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Noise Suppression Experiment - ATF A. Gover, A.Nause, E. Dyunin Tel-Aviv University Fac. Of Engin., Dept. of Physical Electronics, Tel-Aviv, Israel THANKS TO THE OTR TECHNICAL TEAM
Physics of Collective Micro-Dynamics in a Charged Particle Beam: Spatially coherent Coulomb interaction micro-dynamics. Effect of particle self-ordering and current shot-noise suppression at optical frequencies. ECoul ESC n0-1/3 d'
Conditions for a Charged-Particle Beam to Exhibit Current Shot-Noise Suppression: In a random beam: • Cold beam: current shot-noise dominated (non-equilibrium plasma !) • Quarter wavelegth plasma wave oscillation in the longitudinal dimension Uniform beam model: [H. Haus and F. N. H. Robinson, Proc. IRE 43, 981 (1955)] [A. Gover, E. Dyunin, PRL 102, 154801 (2009)]
HOMOGENIZATION IN THE BEAM FRAME (λ=5-10 μm) 3-D simmulation with GPT A.Nause, E. Dyunin, A. Gover, JAP 107, 103101 (2010). Density In beam frame
EXPERIMENTAL SETUP - ATF Note: The chicane was not used (R56 too large). Beam transported through the straight pipe.
Experimental Setup OTR screen E-beam 1:1 imaging system Cam Picture 40 cm CCD
OTR-beam profile (expanded dynamic range of the frame grabber record M. Fedurin - ATF)
Operating Parameters Pulse length: 5 ps Beam energy: 50 – 70 MeV Beam current: 40-100 A Emittance: ~3 mm-mrad Initial beam size: 400-500 mm Convergence: ~2 mrad Acceleration phase: on crest Copper OTR screen Basler CCD camera equipped with a Nikkor macro lens (100 mm) Cam sensitivity: 0.4 – 1 mm
Experimental Results: 40% Relative Noise suppression OTR of an uncorrelated e-beam ~ N ~ Q
In reality the beam profile was far from being uniform. The experiment was conducted with strong convergence in order to pass through the long straight pipe of the chicane. The beam envelope was calculated with GPT (including space-charge) based on beam spot measurements on screens YAG1, YAG2, and quadrupole current data, confirmed in YAG 3, YAG 4. In this situation of strong convergence angle and emittance, the suppression takes place primarily in the waist, and is deteriorated by axial velocity spread.
MODEL COMPUTATION OF NOISE SUPPRESSION WITH VARYING BEAM CROSS-SECTION AND BEAM ANGULAR SPREAD MAATCHING THE EXPERIMENTAL RESULTS
Next Experimental Stage • Complement the successful free-drift noise-suppression experiment: calibrate the OTR measurement of noise, attain increased suppression factor. • Use a short dispersive section (Chicane) based on high-power trimmers. • Vary R56 using Chicane, and measure OTR in a single location after the Chicane.
DRIFT/DISPERSION TRANSPORT Gover, Phys. Plasmas 18, 123102 (2011) Dispersive Section Drift