Transverse envelope dynamics of a 28.5 GeV electron beam in a long plasma Page: 1 of 5
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
Transverse Envelope Dynamics of a 28.5 GeV Electron Beam in a Long Plasma
C.E. Clayton, B.E. Blue, E.S. Dodd, C. Joshi, K.A. Marsh, W.B. Mori, S. Wang
University of California, Los Angeles, CA 90095 USA
P. Catravas, S. Chattopadhyay, E. Esarey, W.P. Leemans
Lawrence Berkeley National Laboratory, University of California, Berkeley CA 94720 USA
R. Assmann*, F.J. Decker, M.J. Hogan, R. Iverson, P. Raimondi, R.H. Siemann, D. Walz
Stanford Linear Accelerator Center, Stanford University, Stanford CA 94309 USA
T. Katsouleas, S. Lee, P. Mugglit
University of Southern California, Los Angeles, CA 90089 USA
(October 9, 2001)
The transverse dynamics of a 28.5 GeV electron beam propagating in a 1.4 m long, 0-2 x 104cm-3
plasma are studied experimentally in the underdense or blow-out regime. The transverse component
of the wake field excited by the short electron bunch focuses the bunch, which experiences multiple
betatron oscillations as the plasma density is increased. The spot size variations are observed using
optical transition radiation and Cherenkov radiation. In this regime, the behavior of the spot size
as a function of the plasma density is well described by a simple beam envelope model. Dynamic
changes of the beam envelope are observed by time resolving the Cherenkov light.
PACS numbers: 29.27.-a, 41.85.-p, 41.75.Lx, 52.38.-rParticle acceleration by space charge waves in plas-
mas is attractive because such waves can have acceler-
ating gradients that are orders of magnitude larger than
those found in conventional radio-frequency structures
[1]. While laser-driven plasma waves have realized ac-
celerating gradients of greater than 100 GeV/m, the ac-
celeration length has been limited to about a millimeter
[2]. On the other hand, electron beam-driven plasma
accelerators have produced plasma waves over a length
of about 12 cm, but the gradients have been limited to
about 25 MeV/m [3]. In the experiment now being con-
ducted at the Stanford Linear Accelerator Center a pro-
totype plasma accelerator stage that would demonstrate
high-gradient acceleration over a distance of greater than
a meter is being developed. It requires the stable propa-
gation of high current (> lkA), very short (few ps) drive
electron bunches through dense (> 1014cm-3) plasmas.
The propagation of such bunches through a long, dense
column of plasma has certain time dependent and plasma
density dependent transverse behavior that can be theo-
retically predicted. In this Letter the predicted phenom-
ena are demonstrated experimentally; namely multiple
oscillations of the beam spot size as a result of betatron
motions, and time dependent variation of the beam enve-
lope because of finite rise time of the beam and response
time of the plasma electrons.
Previous experiments on the focusing of electron beams
in plasmas have shown good agreement with envelope*Present address: CERN, Geneva, Switzerland
tCorresponding author: muggli@usc.edumodels in the overdense regime where the plasma den-
sity is larger than the beam density [5], and in the return
current cancellation regime [4] where the transverse spot
size of the electron beam is comparable to the plasma
skin depth, c/Wp. This Letter presents the first exper-
imental study of mono-energetic beam propagation in
long dense plasmas in the underdense or blow-out regime
where the beam density is larger than the plasma den-
sity; conditions that are relevant to future high energy
plasma accelerators. In the plasma wakefield accelerator
the plasma wave, or wake, is driven by a short, rela-
tivistic electron bunch. The plasma wake has longitu-
dinal accelerating fields and transverse focusing fields.
The transverse component of the wake focuses the beam
which can overshoot, and undergo multiple betatron os-
cillations over the plasma length.
The head of a round bunch of radius or, length a2,
and with with N electrons, with a density nb =
N/(27r)3/2o-20z larger than the plasma density np ex-
pels all the plasma electrons to a radius rc =
(N/(27r)3/2np)1/2, where a = 1 for a long bunch and
a = 2 for a short bunch of the order of a plasma wave-
length long. In this underdense or blow-out regime, the
focusing strength of the pure ion column S is that of a
uniform cylinder of charge density np [6]: S = npe/2co.
It is constant over much of the bunch length, and is con-
stant over the radius of the ion column, which acts as a
plasma lens free of geometrical aberrations. The behav-
ior of the electron beam with normalized emittance EN is
described by the beam envelope equation [7]:d2oy(z) + [K2
dz2E2
2 ]er(z) = 0
r2f z(1)
1
Upcoming Pages
Here’s what’s next.
Search Inside
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.
Clayton, C. E.; Blue, B. E.; Dodd, E. S.; Joshi, C.; Marsh, K. A.; Mori, W. B. et al. Transverse envelope dynamics of a 28.5 GeV electron beam in a long plasma, article, April 1, 2002; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc740220/m1/1/: accessed March 30, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.