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.

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.

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

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.

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 ~ 2.5-4 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

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

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

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, 3-5 mm in Y bunch length: 700 mm beam energy: 30 GeV normal emittance: 3-5 x 10-5 m rad in X 0.3-0.6 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: 250-1000 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

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

Schematic Layout of the Experiment

Differential Pumping System

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

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

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

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

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

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