Beam Plasma Physics Experiments at ORION Mark Hogan SLAC 2 nd ORION Workshop February 18-20, 2003

Outline Large Fields Show Large Promise in Beam-Plasma Physics Highlights of Recent Experiments Example Experiments Look towards the Working Group asking how some of the open questions might be addressed at ORION 2 nd ORION Workshop February 18-20, 2003

Recent Results III: Promise and Challenge  ORION researchers over the past few years, developed a facility for doing unique physics, and also many of the techniques and the expertise necessary for conducting next experiments  E-157 & E-162 have observed a wide range of phenomena with both electron and positron drive beams: e - & e + FocusingWakefield acceleration  1/sin  ≈≈ Electron Beam Refraction at the Gas–Plasma Boundary o BPM Data X-ray Generation – Model Phys. Rev. Lett. 2002, 2003 Nature 2002 Phys. Rev. Lett To Science 2003

o Laser Wake Field Accelerator(LWFA) A single short-pulse of photons o Self Modulated Laser Wake Field Accelerator(SMLWFA) Raman forward scattering instability o Plasma Beat Wave Accelerator(PBWA) Two-frequencies, i.e., a train of pulses Concepts For Plasma-Based Accelerators Pioneered by J.M.Dawson o Plasma Wake Field Accelerator(PWFA) A high energy electron (or positron) bunch evolves to Research into “advanced” technologies and concepts that could provide the next innovations needed by particle physics. In many cases one is applying or extending physics and technology that is its own discipline to acceleration (ex. plasma physics, laser physics…). Active community investigating high-frequency rf, two-beam accelerators, laser accelerators, and plasma accelerators.

A 100 GeV-on-100 GeV e - e + Collider Based on Plasma Afterburners 50 GeV e - 50 GeV e + e - WFA e + WFA IP LENSES Afterburners 3 km 30 m But can it lead to…?

Many Issues Need to Be Addressed First 1. Development of plasma sources capable of producing densities > e - /cm 3 over distances of several meters. 2. Quantify limitations of plasma lenses due to chromatic and spherical aberrations. 3. Stable propagation through such a long high-density ion column – beam matching and no limits due to electron hose instability. 4. Preservation of beam emittance 5. Accelerating gradients orders of magnitude larger than those studied to date – via shorter bunches and optimized profiles. 6. Beam loading of the plasma wake with ~ 50% charge of the drive beam In fact, these issues will need to be addressed for many applications of beam plasma interactions Many advances in recent years…

E-150: Plasma Lens for Electrons and Positrons Phys. Rev. Lett. 87, (2001) Built on early low-energy demonstration experiments in early to mid-nineties: FNAL (1990), JAPAN (1991), UCLA (1994)… Demonstrated plasma lensing of 28.5GeV beams

UCLA LINEAR PWFA SCALING or m However, when n b > n p, non-linear or “blow-out” regime m Scaling laws valid? E z : accelerating field N: # e - /bunch  z : gaussian bunch length k p : plasma wave number n p : plasma density n b : beam density m m For and Accelerating Decelerating Short bunch! E-157, E-162, E-164 and E-164X: All (e - or e + ) Beam Driven PWFA

UCLA Located in the FFTB e - or e + N=2·10 10  z =0.6 mm E=30 GeV Ionizing Laser Pulse (193 nm) Li Plasma n e ≈2·10 14 cm -3 L≈1.4 m Cerenkov Radiator Streak Camera (1ps resolution) X-Ray Diagnostic Optical Transition Radiators Dump 25 m ∫Cdt FFTB Not to scale! Spectrometer E-162, E-164 & E-164X: Common Experimental Apparatus A quick reminder of how we do these experiments in the FFTB…

UCLA 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 Note:  nx >  ny Plasma Focusing of Electrons and Positrons

E-150E-162FFTB G [T/m]> 10 6 > L [m] N p [e - /cm 3 ]6.5x x10 14 N/A RegimeN/A Experiments at ORION may address limitations of plasma lenses High de-magnification plasma lens could help determine the ultimate limitations of plasma lenses. For a plasma lens with length equal to the focal length the de- magnification is given by: Want small emittance, large initial beam size, but enough beam density for blow-out Limitations due to geometric and chromatic aberrations: & J. J. Su et al Phys. Rev. A 41, 3321 (1990)

UCLA Plasma OFF E-157E-162 Run 2 Phase Advance   n e 1/2 L  x (µm) Beam matched to the plasma when: - Matching minimizes spot size variations and stabilize hose instability - Places a premium on getting small spots Physical Review Letters 88, (2002) Stable Propagation Through An Extended Plasma

 No significant instability observed in E-162 with n p up to 2  cm -3, and L=1.4 m - Hose instability grows as 1 exp((k  L) 2/3 ), where k  =  p /(2  ) 1/2 c=(n p e 2 /e 0 m e 2  ) 1/2 c – E-162: n p =2  cm -3, L=1.4 m => e 4.5 =92 – E-164: n p =6  cm -3, L=0.3 m => e 5.4 =227 – E-164X: n p =2  cm -3, L=0.06 m => e 5.4 =227 1.Phys. Rev. Lett. 67, 991 (1991) 2.Phys. Rev. Lett. 88, (2002) Stable Propagation Part II no significant growth expected (?) - Theory assumes a preformed channel, neglects return currents… - Simulations include these effects and also predict little growth 2 Electron Hose Instability?

UCLA  1/sin  ≈≈ o BPM DATA Impulse Model r c =  (n b /n e ) 1/2 r b   Head Plasma, n e Asymmetric Channel Beam Steering Symmetric Channel Beam Focusing e-e Core E-157: Electron Beam Refraction At Plasma–Gas Boundary P. Muggli et al., Nature 411, 2001 Vary plasma – e - beam angle  using UV pellicle Beam centroid BPM6130, 3.8 m from the plasma center

UCLA Refraction of an Electron Beam: Interplay between Simulation & Experiment Laser off Laser on 3-D OSIRIS PIC Simulation Experiment (Cherenkov images) l 1st 1-to-1 modeling of meter-scale experiment in 3-D! P. Muggli et al., Nature 411, 2001

UCLA Phys. Rev. Lett. 88, (2002) E-162: X-Ray Emission from Betatron Motion in a Plasma Wiggler Central Photon Energy = 14.2 keV Number of Photons = 6x10 5 Peak Spectral Brightness = 7x10 18 [#/(sec-mrad 2 -mm %)]

V. Malka et al., Science 298, 1596 (2002) 200 MeV Laser Wakefield Results at Ecole Poly., France Shot 12 (10 kG) Shot 26 (10 kG) Shot 29 (5 kG) Shot 33 (5 kG) Shot 39 (2.5 kG) Shot 40 (2.5 kG) Relative # of electrons/MeV/Steradian Electron energy (in MeV) SM-LWFA electron energy spectrum Accelerating Gradient > 100 GeV/m Accelerating Gradient ~200 GeV/m! 100 MeV Laser Wakefield Results A. Ting et al NRL Plasmas Have Demonstrated Ability to Support Large Amplitude Accelerating Electric Fields Need guiding or other technique to extend interaction distance beyond a few mm

18 Accelerated Tail Particles Average Gradient ~ 70 MeV/ m Particles in the core nearly de-accelerated to zero! PWFA Acceleration Experiments at ANL-AWA and FNL-A0 N. Barov et al, PAC-2001-MOPC010, FERMILAB-CONF , Dec pp Head Tail Simulation

UCLA Head Beam Driven PWFA Single Bunch Energy Transformer OSIRIS Simulation m Average measured energy loss (slice average) : 159±40 MeV m Average measured energy gain (slice average) : 156 ±40 MeV (≈1.5  10 8 e - /slice) Experimental Data

20 A Few Examples of How ORION Might Help Address Some of These Issues

Flexible Electron Source  Opportunities for Plasma Wakefield Acceleration Bunch compression (R 56 < 0) produces a ramped profile with a sharp cutoff  high transformer ratio Gradient (GeV/m) PWFA with optimized drive bunch for transformer ratios (>2)

0-120 ps Vernier Delay chicane Fast kicker and septum magnet Combiner chicane (also compresses drive pulse) Compressed, high-current 350 MeV drive pulse Narrow energy spread, 60 MeV witness pulse, with continuously variable delay Drive and Witness Beam Production HIGH ENERGY HALL NLCTA

1+1 ≠ 2: Simulation vs. Linear Superposition 2nd beam charge density 1st beam charge density Linear superposition Nonlinear wake Use Witness Bunch Capability to Study Effects Of beam Loading on Accelerating Wake

Focusing Force Also Effected By Beam Loading Focusing force on r=0.5c/Wp 2 beam charge densities Linear superposition of focusing force Simulation result …and the Transverse (Focusing) Wake

Ion Channel Laser 1 : Proof of Principle at Optical Wavelengths “Accelerator-based synchrotron light sources play a pivotal role in the U.S. scientific community 2. Free- electron lasers (FEL’s) can provide coherent radiation at wavelengths across the electromagnetic spectrum, and recently there has been growing interest in extending FEL’s down into the X-rays to provide researchers tools to understand the nature of proteins and chromosomes. … there is exciting potential for innovative science in the range of 8-20 keV, especially if a light source can be built with a high degree of coherence, temporal brevity, and high pulse energy. To date, the most promising candidate for such a source is a linac-driven X-ray FEL. It would be a unique instrument capable of opening new areas of research in physics, materials, chemistry and biology. 1 D. H. Whittum et al Phys. Rev. Lett. 64, 2511 (1990). 2 Report of The Basic Energy Sciences Advisory Committee Panel on Novel Coherent Light Sources, Workshop at Gaithersburg Maryland, January Move beyond spontaneous x-rays to stimulated emission via the ICL (analogous to an FEL with plasma wiggler) Requires many betatron oscillations therefore lower energy beam with high density plasma 60MeV, 20cm long plasma of 6x10 15 density for visible 300MeV, 1.5m long plasma of 4x10 14 density for ultraviolet (80nm) ICL potential advantage over FEL: Short wavelength with relatively lower gamma – less linac, better coupling Shorter period and stronger wigglers via plasma ion column Build on the experience of E-157/E-162/E-164 towards an ICL

Beam Plasma Experiments: Observed a wide range of phenomena but still much to do e - & e + FocusingWakefield acceleration  1/sin  ≈≈ Electron Beam Refraction at the Gas–Plasma Boundary o BPM Data X-ray Generation – Model Still much to do:  Quantify limits for plasma lenses due to chromatic and spherical aberrations  Test for continued robustness against instabilities such as electron hose  > GeV/m acceleration via shorter bunches and tailored longitudinal profiles  Plasma source development: higher densities over several meters  Extend radiation generation from spontaneous to stimulated emission via ICL  Load the plasma wake and preserve focusing properties of the ion channel  Load the plasma wake for acceleration with narrow energy spread and high extraction efficiency Focusing of electron beams and stable propagation through an extended plasma Electron beam deflection analogous to refraction at the gas-plasma boundary X-ray generation due to betatron motion in the blown-out plasma ion column Large gradients (>100GeV/m) over mm scale distances Smaller gradients (~100MeV/m) over meter scale distances

We will focus on: Plasma wakefield physics Plasma lenses Beam quality Radiation generation Instabilities Shaped beams Beam loading Simulation and theory needs. Particularly relevant are: Ideas for experiments at ORION Ideas for diagnostics, instruments and models that could support/improve experiments. Requirements for diagnostics, instruments, beams and models (whether or not you have an idea of how to make them) that would enable/improve experiments. Redwood Room “?” Prof. Tom Katsouleas WG Leader 2 nd ORION Workshop February 18-20, 2003 Beam-Plasma Working Group