Plasma Acceleration Presented by Mark Hogan On behalf

Plasma Acceleration Presented by: Mark Hogan On behalf of: The E-164/E-164 X Collaboration C. D. Barnes, I. Blumenfeld, F. J. Decker, P. Emma, M. J. Hogan*, R. Ischebeck, R. Iverson, N. Kirby, P. Krejcik, C. L. O'Connell, R. H. Siemann and D. Walz Stanford Linear Accelerator Center C. E. Clayton, C. Huang, D. K. Johnson, C. Joshi*, W. Lu, K. A. Marsh, W. B. Mori and M. Zhou University of California, Los Angeles S. Deng, T. Katsouleas*, P. Muggli and E. Oz University of Southern California Work supported by Department of Energy contracts DE-AC 02 -76 SF 00515 (SLAC), DE-FG 03 -92 ER 40745, DE-FG 03 -98 DP 00211, DEFG 03 -92 ER 40727, DE-AC-0376 SF 0098, and National Science Foundation grants No. ECS-9632735, DMS-9722121 and PHY-0078715. 1

Plasma Accelerators Showing Great Promise! U C L A Laser Driven Plasma Accelerators: • Accelerating Gradients > 100 Ge. V/m (measured) • Narrow Energy Spread Bunches • Interaction Length limited to mm’s Beam Driven Plasma Accelerators: Large Gradients: • Accelerating Gradients > 30 Ge. V/m (measured!) • Interaction Length not limited Unique SLAC Facilities: • FFTB • High Beam Energy • Short Bunch Length • High Peak Current • Power Density • e- & e+ Scientific Question: • Can one make & sustain high gradients in plasmas for lengths that give significant energy gain?

PWFA: Plasma Wakefield Acceleration U C L A q Looking at issues associated with applying the large focusing (MT/m) and accelerating (Ge. V/m) gradients in plasmas to high energy physics and colliders q Built on E-157 & E-162 which observed a wide range of phenomena with both electron and positron drive beams: focusing, acceleration/de-acceleration, X-ray emission, refraction, tests for hose instability… Linear PWFA Theory: Accelerating Decelerating -- -----+-++ ++ ++-+--+----+--+ ++ ++-+--+--+-++ + +-+- +++ ++ ++++ +-++-+----+--+-+++++ +++--+--+++ ++++ ++ ------- -- - --- --- electron beam Ez Short bunch! m m For and or Ez: accelerating field N: # e-/bunch z: gaussian bunch length kp: plasma wave number np: plasma density nb: beam density q A single bunch from the linac drives a large amplitude plasma wave which focus and accelerates particles q For a single bunch the plasma works as an energy transformer and transfers energy from the head to the tail

PWFA Experiments @ SLAC Share Common Apparatus U C L A Located in the FFTB Energy Spectrum “X-ray” Plasma light e. N=1. 8 1010 z=20 -12µm E=28. 5 Ge. V Li Plasma Gas Cell: H 2, Xe, NO ne≈0 -1018 cm-3 L≈2. 5 -20 cm Coherent Transition Radiation and Interferometer Optical Transition Radiators y x z ∫Cdt Imaging Cherenkov Spectrometer Radiator 25 m X-Ray Diagnostic, e-/e+ Production Dump FFTB

Beam-Plasma Experimental Results (6 Highlights) Focusing e- Phase Advance ne 1/2 L Phys. Rev. Lett. 88, 154801 (2002) Matching e- X-ray Generation Phys. Rev. Lett. 88, 135004 (2002) Wakefield Acceleration e- Phys. Rev. Lett. 93, 014802 (2004) Electron Beam Refraction at the Gas– Wakefield Acceleration e+ Plasma Boundary q 1/sinf q≈f BPM Data – Model o Phase Advance ne 1/2 L Phys. Rev. Lett. 93, 014802 (2004) Nature 411, 43 (3 May 2001) Phys. Rev. Lett. 90, 214801 (2003)

Short Bunch Generation In The SLAC Linac 50 ps U C L A Damping Ring SLAC Linac RTL 1 Ge. V 9 ps 0. 4 ps 20 -50 Ge. V FFTB <100 fs Add 12 -meter chicane compressor in linac at 1/3 -point (9 Ge. V) Existing bends compress to <100 fsec 1. 5% ~1 Å 30 k. A 80 fsec FWHM 28 Ge. V • Bunch length/current profile is the convolution of an incoming energy spectrum and the magnetic compression • Dial FFTB R 56 & linac phase, then measure incoming energy spectrum.

First Measurement of SLAC Ultra-short Bunch Length! CTR Michelson Interferometer • Fabry-Perot resonance: l=2 d/nm, m=1, 2, …, n=index of refraction • Modulation/dips in the interferogram • Smaller measured width: Autocorrelation < bunch ! • Other issues under investigation: - Detector response (pyro vs. Golay) - Alternate materials: HDPE, TPX, Si, Diamond ($$$) z ≈ 9 µm Autocorrelation: z≈9 µm Gaussian Bunch z≈18 µm or ≈60 fs

Non-Invasive Energy Spectrometer Upstream of Plasma U C L A

Phase Space Retrieval via Li. Track* *K. • Extension of previous work on SLC - More compression stages - More free parameters - Shorter bunches • Requires good measurements, good intuition or really good guessing! • Not automated (yet!) • Single shot and non-destructive! Bane & P. Emma U C L A

Plasma Source Starts with Metal Vapor in a Heat-Pipe Oven Peak Field For A Gaussian Bunch: U C L A Ionization Rate for Li: See D. Bruhwiler et al, Physics of Plasmas 2003 Space charge fields are high enough to field (tunnel) ionize - no laser! - However, can’t just turn it off! - No timing or alignment issues - Ablation of the head - Plasma recombination not an issue

Accelerating Gradient > 27 Ge. V/m! (Sustained Over 10 cm) 31. 5 • Large energy spread after the plasma is an artifact of doing single bunch experiments 30. 5 • Electrons have gained > 2. 7 Ge. V over maximum incoming energy in 10 cm 29. 5 Energy [Ge. V] U C L A 28. 5 • Confirmation of predicted dramatic increase in gradient with move to short bunches 27. 5 • First time a PWFA has gained more than 1 Ge. V 26. 5 25. 5 • Two orders of magnitude larger than previous beam-driven results 24. 5 • Future experiments will accelerate a second “witness” bunch No Plasma np = 2. 8 x 1017 e-/cm 3 M. J. Hogan et al. Phys. Rev. Lett. 95, 054802 (2005)

Summer 2004: • Results Recently Published • Outdated within two weeks! Summer 2005: • Increased beamline apertures • Plasma Length increased from 10 to 30 cm

Summer 2004: • Results Recently Published • Outdated within two weeks! Summer 2005: • Increased beamline apertures • Plasma Length increased from 10 to 30 cm • Energy Gain > 10 Ge. V! …but spectrometer redesign necessary to transport more of the low energy electrons

Test of Notch Collimator - December 2005 Exploit Position-Time Correlation on e- bunch in FFTB Dog Leg to create separate drive and witness bunch Access to time coordinate along bunch x DE/E t 1. 2 Insert tantalum blade as notch collimator Do not compress fully to preserve two bunches separated in time 14

Test of Notch Collimator - December 2005 Energy Spectrum Before Plasma: High Energy Low Energy Spectrum After Plasma: Energy Gain Ta Blade 100 -300µm Wide 1. 6 cm Long (4 X 0) Energy Loss Shot # (Time) • Acceleration correlates with collimator location (Energy) • No signature of temporally narrow witness bunch - yet! • Other interesting phenomena also correlate (see next slide) 15 • Collimated spectra more complicated than anticipated

Always New Things to Look At! (Part 1) Energy [Ge. V] Narrow Energy Spread!

Always New Things to Look At! (Part 2) Trapped Particles Dipole Two Main Features • 4 times more charge • 104 more light!

Always New Things to Look At! (Part 2) 30 cm • • • Particles are trapped and accelerated out of the plasma Trapped particle energy scales with plasma length: 5 Ge. V @ 30 cm Primary beam (28. 5 Ge. V) is also radiating after the plasma! 20 cm 10 cm

Future Experiments - Part 1 (Next 2. 5 months) U C L A • Create two bunches via notch collimator in FFTB and accelerate witness bunch with narrow energy spread • FFTB will soon be demolished to make way for LCLS Make Highest Energy Evera@bang? SLAC! Whatthe should we do to. Electrons go out with "Far better is it to dare mighty things, to win glorious triumphs, even though checkered by failure, than to take rank with those poor spirits who neither enjoy much nor suffer much, because they live in the gray twilight that knows not victory or defeat. " Theodore Roosevelt, 1899 Use ~ 1 Meter-long Plasma to Double the Energy of Part of the Incoming Beam 28. 5 Ge. V 57 Ge. V

Future Experiments - Part 2 (A Couple Years) U C L A SABER (South Arc Beamline Experimental Region): Short Pulse e+ Are the Frontier: Evolution of a positron beam/wakefiled and final energy gain in a self-ionized plasma 5. 7 Ge. V in 39 cm

Plasma Wakefield Accelerator Research Summary U C L A Over the past 5 years 20 Peer reviewed publications covering all aspects of beam plasma interactions: Focusing (e- & e+), Transport, Refraction, Radiation Production, Acceleration (e- & e+) E-164 X Accomplishments First measurement of the SLAC Ultra-short Bunch Length Demonstration of Field Ionized Plasma Source Measured Accelerating Gradients > 27 Ge. V/m (over 30 cm) in a PWFA Autocorrelation Amplitude [a. u. ] 31. 5 Energy [Ge. V] 30. 5 29. 5 28. 5 27. 5 26. 5 25. 5 24. 5 Position [mm] Bright Future: Two bunch experiment, Energy Doubler, and longer term positrons @ SABER No Plasma Np = 2. 8 x 1017 e/cc