High Quality Electron Bunches up to 1 GeV from Laser WakefieldAcceleration at LBNL Page: 4 of 7
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
-4.5 - - - -- -0
68 80 92
Electron energy (MeV)
FIGURE 2. Electron bunch. The electron energy spectrum of the channeled accelerator shows the
appearance of monoenergetic features, here with 2 x 10' electrons in a bunch with energy spread of 4%
FWHM at 86 MeV. Divergence was near 3 mrad FWHM.
Transmission at 4 TW was 35%, a reduction of one third from the low power case,
indicating substantial power was deposited in plasma waves. This is consistent with
particle in cell simulations (below), which indicate that a plasma wave averaging 2 -
300 GVfm in the last 0.5 mm of guide length. No electrons are trapped at 4 TW,
indicating a structure for controlled injection experiments [23,24], and colliding pulse
injection  experiments are now under way which may increase beam stability.
Channeled Wakefield Acceleration
At guided drive pulse powers above 4 TW, electrons were trapped and accelerated,
verifying that an intense plasma wake was driven in the channel. At 9 TW, the
channel guided accelerator produced high charge electron beams at high energy with
low energy spread and low divergence . Figure 2 shows a bunch of 2 x 109
electrons within an energy spread of 2% centered at 86 MeV. Optimal performance
was found in a channel with an axial density of 1.9 x 1019 cm3 and with a parabolic
profile with 40% less rise in density over a spot diameter than the low power matched
case. The normalized geometric emittance obtained from assuming the bunch comes
from a source on order of the laser spot size is 1-2 mm-mrad, competitive with state of
the art RF facilities.
The accelerator was operated in the same gas jet without the guiding channel.
Optimum unchanneled performance was at ne ~ 4 x 1019 cm-a, producing an
exponential energy distribution with a 2.6 MeV temperature below 10 MeV and an 8
MeV temperature above 10 MeV, and no detectable electrons above 40 MeV. No
difference was observed between operation in a neutral gas jet and a pre-ionized (but
not channeled) plasma, confirming that channeling greatly enhanced accelerator
Simulations and Dephasing
Two-dimensional particle-in-cell (PIC) simulations using the code VORPAL
(developed at U. of Colorado Tech X ) performed with parameters close to the
experiment indicated that the high quality electron bunches are formed by wake
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Esarey, E.; Nagler, B.; Gonsalves, A.J.; Toth, Cs.; Nakamura, K.; Geddes, C.G.R. et al. High Quality Electron Bunches up to 1 GeV from Laser WakefieldAcceleration at LBNL, article, July 1, 2006; (https://digital.library.unt.edu/ark:/67531/metadc898223/m1/4/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.