1. of High-Energy, High-Density Electron and Positron Beams
Plasma Focusing
of High-Energy, High-Density
Electron and Positron Beams
Hector A. Baldis
ILSA / Lawrence Livermore Nat. Laboratory
and
Dep.Applied Sciences, UC Davis
for
SLAC-E150 Plasma Lens Collaboration
Stanford University
APS-DPP Meeting, Quebec
October 23-27, 2000
This work was performed under the auspices of the U.S. Department of Energy by University of California
Lawrence Livermore National Laboratory, under contract No. W-7405-Eng-48.

2. Principle of the Plasma Lens
Motivation for the plasma lens:
100 to 1000 times stronger than conventional magnets
focuses beam in X and Y simultaneously
focuses both electrons and positrons
smaller spot size and enhanced luminosity
possible simplification of Final Focusing System (FFS)
In vacuum, there is no net
Lorentz force on the beam
In a plasma, E-field is neutralized;
B-field pinches the beam.

3. Why a Plasma Lens ? Linear collider luminosity ~1/sx sy.
~10 km
Linear collider luminosity ~1/sx sy.
Plasma lens is super strong:
of order 1000 Tesla / cm;
about 1000 times stronger than
conventional quadrupoles.
For SLC/NLC, an enhancement of
luminosity by a factor of
approximately 5 is possible.
Potential reduction of complexity and
length of FFS in linear collider.
Plasma lens focuses electrons
as well as positrons
~5 km

4. Theory of plasma lens focusing was first proposed by Pisin Chen in1987
An electron beam
traversing a plasma
The parabolic dashed curves within
the beam indicates the longitudinal
density distribution.
The plasma electron density
relative to the beam electron density
will determine the location of the
return current.

5. Previous Experiments ANL - J.Rosenzweig,et al.,(1998)
Thick plasma lens 35 cm long with n~1-7 x 1013 cm-3
21 MeV electron beamwith n ~ x 1010 cm-3
Beam size reduced from s = 1.4 mm to s = 0.9 mm
Tokyo university - H. Nakanishi, et al., (1990)
Thin plasma lens with density n~1.4 x 1011 cm-3
18 MeV electron beam with n ~ 1.2 x 1010 cm-3
Theory for thin plasma lens is confirm
UCLA - G. Hairapetian, et al., (1993)
Thin plasma lens with n ~ 4 x 1012 cm-3
LBNL - W. Leemans, et al., (1996)
These experiments confirmed the plasma lens concept,
but operated at low electron energies
and low plasma densities

6. Goals of the E150 Experiment
Study plasma focusing for high-energy,
high-density electron and positron particle beams
in the regime relevant to high energy colliders
Better understanding of beam-plasma interactions
and benchmarking of computer codes
for future plasma lens designs
Develop compact, simple and economical
plasma lens designs suitable for high-energy
collider applications

7. E150 Collaboration
P. Chen, W. Craddock, F.J. Dekker, C. Field, R. Iverson, F. King,
J. Ng, P. Raymond,D. Walz
Stanford Linear Accelerator Center, Stanford University
H.A. Baldis, P. Bolton
Lawrence Livermore National Laboratory
D. Cline, Y. Fukui, V. Kumar
University of California, Los Angeles
C. Crawford, R. Noble
Fermi National Accelerator Laboratory
K. Nakajima
KEK-National Laboratory for High Energy Physics
A. Ogata
Hiroshima University
A. W. Weidemann
University of Tennessee

8. Parameters of the E150 Experiment
Final Focus Test Beam Facility (FFTB) beam parameters (e- and e+)
bunch charge: 1,5 x 1010 (electrons or positrons) per pulse
beam size: 5-8 mm in X, mm in Y
bunch length: 700 mm
beam energy: 30 GeV
normal emittance: 3-5 x 10-5 m rad in X
x 10-5 m rad in Y
Gas Jet
gas: N2 or H2, neutral density ~3 x 1018 /cm3
nozzle size: 3 mm
gas pressure: lb per square inch
Plasma Production
beam-induced ionization: ~7% efficiency
laser-induced ionization: ~45% efficiency
laser pulse: l=1.06mm, E~1J, T~2-3 ns
plasma characterization: optical interferometry

9. Two ways to produce an Ionized medium
Beam Induced Ionization
Two ways to produce an Ionized medium
Self induced ionization
front part of the beam ionize the gas
remanding part focuses
Pre-formed plasma
laser pulse ionize the gas
full beam focuses

10. Schematic Layout of the Experiment

11. Differential Pumping System

12. Experimental Setup Entry port for laser and plasma diagnostics
IR Laser and Optics
Wire scanner and gas jet
Entry port for laser and
plasma diagnostics
Experimental Setup

13. Wires will break after plasma
Carbon Wire Scanner (Robert Kirby/SLAC)
Scanning wires were placed
at 0o, 45o, and 90o
Gold foils provide additional
diagnostic (bremstrahlung)
Wires will break after plasma
focussing of beams

14. Plasma Lens Measurements Setup
Beam size measurements
Scan e- or e+ beam transversely, after plasma gas target
Interleave measurements with and without plasma
Detect bremstrahlung signal off carbon fibers (4-7 mm diameter)
(as a function of beam position)
Synchrotron Radiation (SR) monitor
Detects photon flux from plasma lens induced SR
Provides an “on-line” measurement of plasma focusing gradient
Segmented monitor, 35 m down beam from the plasma lens
Beam associated background removed statistically
Plasma focusing dynamics
Cherenkov target provides a measure of divergence
Measure time-resolved (~ ps resolution) beam profile down stream

15. Beam Induced Plasma Focusing
30 GeV Electron Beam
Beam diameter at fixed Z
Beam size along Z

16. Focusing of positron beams
Plasma Focusing of Positron Beams
Focusing of positron beams
(30 GeV positrons, 1.5 x 1010 e+ per pulse)

17. Summary
Plasma lens focusing of 30 GeV positrons beam observed for the first time
Plasma focusing of both
30 GeV electrons and positrons:
spot size reduction better than 40%
plasma lens induced SR observed
plasma focusing gradient reaches 5 MTesla / m