WELCOME TO IHEP
RF Phase Control for BEPCII Linac Accelerator
Wenchun Gao
CONTENTS PART 1 Requirement and Capability PART 2 Configuration and Technology PART 3 Implementation of Key
Components
PART 1
Requirement and Capability
The Origin of RF Phase Control
The particle energy spread is effected by phase error according the following equation,
E/E1/2(/2+n/N)2
where is angular spread of particle distribution, n is the algebraic sum of the individual phasing errors of accelerating sections and N is the number of accelerating sections.
RF phase control aims at keeping the phase error n within its designated range.
Phase Requirement of BEPCII
The microwave of 2856MHz is used in BEPCII injector to boost the energy of electrons and positrons.
The limitation of maximum deviation of 2 from optimum phasing location is put on the RF phasing system by general design of BEPCII injector.
|Phase error|≤ 2
RF Phase decomposition Given a point on beam line, if the optimum
drive phase of microwave may be acquired by adjust the corresponding phase shifter, then the drive phase at this point may be decomposed as
=0+s(t)+q(t) where 0 is the optimum drive phase, s(t) is
phase drift caused by all sorts of real physical devices and varies slowly, q(t) is random item called phase noise also caused by physical devices and varies quickly.
RF Phase Control Capability
RF phasing system can only work out phase drift item of s(t) through measurement and dynamically eliminate the effect of s(t).
Estimation theory will be used in RF phasing control algorithms.
PART 2
Configuration and Technology
Framework of BEPCII Injector
e- gun
K1
Osc. PSK
PB B A1
PS
Att
Amp
Drive line
Beam line
PS
A2 A3 A4 A5
e+ PS
K2
ED
PS
Kj
Topology Structure of RF Phasing System of BEPCII
InjectorSubsystem of computer analysis and control on the basis of EPICS
(Phasing control, data collection and analysis in mid and long term, interface to other systems)
phase reference line
optic fibercommuni-cation link
servocontrol
shifterattenuator
energy doubler
PAD
PAD
servocontrol
shifterattenuator
PAD
oscillator2856MHz
modulatoramplifier
Drive linee+ phase shifter
K1 K16
accelerating structure accelerating structure
PAD
e
Technology of RF Phase Control for BEPCII Injector
To put up phase reference line along BEPCII injector gallery by means of optical technology to provide a benchmark for phase measurement at each individual klystron station.
To make precise phase & amplitude measurement devices with technology of digital signal processing.
Autonomous phase & amplitude adjustment equipment based on phase-locked loop fundamentals will be installed for each individual klystron station.
To connect the distributed RF phase system with optic fiber and have its parts communicate with digital stream through these optic links in order to enhance the capability of the system to immunize against interference.
To study the RF phasing system of BEPCII injector and design the control algorithm on the basis of probability, statistics and stochastics.
To prepare to introduce EPICS into high level phase control.
Configuration of RF phasing system of BEPCII
injector Next page
Large capacity data recorder
LAN
ServocontrollerIA
Kj
Drive line
Energy doubler
Linac control
Accelerating structure
PAD PAD
ADC
Oscillator2856MHz E/O
O/E
K1
Signal validity identifier
VME frame
calculator Data packer & upward communicatorcontroller
e- gunBeam line
Phase reference line, single mode optic fiber
Four levels of RF Phasing System Configuration
The top level includes the large capacity data recorder for mid-term and long-term data collection, and a global computer for data analysis, global task control and task interface to other exterior systems.
The second level is a LAN connecting global level with local control level situated at each individual klystron station by optic fiber communication links.
The third level is the local control level distributed with similar devices at each individual klystron station along the klystron gallery. Its main parts are PAD and VME units.
The bottom level is optic fiber phase reference line established as a phase measurement benchmark for PAD at each klystron station.
PART 3
Implementation of Key Components
Autonomous phase adjuster for each individual klystron
station.
Input si(t) Klystron stationPhase shifterOutput so(t)
Phase measurement
PAD
Kalman filter
controller
i(t) o(t)
o,r(t)=o(t)-r(t)
sr(t)
Optic fiber phase reference line
E[s(t)]
Digital PAD
Digital signal is not apt to be interfered. Digital PAD may reduce the difficulties of analog circuit design in
PAD and a PAD insensitive to temperature is available.
so(t) RFMixer
Local Osc.
Mixer
sr(t)
Phase reference line
IF
IF
ADC
ADC
Digital signalprocessing
o,r(t)=o(t)-r(t)Drive pulsedetector
Memory
Memory
optic phase reference line
The figure above is only a simplified optic phase reference line. phase-locked technique is often needed in optic phase reference line.
Osc.2856MHz
Modulator
Single mode laser
Optic fiber Optic phase reference line
Optical receiver
Optical transmitter
2856MHz reference signal
PAD
SUMMARY RF phase control plays an important role in BEPC
II Linac accelerator. A phase error of less than 2 is put on RF phase co
ntrol by BEPCII Linac design. Many types of advanced technology, such as opti
cal technique, digital signal processing and EPICS, etc, will be applied to ensure the RF phase control performance.
The preliminary design is finished and detail design has begun.
THANK YOU