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 mm, accuracy 8-16 mm, quantity few thousands. (low impedance) resolution mm, accuracy mm, quantity few tens, angle, tilt, phase. resolution mm (?), (divergence 300 mrad), accuracy mm

Cavity BPM model. TM110 mode

Cross-sectional view of BINP cavity BPM 6426 MHz, (5p. in KEK ATF + 1p.) 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 X position output. 13 – Heater control connector. Std=200 nm

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

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

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 TM010 TM110 TM020 For 1 nm resolution Frequency difference: TM db TM db Space mode selection: For TM db(?) For TM db(?) Sum: TM db,  ~ +60 nm TM db,  ~ -17 nm Seemingly no big problem, only electrical center of cavity move up to +43 nm, but!!!

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 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 use electrical type mode in cavity to measurement bunch angle (Frequency ~ 8 GHz) TE111

      MHz reference cavity BPM cavity Sin  Cos  714 MHz Sin  Cos   Uin Usw. Q010 Q110 Principle of electronics for FF BPM Uout=U0*T(Q) Q010=500 Q110=3300  nSec T(Q)=exp(-  *  /2*Q) 20*log(U010/U110) = 35db 5712 MHz 6426 MHz dF 50 MHz U F 714 MHz 6426

ATF2 cavity BPM, frequency ~ 9 GHz with damped Q for symmetrical modes, and magic T inside BPM Test BPM for FF composite of two cavity. Not real size! Not real bunch length! reference phase and bunch length measurement. First: for position measurement. Second: Cavity with very short gap 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 get full 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.