BPM for FF test (ATF2)

Vladimir Vogel

KEK

2nd Nano Workshop, KEK, December 12, 2004

Three types of BPMs for LC

Main linac, ordinary BPMs

Main linac, special type BPMs

Final Focus BPMs

resolution 5 - 10 m, accuracy 8-16 m, quantity few thousands. (low impedance)

resolution 1 - 5 m, accuracy 4.0-8.0m, quantity few tens, angle, tilt, phase.

resolution 0.002 m (?), (divergence 300 mrad), accuracy 1.0-2.0m

Cavity BPM model. TM110 mode

0.5

0.5 21 11

1max

sin( / 2) ( )( ) ( / ) exp( / 2)/ 2

cav loadb

cav l

RJ kV q R QJ Q

Cross-sectional view of BINP cavity BPM 6426 MHz, (5p. in KEK ATF + 1p.). 2000. 1.- Cavity sensor . 2- Heater. 3 – Temperature sensor. 5 – Coupling slot. 6 – Output waveguide. 7 – Output feedthrough. 8 – Beam pipe. 9 – Vacuum flange. 10 – Support plate. 11 – Y position output. 12 - X position output. 13 – Heater control connector.

Std = 0.5929/1.225

Calculate position (micron)

-120 -100 -80 -60 -40 -20 0

BP

M#2

(mic

ron)

-80

-70

-60

-50

-40

-30

-20

-10

0

Std=200 nm

BINP cavity BPM for DESY TTF (2p.now SLAC?), 1999

VLEPP 14 GHz cavity BPM (3p. At BNL ATF) 1997

-24.0 -20.0 -16.0 -12.0 -8.0 -4.0(Yu+Yd)/2, m icrons

-28.0

-24.0

-20.0

-16.0

-12.0

-8.0

Ym, m

icro

ns

F it Y = 0 .99 7 * X - 2 .2 5sig m a = 0 .15 m icron s

BPM for VLEPP, 14GHz, 1991

Cavity BPM 6426 MHz F010=4.4GHz, Qex=2.600,

F110=6.426GHz, Qload=3300,F020=10.2 GHz, Qex=5800

3 1010 4 1010 5 1010 6 1010 7 10101 10 161 10 151 10 141 10 131 10 121 10 111 10 10

1 10 91 10 81 10 71 10 61 10 51 10 41 10 3

0.01

0.1

1

10

100

1 103

1 103

1 10 16

W Q 010 W02 Q 02 W11 Q 110

7.5 101024.0 109

TM010

TM110

TM020

For 1 nm resolutionmax

010 110/ 135P P db

Frequency difference:TM010 - 60 dbTM020 - 65 dbSpace mode selection:For TM010 - 40 db(?)For TM020 - 25 db(?)

Sum:TM010 - 35 db, ~ +60 nmTM020 - 25 db, ~ -17 nm

max020 110/ 125P P db

Seemingly no big problem, only electrical center of cavity move up to +43 nm, but!!!

2 2

* * ( )sin( /2* )( ) /2*

( ) exp( * / 2* )

z

z

z z

zz

U Q k ScS c

S c

For rectangular bunch charge distribution

For Gaussian bunch charge distribution

ATF beam size ~ 6 mm, if

U010/U110 ~ 6%

U110/U020 ~ 22%Position of electrical center of cavity = (60 nm +/- 3.6nm) – (17 nm-/+ 3.7nm)

For LC 300z m

BPM frequency about 18 GHz, this effect seems will be small.

Move the X-band phase sensor cavity from linac to extraction line to start study of depends BPMs resolution from bunch length

Proposal

Phase sensor F010=5712 MHz, F020=11424MHz

Reference cavity, F010=2856MHz, F020=6426MHz) Position sensor cavity 6426MHz

Angle monitor

Sensor cavity signal versus the beam trajectory angle, the phase shifter tune to +90°2002, KEK ATF

We should investigate possibility to useelectrical type mode in cavity to measurementbunch angle (Frequency ~ 8 GHz)

TE111

MHz

referencecavity

BPM cavity

Sin

Cos

714 MHz

Sin

Cos

Uin

Usw.

Q010

Q110

Principle of electronics for FF BPM

Uout=U0*T(Q)

Q010=500Q110=3300nSec

T(Q)=exp(-*/2*Q)

20*log(U010/U110) = 35db

5712 MHz

6426 MHzdF 50 MHz

U

F

714 MHz

6426

ATF2 cavity BPM, frequency ~ 9 GHz with damped Q for symmetrical modes, and magic T inside BPM

ИН

п.1

ИН

Test BPM for FFcomposite of two cavity.Not real size!Not real bunch length!

reference phase andbunch length measurement.

First:for position measurement.

Second:Cavity with very short gap 0.5-1 mm (for big divergence 300 rad.)

?

Conclusion

BPM for FF, it seems will be no problem with thermal noise,but problems with common mode rejection and angle/ tilt signals.

Further experimental studies at ATF extraction line will be required to getfull understanding of the common mode effect in cavity.

New I/Q electronics should be tested.

The new type of position sensor cavity, angle, tilt and divergence sensor cavity have be studies at ATF2.