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An Inductive Pick-Up (IPU) for Beam Position and Current Measurement. Marek GASIOR, CERN, AB/BDI email: marek.gasior@cern.ch. 6th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators 5 – 7 May 2003, Mainz, Germany Contributed Talk #01.

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an inductive pick up ipu for beam position and current measurement

An Inductive Pick-Up (IPU) for Beam Position and Current Measurement

Marek GASIOR, CERN, AB/BDI

email: marek.gasior@cern.ch

6th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators

5 – 7 May 2003, Mainz, Germany

Contributed Talk #01

an inductive pick up ipu for beam position and current measurement1
An Inductive Pick-Up (IPU) for Beam Position and Current Measurement
  • Third CLIC Test Facility
    • Evolution from a WCM to an IPU
      • IPU Design and Model
        • Active Hybrid Circuit
          • Results

Marek GASIOR, CERN, AB/BDI

email: marek.gasior@cern.ch

An Inductive Pick-up for Beam Position and Current Measurement

third clic test facility ctf3
Third CLIC Test Facility (CTF3)

Delay Loop,f’=f 2, I’B= IB2

1.5 s bunch train  5 pieces of 140 ns

Drive Beam Linac (f=1.5GHz, IB=3.5A)

A 1.5 s bunch train, some 2300 pulses

Drive Beam Decelerator

Main Beam Accelerator

Combiner Ring, f”=f’5, I”B= I’B5

5 pieces of 140 ns  1 train of 140 ns

Requirements for a DBL Beam Position Monitor:

Low cut-off frequency at least 10 kHz to limit a droop of the 1.5 s pulse to about 10 %

High cut-off frequency at least 100 MHz to observe fast beam movements (rise time some 3 ns)

The bandwidth 10 kHz – 100 MHz means 4 decades

The pick-up structure must be as transparent as possible for the beam and corresponding longitudinal coupling impedance should be low in the GHz range

An Inductive Pick-up for Beam Position and Current Measurement

wall current monitor wcm principle
Wall Current Monitor (WCM) principle
  • The BEAM current is accompanied by its IMAGE
  • A voltage proportional to the beam current develops on the RESISTORS in the beam pipe gap
  • The gap must be closed by a box to avoid floating sections of the beam pipe
  • The box is filled with the FERRITE to force the image current to go over the resistors
  • The ferrite works up to a given frequency and lower frequency components flow over the box wall

An Inductive Pick-up for Beam Position and Current Measurement

wcm as a beam position monitor
WCM as a Beam Position Monitor

For a centered BEAM the IMAGE current is evenly distributed on the circumference

The image current distribution on the circumference changes with the beam position

Intensity signal () = resistor voltages summed

Position dependent signal () = voltages from opposite resistors subtracted

The  signal is also proportional to the intensity, so the position is calculated according to /

Low cut-offs depend on the gap resistance and box wall (for ) and the pipe wall (for ) inductances

An Inductive Pick-up for Beam Position and Current Measurement

a beam position sensitive wcm
G.C. Schneider, A 1.5 GHz Wide-Band Beam Position and Intensity Monitor for the Electron-Positron Accumulator (EPA), CERN/PS 87-9 (BT), 1987

A position sensitive WCM is still used in the CERN PS

It contains 96 resistors of 10  in 32 groups of 3 in series), V/IB  1 

Position measurement bandwidth is

9 MHz – 1.5 GHz (2.2 decade)

Current measurement bandwidth is

3 MHz – 1.5 GHz (2.7 decade)

A Beam Position Sensitive WCM

An Inductive Pick-up for Beam Position and Current Measurement

a new design inductive pick up ipu
An eight electrode “tight” design to avoid resonances in the GHz range

The electrodes cover 75 % of the circumference

The electrode internal diameter is only 9 mm larger then the vacuum chamber of 40 mm and it is occupied by the ceramic insertion (alumina)

The transformers are as small as possible to gain high frequency cut-off with many turns

The transformers are mounted on a PCB

The connection between the electrodes and the cover is made by screws

Electrode diameter step is occupied by the ceramic tube

The tube is titanium coated on the inside

A new design: Inductive Pick-Up (IPU)

MORE INDUCTANCE

LESS RESISTANCE

An Inductive Pick-up for Beam Position and Current Measurement

inductive pick up a low frequency model
Inductive Pick-Up – A Low Frequency Model

Electrodes are combined in pairs so that each transformer sees half of the load

Frequency low cut-offs are limited by connection parasitic resistances

Each transformer has one calibration turn (not shown)

n=30, RS  7  giving RT  0.1  and RP  4 m

fL  150 Hz (RP with L  5 H)

fL  10 kHz (RP with L  70 nH)

The electrode signal high cut-off frequency is beyond 300 MHz

An Inductive Pick-up for Beam Position and Current Measurement

inductive pick up new design
Inductive Pick-Up New Design
  • The ceramic tube is coated with low resistance titanium layer, resistance:end-to-end 10 , i.e.  15 /
  • Primary circuit has to have small parasitic resistances (Cu pieces, CuBe screws, gold plating)
  • Tight design, potential cavities damped with the ferrite
  • The transformers are mounted on a PCB and connected by pieces of microstrip lines (minimizing series inductances)

An Inductive Pick-up for Beam Position and Current Measurement

active hybrid circuit ahc
Active Hybrid Circuit (AHC)
  • More than four decades of bandwidth required
  • High Common Mode Rejection Ratio needed, at least -40 dB at 100 MHz
  • Active circuit with a differential amplifier
  • AD8129 – “active feedback” architecture, i.e. one feedback network needed
  • Datasheet CMRR is -42 dB at 100 MHz
  • Bandwidth 200 MHz with a gain of 10

An Inductive Pick-up for Beam Position and Current Measurement

active hybrid circuit performance
The CMRR at 100 MHz is as high as 55 dB (datasheet 42 dB)

The CMRR for frequencies below 10 MHz is limited by the measurement setup

 signal high cut-off frequency about 200 MHz

Active Hybrid Circuit – Performance

An Inductive Pick-up for Beam Position and Current Measurement

ipu and ahc frequency characteristics
IPU and AHC – Frequency Characteristics

A wire method with a 50  coaxial setup which the IPU is a part

 signal – flat to 0.5 dB within 5 decades, almost 6 decades of 3 dB bandwidth (no compensation)

 signal – 5 decades (four decades + one with an extra gain for low frequencies)

BW: 300 Hz – 250 MHz ( 6 decades)

BW: 1 kHz – 150 MHz (> 5 decades)

An Inductive Pick-up for Beam Position and Current Measurement

ipu and ahc displacement characteristics
IPU and AHC – Displacement Characteristics

A thin wire forming a coaxial line was displaced diagonally across the pick-up aperture. The measurement was done with a network analyzer: signal was applied to the wire and hybrid signals were observed.

An Inductive Pick-up for Beam Position and Current Measurement

ipu longitudinal coupling impedance
IPU – Longitudinal Coupling Impedance

reference

The pick-up was inserted into a 50  coaxial line(again the wire method)

The signal drop along the pick-up was evaluated bymeasuring the S21 scattering transmission coefficient

As a reference was measured the same setup with the pick-up replaced by an equivalent length of a tube(to be independent of the setup)

An Inductive Pick-up for Beam Position and Current Measurement

ipu time domain reflectometry measurements
IPU – Time Domain Reflectometry Measurements

The wire method with the 50  coaxial setup

A fast step was applied to the coaxial line and the reflection was observed

The electrode diameter step is visible only for components of lower frequency. Higher frequency components do not see the step since they flow over the titanium low resistance coating

An Inductive Pick-up for Beam Position and Current Measurement

ipu and ahc beam tests in the ctf2

 - CH2

H - CH3

V - CH4

IPU and AHC – Beam tests in the CTF2

IPU

AHC

  • Electron beam of one 1 nC , 5 psRMS bunch
  • The signals have the rise time of about 2 ns (one division)

An Inductive Pick-up for Beam Position and Current Measurement

conclusions
Conclusions
  • An inductive pick-up and a dedicated active hybrid circuit were designed for the drive beam linac of the CTF3
  • They allow to measure beam position with a bandwidth of 5 decades and absolute beam current over 6 decades
  • The chain IPU-AHC can be tested and calibrated in place with precise current pulses, applied to calibration turns of the IPU transformers
  • Neither the pick-up nor the AHC contain adjustable elements
  • The pick-up longitudinal coupling impedance is limited to about 10  in the GHz range

Very many thanks to J. Belleman, J. Durand, J.L. Gonzalez, L. Søby, J.P. Potier, Y. Cuvet and J.L.Chouvet

http://www.cern.ch/gasior/pap/dipac2003.ppt

An Inductive Pick-up for Beam Position and Current Measurement

thank you for your attention
Thank you for your attention

http://www.cern.ch/gasior/pap/dipac2003.ppt

An Inductive Pick-up for Beam Position and Current Measurement

emergency slide the parameter table
Emergency slide – the parameter table

An Inductive Pick-up for Beam Position and Current Measurement