High resolution profile measurements Enrico Bravin CERN AB-BI DIPAC 07 21-23 May 2007 Mestre, Italy

What is high resolution for? Emittance preservation Injector chains Coasting Luminosity maximization Beam sizes at the IP Beam loss reduction High current “drivers” Beam halo / beam blow-up Development of new machines Future linear colliders Complex damping rings for nano beams 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 Profile monitors Two main families Ring Fast beam scanners Laser wire scanners Synchrotron light Rest gas ionization LINAC / transfer lines Slow beam scanners Imaging (scintillators / OTR) Wire grids (harps) 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

Emittance preservation Particularly important for hadron and linear colliders where there is no SR damping Luminosity of colliders depend on beam emittance Tight emittance budget for the acceleration chain Emittance has to be monitored precisely at each stage Measurements from ~100keV to 7TeV 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

LHC Acceleration chain e* s [p mm] [mm] LINAC ~1.0 BOOSTER 2.5 0.3 - 6.5 PS 3.0 0.3 - 15 SPS 3.5 0.1 - 6 LHC 3.7 0.1 - 2 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 Beam Size at IP In order to maximize the luminosity beams are strongly focused at the IP Tevatron x,y  30m LHC x,y  16m PEP-II x  200m y  7m SLC x  1.5m y  0.65m ILC x  600nm y  6nm CLIC x  43nm y  1nm 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 Wire scanners Principle Scan a thin wire trough the beam Detect secondary particles created in the interactions between the beam and the wire SEM (low energy electrons evaporated from the wire) by measuring the electric current on the wire High energy secondary from nuclear interactions between the atoms of the wire and the beam using a scintillator + PMT downstream of the wire 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

Flying wires in the CERN PS & PSB Need fast scans to sample the profile at a precise time in the ramp and to avoid burning the wires. scintillators + PMT and SEM 24m carbon fibres 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

Wire scanner studies @ SPS 48 0.235 IN 0.921 Blow-up [nm] 0.283 Emitt. [mu] 1.010 Sigma [mm] OUT Scan Beam blow-up due to the scans can be important LHC pilot bunch @ 26GeV Blow up is ~20% per scan Linear scanners res. ~10m 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

SLC Wire Scanners Step size 1mm 3 Scanners Horizontal + Vertical +45° Second design all 3 planes in one device 2 Carbon wires on each arm 7mm + 25mm 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 SLC Wire Scanners There were over 30 scanners installed on SLC 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 SLC Wire scanners 7m wire H=8.3m V=6.5m 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 Wire Scanners Well known and reliable technology Resolution down to a few microns, currently limited by the diameter of the wire Signal is generally large and clean (secondary particles) Need sufficient space downstream of scanner for secondary particle detectors Wires can burn if not carefully handled Can not be used near super conducting cavities due to risk of contamination (broken filament) In most accelerators the scanners are used as reference for beam sizes and emittance measurements 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 Synchrotron light Principle Charged particles emit synchrotron radiation (visible light or X Rays) when accelerated (curved) by the magnets Use an optical system to acquire images of the beam As the source is not well defined in case of bending magnets, angular filtering is needed (slits) 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

LEP synchrotron light telescopes In LEP two different types of synchrotron radiation monitors existed BEUV observing (images) in the visible (near UV) range with a complex optical system. Resolution ~ 100mm BEXE observing (profiles) the X-Ray range without imaging (or pinhole imaging). Resolution of ~50mm 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 LHC telescopes Light from D3+ undulator Light pickoff Long. diags Optical Attenuator + colour filters Cameras with pulsed intensifiers Video camera Stepping motors Slit, Corona, At 1st image plane Sph. focusing mirror f=4m Sph. Relay mirror, f=750mm 90/10 beam splitter cubes All reflective optics, diffraction limited performance from 400nm-2.5µm Optical path folded, need to keep angles low to minimise astigmatism Silicon mirror in vacuum chamber 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 Synchrotron light Widely used in electron machines Also used in high energy hadron machines (above 400 GeV) Allows continuous monitoring of the beam Ultimate limitation is diffraction Profile monitors in the X-Ray range using Fresnel zone plates have been developed with resolutions of the order of microns (KEK-ATF) 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 Laser Wire Scanners Collide a high power, focused, pulsed laser with an electron beam X-ray or g-ray are produced by Compton scattering Detect the x-ray / g-ray or the degraded electrons downstream 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

PETRA Laser Wire Scanner 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 SLC Laser Wire near IP In SLC the space available for the LWS was reduced. A different concept was used where the particle beam is scanned across the laser beam Laser waist size 400nm s= 1.14mm 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

KEK-ATF LWS (Damping Ring) At KEK-ATF a low power CW laser and Fabry-Pérot optical cavities are used in place of the high power laser Beam Sizes x100m y10m Laser Waist size W05.6m 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 Laser wire scanners Non interceptive Can be tuned to very small laser sizes Complex optical and laser system Problem measuring flat beams due to the relation between laser spot size and Raleigh length Can only be used with electrons and positrons as Compton x-session with protons is too small 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

Optical transition radiation OTR is emitted when charged particles cross the surface of a metal foil The backward emission can easily be observed by an optical system The image of the beam can be acquired BW OTR Light View port FW OTR Light e- 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 TTF2 OTR Si radiators, 3 selectable optics + filters, 10m resolution 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 OTR @ KEK-ATF Mirror has 10° angle to reduce depth of field problem Microscope optics used to achieve high resolution Beams ~5mm measured Problem with damage of the mirror surface 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

Matching in the SPS and LHC OTR foil can be very thin (little blow-up), turn by turn image acquisition over a limited number of turns is thus possible SPS has 12m Ti OTR + fast camera for matching studies Oscillations are caused by optics mismatch between the TT10 transfer line and the SPS ring 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07 OTR Very simple and reliable devices Thin radiators reduce blow-up making possible to have multiple simultaneous measurements in LINAC or transfer lines Very good spatial resolution (diffraction limited) Very high time resolution No radiators (yet) for beams densities above few 1015 e-/cm2 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07

Outlook and Acknowledgments A lot of work has been done in the field of high resolution profile measurement A lot more remains to be done and this will remain an active field for a while… I would like to thank all of you for providing excellent documentation and making this kind of presentations possible 21 May 2007 E. Bravin - CERN - "High resolution profile measurements" - DIPAC 07