U C L A P. Muggli, Paris 2005, 06/09/05 Halo Formation and Emittance Growth of Positron Beams in Long, Dense Plasmas Patric Muggli and the E-162 Collaboration: C.D. Barnes, F.-J. Decker, M. J. Hogan, R. Iverson, C. O’Connell, P. Raimondi, R.H. Siemann, D. Walz Stanford Linear Accelerator Center B. Blue, C. E. Clayton, C. Huang, C. Joshi, K. A. Marsh, W. B. Mori, M. Zhou University of California, Los Angeles T. Katsouleas, S. Lee, P. Muggli University of Southern California

U C L A P. Muggli, Paris 2005, 06/09/05 Optical Transition Radiation (OTR) CHERENKOV (aerogel) - Spatial resolution ≈100 µm - Energy resolution ≈30 MeV - Time resolution: ≈1 ps y x y x E XPERIMENTAL S ET U P E-157: y,E x x E-162: - 1:1 imaging, spatial resolution <9 µm e -, e + N=2   z =0.7 mm E=28.5 GeV Ionizing Laser Pulse (193 nm) Li Plasma n e ≈2  cm -3 L≈1.4 m Cherenkov Radiator Streak Camera (1ps resolution) Bending Magnet X-Ray Diagnostic Optical Transition Radiators Dump ∫Cdt Quadrupoles Imaging Spectrometer 25 m IP0: IP2:

U C L A P. Muggli, Paris 2005, 06/09/05 e - : n e0 =2  cm -3, c/  p =375 µme + : n e0 =2  cm -3, c/  p =3750 µm  r =35 µm  r =700 µm Uniform focusing force (r,z)  =1.8  Non-uniform focusing force (r,z) d=2 mm Blow Out 3   beam Front Back 3  0 beam Front Back 3-D QuickPIC simulations, plasma e - density: e - & e + B EAM N EUTRALIZATION e-e- e+e+

U C L A P. Muggli, Paris 2005, 06/09/05 e - & e + F OCUSING F IELDS* E x (GV/m) x (µm) z (µm) e-e- E x (GV/m) x (µm) z (µm) e+e+ e-e- e+e+  x0 =  y0 =25 µm  z =730 µm N=1.9  e + /e - n e =1.5  cm -3 *QuickPIC Linear, no abberations Non-linear, abberations

U C L A P. Muggli, Paris 2005, 06/09/05 e - & e + F OCUSING F IELDS r=  r r=3  r r=  r r=3  r QuickPIC  x0 ≈  y0 ≈25 µm,  Nx ≈390  10 -6,  Ny ≈80  m-rad, N=1.9  e +,  z ≈730 µm, n e =1.5  10 -6, L≈1.1 cm Uniform focusing force (r,z) Non-uniform focusing force (r,z) Weaker focusing force Stronger focusing force FrontBackFrontBack e + : focusing fields vary along r and z!

U C L A P. Muggli, Paris 2005, 06/09/05 F OCUSING OF e - / e + e-e- e+e+ n e =0n e ≈10 14 cm -3 2mm Ideal Plasma Lens in Blow-Out Regime Plasma Lens with Aberrations OTR images ≈1m from plasma exit (  x ≠  y ) Qualitative differences

U C L A P. Muggli, Paris 2005, 06/09/05 E XPERIMENT / S IMULATIONS  x0 =  y0 =25µm,  Nx =390  10 -6,  Ny =80  m-rad, N=1.9  e +, L=1.4 m Downstream OTR Excellent experimental/simulation results agreement! Simulation Experiment UV Energy (mJ)

U C L A P. Muggli, Paris 2005, 06/09/05 Downstream OTR Defocusing in x and y “low”  in both planes, larger  No distinctive features (  -tron oscillations) Excellent experimental/simulation results agreement!  x0 ≈65  y0 ≈48 µm,  Nx ≈115  10 -6,  Ny ≈184  m-rad, N≈1.9  e +, L≈1.4 m E XPERIMENTAL/SIMULATION R ESULTS ExperimentSimulation UV Energy (mJ)

U C L A P. Muggli, Paris 2005, 06/09/05 y,E x E XPERIMENTAL R ESULTS e +  x0 ≈  y0 ≈25 µm,  Nx ≈390  10 -6,  Ny ≈80  m-rad, N=1.9  e +, L≈1.4 m Cherenkov/Plasma Exit UV Energy (mJ) Strong focusing in x (large  ), defocusing in y (low  ) No distinctive features (  -tron oscillations) Resolution Limit?

U C L A P. Muggli, Paris 2005, 06/09/05 Beam Size=FWHM (BAB’) Charge in the Peak=Area(BAB’) Charge in the Halo=2*Area(CDB) F IT FOR B EAMS WITH H ALO X-profile y-profile Halo

U C L A P. Muggli, Paris 2005, 06/09/05 H ALO F ORMATION  x0 ≈  y0 ≈25 µm,  Nx ≈390  10 -6,  Ny ≈80  m-rad, N=1.9  e +, L≈1.4 m Charge is conserved by the triangular fits The halo forms at low density

U C L A P. Muggli, Paris 2005, 06/09/05 H ALO F ORMATION  x0 ≈  y0 ≈25 µm,  Nx ≈390  10 -6,  Ny ≈80  m-rad, N=1.9  e +, L≈1.4 m Very nice agreement ExperimentSimulation

U C L A P. Muggli, Paris 2005, 06/09/ mJ 0.01 mJ (OFF) 1mm OFF n e =2  cm -3 H ALO F ORMATION  x0 ≈  y0 ≈25 µm,  Nx ≈390  10 -6,  Ny ≈80  m-rad, N=1.9  e +, L≈1.4 m Experiment Simulation Very similar

U C L A P. Muggli, Paris 2005, 06/09/05 B EAM/ F IELD E VOLUTION Radius (cell)  x0 =  y0 =25µm,  Nx =390  10 -6,  Ny =80  m-rad, N=1.9  Beam becomes non-Gaussian Beam size and focusing field “stop” at z≈0.7 m

U C L A P. Muggli, Paris 2005, 06/09/05 e - / e + : S LICES S IZE IN THE P LASMA Front Back e-e- e+e+  o =0.34 m, n e matched =1.6  cm --3 Head diverges ≈  0 Coherent betatron motion of the core Phase mixing of the following slices

U C L A P. Muggli, Paris 2005, 06/09/05 e - / e + : S LICE E MITTANCE Front Back e-e- e+e+ Increase in the head... Blow-out, pure ion column preserves beam emittance Phase mixing of the following slices

U C L A P. Muggli, Paris 2005, 06/09/05 C ONCLUSIONS Simulation results show emittance growth, mostly in the front and back of the bunch Simulation results confirm the experimental observations Simulation results show “hosing” in the back of the bunch Focusing of e + by a plasma is qualitatively different from that of e - : Positron bunches are focused without showing betatron oscillations … … focusing depends on  and  at plasma entrance… … show formation of a beam halo. Focusing force is nonlinear in r and z Emittance growth is expected

U C L A P. Muggli, Paris 2005, 06/09/ mJ 0.23 mJ 0.93 mJ 6.47 mJ 0.01 mJ (OFF) 1mm E XPERIMENTAL P OTR y x  x0 =  y0 =25µm,  Nx =390  10 -6,  Ny =80  m-rad, N=1.9  10 10, n e =0.75  cm -3 Focusing in x, not in y, n e “independent” No halo at low n e Triangular projected beam profiles (n e ≠0)

U C L A P. Muggli, Paris 2005, 06/09/05 S IMULATION P ROFILES  x0 =  y0 =25µm,  Nx =390  10 -6,  Ny =80  m-rad, N=1.9  Beam halo, as in experiment Focusing in DS OTR n e =0.75  cm Plasma DS OTR n e =0 Triangular projected beam profiles (n e ≠0)

U C L A P. Muggli, Paris 2005, 06/09/05 F OCUSING OF e + : H IGH n e from OTR images ≈1m from plasma exit Focusing limited by emittance growth due to plasma focusing aberrations? M.J. Hogan et al., PRL (2003). x-size reduction >3, no betatron oscillations  0x =  0y =25 µm N=1.9  e +  xN ≈10  yN ≈10  m-rad L=1.4 m