The Quadrupole Pick-up in the CPS -intro and progress report PPC 3 Dec 1999 A. Jansson

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Outline  What is a quadrupole pick-up and how does it work?  What is special about the pick-up in the PS ring?  Basic idea  Prototype design  Data acquisition and treatment  Measurements  Recent design improvements  Ideas for the future...  Summary

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Introduction  In a position pick-up, the signal induced by each particle is thus the total signal gives the beam position  Assume we dispose of a signal then we can deduce the beam width

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Field Expansion in Source Moments  Assume a single particle (approximated by a line charge)  Maclaurin expansion with respect to source coordinates  Sum (integrate) over all particles in the beam  Where m ij are the moments of the beam distribution and E ij are the corresponding electric field components

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Moments and Field Components m 00 m 10 m 01 m 20 m 11 m 02  There are n+1 moments of each order n, but never more than 2 orthogonal field components!

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson The ‘Quadrupole Signal’  Measurement of the upright quadrupole field component gives the so-called quadrupole signal  Signal strenght  Dominating signal

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Quadrupole Signal Components  The frequency components of the quadrupole signal Emittance and Betatron Matching Dispersion and Dispersion Matching Injection Steering and Closed Orbit

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Electric Quadrupole Pick-up  Buffer Amplifiers  Saturation - frequency mixing  Radiation sensitive - close to beam  Hybrid  Very high CMRR needed Pick-up BufferHybridAmplifier SHVQSHVQ

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson What’s special about the PS pickup?  Magnetic coupling!  Low impedance - no active electronics needed near beam (no saturation effects or radiation problems)  Can suppress the common mode signal by coupling to radial field component Sum HorVerQuad

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson The Prototype Pick-up  Using a ceramic vacuum chamber (old Booster spare)  Vacuum reasons (no feedthrus)  Longitudinal impedance (resistive layer screens the cavity, but lets the quadrupole signal thru)  Each loop signal goes thru a 1:15 current transformer directly into the hybrid (no impedance buffer)  Installed in the PS ring in the (last days of the) winter shut down 98/99

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Data Acquisition and Analysis  Data is analysed primarily in time domain  LHC beam: 2×4 booster bunches all coming from ‘different machines’, thus each bunch has to be treated separately  The injection is a transient process Pick-up HybridAmplifier SHVQSHVQ Scope Pick-up/Wall current monitor PC

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Data treatment  Sum signal: Gaussian fit to find peak current, bunch length and arrival time for each bunch passage.  Use knowledge of arrival time and bunch length to reduce the number of free parameters in the fit to the H, V, and Q signals (significantly reduces noise)  Spin-off  Bunch synchronisation  RF matching  Coherent oscillations  Inclusion of known pick-up imperfections (ongoing)

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson LabView Application Program

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Beam measurements Beam measurements  Beam envelope oscillations due to betatron and dispersion mismatch  Strong damping due to space charge tune spread  Beam envelope oscillations due to coupling  ‘Uncoupled’ beam injected into a coupled machine

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson An improved lab prototype  Metal sheets in the (electric) symmetry planes for the quadrupole mode.  Suppresses dipole and sum signal  Improves the longitudinal impedance  Improvement of the pick-up transformers in order to further enhance the high frequency CMRR (ongoing)  Simulations show that the coating resistance can be reduced to 2-3   (Z L ~ 1.5  )

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson  Pick-up response to a wire antenna displaced along the horizontal axis  CMRR of single loop dB (improvements for HF underway) Lab measurements

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson An ‘ideal’ detection system  Two complementary pick-ups!  Can detect all combinations of horizontal and vertical mismatch, independent of tune (and without FFT analysis)  Can (roughly) measure transverse emittances on a turn-by-turn basis  Single shot accuracy ~0.5  m (statistical, main systematics from , ~10%) with present pick-up system  Possible in the PS ring, from point of view of space and beam optics  ~ n  /2  H <<  V  V <<  H

3/12/99PPC - The Quadrupole Pick-up in the CPS - A. Jansson Summary  Quadrupole pick-ups can be used as a ‘watchdogs’ for detecting (and correcting)  Betatron and dispersion matching  Injection steering  RF matching  Bunch synchronisation  Two quadrupole pick-ups can measure the emittance!  In addition, quadrupole pick- ups are useful to study things like  Space charge effects (detuning and damping)  Coupling and matching of coupled machines  …  Our experience with the new quadrupole pick-up design is good. Further improvements are foreseen for the final version (both HW & SW).