a high-power high-efficiency ku-band transit-time ... · table :comparative analysis between the...
TRANSCRIPT
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Content
Introduction
Overview of the novel Ku-band TTO
Improvement and simulation
Conclusions
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
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.
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
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.
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
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:
Distance-tunable reflector
Overview of the novel Ku-band TTO
Three-cavity extractor
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Improvement and simulation
Three-cavity extractor
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Improvement and simulation
Three-cavity extractor
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Improvement and simulation
Three-cavity extractor
TABLE :Comparative analysis between the three-cavity extractor and the dual-cavity one
2M extQ The three-cavity has higher value of , Zc and
High conversion efficiency
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Improvement and simulation
Three-cavity extractor
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%)
High conversion efficiency
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Improvement and simulation
Distance-tunable reflector
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
High conversion efficiency
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Improvement and simulation
Distance-tunable reflector
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Improvement and simulation
Distance-tunable reflector
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Improvement and simulation
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
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
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%.
J. D. Zhang: EAPPC 2016, ESTORIL, 18-22/09/2016
Thanks for your attention!