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Dive into the research topics where W. Schumaker is active.

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Featured researches published by W. Schumaker.


Nature Communications | 2015

Generation of neutral and high-density electron-positron pair plasmas in the laboratory

Gianluca Sarri; K. Poder; J. M. Cole; W. Schumaker; A. Di Piazza; Brian Reville; T. Dzelzainis; D. Doria; L. A. Gizzi; G. Grittani; S. Kar; Christoph H. Keitel; K. Krushelnick; S. Kuschel; S. P. D. Mangles; Z. Najmudin; N. Shukla; L. O. Silva; D. R. Symes; A. G. R. Thomas; M. Vargas; Jorge Vieira; M. Zepf

Electron–positron pair plasmas represent a unique state of matter, whereby there exists an intrinsic and complete symmetry between negatively charged (matter) and positively charged (antimatter) particles. These plasmas play a fundamental role in the dynamics of ultra-massive astrophysical objects and are believed to be associated with the emission of ultra-bright gamma-ray bursts. Despite extensive theoretical modelling, our knowledge of this state of matter is still speculative, owing to the extreme difficulty in recreating neutral matter–antimatter plasmas in the laboratory. Here we show that, by using a compact laser-driven setup, ion-free electron–positron plasmas with unique characteristics can be produced. Their charge neutrality (same amount of matter and antimatter), high-density and small divergence finally open up the possibility of studying electron–positron plasmas in controlled laboratory experiments.


Physical Review Letters | 2013

Table-Top Laser-Based Source of Femtosecond, Collimated, Ultrarelativistic Positron Beams

Gianluca Sarri; W. Schumaker; A. Di Piazza; M. Vargas; B. Dromey; Mark E Dieckmann; V. Chvykov; Anatoly Maksimchuk; V. Yanovsky; Zhaohan He; B. Hou; John A. Nees; A. G. R. Thomas; Christoph H. Keitel; M. Zepf; K. Krushelnick

The generation of ultrarelativistic positron beams with short duration (τ(e+) ≃ 30  fs), small divergence (θ(e+) ≃ 3  mrad), and high density (n(e+) ≃ 10(14)-10(15)  cm(-3)) from a fully optical setup is reported. The detected positron beam propagates with a high-density electron beam and γ rays of similar spectral shape and peak energy, thus closely resembling the structure of an astrophysical leptonic jet. It is envisaged that this experimental evidence, besides the intrinsic relevance to laser-driven particle acceleration, may open the pathway for the small-scale study of astrophysical leptonic jets in the laboratory.


Applied Physics Letters | 2011

X-ray phase contrast imaging of biological specimens with femtosecond pulses of betatron radiation from a compact laser plasma wakefield accelerator

S. Kneip; C. McGuffey; F. Dollar; M. S. Bloom; V. Chvykov; G. Kalintchenko; K. Krushelnick; Anatoly Maksimchuk; S. P. D. Mangles; T. Matsuoka; Z. Najmudin; C. A. J. Palmer; J. Schreiber; W. Schumaker; A. G. R. Thomas; V. Yanovsky

We show that x-rays from a recently demonstrated table top source of bright, ultrafast, coherent synchrotron radiation [Kneip et al., Nat. Phys. 6, 980 (2010)] can be applied to phase contrast imaging of biological specimens. Our scheme is based on focusing a high power short pulse laser in a tenuous gas jet, setting up a plasma wakefield accelerator that accelerates and wiggles electrons analogously to a conventional synchrotron, but on the centimeter rather than tens of meter scale. We use the scheme to record absorption and phase contrast images of a tetra fish, damselfly and yellow jacket, in particular highlighting the contrast enhancement achievable with the simple propagation technique of phase contrast imaging. Coherence and ultrafast pulse duration will allow for the study of various aspects of biomechanics.


Nature Communications | 2016

Nanosecond formation of diamond and lonsdaleite by shock compression of graphite

D. Kraus; A. Ravasio; Maxence Gauthier; Dirk O. Gericke; Jan Vorberger; Simon Frydrych; J. Helfrich; L. B. Fletcher; G. Schaumann; B. Nagler; B. Barbrel; B. Bachmann; E. J. Gamboa; S. Göde; Eduardo Granados; G. Gregori; Hae Ja Lee; P. Neumayer; W. Schumaker; T. Döppner; R. W. Falcone; S. H. Glenzer; Markus Roth

The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.


Physical Review Special Topics-accelerators and Beams | 2012

Characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation

S. Kneip; C. McGuffey; J. L. Martins; M. S. Bloom; V. Chvykov; F. Dollar; Ricardo Fonseca; S. Jolly; G. Kalintchenko; K. Krushelnick; A. Maksimchuk; S. P. D. Mangles; Z. Najmudin; C. A. J. Palmer; K. Ta Phuoc; W. Schumaker; L. O. Silva; Jorge Vieira; V. Yanovsky; A. G. R. Thomas

We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by v(perpendicular to)/v(parallel to), the measured spectrum gamma, and the transverse electron bunch size in the bubble r(perpendicular to). The latter is obtained via the measurement of the source size of the x rays emitted by the accelerating electron bunch in the bubble. We measure a normalized rms beam transverse emittance <0.5 pi mm mrad as an upper limit for a spatially Gaussian, spectrally quasimonoenergetic electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.


Applied Physics Letters | 2014

Improvements to laser wakefield accelerated electron beam stability, divergence, and energy spread using three-dimensional printed two-stage gas cell targets

M. Vargas; W. Schumaker; Zhaohan He; Z. Zhao; K. Behm; V. Chvykov; B. Hou; Karl K. Krushelnick; A. Maksimchuk; V. Yanovsky; A. G. R. Thomas

High intensity, short pulse lasers can be used to accelerate electrons to ultra-relativistic energies via laser wakefield acceleration (LWFA) [T. Tajima and J. M. Dawson, Phys. Rev. Lett. 43, 267 (1979)]. Recently, it was shown that separating the injection and acceleration processes into two distinct stages could prove beneficial in obtaining stable, high energy electron beams [Gonsalves et al., Nat. Phys. 7, 862 (2011); Liu et al., Phys. Rev. Lett. 107, 035001 (2011); Pollock et al., Phys. Rev. Lett. 107, 045001 (2011)]. Here, we use a stereolithography based 3D printer to produce two-stage gas targets for LWFA experiments on the HERCULES laser system at the University of Michigan. We demonstrate substantial improvements to the divergence, pointing stability, and energy spread of a laser wakefield accelerated electron beam compared with a single-stage gas cell or gas jet target.


Physics of Plasmas | 2014

Measurements of high-energy radiation generation from laser-wakefield accelerated electron beams

W. Schumaker; Gianluca Sarri; M. Vargas; Z. Zhao; K. Behm; V. Chvykov; B. Dromey; B. Hou; Anatoly Maksimchuk; John A. Nees; V. Yanovsky; M. Zepf; A. G. R. Thomas; Karl K. Krushelnick

Using high-energy (∼0.5 GeV) electron beams generated by laser wakefield acceleration (LWFA), bremsstrahlung radiation was created by interacting these beams with various solid targets. Secondary processes generate high-energy electrons, positrons, and neutrons, which can be measured shot-to-shot using magnetic spectrometers, short half-life activation, and Compton scattering. Presented here are proof-of-principle results from a high-resolution, high-energy gamma-ray spectrometer capable of single-shot operation, and high repetition rate activation diagnostics. We describe the techniques used in these measurements and their potential applications in diagnosing LWFA electron beams and measuring high-energy radiation from laser-plasma interactions.


Plasma Physics and Controlled Fusion | 2013

Laser-driven generation of collimated ultra-relativistic positron beams

Gianluca Sarri; W. Schumaker; A. Di Piazza; K. Poder; J. M. Cole; M. Vargas; D. Doria; S. Kushel; B. Dromey; G. Grittani; L. A. Gizzi; Mark E Dieckmann; A. Green; V. Chvykov; Anatoly Maksimchuk; V. Yanovsky; Zhaohan He; B. Hou; John A. Nees; S. Kar; Z. Najmudin; A. G. R. Thomas; Christoph H. Keitel; K. Krushelnick; Matthew Zepf

We report on recent experimental results concerning the generation of collimated (divergence of the order of a few mrad) ultra-relativistic positron beams using a fully optical system. The positron beams are generated exploiting a quantum-electrodynamic cascade initiated by the propagation of a laser-accelerated, ultra-relativistic electron beam through high-Z solid targets. As long as the target thickness is comparable to or smaller than the radiation length of the material, the divergence of the escaping positron beam is of the order of the inverse of its Lorentz factor. For thicker solid targets the divergence is seen to gradually increase, due to the increased number of fundamental steps in the cascade, but it is still kept of the order of few tens of mrad, depending on the spectral components in the beam. This high degree of collimation will be fundamental for further injection into plasma-wakefield afterburners.


Physical Review Letters | 2017

Relativistic Electron Streaming Instabilities Modulate Proton Beams Accelerated in Laser-Plasma Interactions

S. Göde; Christian Rödel; K. Zeil; Rohini Mishra; Maxence Gauthier; Florian-Emanuel Brack; T. Kluge; Michael MacDonald; Josefine Metzkes; Lieselotte Obst; Martin Rehwald; C. Ruyer; H.-P. Schlenvoigt; W. Schumaker; P. Sommer; T. E. Cowan; U. Schramm; S. H. Glenzer; F. Fiuza

We report experimental evidence that multi-MeV protons accelerated in relativistic laser-plasma interactions are modulated by strong filamentary electromagnetic fields. Modulations are observed when a preplasma is developed on the rear side of a μm-scale solid-density hydrogen target. Under such conditions, electromagnetic fields are amplified by the relativistic electron Weibel instability and are maximized at the critical density region of the target. The analysis of the spatial profile of the protons indicates the generation of B>10  MG and E>0.1  MV/μm fields with a μm-scale wavelength. These results are in good agreement with three-dimensional particle-in-cell simulations and analytical estimates, which further confirm that this process is dominant for different target materials provided that a preplasma is formed on the rear side with scale length ≳0.13λ_{0}sqrt[a_{0}]. These findings impose important constraints on the preplasma levels required for high-quality proton acceleration for multipurpose applications.


Physics of Plasmas | 2012

Experimental laser wakefield acceleration scalings exceeding 100 TW

C. McGuffey; T. Matsuoka; S. Kneip; W. Schumaker; F. Dollar; C. Zulick; V. Chvykov; G. Kalintchenko; V. Yanovsky; A. Maksimchuk; A. G. R. Thomas; K. Krushelnick; Z. Najmudin

Understanding the scaling of laser wakefield acceleration (LWFA) is crucial to the design of potential future systems. A number of computational and theoretical studies have predicted scalings with laser power for various parameters, but experimental studies have typically been limited to small parameter ranges. Here, we detail extensive measurements of LWFA experiments conducted over a considerable range in power from 20 to 110 TW, which allows for a greater plasma density range and for a large number of data points. These measurements include scalings of the electron beam charge and maximum energy as functions of density as well as injection threshold density, beam charge, and total beam energy as functions of laser power. The observed scalings are consistent with theoretical understandings of operation in the bubble regime.

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V. Chvykov

University of Michigan

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Z. Najmudin

Imperial College London

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Gianluca Sarri

Queen's University Belfast

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C. McGuffey

University of Michigan

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F. Dollar

University of Michigan

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V. Yanovsky

University of Michigan

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