1. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 1 Quadrupole Pick-ups  What is a quadrupole pick-up?  PS pick-ups and experimental results.  Can we do the same in the LHC?Outline A. Jansson PS/OP

2. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 2 What is a quadrupole pick-up?  A non-invasive instrument sensitive to r.m.s. beam size.  Uses the non-linear terms in electrode response to particle position (very small) to measure quadrupole moment. Beam Pick-up seen along beam path A BD C Vacuum chamber

3. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 3 PS quadrupole pick-up  Position contribution can not be avoided, but can be measured and subtracted.  Design suppresses the dominating intensity signal by coupling to the radial magnetic field component. Induction loop Pick-up seen along beam path A BC D Flux line Beam

4. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 4 Installation in PS hh vv Dh Dh SS 0322 m12 m3.2 m SS 0412 m22 m2.3 m “One pick-up per plane”

5. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 5 Beam: EASTB Date: March 28, 2001 First signals 2001  Large beam size oscillations detected at start-up (due to wrong magnet settings in transfer line). Quadrupole moment evolution after PS injection Position contribution has been subtracted  First 10-20 turns are used to measure matching.  Values after filamentation are used to check position correction and measure filamented emittance.

6. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 6 10 free parameters, 20 data points Measurement of matching  Simultaneous fit to the two pick-up signals gives:  Injected emittances.  Betatron mismatches.  Horizontal dispersion mismatch.  Input parameters   H,  V, D H,  H,  V,  p,q h,q v  Most input parameters can be checked experimentally

7. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 7 Injection matching measurement  Betatron mismatch  Dispersion mismatch

8. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 8 Measurement of filamented emittance  For a stable beam, the emittance can be calculated from two (constant) pick-up readings.  Different horizontal/vertical beta function ratios at the two pick-ups are required.  Signal noise is reduced by averaging over many turns. Horizontal Vertical Wire-scanners Quad PUs Statistical error

9. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 9 Beam based calibration  Comparison Quad PU vs. Wire-scanner on stable beam.  Several different beam types.  Systematic error from:  Beta function ~10%  Dispersion ~10%  Mom. spread ~3%

10. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 10 Sensitivity  Estimated from measurement on stable beam.  Fluctuation lower than 0.5 mm 2 r.m.s. (4 10 11 p/bunch ).  This corresponds to a 1-2% beta beating at PS injection.  Improvement still possible.

11. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 11 Can the same pick-ups be used in LHC?  The pick-ups were optimized for the LHC beam parameters at injection into the PS.  The most important difference between PS and LHC is the bandwidth requirement. PSSPS LHC Bunch length50 ns1 ns Bunch spacing300 ns25 ns Max beam size5 mm4 mm1.2 mm Chamber radius76 mm78 mm22 mm Note that a design that works in the SPS would work in the LHC!

12. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 12 A pick-up adapted for the LHC  At high frequencies, the loops essentially behave like badly matched strip-line couplers. B PS: magnetic induction loop 50  OUT B  LHC/SPS: strip line couplers 50  180° 0°0° 0°0° 0°0° J.M. Belleman, PS/BD/Note 99-09 60dB  Replace each loop with two matched strip-lines and a wideband hybrid.  Good hybrid required (available).  Transfer impedances x10 larger than in PS.

13. Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001 13 Summary  Quadrupole pick-ups can measure continuously without perturbing the beam.  Both matching and emittance can be measured, on each bunch individually.  The results in the PS have been very good.  It can be done in the LHC, e.g. using strip-line couplers.