ORIGINAL RESEARCH
High-Power TE
01
–TE
11
Mode Converter for Gyroklystron
Xinjian Niu
•
Xinhua Yu
•
Simin Li
•
Xi Gao
•
Weiping Cao
•
Yannan Jiang
•
Hongfu Li
Published online: 1 December 2012
Ó Springer Science+Business Media New York 2012
Abstract ATE
01
–TE
11
mode converter with a specific
geometric structure is proposed for Gyroklystron. The
geometry configuration of the converter is obtained to
realize the optimal mode conversion by a code based on the
mode coupling theory. Comparisons with a traditional one
show that the specific converter holds shorter length, wider
bandwidth than the traditional one. Experiments show the
specific converter exhibits good.
Keywords Gyroklystron TE
01
–TE
11
mode conversion
Specific converter
Introduction
Gyroklystron is a high-power millimeter-wave coherent
radiation source. As a result of its high-power capability,
high-efficiency and moderate bandwidth advantages [1–7],
it has received a great deal of attention in the past decades
for a variety of applications in field of high-power milli-
meter waves, including electron cyclotron resonance
heating (ECRH) of magnetically confined thermonuclear
fusion plasmas [1] and deep-space millimeter-wave radar
[7]. General commercial gyroklystron, however, outputs
only TE
0n
circular electric modes which are unpolarized
and generate an undesirable conical radiation pattern from
an open-ended waveguide. Therefore converting the power
into a more suitable propagating mode is necessary.
The HE
11
mode, also known as the ‘‘Gaussian-like’’ mode
(mixture of the TE
11
and TM
11
modes) has a field distribution
very close to that of an ideal Gaussian mode. This Gaussian-like
mode is very suitable for low-loss, high-power transmission
through highly overmoded tubular waveguides for its ohmic
attenuation is lower than that of any other mode and further-
more when radiated from an open-ended waveguide antenna, it
exhibits desirable radiation characteristics such as almost per-
fect linear polarization with very low cross-polarization and an
axisymmetric narrow pencil beam containing about 98 % of the
radiated power with very low side-lobe levels. Thus, the HE
11
mode propagating in an overmoded, circumferentially corru-
gated waveguide is ideal for a variety of applications in high-
power millimeter waves ranges [8, 9].
The ‘‘Gaussian-like’’ mode can be generated from TE
0n
gyrotron output modes via the two three-step mode conver-
sion sequences. One of the sequences is TE
0n
–TE
01
–TE
11
–
HE
11
[8, 9]. Among the sequence, TE
01
–TE
11
mode con-
version can be realized by a circular waveguide with constant
periodic perturbation of axis curved in one plane (see Fig. 1,
it is referenced as the traditional converter hereafter).
Axis of the traditional converter varies in one plane
according to
yðzÞ¼e
1
cos
2pz
k
1½mp;m
0
q
e
2
sin
2pz
k
2½mp;m
1
n
1
e
3
sin
2pz
k
3½mp;m
2
n
2
ð1Þ
where the main perturbation period
k ¼ð1 þ dÞk
B½mp;mq
: ð2Þ
In (1) and (2),k
B
is the beat-wave length between two
modes,k,d,e is the axis perturbation period, perturbation
X. Niu H. Li
Institute of High Energy Electronics, University of Electronic
Science and Technology of China, Chengdu 610054, Sichuan,
People’s Republic of China
X. Yu (&) S. Li X. Gao W. Cao Y. Jiang
School of Information and Communication, Guilin University
of Electronic Technology, Guilin 541004, Guangxi, People’s
Republic of China
e-mail: redyxhred@yahoo.cn
123
J Fusion Energ (2013) 32:426–430
DOI 10.1007/s10894-012-9589-2