# Presentation: 687702

## BEPC II TIMING SYSTEM

- EPICS Seminar
- Presented by Ma zhenhan IHEP
- 20.August 2002

## Functions 

- Providing a series of synchronization signals for accelerator and other related devices.
- Providing start pulse signals for the storage ring  diagnostic system as time references.

## Operation Modes

- Colliding mode
-         a. Single bunch injection
-                  One bunch for one injection.
-                  93 bunches will be reached.
-                  the beam interval is 2.4m.
-         b.  Two bunch injection
-                  Two bunches for one injection, their interval time is 56ns.
-                  93 bunches will be reached.
-                  the beam interval is 2.4m.

## Operation Mode

- SR mode
-          Single bunch injection
-          The minimum bunch interval time is 2ns.

## Basic parameters and  requirements 

-                                   **colliding mode                SR mode**
**Storage ring RF                                499.8 MHZ****                  ****499.8 MHZ**** **
**Storage ring Perimeter                     237.193 m                         241.396 m**
**Rotation Frequency                         1.264 MHZ                        1.242MHZ**** **
**Storage ring harmonic          **
**wave number                                     396                                       402 **
**Linac RF                                            2856MHZ                          2856MHZ **
**Injection repeat Frequency               50                                           50**

## Requirement to Timing System

- The trigger signal of Linac electronic gun must be strictly  synchronous with storage ring high frequency signal.
- The jitter of timing system to the bucket reception center will be less than ±70 ps。
- The jitter of trigger signals for Linac klystrons will be less than 5ns.
- The storage ring reference signal phase can be adjusted from-180o to+180o.
- 396 buckets can be selected freely during the colliding mode injection.
-           402 buckets can be selected freely during the SR mode injection.
- In order to ensure that  e- and e+ can collide right at the colliding point,  the e- timing phase and e+ timing phase can be adjusted.
- The bucket selection of timing system and part of parameters can be controlled by IOC through central console. The software will be EPICS.

## BEPCII Timing System Design

- Reference signals will be considered to adopt phase locked loop technology to depress the time jitter.
- Rotation frequencies will be switched according to the operation modes.
-  The timing system will be considered to compensate for the tiny difference of the two rings.
- The timing system will use E/O and O/E and other connectors to eliminate the electromagnet interference.

## BEPCII Timing System Block Diagram

## BEPCII Timing System Phase Lock Scheme 

- We select high stable 571.2 MHz synthesizer frequency source to generate the 2856 MHz and 499.8MHZ reference signals.
-      .   The 571.2 MHz reference frequency will be multiplied by 5 to generate the
-          2856 MHz reference signal .
-      .   The 571.2 MHz synthesizer frequency  will generate 499.8MHz reference
-          signal with phase locked technology.  We consider 71.4 MHZ common
-          reference frequency as phase detector inputs.  499.8MHz reference
-          frequency is the voltage controlled oscillator output . 71.4 MHZ common
-          reference frequencies are generated from 8 divide 571.2MHz and 7 divide 499.8MHz.

## BEPCII Timing System Reference Signal Transmission

- BEPCII reference signal 499.8 MHz and other fractional frequencies will be used frequently,so the degree of accuracy needed will be high enough to make sure all the systems can work well.
- PSOF can be used to transfer reference signals and trigger pulses.
- Some other anti-interference  measures will also be adopted to resist the electromagnet interference .

## BEPCII Timing System Bucket Selection

- The time interval can be set freely.
- All of the 396 buckets can be selected to receive the bunches.
-  At most 93 bunches can be injected to the storage ring according to the BEPCII physical request.

## BPECII Timing System Reference Signals’ synchronization  

- The timing system reference signal should be synchronous with trigger pulse.
- RF 499.8 MHz and rotation frequency should be strictly synchronous with repetition frequency of 50HZ.
- Besides, the signal transmission method, cable delay and signal attenuation of the synchronizing pulses which are sent to the devices should also be considered.

## BEPCII Timing System Time Relationship Graph

## Main Devices of BEPCII Timing System

**RF Signal                  Agilent 8648C**
- Frequency Range      9 kHz - 3200 MHz
- Resolution                  0.001 Hz
- Output  Power            <= 2500 MHz          +13 dBm - -136 dBm
-                                              <= 4000 MHz          +10 dBm - -136 dBm
- Precision & Stability
-                 Normal:without the time stabilizing  plug-in 1E5
-                                aging     <±2 ppm/year
-                                 temp      <±1 ppm(Environment temperature 25±5oC)
-                                 voltage  <±0.5 ppm (220V±5%)
-                 High stability:with the time stabilizing  plug-in 1E5
-                                aging <±0.1 ppm/year,<±0.0005 ppm/day
-                                 temp  <±0.01 ppm( Environment temperature 25±5oC)
-                                 voltage <±0.1 ppm (220V±5%)
- Spectrum purity  Good

## BEPCII Timing System Main Equipment Modules

- Phase Shifter
-        a. The phase shifter is used to adjust the output phase of the 499.8 MHz to ensure that the bunch can be injected into the bucket properly.
-        b. The phase shift range should be ±180o,the phase adjust voltage should be ±10 V.
- Rotation Frequency generator
-         a. There are two rotation frequencies in BEPCII system, so the generator should generate two frequencies.
-         b. The rotation frequency can be acquired by dividing the RF 499.8 MHz.

## BEPCII Timing System Main Equipment Modules

- High precision synchronization module
-           a. This module can lock the trigger signal and reference frequencies
-                together.
-           b.  The synchronous pulse trigger signals which are generated by
-                 this module are:   electronic gun trigger, LINAC synchronizing
-                device  triggers and storage ring synchronizing device
-                triggers.
- High precision delay module
-          This module is used in the bucket selection. The module should adopt VME plug-in. 499.8 MHz signal is the time input of the module, and the time step is 2ns.

## BEPCII Timing System Main Equipment Modules

- Optical Fiber Transceivers
- BEPCII timing system should adopt optical fiber to eliminate electromagnet interference.
- Time adjustment modules
- BEPCII Timing system will use lots of high precision and high stability time counters. The time resolution should be  several ns to several μs. These parameters can be set through computers.

## Summary

- BEPCII timing system can work under the colliding mode and SR mode,and can also serves  for the two rings structure of BEPCII。
- BEPCII timing system  can easily realize the bucket selection.
- The requirement to the BEPCII timing system is so high that this timing system will be the best timing system domestically after its establishment.
- We still have many problems to be solved in the future.