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MURI 99 on Innovative Vacuum Electronics

Review of Researchat the

University of Maryland

Presented by

Victor L. Granatsteinat the

AFOSR MURI 99 MVE ReviewMonterey, CAApril 22, 2002

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MVE Research Group• Faculty

Thomas M. Antonsen, Jr.*, Victor L. Granatstein*, Hezhong Guo*, Wesley Lawson*, Gregory Nusinovich*, John Rodgers*, Bart Hogan, Anatoly Shkvarunets, Amarjit Singh, Agust Valfells

• Graduate Students T. Abu-Elfadl, W. Chen*#, M. Castle#, E. Gouveia, B. Huebschman, Y. Miao*, A. Sinitsin*, G. Xu*, M. Yeddulla*, J. Zhao*#

• Microwave Sintering Research GroupY. Carmel*, I. Lloyd*, T. Olorunyolemi, O. Wilson, Jr.*

*Support from MURI 99 #Received Ph.D. in 2000-2

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MURI 99 MVE Research ProgressI. Theoretical Studies of Innovative MVE Devices

(IVEC 2002 papers 8.4 and 20.5)

II. Experimental Studies of Frequency-Doubling Gyro-Amplifiers (IVEC paper 1.15)

III. Developing Advanced Ceramics for Microwave Tubes Using Microwave Sintering (IVEC 2002 paper 3.4)

Related studies at the University of Maryland include: - High Power Gyroklystrons for Linear Accelerator (paper 8.1) - Depressed Collectors to Enhance Gyrotron Efficiency (paper 12.4) - Plasma-filled Microwave Oscillators (paper 5.1) - Also see other papers with U. Md. Participation: (papers 1.5, 7.3, 7,4, 8.3, 8.5, 10.3, 17.5, 18.2, 18.3, 18.5)

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Progress in theoretical studies

• Theory of clustered-cavity gyroklystrons

• Theory of gyro-TWTs with distributed losses

• Kompfner dip effect in two-stage gyro-TWTs of high average power

• Nonstationary phenomena in gyro–BWOs

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Theory of Clustered-cavity GKL

• Point-gap model:- short cavities- long drift sections

Comparison of CC-GKLs with conventional GKLs:A. No stagger-tuning.• The maximum efficiency is the same• In the device with the same Ldr , but Qcc=Q/2 the bandwidth can be

doubled while keeping the same gain• Doubling of the gain-bandwidth product is possible

B. Stagger-tuning between clusters and within each cluster allows one to enlarge bandwidth in CC-GKLs more than in conventional GKLs

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Theory of gyro-TWTs with distributed losses

Linear theory was presented last year (published in Phys. Plasmas, July 2001)

Nonlinear theory (Spec. Issue IEEE-PS, to be published)

Comparison of results based on the use of gyro-averaged equations with MAGY simulations (UMD+NRL)

• Good agreement in the regular waveguides far enough from cutoff

• Disagreement near cutoff (a simple theory neglects the interaction with backward waves)

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Kompfner dip in two-stage gyro-TWT

Two-stage gyro-TWT:

Kompfner dip in linear-beam TWTs:When the EM-wave is coupled to the

fast space charge wave, the beam

absorbs the EM wave.(Invited Keynote, 26 Int. Conf. on IR & MM waves, September 2001, Toulouse, France)

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Nonstationary phenomena in tapered gyro-BWOsMotivation:

• Group led by K.R.Chu experimentally demonstrated in their tapered gyro-BWO a stable operation at currents which greatly exceed the starting current: I/Ist ~250 times.

• It is known that in untapered linear beam BWOs the operation with constant amplitude becomes unstable when .

To explain the reasons for this discrepancy we undertook a detailed analysis of the NTHU gyro-BWO by using the nonstationary code MAGY.

3stI/I

Second zone of stationary oscillations appears at large enough taperings.

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Progress in experimental studies

• Initial operation of a new 3-stage harmonic-doubling gyrotron amplifier (“Gyrotriotron”)

• Noise studies in harmonic-doubling gyro-amplifiers

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Frequency-Doubling Gyro-Amplifiers• Features

– TE0n operating modes– Multiple stages– Mode selective interaction circuits

• Advantages– Compact magnets– Lower drive frequency

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Schematic and photo of the Gyrotriotron

Combined advantages of clustered-cavity gyroklystron and harmonic multiplying Gyro-TWT might result in high gain, high efficiency, and broad bandwidth.

Multistage mode selective interaction, highly overmoded operation with TE04 output might result in high operation stability and high power capability.

Gyro-TWT Gyro-TWTClustered-

Cavity

Ka TE04 output

s1=1 s2 =2drift drift

TE10 Ku Input

MIG Beam

Matching load

s3 =2

Matching load

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The TE0n Mode Clustered- Cavity with Stagger Tuning

• 2 or more short TE0n mode cavities, closely adjacent but uncoupled can be used as beam buncher for gyro-amplifier.

• Frequency bands of adjacent cavities overlap• No beam bunching occurring between the cavities in each cluster.

f1

TE0n1

f2

TE0n1

f3

TE0n1

absorber

f4

TE0n1

ff3f2f1

imp

edan

ce

f4

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Output Power Pattern Output in TE04 mode was demonstrated by thermo-

sensitive paper mode pattern.

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Drive Curve of the Gyrotriotron

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1

Normalized Input Power

No

rmal

ized

Ou

tpu

t P

ow

er

Drive curve for output frequency of 33.75 GHz .

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Initial Gyrotriotron Results

2-stage Gyrotriotron gyro-TWT (initial results) (design)

Voltage 48 kV 60 kV 65 kV Current 22 A 2.5 A 40 A Freq. In 16-16.5 GHz 16.8 GHz 16.5-17.5 GHz Freq. Out 32-33 GHz 16.8, 33.6 GHz 33-35 GHz Bandwidth 3% instantaneous 5% amplf. range 5% inst. Peak Power 120 kW 50 kW 500 kW Gain 36 dB -------- 50dB Efficiency 12 % 32 % 19% Mode Out TE03 TE04 TE04

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Experimental Studies of FDSH Gyro-TWT Intermodulationand Harmonic Gain

Comparison of SS and LS Gain in Gyro_TWT with 2-Tone Drive(SS/LS ~ -60 dB at saturation)

10

15

20

25

30

35

20 25 30 35 40 45 50

Drive Power [dBm]

Ga

in [d

B]

20

30

40

50

60

70

80

Ou

tpu

t Po

we

r [d

Bm

]

LS Gain

SS Gain

Output Power

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Comparison of Total AM Noise (Amplified Driver + Internal) and Residual AM with Driver Noise Cancelled in FDSH Gyro-TWT Output

-130

-120

-110

-100

-90

-80

-70

20 40 60 80 100

Frequency Off Carrier [MHz]

No

ise

po

wer

[d

Bc]

Total AM Noise

Residual AM Noise

IF Noise baseline

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Advanced Ceramics for Microwave Tubes

Motivation: To study AlN-SiC and

AlN-TiB2 composites as possible replacements for Be0-SiC composites.

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Uses for RF Loss Materials

LossButtons

LITTON L-5892 KLYSTRON CAVITY

Helix Supports

HELIX TRAVELING-WAVE TUBE

Motivation /Objectives: Alternatives to toxic BeO and BeO/SiC composites Develop and characterize advanced ceramic composites for power microwave tubes: high thermal conductivity, controlled dielectric properties

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Challenges and Solutions in Synthesis of High Thermal Conductivity Ceramic Composites

Challenges:• Commercial AlN-SiC composites exhibit lower than expected thermal conductivity• Low thermal conductivity due to solid solution formation in AlN/SiC

Approaches:• Adopt intelligent densification strategies to minimize solid solution formation• Design new, alternative material system (AlN/SiC and AlN/TiB2) with improved properties

• Use pressureless microwave sintering (Near Net Shape)

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Thermal Conductivity ResultsNear net shape, fully dense AlN, AlN-TiB2 and AlN-SiC

composite were developed

Thermal conductivity and Dielectric Properties could be tailored

through controlling sintering conditions and altering composition

of materials. For examples,

AlN: Thermal Conductivity range from 180 to 225 W/(mK)

AlN-TiB2: Thermal Conductivity range from 117 to 150 W/(mK)

AlN-SiC: Thermal Conductivity range from 102 to 129 W/(mK)

(BeO has thermal conductivity of 243 W/(m.K);

60%/40% BeO-SiC ceramic has thermal conductivity 130 W/ (m.K))

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MURIMicrowave Vacuum Electronics

I. R. E. A. P.I.R.E.A.P.MURIMicrowavw Vacuum Electronics

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MURI 99 Journal Publications, 2001• G. Nusinovich, W. Chen & V. Granatstein, “Analytical Theory of Frequency-Multiplying Gyro-Traveling-

Wave-Tubes”, Phys. Plasmas, v. 8, pp.631-637, 2001.• G. Nusinovich, J. Rodgers, W. Chen & V. Granatstein, “Phase Stability in Gyro-TWTs”, IEEE Trans.

Electron Devices, v. 48, pp.1460-1468, 2001.• G. Nusinovich, O. Sinitsin & A. Kesar, “Linear Theory of Gyro-TWTs with Distributed Losses”, Physics of

Plasmas, v. 8, pp.3427-3433, 2001.• G. Nusinovich, W. Chen, and V. Granatstein, “Analytical Theory of Frequency-Multiplying Gyro-

Traveling-Wave-Tubes”, Phys. Plasmas, v.8, pp. 631-637, 2001.• J. Rodgers, H, Guo, G. Nusinovich and V. Granatstein, “Experimental Study of Phase Noise and Pushing

in a Frequency Doubling Gyro-Amplfier”, IEEE Trans. Electron Devices, v. 48, pp. 2434-2441, 2001.

• G. Nusinovich, A.Vlasov, and T. Antonsen, “Nonstationary Phenomena in Tapered Gyro-Backward-Wave Oscillators”, Phys. Rev. Lett., v. 87, paper #218301, pp. 1-4, 2001

• D. Gershon, J.P. Calame, Y. Carmel, and T.M. Antonsen, Jr., “An Adjustable Resonant Cavity for Measuring the Complex Permittivity of Dielectric Materials, Rev. Sci. Instr. v.71, 8 (2001).

• D. Gershon, J.P. Calame and A. Birnboim, “Complex Permittivity Measurements and the Mixing Laws of Alumina Composites”, J. Appl. Phys. v.89, 8110 (2001).

• D. Gershon, J.P. Calame and A. Birnboim, “Complex Permittivity Measurements and the Mixing Laws of Porous Alumina”, J. Appl. Phys. v.89, 8117 (2001).

• G. Xu, I. Lloyd, Y. Carmel, T. Olorunyolemi, O. Wilson, “Microwave Sintering of ZnO at ultra high heating rate”, J. Mater. Res. v.16, 10 (2001).

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MURI 99 Journal Publications, 2002• O. Sinitsin, G. Nusinovich, K. Nguyen & V. Granatstein, “Nonlinear Theory of the

Gyro-TWT: comparison of analytical method and numerical code data for the NRL gyro-TWT”, IEEE Trans. Plasma Sci., to be published, June 2002.

• G. Nusinovich, T. Antonsen, H.Guo & V. Granatstein, “Theory of Clustered-Cavity Gyroklystron”, submitted to Phys. Plasmas

• G. Xu, T. Olorunyolemi, O.Wilson, I. Lloyd, Y. Carmel, “Microwave sintering of high-density, high thermal conductivity AlN”, submitted to J. Am. Ceramic Soc.

• G. Xu, Y. Carmel, O. Wilson, T. Olorunyolemi, I. Lloyd, “ Sintering and properties of AlN-TiB2 composite ceramic”, submitted to J. Material Research

• G. Xu, T. Olorunyolemi, Y. Carmel, I Lloyd and O. Wilson, “Design and construction of insulation configuration for ultra high temperature microwave processing of ceramics”, submitted to J. Am. Ceramic Soc.

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University of MarylandMURI 99 Summary, April 2002

• Theoretical study of replacing usual gyroklystron cavities with clustered-cavities has demonstrated enhancement of bandwidth without sacrifice of gain or efficiency

• Analysis demonstrated use of Kompfner dip effect in high power gyro-TWT

• Theoretical analysis of important gyrotron amplifier amplifier and oscillator experiments carried out (gyro-TWT with distributed loss, gyro-BWO with tapered wall radius)

• New gyro-amplifier configuration combining 2 gyro-TWT sections with an intermediate staggered cavity section has been put into operation.

• AlN-TiB2 composite ceramics fabricated with pressureless microwave sintering have been demonstrated to be creditable replacements for BeO-SiC in all respects (thermal conductivity, permittivity, loss tangent)

• Ten papers published in refereed research journals during 2001