The Beam Position Monitor Readout System

1
The Beam Position Monitor Readout System

• John Carter
• 16th January 2004

carter_at_pp.rhul.ac.uk
2
Overview

• Introduction
• Beam Position Monitor (BPM) Details
• SEDAC Hardware
• Software design
• BPM Readout Software
• Conclusions Outlook

3
Introduction

• BPM situated next to the Interaction Point
• Provides a timing signal
• Pulse used to measure instant that a positron
  bunch passes the Laser IP
• Can check that e bunch and laser crossing paths
  in time
• Position measurement
• Verify the interaction point spatially

4
BPM Technical Info

• How the BPM works
• Consists of four Pickups
• Registers a voltage when a charged bunch passes
• Plate reading dependant on distance to the bunch
• signal-processing method

HERA Beam Dynamics Seminar, J. Keil, July 2003
5
BPM Technical Info

• Processing the BPM signal
• Filter out the high frequency noise using
  low-pass filter
• 0 63dB selectable attenuator to further enhance
  signal/noise ratio
• Track and Hold Amplifier module to measure the
  amplitudes to pass on to the ADC card
• ADC data read into the computer

6
SEDAC Hardware

• SErial Data ACquisition Hardware
• In-house system designed for DESY in 1979
• CC3e Crate Controller directly receives the BPM
  data
• SEDAC-PC System provides the interface between
  CC3e and computer via LPT port
• Data transferred as 16-bit packets (Telegrams)
• Contains data and data status information
• Up to 4KHz read/write rate

Standard Crate Controller CC3e
SEDAC-PC System
http//desyntwww.desy.de/mdi/mdi1/Wendorf/Sekomp/A
nfang.html
7
The BPM Signal

• Four symmetric pulses 24ns apart

BPM Signal
Photodiode at the IP
8
Software Design

• Interface with the SEDAC hardware
• Initialising the hardware
• Set trigger to internal mode
• Set initial attenuation value
• Set number of bunch passings to accumulate and
  average over
• Reset any overload or signal error flags
• Setting attenuation value
• Need ability to adjust the attenuator value if
  overload errors received
• Checking for errors
• Every time data is read/written checks must be
  made on the Telegram status
• Errors in data can result in inaccurate position
  information

9
Software Design

• Access the BPM plate data
• Check for overflow and over-speed errors
• Overflow errors due to saturation of data (e.g.
  too much noise or large change in PETRA beam
  current)
• Over-speed errors due to requesting information
  too fast or when SEDAC hardware not ready
• Adjust attenuator accordingly
• Produce Vertical and Horizontal position of
  bunches
• Process the BPM plate data using the x and y
  algorithms
• Display values onscreen
• Graphical representation

10
Writing the Code

• Written in Microsoft Visual Basic environment
• Preferred language for PETRA control-room
  diagnostics
• Possibility to include controls for
• LabVIEW software
• ActiveX Controls
• DESYNT networking protocols
• Accelerator Component Orientated Programming
  (ACOP)
• Uses standard SEDAC programming libraries

11
BPM Readout Software

• Software Features
• Auto-initialising of hardware
• Auto-attenuation (at start-up)
• Auto-reading of BPM data
• Adjustable time intervals between readings
• Logging position data to file
• At same rate as BPM readings or
• Custom logging rate or
• When specifically requested
• One-touch preset to open a file and start data
  taking
• Tracing of recent beam positions
• Full trace history
• Last ten positions displayed at all times
• Numerical average of last ten positions
• Zoom function on the Graph
• Zoom into a particular region
• Network capability using ACOP

12
Conclusion Outlook

• A BPM readout system was designed to aid the LBBD
  Laserwire project
• Currently used to maintain positron beam
  positions whilst testing the Laserwire
• For example, keeping same position whilst
  changing the angle of the positron beam at the
  Laserwire IP
• Future plans
• Combine with the CCD software to provide a single
  application
• Link this application to the PETRA control-room
  to perform as a diagnostic tool
• Design a general framework to combine all the
  sub-systems, including BPM software, under a
  single command
• Any other upgrades/modifications as required