31 July 2016 to 5 August 2016
Gaylord Hotel and Conference Center
US/Eastern timezone

Production of 10-75 MeV Compton Gamma-rays from a 1-2 GeV Laser Wakefield Accelerator

2 Aug 2016, 11:30
15m
Woodrow Wilson B (Gaylord Hotel)

Woodrow Wilson B

Gaylord Hotel

Oral Working Group 7 WG7

Speaker

Mr. Joseph M. Shaw (The University of Texas at Austin)

Abstract

We demonstrate a <1 mrad, 10-75 MeV, inverse-Compton photon source capable of penetrating several centimeters of Pb. First a petawatt pulse is focused into a gas cell, driving a laser wakefield that injects and accelerates electrons to >GeV energies with <0.6 mrad divergence. Upon exiting the gas cell, the same pulse forms a retro-reflecting Plasma Mirror on a thin substrate downstream which stimulates Compton Backscatter from the closely trailing, copropagating electrons.

Summary

We report the generation of a Compton backscatter (CBS) source with photon energies prominently peaked in the range of 10-75 MeV and capable of penetrating several centimeters of lead. The Texas Petawatt laser drives a laser wakefield which injects and accelerates electrons up to 2 GeV in a 7 cm, low density, helium gas cell [1]. A plasma mirror (PM) retro-reflects the wakefield-driving laser, at a small angle, into the closely following electrons. The plasma mirror substrate, a 100 micron thick, glass coverslip, was placed 3 centimeters after the gas cell exit to allow its interrogation by a probe beam to verify the PM reflectivity. This scheme consistently generated a CBS source exhibiting sub-milliradian divergence. The CBS beam qualities were evaluated using: two pixelated-CsI(Tl) scintillators placed at 3 m and 5.5 m from the source; a modular array of metal attenuators comprised of aluminum, copper, tungsten, tungsten carbide, and lead; Fujifilm image plates; and simulations using GEANT4. A shot-to-shot comparative analysis on the accelerated electron bunch, subsequent betatron x-ray, and CBS gamma-ray signals reveals strong agreement in their pointing and divergence properties, suggesting a reliable and non-invasive extension for GeV-beam metrology. Furthermore the use of on-axis image plates facilitated the observation of secondary particles emitted by multi-MeV photon absorption within the metal attenuators, offering a corroborating, indirect measurement of photon number.

[1] Wang, X. et al. Quasi-monoenergetic laser-plasma acceleration of electrons to 2 GeV. Nat Commun. 4:1988 doi: 10.1038/ncomms2988 (2013).

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Primary author

Mr. Joseph M. Shaw (The University of Texas at Austin)

Co-authors

Dr. Aaron Bernstein (University of Texas at Austin) Ms. Andrea Hannasch (University of Texas Austin) Dr. Erhard Gaul (The University of Texas at Austin) Dr. Gilliss Dyer (The University of Texas at Austin) Dr. Hai-En Tsai (Lawrence Berkeley National Laboratory) Mr. James Welch (University of Texas at Austin) Mr. Joe Gordon (The University of Texas at Austin) Kathleen Weichman (University of Texas at Austin) Mr. Maxwell LaBerge (University of Texas - Austin Physics) Mr. Michael Spinks (The University of Texas at Austin) Mr. Mikael Martinez (The University of Texas at Austin) Dr. Mike Donovan (The University of Texas at Austin) Prof. Mike Downer (The University of Texas at Austin) Dr. Neil Fazel (The University of Texas at Austin) Dr. Rafal Zgadzaj (University of Texas at Austin) Prof. Todd Ditmire (The University of Texas at Austin) Dr. Toma Toncian (The University of Texas at Austin) Dr. Watson Henderson (The University of Texas at Austin) Dr. Xiaoming Wang (The University of Texas at Austin) Mr. Yenyu Chang (The University of Texas at Austin)

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