On the design of high conversion efficiency quasi-optical mode converter for 140 GHz high-power gyrotron applications

Ming JIN; Dan-Yang WANG; Yi-Chi ZHANG; Yu-Nan HAN; Ming BAI

doi:10.11972/j.issn.1001-9014.2023.02.014

Journal of Infrared and Millimeter Waves, Volume. 42, Issue 2, 234(2023)

On the design of high conversion efficiency quasi-optical mode converter for 140 GHz high-power gyrotron applications

Ming JIN¹, Dan-Yang WANG¹, Yi-Chi ZHANG², Yu-Nan HAN¹, and Ming BAI^3、*

Author Affiliations

¹College of Information Science and Technology, Beijing University of Chemical Technology, Beijing 100029, China

²National Key Laboratory of Science and Technology on Vacuum Electronics, Beijing Vacuum Electronics Research Institute, Beijing 100015, China

³School of Electronic Information Engineering, Beihang University, Beijing 100191, China

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Figures & Tables(11)

Fig. 1. Configuration of 140 GHz TE_22，6 3-mirror quasi-optical mode converter

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Fig. 2. Configuration of 140 GHz TE_22,6 3-mirror original quasi-optical mode converter, (a) vertical focusing functions of the mirrors in the original design (shown with ray-tracing), and the converted beam pattern at the output window, co-pol fields (E_y), normalized magnitude, linear, (b) horizontal focusing functions of the mirrors in the original design (shown with ray-tracing)

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Fig. 3. Comparison of induced current distribution along the Denisov waveguide wall, and the illumination field distributions on the first and second mirror in the original QOMC design, for demonstrating the non-ideal edge fields，all the results are of normalized magnitude, in dB

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Fig. 4. Diagram of phase correction mirror generation，based on Eq.（3）and Eq.（4）

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Fig. 5. Computed Gaussian contents in the output field at output window，after each round of phase correction

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Fig. 6. Illumination field patterns on each mirror，and output fields（Ey，normalized magnitude，dB），after different rounds of iterative 3-mirror phase correction，the field results are calculated by Eq.（1）and（2）

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Fig. 7. Converted fields at output window in both cases of 2-mirror corrected converter and 3-mirror corrected converter. The referencing Gaussian beam is with beam waist of ω₀ = 13.5 mm at the output window

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Fig. 8. Illumination Field patterns（E_y，normalized magnitude，dB）on each mirror，in cases of original quadric mirror systems，2-mirror corrected mirror system，and 3-mirror corrected mirror system. The illuminated field results are calculated by Eqs.（1）and（2）

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Fig. 9. Showcase of output fields at different apertures，of the 3-Mirror corrected TE₂₂₆ QOMC design（a）：concluded total conversion efficiency η_c，Gaussian content η_v and power efficiency η_p of the aperture fields distant from the output window，（b）：output field patterns at different apertures，co-pol fields（E_y），normalized magnitude，linear

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Table 1. Layout parameters of the 140 GHz TE_22,6 QOMC

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Table 1. Layout parameters of the 140 GHz TE_22,6 QOMC

Launcher Radius/mm	16.8	Launcher Radiation Angle/deg：	67.8
Launcher Height/mm	35.4	Center of Mirror 1（x，z，mm）	（-40，34.1）
Center of Mirror 2（x，z，mm）	（45，110）	Center of Mirror 3（x，z，mm）	（-130，320）
Center of Output Window（x，z，mm）	（234，320）	Waist Radius of Ref Gaussian Beam /mm	13.5

Table 2. Procedures of iterative multi-mirror phase correction

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Table 2. Procedures of iterative multi-mirror phase correction

I Iteration 0

I.A Phase correction on the mirror 3（in detail）

（1） Forward calculation：

Ø Calculate the surface current（ ${\vec{J}}^{F_M 1} = 2 \hat{n} \times {\vec{H}}^{F_M 1}$ ）on the original Mirror 1 from the Huygens Box（ ${\vec{J}}^{H u y} = \hat{n} \times {\vec{H}}^{H u y}$ ， ${\vec{J}}_{M}^{H u y} = {\vec{E}}^{H u y} \times \hat{n}$ ），using Eq.（1）.

Ø Calculate the surface current（ ${\vec{J}}^{F_M 2} = 2 \hat{n} \times {\vec{H}}^{F_M 2}$ ）on the original Mirror 2 from the Mirror 1 surface current（ ${\vec{J}}^{F_M 1}$ ），using Eq. 1.

Ø Calculate the illumination fields（ ${\vec{E}}^{F_M 3}$ ）on the Mirror 3 correction lattice，from the Mirror 2 surface current（ ${\vec{J}}^{F_M 2}$ ），using Eq. 2.

（2） Backward calculation：

Ø Calculate the referencing fields（ ${\vec{E}}^{B_M 3}$ ）on the Mirror 3 correction lattice，from the referencing fundamental Gaussian field sources（ ${\vec{J}}_{M}^{G} = 2 {\vec{E}}^{G} \times \hat{n}$ ），using Eq. 2.

（3）Phase Correction：

Ø Take the co-polar component of forward fields（ $E_{y}^{F_M 3}$ ）and backward fields（ $E_{y}^{B_M 3}$ ）on Mirror 3 correction lattice，turns the phase difference into geometry correction，using Eqs. 3-4. Specifically，the diagram of phase correction can be concluded in Fig. 4. After the phase correction process，the generated mirror is described as triangle meshes which can be exported as a STL format file for further calculation and fabrication.

II Iteration 1..N

II.A Phase correction on the mirror 2（in detail）

（1） Forward calculation：

Ø Calculate the surface current（ ${\vec{J}}^{F_M 1} = 2 \hat{n} \times {\vec{H}}^{F_M 1}$ ）on the Mirror 1 from the Huygens Box（ ${\vec{J}}^{H u y} = \hat{n} \times {\vec{H}}^{H u y}$ ， ${\vec{J}}_{M}^{H u y} = {\vec{E}}^{H u y} \times \hat{n}$ ），using Eq. 1.

Ø Calculate the illumination fields（ ${\vec{E}}^{F_M 2}$ ）on the Mirror 2 correction lattice，from the Mirror 1 surface current（ ${\vec{J}}^{F_M 1}$ ），using Eq. 2.

（2） Backward calculation：

Ø Calculate the surface currents（ ${\vec{J}}^{B_M 3} = 2 \hat{n} \times {\vec{H}}^{B_M 3}$ ）on the Mirror 3，from the referencing fundamental Gaussian pattern（ ${\vec{J}}_{M}^{G} = 2 {\vec{E}}^{G} \times \hat{n}$ ），using Eq. 1.

Ø Calculate the referencing fields（ ${\vec{E}}^{B_M 2}$ ）on the Mirror 2 correction lattice，from the Mirror 3 surface current（ ${\vec{J}}^{B_M 3}$ ），using Eq. 2.

（3） Phase correction..

II.B Phase correction on the mirror 1（in detail）

（1） Forward calculation：

Ø Calculate the illumination fields（ ${\vec{E}}^{F_M 1}$ ）on the Mirror 1 from the Huygens Box（ ${\vec{J}}^{H u y} = \hat{n} \times {\vec{H}}^{H u y}$ ， ${\vec{J}}_{M}^{H u y} = {\vec{E}}^{H u y} \times \hat{n}$ ），using Eq. 2.

（2） Backward calculation：

Ø Calculate the surface current（ ${\vec{J}}^{B_M 2} = 2 \hat{n} \times {\vec{H}}^{B_M 2}$ ）on the Mirror 2 from the Mirror 3 surface current（ ${\vec{J}}^{B_M 3}$ ），using Eq. 1.

Ø Calculate the referencing fields（ ${\vec{E}}^{B_M 1}$ ）on the Mirror 1 correction lattice，from the Mirror 2 surface current（ ${\vec{J}}^{B_M 1}$ ），using Eq. 2.

（3） Phase correction..

II.C Phase correction on the mirror 2..

II.D Phase correction on the mirror 3..

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Ming JIN, Dan-Yang WANG, Yi-Chi ZHANG, Yu-Nan HAN, Ming BAI. On the design of high conversion efficiency quasi-optical mode converter for 140 GHz high-power gyrotron applications[J]. Journal of Infrared and Millimeter Waves, 2023, 42(2): 234

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