A high-power high-efficiency Ku-band transit-time ... · TABLE :Comparative analysis between the three-cavity extractor and the dual-cavity one M2 Q ext The three-cavity has higher

J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016

A high-power high-efficiency Ku-band transit-time oscillator with low guiding magnetic field

Junpu Ling, Jiande Zhang, Juntao He, Chen Geng

National University of Defense Technology

P. R. China


Content

Introduction

Overview of the novel Ku-band TTO

Improvement and simulation

Conclusions


Introduction

Improving the operation frequency and the output

power of the HPM device has been of great interest.

Potential applications in high power radar, communication

and other fields

Radar Communication

Ku-band HPM gains more and more attention


Introduction

HPM devices mainly operate at the frequency regime

of L-band, S-band, C-band and X-band

Can output gigawatt level microwave

When the operation frequency of the device is expanded

to Ku-band

Electric breakdown in the device limits its effective performance


Introduction

Combining the advantages of the traditional TTO and the

coaxial structure

Ku-band coaxial foilless TTO

Sketch of the Ku-band coaxial foilless TTO

- High power capacity

- low guiding magnetic field

- Low impedance

- Monochromatic operation mode

A microwave pulse with power of 1GW, frequency of 14.3 GHz, pulse

duration of 26 ns and efficiency of 25% was generated experimentally.


Introduction

Generation of the HPM with higher power such as

multi-gigawatt level can further expand the application

prospects of the device

High conversion efficiency can lower the HPM

generation’s volume, weight and energy consumption

Investigation on the high-power high efficiency Ku-band TTO

with low guiding magnetic field becomes more attractive.


Improved Ku-band coaxial foilless TTO

Sketch of the improved Ku-band coaxial TTO

Annular cathode

Distance-tunable reflector

Non-uniform buncher

Drift tube

Three-cavity extractor

Electron collector

Output waveguide

Compared with the previous one, this novel device has two main improvements:


Overview of the novel Ku-band TTO





three-cavity, 950kV/cm

Electric field distribution in the three-cavity structure and the

dual-cavity one under the same energy storage

With a lower electromagnetic field , the three-

cavity extractor has higher power capacity

dual-cavity, 1100kV/cm

Higher power capacity

Simulated by 2.5D CHIPIC




According to the equivalent circuit theory, the output power of the

extractor is mainly affected by the following parameters.

22

1(0)out c extP M Z Q i

M : beam-wave coupling coefficient

: characteristic impedance of the extractor

: externally loaded quality factor

:amplitude of the fundamental harmonic current at the

beginning of the extractor

1(0)i

extQ

cZ

High conversion efficiency




TABLE :Comparative analysis between the three-cavity extractor and the dual-cavity one

2M extQ The three-cavity has higher value of , Zc and


22

1(0)out c extP M Z Q i

Under the same fundamental harmonic current, the three-cavity extractor has

more potential to improve the beam-wave conversion efficiency




Electron power distributions with three-cavity and dual-cavity

Compared with dual-cavity one, the electron beam lose more power in the

three-cavity extractor, which means it has higher conversion efficiency ( 37%)





For the transmission electron beam in the drift-tube of the TTO

Initial velocity modulation is mainly caused by the buncher

Initial density modulation is mainly caused by the reflector

Initial phase difference ( ) can be adjusted by tuning the distance

between the reflector and the buncher

Sketch of the electron beam transmission in the TTO





For the beam with beam voltage: 570kV, current: 10.5kA, modulation

frequency :12.4 GHz , by tuning the distance between the reflector and the

buncher, the maximum of the harmonic current peak 13.8kA can be obtained

Harmonic current distribution

2

1(0)outP i Conversion efficiency can be optimized to the maximum




Fundamental harmonic current and the conversion efficiency

versus the distance between the buncher and the reflector

By introducing this reflector and optimizing the distance between the reflector and

the buncher, the device can obtain a favorable harmonic current distribution to meet

the requirement of high-efficiency beam-wave interaction.

Peak of the harmonic

current : 13.77 kA

Maximum modulation

coefficient: 131%

Distance with 1.9cm



Typical simulation results

Output power : 2.2 GW

Conversion efficiency : 37%

Frequency : 12.4 GHz

Average output power and the microwave frequency versus time

Average output power and the microwave

frequency versus time Output microwave frequency spectrum


Conclusions

By employing a three-cavity extractor instead of the dual-cavity one,

the conversion efficiency of the device increases by an increment of 7%,

and the maximum surface electric field drops from the value of 1.10 MV/cm

to that of 950 kV/cm By introducing the distance-tunable reflector and tuning the distance

between the reflector and buncher, a fundamental harmonic current with

13.77 kA peak current and 131% modulation coefficient has been

obtained , such a harmonic current makes the device have 37% beam-wave

conversion PIC simulations show that the device with the three-cavity extractor and

distance-tunable reflector can produce 2.2 GW HPM at frequency of

12.4 GHz when the diode voltage is 570 kV, beam current 10.5 kA and

guiding magnetic field 0.7 T corresponding to an efficiency of 37%.


Thanks for your attention!

Documents

A high-power high-efficiency Ku-band transit-time ... · TABLE :Comparative analysis between the three-cavity extractor and the dual-cavity one M2 Q ext The three-cavity has higher