Upload
noah-washington
View
217
Download
4
Tags:
Embed Size (px)
Citation preview
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
d'
n0-1/3 ESC
Conditions for a Charged-Particle Beam to Exhibit Current Shot-Noise Suppression:
bttt
eIii 0
22
2
1. Cold beam: current shot-noise dominated (non-equilibrium plasma !)2. Quarter wavelegth plasma wave oscillation in the longitudinal dimension
bN
eIiT
iT
22 1
In a random beam:
[H. Haus and F. N. H. Robinson, Proc. IRE 43, 981 (1955)]
[A. Gover, E. Dyunin, PRL 102, 154801 (2009)]
Uniform beam model:
HOMOGENIZATION IN THE BEAM FRAME (λ=5-10 μm)
DensityIn beamframe
3-D simmulation with GPT A.Nause, E. Dyunin, A. Gover, JAP 107, 103101 (2010).
EXPERIMENTAL SETUP - ATF
Note: The chicane was not used (R56 too large). Beam transported through the straight pipe.
Experimental SetupOTR screen
E-beam
1:1 imaging system
CCD
40 cm
Cam Picture
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 m
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 m
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)
Drift Dispersive Section
Experimental Setup