PSE Success Story:
Argonne Wakefield Accelerator (AWA) Experiments
Photonic Band Gap (PBG) structures, with their capability for single mode confinement, are
attractive for future particle accelerator design that requires large transverse deflecting wakefield
mode suppression (severe transverse wakefield will cause beam breakup). However, wakefield
modes, including the monopole (accelerating) and dipole (deflecting) modes generated in a PBG
by an electron beam, have never been clearly characterized in a beam test.
Experimental setup in the AWA beamline
The Challenge
To generate, identify and characterize
the fundamental (monopole) and
higher order modes (HOMs) of
wakefields using a precise positioncontrolled
electron beam.
The Solution
The Argonne Wakefield Accelerator
(AWA) group, in collaboration
with Tsinghua University of China,
designed and fabricated an Xband,
three-cell, PBG-accelerating structure
using a two-dimensional triangular
lattice of copper rods between two
copper plates. This structure was
successfully beam-tested at the AWA
beamline in September 2009.
(a) Power spectrum of the typical wakefield signal from an off-axis bunch captured by the rf
probe and the simulated electrical field pattern
for each major mode; (b) Signal of the filtered
fundamental monopole mode (11.55 GHz); (c) Signal
of the filtered lowest dipole mode (14.46 GHz)
The Results
-
The accelerating structure
successfully generated, identified
and characterized the HOMS
of wakefields.
- Testing showed that the quality
factor (Q) of the HOMs is
significantly lower than that of
the monopole mode.
- Testing demonstrated the intrinsic
advantage of the PBG accelerating
structure in terms of HOM suppression,
which makes the structure a compelling
candidate for future accelerator design.
- The technique used in this experiment
could be used to study wakefields in other geometrically complicated accelerating structures.
“The advanced acceleration schemes we are developing here at Argonne, as well as our state-of-the-art facilities, will pave the way for future high energy physics discoveries,” said Wei Gai, accelerator physicist, Argonne National Laboratory.
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July 2010
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