# Presentation: 200141

## Beam Current MonitorsLunch-Time Seminar

- Martin Kesselman
- April 12, 2001

- BCM Lunchtime Seminar

## WHAT DO WE WANT TO MEASURE?

- Number of charged particles in the beam
- A non-destructive measurement
- Measure current
- Number of charged particles per unit time
- Integrate over total beam pulse to get total charge

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## BASICS - Fields & Forces

- v

- CHARGE

- MOVING
- CHARGE

- MAGNETS

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## CURRENT MEASURING INSTRUMENTS

- Faraday Cup
- Wall Current Monitor
- Beam Position Monitor
- Current Transformer
- Others

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## Faraday Cup - Simplified

- +

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## Wall Current Monitor - Simplified

- Volt
- Meter

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## Beam Position Monitor - Simplified

- Zo

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## Beam Position Monitor - Simplified

- +

- ++++++++

- ++++++++

- - - - - - -

**- - - - - - -**

**- - - - - - -**

**- - - - - -- -**

- Zo

- Zo

- Zo

- Reflection

- R

- R

- Zo

- Ibeam

- Iwall

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## BASIC CURRENT TRANSFORMER

- v

- Varying
- Current

- Magnetic Field

-  is proportional to I

- Toroidal Core

- R

- I out is 1/N times I in

- N turns

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## Placing Transformer Inside the Beam Pipe

***Placing Transformer Inside the Beam Pipe***

- Beam Pipe

- Shroud

- Ceramic Gap
- Vacuum Seal

- Transformer

- Connected to pipe

- Connected to pipe

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## BCM Testing Fixture

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## Large Testing Fixture

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## 220mm Inside Diameter Current Transformer

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## Example Transformer

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## SNS Ring Beam Current Readout

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## Short Rise Time- Long Decay Time

- 

- 

- 

- LOW PASS

- HIGH PASS

- BAND PASS

- Rise Time

- Droop

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## Droop in Current Transformer Signals

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## Compensating for Droop

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## HEBT Beam Instrumentation

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## SNS Ring Instrumentation

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## RTBT Beam Instrumentation

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## Beam Current Monitor Distribution

- * not finalized

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## Analog Front End & Digitizer Block Diagram

- -40 dB

- AD602A
- or AD603
- -10dB to +30dB

- FILTER

- -34dB to +26dB

- 40MHz or 60MHz Clock (continuous)

- 8 Bits

- 14 Bits

- GAIN

- DATA

- 78 Ohms

- SWITCHED
- ATTENUATOR
- 0dB,-20dB,-40dB

- 1:100
- 15mA to 60 Amps

- 6mV
-  to
- 23.4 V

- 0.12 V for 15mA
- 0.47V for 60mA
- 0.47V for 60A

- AD6644
- 14 Bit
- +/- 1.1V

- 1.05MHz rf

- REG.

- AD8131
- Diff. Out

- DIGITAL INTERFACE

- DIGITIZER

- FRONT END

- Dual-amps switched

- Duplicated for switched amps

- 7MHz Gaussian
- LP Filter

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## Partitioning Options

- ANALOG FRONT END
- and BAND-LIMITING

- DIGITIZER

- DIGITAL INTERFACE
- Averaging, Circular Buffer, Gain Memory,
- Gain Correction, Baseline Restore,
- Integration, Time-stamp

- TIMING
- REFERENCES
- 60MHz Sampling Clock
- RING Ref., etc.

- DIFFERENTIAL
- INPUT

- DIFFERENTIAL
- INPUT

- SENSOR

- STATUS

-  SETTING INFO

- Gain, Ref., etc.

-  SETTING INFO

- Gain, Ref., etc.

- STATUS

- Separate Boards

- Digitizer with Interface

- Digitizer with Analog Front End

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## Digital Interface

- 1.05MHz ( f) RING Ref.

- 1.05MHz RING Ref

- PLL and  TIMING

- 67MHz Clock

- CIRCULAR
- DATA MEMORY
- FIFO

- 8 Bits

- GAIN &
- SETTINGS
-  MEMORY

- Gate Control

- 1mS GATE

- PC INTERFACE

- EVENT TRIGGER

- LOCAL COMPUTER

- DIGITIZER

- DATA

- Data Timing Out

- Data Timing In

- TIMING

- Timing

- DATA

- DATA

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## Information to Controls

- All data time-stamped
- Average Current/Charge per macro-pulse
- Average Current/Charge per Mini-pulse
- Time history for a macro-pulse
- Time history for a single mini-pulse
- Mode Information
- Gain selection
- Event markers
- Ring Revolution rate
- High speed digitizer capability

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## Simplified Equivalent Circuit

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