-converting channels: Clock & PLL circuitry One Virtex II FPGA Incident and Reflected RF One 14 bit, 80 MHz DAC (XC2V1500 – 1.5M gates) (402.5 or 805 MHz) Up-Conversion to 402.5/805 MHz IF channels: Filtering O AK R IDGE N ATIONAL L ABORATORY Cavity and Reference (50 MHz) 14
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Field Control Module (FCM): P-I feedback + AFF control Waveform plotting O AK R IDGE N ATIONAL L ABORATORY 15
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Digital implementation: from continuous ⎛ + K ⎞ = ⋅ ⋅ ⋅ G (S) H (S) R K ⎜ 1 i ⎟ c f p (1) ⎝ S ⎠ to discrete time ⎧ ⎫ ⎛ − ⎞ ) ( ) 1 Z ( = − − ⋅ − ⋅ ⋅ − + ⋅ − ⋅ ⋅ ⎜ + ⋅ ⎟ 2 1 2 G (Z) (1 Z ) 1 S C Z C Z K 1 K T ⎨ ⎬ ⎜ ⎟ c c s p i s − − 1 1 Z (2) ⎝ ⎠ ⎩ ⎭ ⎧ ⎫ ⎛ ⎞ N ∑ ⋅ + ⋅ − ⎜ n ⎟ K p 1 a Z ⎨ ⎬ n ⎝ ⎠ ⎩ ⎭ = n 0 O AK R IDGE N ATIONAL L ABORATORY 16
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Digital implementation: data flow -Kp·Cos( θ ) Kp·Sin( θ ) Kp·Cos( θ ) Kp·Cos( θ ) __ ___ __ __ -Kp·Cos( θ ) -Kp·Sin( θ ) Kp·Sin( θ ) Kp·Sin( θ ) -Is,-Qs Qs,-Is Is, Qs Is, Qs O AK R IDGE N ATIONAL L ABORATORY 17
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Digital implementation: Development system Verilog Modeling: Functionalities NO ? K O Machine YES Verification Code gen.: Test Lab. Netlists RTL GUI/Control Compilation PAR Automation software Iverilog / Xilinx ISE development ModeSim Machine Synthesis Code Gen. : XST / Synplify drivers NO YES End-to-End System Behavioral Simulation current llc system Previous VHDL flow O AK R IDGE N ATIONAL L ABORATORY 18
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Controller Performance: Stability Effect of loop delay With no loop delay With 1us loop delay O AK R IDGE N ATIONAL L ABORATORY 19
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Controller performance: Steady-state error Constraints between control gain, stability and steady-state error. Example 1: 1us delay, cavity BW=10kHz (NC) Kp=4, Kp=100 Kp=5 Ki=0 Ki=0 Ki/Ts=10kHz stable unstable stable Er=20% Error=0 O AK R IDGE N ATIONAL L ABORATORY 20
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Controller performance: Steady-state error Example 2: 1us delay, cavity BW=500Hz (SC) Kp=100, Kp=400 Kp=100 Ki=0 Ki=0 Ki/Ts=150Hz stable unstable stable Er=1% Error=0 O AK R IDGE N ATIONAL L ABORATORY 21
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Controller performance: Transient response Exam the response of a P-I controller to a step disturbance (beam loading) at the input of the plant (cavity). Rearrange so that the disturbance Becomes the input. O AK R IDGE N ATIONAL L ABORATORY 22
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Controller performance: Transient response Comparison: P-I control (dipole tune, delay=1us) vs. performance benchmark : a 2 nd -order deadbeat tune, ( Ts=5us, Wn*Ts =4.82, alpha = 1.82, undershoot 0%, overshoot<0.1%, Trise100% =6.58*Wn ) O AK R IDGE N ATIONAL L ABORATORY 23
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Basic cavity model: − ⎡ ⎤ ⎡ ⎤ ⎡ ⎤ ω Δω V I 1/2 ⋅ r = ⋅ ⋅ r ω R ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ 1/2 L Δω ω V I ⎣ ⎦ ⎣ ⎦ ⎣ ⎦ 1/2 i i Is it reasonable to use a simplistic P-I controller of LTI design in a nonlinear application ? Yes, provided in a linearized operating condition. O AK R IDGE N ATIONAL L ABORATORY 24
Hengjie Ma, 1/18/2007, JLab SNS Linac RF Control – implementations Operating feedback control with assistance of cavity filling and adaptive feedforward. Cavity filling Cavity filling + FF (with no beam) (with beam) O AK R IDGE N ATIONAL L ABORATORY 25
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