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

M. Gasior, CERN

An Inductive Pick-Up (IPU)

for Beam Position and Current Measurement

Marek GASIOR, CERN, AB/BDIemail: [email protected]

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

5 – 7 May 2003, Mainz, Germany

Contributed Talk #01

An Inductive Pick-up for Beam Position and Current Measurement 2M. Gasior, CERN

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/BDIemail: [email protected]


Third CLIC Test Facility (CTF3)

Drive Beam Linac (f =1.5 GHz, IB = 3.5 A)A 1.5 s bunch train, some 2300 pulses

Delay Loop, f’ = f 2, I’B = IB 21.5 s bunch train 5 pieces of 140 ns

Combiner Ring, f” = f’ 5, I”B = I’B 55 pieces of 140 ns 1 train of 140 ns

Drive Beam DeceleratorMain Beam Accelerator

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


Wall Current Monitor (WCM) principle

The BEAMBEAM current is accompanied by its IMAGEIMAGE A voltage proportional to the beam current develops on the RESISTORSRESISTORS 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 FERRITEFERRITE 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


WCM as a Beam Position Monitor

For a centered BEAMBEAM the IMAGEIMAGE 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

LR

fL π2

L

RfL π2


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 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


Inductive Pick-Up – A Low Frequency Model

n

R

I

VR S

BT 2

22π2

1

n

R

Lf S

L

22π2

1

n

R

Lf S

L

22n

RR S

P

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

C

SL R

n

RL

f22π2

1

C

SL R

n

R

Lf 22π2

1


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)


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


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

2 3 5 2 3 5 2 3 5 2 3 5

F re q u en cy [H z ]

-6 0

-4 0

-2 0

0N

orm

aliz

ed a

mpl

itud

e [d

B]

1 0 0 k 1 M 1 0 M 1 0 0 M

C M R R = c o m m o n s ig n a l / d if fe re n tia l s ig n a l

d if fe ren tia l m o d e s ig n a l

c o m m o n m o d e s ig n a l

C M R R = -5 5 d B @ 1 0 0 M H z


F req u en cy [H z ]

-1 0

-5

0

Nor

mal

ized

am

plit

ude

[dB

]

1 k 1 0 k 1 0 0 k 1 M 1 0 M 1 0 0 M1 0 0

s ig n a l

s ig n a l

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: 1 kHz – 150 MHz (> 5 decades)

BW: 300 Hz – 250 MHz ( 6 decades)


IPU and AHC – Displacement Characteristics

[mm] 05.078.9position vertical

[mm] 01.061.9positionhorizontal

V

H

-1 0 -8 -6 -4 -2 0 2 4 6 8 1 0W ire d isp lacem en t [m m ]

-1

-0 .8

-0 .6

-0 .4

-0 .2

0

0 .2

0 .4

0 .6

0 .8

1

Rat

io

/

D isp lacem en t m ax . = 2 0 m m

-6 -4 -2 0 2 4 6H o rizo n ta l (H ), v e rtic a l (V ) d isp lac em en t [m m ]

-0 .2

-0 .1

0

0 .1

0 .2L

inea

rity

err

or [

mm

]H e rro r = V e rro r =

D isp la c em en t m a x . = 2 0 m m

s ig n a l is c o n s ta n tw ith in re so lu tio n o f th e m e a su re m e n t o f 0 .1 %

F req u e n c y = 1 M H z

9 .6 1 / + 0 .0 1 [m m ]9 .7 8 / + 0 .0 5 [m m ]

x = H

x =V

x - w ire d isp lac e m e n t [m m ]H

x - w ire d isp lac e m e n t [m m ]V

H

V

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.


IPU – Longitudinal Coupling Impedance

2 3 5 2 3 5 2 3

F req u en cy [H z]

0

2

4

6

8

1 0

Cou

plin

g im

peda

nce

[ ]

Z C

rea l p a r tim a g in a ry p a rt

m a g n itu d e

S 2 1 - S 2 1S 2 1

R E F IP U

R E F=Z C ZL2

1 0 M 1 0 0 M 1 G

reference

The pick-up was inserted into a 50 coaxial line

(again the wire method)

The signal drop along the pick-up was evaluated by

measuring 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)


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

0 5 1 0 1 5 2 0T im e [n s]

0

2 0

4 0

6 0

8 0

1 0 0

Nor

mal

ized

am

plit

ude

[%

]

tr 3 0 p s

1 2 1 3 1 4 1 5 1 6

9 8

1 0 0

1 0 2

1 0 4 IP Use tu p


IPU and AHC – Beam tests in the CTF2

- CH2 H - CH3 V - CH4

IPU

AHC

Electron beam of one 1 nC , 5 psRMS bunch

The signals have the rise time of about 2 ns (one division)


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


Thank you for your attention

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


Emergency slide – the parameter table

Electrical centre position error 0.1 mm

Range of linearity to 50 m 5 mm

Transformer load RS / turn number n 7 / 30

L /L inductances / ferrite r 5 H / 70 nH / 100

Primary winding resistance RP 4 m

Primary parasitic resistance RC 0.5 m

Transresistance V /IB 0.1

IPU electrode high cut-off frequency 300 MHz

IPU low cut-off frequency 150 Hz

IPU low cut-off (without the slope) 10 kHz

Titanium coating end-to-end resistance 10 (i.e. 15 / )

Coupling imp. ZC @ 1.5 / 3 GHz 9 + j2 / 10 – j0.5

Beam pipe / electrode inner diameter 40 mm / 49 mm

IPU

Length with bellows / body diameter 168 mm / 130 mm

Position sensitivity 10 mm /

Overall signal bandwidth 300 Hz – 250 MHz

Overall bandwidth (without slope) 800 Hz – 150 MHz

equivalent noise @ IB 3A / 0.3A 5 mRMS / 50 mRMS

equivalent noise, low / high gain 3 mARMS / 3 mARMS

signal amplifier gain low / high 5 / 25 dB

signal amplifier gain low / high 15 / 35 dB

IPU +

AHC

AHC CMMR @ 1 / 100 MHz 60 dB / 50 dB

Calibration current pulse 300 mA 0.1 %, 150 s

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

Documents

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