Optical Diagnostics of High- Brightness Electron Beams Victor A. Verzilov Synchrotrone Trieste ICFA AABD Workshop, Chia Laguna, Sardenia Introduction ID of a high-brightness beam high charge per bunch (1 nC and more) small transverse and longitudinal beam dimensions extremely small normalized emittances high peak current space-charge effects in the beam dynamics Two missions of beam diagnostics Provide instruments for study of the physics Assist in delivering high quality beams for applications Every machine is as good as its diagnostics Introduction (continue) Vertical and horizontal emittances Transverse beam profile Beam trajectory Energy and energy spread Bunch length Longitudinal bunch shape Charge per bunch Current (peak and average) Bunch-to-bunch jitter Some of the parameters are measured by traditional methods, others require specific techniques and instrumentations For high-brightness beams control of following parameters is essential Specific requirements Take into account space charge forces Resolution from several millimeters to few tens of micrometers in both longitudinal and transverse plane Large dynamic range both in terms of beam intensity and measuring interval Non-invasive Single-shot Real time Jitter-free and synchronized Usual (stability, reliability,etc) Optical diagnostics and others Optical diagnostics are based on analysis of photons generated by a beam in related processes or make use of other optical methods (lasers, etc.) This talk reports the current status of optical diagnostics of high- brightness beams Reasons significant progress make an essential part of available tools impossible to cover everything Other techniques wire scanners zero phasing transverse rf deflection cavity high-order BPM Outline Transverse and longitudinal profile measurements give the largest amount of information about beam parameters Transverse plane Spatial resolution is a key issue Survival problem for intercepting monitors Non-invasive methods Emittance measurement issues Longitudinal plane Coherent radiation is a primary tool Direct spectral measurements Fourier transform CDR vs CTR Electro-optical sampling Transverse plane OTR vs inorganic scintillators at a glance OTR instantaneous emission linearity (no saturation effects) high resolution surface effect: thickness doesnt matter small perturbation to the beam (small thickness) small radiation background (small thickness) can be used in a wide range of relatively low photon yield (limitation in pepper-pot measurements) Scintillators ( YAG:Ce, YAP:Ce, oth.) high sensitivity no grain structure time response ~ 100ns conformance to HV radiation resistance bulk effect TR spatial resolution FWHM resolution is 2-3 times of the classical PSF scales as ~ tails problem; mask can help high-resolution is experimentally confirmed [CEBAF(4 GeV) SLAC (30 GeV)] OTR resolution is determined by the angular acceptance Scintillator resolution A.Murokh et al. BNL-ATF Recent experiment at BNL expressed concerns about micrometer-level resolution. Strong discrepancy in the beam size compared to OTR and wire scans was observed. Confirmed at ANL nC 30-40% discrepancy Q=0.5nC Instantaneous heating. TR case N.Golubeva, V.Balandin TTF Temperature limits Si Melting Thermal stress 1200 Al Melting Thermal stress Si: 300um. For Al values ten times smaller Heating by a bunch train 20um 50um 9MHz 1MHz N.Golubeva, V.Balandin TTF Two cooling processes contribute to the temperature balance Radiation cooling ~ temperature to the power of 4 Heat conduction depends on the thermal conductivity and temperature gradient 20 um 1nC 90 Thompson scattering W.P.Leemans et al. LBNL Noninvasive Both transverse and longitudinal profiles Synchronization Powerful laser Limited applicability e-beam: 50 laser: m; fs 5 ph/bunch 66 m FWHM Diffraction radiation Diffraction radiation is emitted when a particle passes in the proximity of optical discontinuities (apertures ) DR characteristics depend on the ratio of the aperture size to the parameter DR intensity ~ e -a/ and is strongly suppressed at wavelengths