Oversized RF windows with traveling H-waves in the dielectric area
A method of constructing the adapter from one-mode to oversized waveguide, that creates a prescribed distribution of higher order modes in the output channel, is proposed. Variants of oversized waveguide window with one and three Н-modes in dielectric are discussed, the modes can be shifted by p...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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| Zitieren: | Oversized RF windows with traveling H-waves in the dielectric area / V.D. Shemelin // Вопросы атомной науки и техники. — 1999. — № 4. — С. 24-25. — Бібліогр.: 7 назв. — англ. |
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irk-123456789-815182015-05-18T03:02:12Z Oversized RF windows with traveling H-waves in the dielectric area Shemelin, V.D. A method of constructing the adapter from one-mode to oversized waveguide, that creates a prescribed distribution of higher order modes in the output channel, is proposed. Variants of oversized waveguide window with one and three Н-modes in dielectric are discussed, the modes can be shifted by phases. 1999 Article Oversized RF windows with traveling H-waves in the dielectric area / V.D. Shemelin // Вопросы атомной науки и техники. — 1999. — № 4. — С. 24-25. — Бібліогр.: 7 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81518 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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A method of constructing the adapter from one-mode to oversized waveguide, that creates a prescribed
distribution of higher order modes in the output channel,
is proposed. Variants of oversized waveguide window
with one and three Н-modes in dielectric are discussed,
the modes can be shifted by phases. |
| format |
Article |
| author |
Shemelin, V.D. |
| spellingShingle |
Shemelin, V.D. Oversized RF windows with traveling H-waves in the dielectric area Вопросы атомной науки и техники |
| author_facet |
Shemelin, V.D. |
| author_sort |
Shemelin, V.D. |
| title |
Oversized RF windows with traveling H-waves in the dielectric area |
| title_short |
Oversized RF windows with traveling H-waves in the dielectric area |
| title_full |
Oversized RF windows with traveling H-waves in the dielectric area |
| title_fullStr |
Oversized RF windows with traveling H-waves in the dielectric area |
| title_full_unstemmed |
Oversized RF windows with traveling H-waves in the dielectric area |
| title_sort |
oversized rf windows with traveling h-waves in the dielectric area |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
1999 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/81518 |
| citation_txt |
Oversized RF windows with traveling H-waves in the dielectric area / V.D. Shemelin // Вопросы атомной науки и техники. — 1999. — № 4. — С. 24-25. — Бібліогр.: 7 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT shemelinvd oversizedrfwindowswithtravelinghwavesinthedielectricarea |
| first_indexed |
2025-07-06T06:31:03Z |
| last_indexed |
2025-07-06T06:31:03Z |
| _version_ |
1836878100605960192 |
| fulltext |
OVERSIZED RF WINDOWS WITH TRAVELING H-WAVES IN THE
DIELECTRIC AREA
V.D. Shemelin
Budker Institute of Nuclear Physics, Novosibirsk, Russia
INTRODUCTION
By output of power about 100 MW from RF
generator the problem of strength of output windows
arises. To diminishing the power density an oversized
window was proposed, i.e. the window with a diameter
of several wavelengths [1]. A window with a traveling
wave in dielectric [2] was not realized as yet in
oversized systems in a pure form because of presence of
higher order modes (HOMs). In the oversized window
developed in KEK [3], «the quasi TW-mode solution»
was realized. One can use higher order modes for
decreasing fields in the ceramic-metal brazing area [4].
In the proposed solution there also exists an impurity of
a standing wave in the ceramic region.
Nevertheless, the possibility of one-mode regime
in the oversized waveguide exists. The trivial solution is
a smooth cone taper that does not produce HOMs but it
is unacceptably long. In the present work the windows
are considered that include a step adapter from one-
mode channel (∅30 mm, 11.424 GHz) to the oversized
one (∅81 mm), such that amplitudes and phases of the
higher order modes in ceramics (ε = 9.3) may be
predetermined.
1. OVERSIZED WINDOW WITH ONE
OPERATING MODE
1.1 STEP ADAPTER
If one launches the dominant wave from the side
of a smaller diameter (Fig. 1), the propagating higher
dipole modes can be excited at a larger diameter. One
can try to reduce their amplitudes to zero by choosing
sizes of steps. So, the radii and lengths of the steps are
the variables, and the sum of powers contained in
HOMs is the goal function. By specified diameters of
input and output, it has been possible to put the sum of
HOMs power down to –50 dB relative to the input
power. A reflection of the dominant mode from the
adapter obtained in the process (r = 0.275) can be
compensated by disturbance, for example, by a groove
in the one-mode channel. The calculation was done
using numerical-simulation code COAX [5] that takes
less than 1 s to calculate one version of the geometry
with Pentium 120.
The search of the optimal geometry was done
without taking the roundings of right angles of the
adapter into account. To diminish the local field, the
inward projecting angles should be rounded. For the
found geometry the roundings were simulated using the
same COAX code: by dividing into smaller steps. Then
the same calculation was performed by the HFSS code
[6] for the rounding radii of 1 mm.
Fig. 1.Step adapter from one-mode channel
of ∅30 mm to ∅81 mm.
In Fig. 2, А stands for a share of the input power
transformed into higher order modes. One can see that
failure to take account of the roundings is essential at
the maximum compensation only of the HOMs.
Fig. 2. Content of HOMs at the output of the step
adapter.
The presented results demonstrate a possibility to
realize an adapter to an oversized diameter by a
relatively short length without an excitation of HOMs.
The COAX code provides a sufficient accuracy for the
axially symmetric geometry. It is necessary to calculate
the goal function many times through a process of
optimization, so the fast code is irreplaceable.
1.2 MATCHING THE ADAPTER WITH A
DIELECTRIC-FILLED WAVEGUIDE
Let us unite the step adapter from the bigger
diameter side with the same diameter round waveguide
filled with dielectric. At the step adapter output there are
no HOMs, so the wave reflected by the ceramics does
not contain HOMs as well and can be matched by
choosing a diameter and a position of the groove in the
one-mode channel.
One has to take into account that HOMs for
which the output diameter is smaller than the cut-off
diameter, can propagate in the dielectric and can be
excited there if the distance from the last step to the
dielectric is not sufficiently large.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 24-26.
24
Fig. 3. Formation of the traveling wave in dielectric.
A similar effect should be taken into account
when choosing the distance between the matching
disturbance and the first step.
On the other hand the indicated distances should
be decreased to provide maximum operating band of
the adapter.
The builded in such a way structure that creates
a traveling wave of the dominant mode in ceramics, and
the transverse field amplitude at the axis of this
geometry, are presented in Fig. 3. The field calculated
for the input power of 100 MW, makes 32 kV/cm in
ceramics as maximum (the fields on the graphs are
shown for the power of 1 W). This value is much less
than 80 kV/cm, taken as a limit for ceramic windows
[7]. The field of Н-waves is tangent to the surface of
ceramics. It is possible that the breakdown of ceramics
is less probable with this direction of the field. In the
presented case the distances between adapter and
ceramics and between the groove and the first step are
chosen so that the longitudinal field maximum is less
than 1.5 % of the maximum of transverse field in
ceramics.
The field in ceramics is practically pure Н11
wave, as it can be seen from Fig. 4. Here the amplitude
of the transverse field Et is shown for two mutually
perpendicular radii against the radius, and the
longitudinal field Ez, that is formed by residual Е-
modes.
Fig. 4. Fields in ceramics versus radius. The Ez field is
scaled by factor × 100.
To construct a window with a traveling wave in
dielectric, one has to add to the obtained geometry
precisely the same one only rotated 180° relative to the
plane parallel to the ceramics surface and going through
ceramics. With the disk thickness of λ/4 the operating
band-width is about 60 MHz at the –20 dB level.
2. A WINDOW WITH ZERO ELECTRIC
FIELD IN THE BRAZING AREA
For the Н1m-waves the fields near the wall of the
round waveguide vary in the same fashion: like sin ϕ (ϕ
is an azimuth angle). So, if the amplitudes of Н-modes
are chosen correctly, and because of their equal
polarization, their electric fields near the wall can be
done mutually compensated.
Fig. 5. On the construction of goal function for the case of three traveling waves.
To construct the goal function, let us consider the
reverse direction of the input waves: let the waves enter
from the side of ceramics. Let us prove that if the step
sizes are chosen correctly, the reflections of each mode
from the ceramics-vacuum interface are either absent or,
in general case, proportional to the amplitudes of the
incident waves (α′ = kα, β′ = kβ, γ′ = kγ), see Fig. 5a.
As α, β and so on the amplitudes of the corresponding
waves are designated.
By changing directions and multiplying
amplitudes of all the waves by r, one obtains
configuration shown in Fig. 5b. Adding the waves for
the cases (а) and (b), and demanding that the leftward
waves be compensated, one obtains that there are no
reflected waves in ceramics if k + r = 0 (Fig. 5c).
So, when constructing the goal function, it is
necessary to demand that the reflected Н-waves are
proportional to the incident ones. It is also necessary
that amplitudes of the Е-modes equal zero.
The powers of each of three Н-modes for the
geometry specified in the Introduction are calculated.
Phases of Н12 and Н13 modes are chosen to be 0 and
π,relative to the Н11-mode phase. In this case both the
modes have the electric field at the edge opposite to the
Н11-mode field. So, the field in ceramics can be
considered as prescribed. It comprises 37 kV/cm in
maximum at the full power of 100 MW.
This value is less than in constructions proposed
by S. Kazakov [4]: 72 and 57 kV/cm at 100 MW. True,
in the cited paper the diameter of ceramics is chosen to
be less: two versions - ∅53 and ∅64. But, even taking
this fact into account, the relative diminishing of the
field in our case (1.54 ÷ 1.95 times) is greater than the
increase of diameter (1.27 ÷ 1.53), the longitudinal field
is absent and the field at the edge is lowered down not
to 10 ÷15 % relative to maximum but practically to
zero.
The final construction of the window is to be
done in the same way that in Section 1.2: choosing the
distances from the adapter to ceramics and to the groove
and by reflection of the construction relative to a plane.
3. WINDOW WITH A PHASE SHIFTING OF
THE MODES
For the window with three Н modes discussed
above, the modes Н11 and Н12 are in phase and the Н13 is
in antiphase to them. A consideration of other relations
between the phases of modes does not give any
significant decrease of the field because the demand of
zero field at the edge is too strongly limiting.
If to abandon this requirement, the calculations
show that at the optimal distribution of three Н-modes
in amplitudes and phases for the border diameters and ε,
specified above, the maximal field is equal to 27 kV/cm
at 100 MW.
CONCLUSION
A method of constructing the adapter from one-
mode to oversized waveguide, that creates a prescribed
distribution of higher order modes in the output channel,
is proposed. Variants of oversized waveguide window
with one and three Н-modes in dielectric are discussed,
the modes can be shifted by phases.
Other applications of the method are possible: a
construction of the field with minimum losses or with
minimum heating of the ceramics, usage of the
oversized waveguide without dielectric filling in the
one-mode regime as a delay line with low losses,
creation of a traveling wave resonator with oversized
waveguide i.e. with low losses, or with two or more
traveling waves.
REFERENCES
1. V. Balakin. VLEPP Status. Third International
Workshop on Linear Colliders (LC91). September 17-
27, 1991, BINP, Protvino, USSR. BINP, January 1992.
2. S.Yu. Kazakov. RF Window with TW in Ceramics.
Int. Workshop on Pulsed RF Power Sources for Linear
Colliders (RF93). July 5-9, 1993, Dubna-Protvino,
Russia. BINP, July 1993.
3. Y. Otake et al. High Power Tests of X-Band RF
Windows at KEK. Third Workshop on Pulsed RF
Power Sources for Linear Colliders (RF96). April 8-12,
1996. Shonan Village Center, Hayama, Kanagawa,
Japan. KEK Proceedings, 97-1. April 1997.
4. S.Yu. Kazakov. A Powerful RF Window with a Low
Electric Field in Ceramic-Metal Brazing Area. KEK
Preprint 98-120, August 1998.
5. O.N. Alyakrinsky et al.. Development of Overmode
RF Window Using Multimode Matrix Formalism.
Seventh International Workshop on Linear Colliders
(LC97). Sept. 29 - Oct. 3, 1997, Zvenigorod, Russia.
6. «High Frequency Structure Simulator», Catalog of
Hewlett-Packard Ltd., 1995.
7. Y. Saito et al. Surface Flashover on Alumina RF
Windows for High-Power Use. IEEE Transactions on
Electrical Insulation, V. 28, No. 4, 1993.
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