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

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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