Fill-pattern Control System for KEKB

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Fill-pattern Control Systemfor KEKB

• Eiji KIKUTANI
• KEK
• (Factories03, Oct. 2003 SLAC)

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Plan of talk

• What is the Fill Pattern Control System?
• KEKB fast timing system (brief)
• Architecture of the system
• Software system
• Summary

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1. IntroductionWhat is the Fill Pattern Control
System?
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Fill Pattern is important !

• Fill pattern ----- which rf-buckets are filled
  with beam, while which are not ---
• Fill pattern is one of the important para-meters
  in operating the rings, because
• strength of the coupled-bunch instability is
  strongly depends on the fill pattern, however,
• it is practically hard to find an ideal pattern
  from calculations.

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What is a Fill Pattern control system?

• We must find the ideal filling-pattern with the
  trial-and-error method, it means ..
• we need a fill pattern control system, which
  should be
• operator-friendly
• flexible for modification

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Fill pattern with mod. 4-bucket
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Structure of the fill pattern control system

• fill-pattern generating mechanism
• bucket selection system

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What is the fill pattern generating mechanism?

• An environment for generating a suitable fill
  pattern easily
• creates a table of rf-buckets which should be
  filled with beam (the fill-pattern table) from
  given fill pattern

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What is the bucket selection system?

• distributes the linac beam-pulses into the ring
  rf-buckets, and consequently realizes a desired
  fill pattern in the rings
• a sub-system of the KEKB fast timing system
• Real time

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2. KEB fast timing system
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KEKB fast timing system

• We have no damp-ing rings.
• Phase relation between the linac-rf and the
  ring-rf should be finely controlled to main-tain
  the injection rate high.

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RF freq. of the linac and the rings
Each rf-signal is obtained by frequency-multiplyin
g the common signal of 10.38MHz

• 10.38MHz x 275 2856MHz (for linac)
• 10.38MHz x 49 508.9MHz (for rings)

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Conceptual Block Diagram of the KEKB fast timing
system
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Timings for the injection(to maintain good
injection)
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Method for the bucket selecting

• Control the timing triggering the linac gun
• the timing is controlled by delay modules named
  TD4.

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The subrack of the Linac IOC
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3. Architecture
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Architecture of the Fill Pattern Control System

• Basically, system is constructed under the EPICS
  environment
• The system consists of 3 parts.
• The delay control (TD4) part, (in linac)
• (Linac IOC)
• the Operator-communication-part
• (Op-IOC)
• the Bunch-Current monitor part
• (BC-IOC)

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Central control room
bunch-current monitor
linac
delay modules
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Architecture of the fill pattern control system
(cont.)

• These are connected with a dedicated
  communication system with optical fiber cables
• which is realized with a commercial product
  Shared Memory System (Advanet Company in Japan)

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Shared Memory Systemhttp//www.advanet.co.jp

• Communication Port/module 1
• Communication System Fiber channel
• Bit rate 250Mbit/s
• of connectable of boards in a loop 255
  (max.)
• Wiring Distance between Board 1km (max.)
• Connector SC
• Size of Shared Memory
  128Kbyte (Expandable to 1M/2M/4M/8Mbyte
  s)

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Shared Memory System(VME memory board)
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Connection of the three IOCs
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4. Software
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Software structure of the fill pattern control
system
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Software in the Op-IOC

• Communicates with operators
• accepts the fill patterns from the built-in
  panel, as well as the fill pattern files
• generates the fill pattern table (in Shared
  Memory System), in accordance with the fill
  pattern specified by the operator

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Pattern generation
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The panel for the built-in pattern generator.
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A panel for fill pattern generation (custom)
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Software in the Linac IOC

• a Vx-Works real time task
• essentially no I/O, except for the Shared Memory
  System
• fetch the bucket address to be filled from the
  shared memory, and set the delay
• Two operation modes (BCE and non-BCE)

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Operation modes of the bucket selection system

• Bunch current equalizing (BCE) mode
• Compares bunch current of each bucket, and fill
  the beam into the bucket with smallest current
  (except for those near the last-filled buckets)
• The comparison is done pulse to pulse (every
  injection trigger)
• switch on/off easily
• Non-BCE mode
• Ad (this pulse) Ad (last pulse) some prime
  number

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Timing shake-hands of the IOC tasks

• A task in the BC-IOC is triggered by the
  injection triggering signal. After writing the
  bunch-current information into the shared memory,
  it generate the interrupt signal to the Linac-IOC
• A task in the Linac-IOC is triggered by this
  interrupt signal

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Uses of the bunch-current information

• Simple bunch current monitoring (relative
  bunch-current)
• For bucket selection. Bunch Current Equalizer
  (BCE) is working
• High bunch-current alarming

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The bunch-current board

• Bunch-current information is stored in the
  memory board ----- a by-product of the KEKB
  bunch-feedback systems.
• The stored information is read out by the trigger
  signal of the injection kicker
• No averaging process

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Bunch-current detector
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Recent improvements

• For positron beam, we started use the 2-bunch
  acceleration in the Linac
• In the positron linac, two bunches, separated
  by 98ns, are accelerated and injected to the
  ring.
• It increases the injection rate of positrons
  by a factor 2.

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Two bunch acceleration in the Linac
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Two bunch acceleration
Real-time two/single switch

• Two-bunch acceleration gt BCE off
• Every 50-th pulse single bunch acceleration gt
  BCE on (equalization)

variable
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Summary

• KEKB Fill Pattern Control System is working for
  realizing a desired fill patterns in the rings.
• The BCE technique works very well
• 2-bunch acceleration scheme works with a
  satisfactory performance