IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 41, NO. 9, SEPTEMBER 2013 2501

Preliminary Experimental Research onKu-Band MILO

Jie Wen, Dai-bing Chen, Dong Wang, and Fen Qin

Abstract— A Ku-band magnetically insulated transmission lineoscillator is investigated numerically and experimentally for thefirst time. The magnetically insulated transmission line oscillator(MILO) is optimized in particle-in-cell simulation software.Reflect cavities are introduced to reduce the field intensitybetween cathode and anode. In the particle-in-cell simulation,the Ku-band MILO generates microwave with power of 2.48 GWand frequency of 12.5 GHz, whereas the voltage is 478 kV andthe current is 48.9 kA. Based on the structure in simulation,an experiment system is designed and the measure method andsystem are introduced. After the collector improved, Ku-bandmicrowave with frequency of 12.9 GHz is generated, whereasthe voltage is 539 kV and current is 57 kA. The peak power is89 MW and pulse width is 15 ns. The radiation mode is TM01

mode.

Index Terms— High power microwave (HPM), Ku-band,magnetically insulated transmission line oscillator (MILO).

I. INTRODUCTION

THE magnetically insulated transmission line oscillator(MILO) is a kind of compact and lightweight cross-field

device, which can generate high power microwave (HPM)without external magnetic field [1], [2]. Thus, as an attractivesource of compact HPM system MILO has been widelyinvestigated all over the world since 1987 and the microwavepower, pulse width, and conversion efficiency have received ahuge increase.

In the recent 20 years, MILO has been developed rapidlyin our country, especially in China Academy of EngineeringPhysics (CAEP) and National University of Defense Tech-nology. Some new kinds of MILO are investigated in ourlab, which have different advantages. The bifrequency MILO(bf-MILO) can generate microwave with bifrequency [3]. TheHigher-Order-Mode Depressed MILO (HDMILO) depress thehigher order mode generation [4]. A novel MILO with stablefrequency during modes competition is also introduced [5].

The National University of Defense Technology make anoutsized contribution in the experimental investigation ofMILO. They generate microwave with power of 3.2 GW at1.2 GHz and power of 3.1 GW at 1.7 GHz that is the top levelin the world so far [6], [7]. They also carried out the prelimi-nary experimental investigation on MILOs repetitive operation,which is of great importance to the MILOs development infuture [8].

Manuscript received April 9, 2013; revised May 31, 2013; accepted July 24,2013. Date of current version September 9, 2013. This work was supportedby the Chinese National Program.

The authors are with the Institute of Applied Electronics, ChinaAcademy of Engineering Physics, Mianyang 621900, China (e-mail:ababman@mail.ustc.edu.cn).

Color versions of one or more of the figures in this paper are availableonline at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TPS.2013.2276402

(a)

(b)

Fig. 1. SWS and dispersion curves. (a) Two kinds of SWS. (b) Dispersioncurves.

However, the investigation of MILO above centers upon lowfrequency band. Research on X-band MILO simulation andexperiment preliminarily carried out to increase the frequencyof this kind of no-magnetic HPM device [9]–[12]. To increasethe pf2 factor more that is the most important one of HPMdevice, a Ku-band MILO is investigated numerically andexperimentally in this paper for the first time.

In MILO, the slow wave structure (SWS) where the beamwave interaction occurs determines the working frequency.The inner radius of the choke vanes is often smaller than themain slow wave vanes, which makes the choke cavity to havea lower cutoff frequency to depress the microwave leak to theimport. Higher frequency device, however, requires smallersize. To reduce the field intensity between the cathode andanode to increase the breakdown voltage in Ku-band MILO,the outer radius of the choke cavity is enlarged instead, whichworks the same as the ordinary choke vane with the dispersioncurves as shown in Fig. 1.

0093-3813 © 2013 IEEE

2502 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 41, NO. 9, SEPTEMBER 2013

Fig. 2. Structure of Ku-band MILO.

Fig. 3. Voltage waveform in simulation.

Fig. 4. Output power versus time.

II. SIMULATION RESULTS

Fig. 2 is the structure of the investigated Ku-band MILObased on the new SWS in Section I. It has two choke vanesand five main slow wave vanes that have the same innerradius. An extract vane is introduced to increase the extractingefficiency of the Ku-band microwave generated in the SWS.At the same time, the end face or cathode emits to increasethe load current to enhance the magnetically insulation effect.Part of the electron that emitted to the extract gap can formanother spoke to increase the efficiency while the extract vaneis placed above the collector.

Fig. 3 shows the voltage that matches the real waveformof the low-impedance accelerator in our lab. Figs. 4 and 5show the instant power and its power spectrum. Microwavewith average power of 2.48 GW and frequency of 12.5 GHzis generated, whereas the voltage is 478 kV and the current is48.9 kA. Its impendence is nearly 9.7 Ω and the correspondingpower conversion efficiency is calculated to be 10.6%.

Fig. 5. Output power spectrum.

Fig. 6. Structure of Ku-band MILO fabricated.

Fig. 7. Measurement system.

III. EXPERIMENT SYSTEM

Fig. 6 shows the structure of the Ku-band MILO fabricatedbased on the simulation. Fig. 7 shows the measurement systemset up. In experiment, this Ku-band MILO is driven by a600 kV, 10 Ω, Marx-driven accelerator in Institute of AppliedElectronics, China Academy of Engineering. The coaxial TEMwave generated after the beam wave interaction is transformedinto TM01 mode by the mode converter in circular waveguide,which is then radiated in to air.

The BJ-84 waveguide-to-coaxial adapters are set at differ-ent angle to receive the microwave generated under propercurrent and vacuum condition. The frequency of microwavecan be attained with the frequency mixer after the microwavetransmits to the oscilloscope for the bandwidth of the oscil-loscope. We can calculate the power and the mode with thecharacteristic curve of the cable, attenuator, and detector at thefrequency measured.

WEN et al.: PRELIMINARY EXPERIMENTAL RESEARCH ON Ku-BAND MILO 2503

Fig. 8. Destroyed cathode.

Fig. 9. Destroyed collector.

IV. EXPERIMENTAL RESULT

At first, no microwave is generated from the oscilloscope.After we examined the device, we found the cathode and thecollector were destroyed heavily (Figs. 8 and 9).

In the simulation, the load current of the MILO is ∼40%of the total current. In this case, the load current is ∼20 kA,whereas the voltage is ∼480 kV. With the duration of 150 ns,the dose of electron energy deposition on the stainless steelsurface can be calculated to be 370 J/g [9], which causes anodeplasma formed on the collector surface.

The anode plasma formation has many adverse results. Theincrease of the load current caused by the bipolar space-charge flow would destroy the beam-wave synchronous and theplasma would also result in the severe erosion of the cathodeand collector.

To reduce the energy deposition, a kind of graphite collectorwith higher thermal diffusivity is introduced to increase thepenetration depth of the temperature field while the continu-ous slowing-down approximation for electrons multiplied bydensity is determined by diode voltage directly.

The surface of the cathode and improved collector afterexperiment later are shown in Figs. 10 and 11 when the deviceis improved. We can see that there is only regular electronimpression on the both surface that is not destroyed.

The typical voltage and current waveforms are shown asCH1 and CH2 in Fig. 12. With the voltage divider andRogowski coil calibrated, the voltage is calculated to be539 kV and the current is to be 57 kA. The impedance is∼9.5 Ω, which matches the 9.7 Ω in simulation.

CH1 and CH2 in Fig. 13 shows the detection waveforms at5° and 10° , where the microwave width can be read as 15 nsdirectly.

Fig. 10. Cathode after improved experiment.

Fig. 11. Graphite collector after experiment.

Fig. 12. Diode voltage and current waveform.

Fig. 13. Detection waveform at different angle.

The frequency of the microwave should be determined atfirst to get the power or mode. For the high frequency ofKu-band microwave, a frequency mixer is used here. Afterthe signal from the space and the signal source are mixed,the waveform with beat frequency can be obtained in Fig. 14,

2504 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 41, NO. 9, SEPTEMBER 2013

Fig. 14. Waveform with beat frequency.

TABLE I

MIXED FREQUENCY UNDER SIGNAL OF DIFFERENT FREQUENCY

Frequency of signal source

Mixed frequency

Frequency of microwave

12GHz 0.93GHz 12.93GHz 12.3GHz 0.58GHz 12.88GHz 11.8GHz 1.08GHz 12.88GHz 11.3GHz 1.6GHz 12.9GHz

Fig. 15. Directional diagram comparison between experiment and theory.

whereas the microwave with sum frequency is filtered by thelow pass filter. Of course the attenuator is not used to destroythe frequency mixer for the high amplitude of the microwave.Under the signal with different frequency from the source, theexperiment result is listed in Table I. The frequency is obtainedas 12.9 GHz for several experiments.

With the characteristic curve of the detector and BJ-84waveguide-to-coaxial adapter at the frequency of 12.9 GHz,the power density at 5° and 10° can be calculated to be5.3 and 17.7 MW/m2 from Fig. 13, which matches thenormalized theory far field directional diagram of the TM01

mode of the antenna calculated by 3-D electromagnetic soft-ware (Fig. 15). It means TM01 mode is generated from thisKu-band MILO that works at the basic mode.

The microwave power can be expressed as

P =4πR2 · pi

10G10

(1)

where R is the distance between antenna and BJ-84 waveguide-to-coaxial adapter, pi is the power density at 10° and Gis the direction coefficient at 10°. In the experiment ofFigs. 12 and 13, the microwave power is calculated to be89 MW, and the pulse width can be read as 15 ns directlyfrom the waveform.

V. DISCUSSION

In the preliminary experiment, there are two reasons for thelow amplitude of the microwave power and short pulse width.1) The preliminarily designed antenna has a low power capa-bility for its limited size. 2) The MILO working at high fre-quency requires electron beam with higher quality, but in theKu-band MILO, the electron beam matches the requirement ofthe beam wave interaction only for a short time. At the sametime the fabrication error make the working frequency shiftto 12.9 GHz in experiment from 12.5 GHz in simulation forthe cavity depth in the SWS determine the working frequencydirectly.

VI. CONCLUSION

A Ku-band MILO is investigated numerically and exper-imentally for the first time. Reflect cavities are introducedto reduce the field intensity between cathode and anode.In the particle–in-cell simulation, the Ku band MILO gen-erates microwave with power of 2.48 GW and frequency of12.5 GHz, whereas the voltage is 478 kV and the current is48.9 kA. Based on the structure in simulation, an experimentsystem is designed and the measure method and system areintroduced. After the collector improved, Ku-band microwavewith frequency of 12.9 GHz is generated, whereas the voltageis 539 kV and current is 57 kA. The peak power is 89 MWand pulse width is 15 ns. The radiation mode is TM01 mode.

REFERENCES

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Jie Wen was born in Sichuan, China, in January 1986. He received the Ph.D.degree from the National Synchrocyclotron Radiation Laboratory, Universityof science and technology of China, Anhui, China, in 2011.

His current research interests include high-power microwave sources.

Dai-Bing Chen was born in Sichuan, China, in March 1975. He receivedthe B.S. degree, from the University of Electronic Science and Technology ofChina, Sichuan, in 1999, and the M.S. degree in physical electronics and thePh.D. degree in physics of wireless electronics from the Graduate School ofChina Academy of Engineering Physics, Beijing, China, in 2002 and 2008,respectively.

His current research interests include high-power microwave sources,microwave measurement, and antenna technology.

Dong Wang received the B.S. degree from the Department of EngineeringPhysics in 2004, and the Ph.D. degree from the Department of Physics,Tsinghua University, Beijing, China, in 2008.

His current research interests include pulsed power technology and high-power microwave sources.

Fen Qin was born in Sichuan, China, in July 1986. He received the B.S.degree in applied physics from the Department of Modern Physics, Universityof Science and Technology of China, Anhui, China, in 2006. He is currentlypursuing the M.S. degree in physics of wireless electronics from the GraduateSchool of China Academy of Engineering Physics, Beijing, China.

His current research interests include high-power microwave sources,antenna technology, and pulse power technology.