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Varian Mw 3 % H ORNL/Sub-75/49438/2 BP n ^TfFl varian mw 3 % h NOTICE PORTIONS OF TV'!? HFTL0'' SHE M.I.HGIB'.E. IF lT~~rvnrT;irri*"rr?.--p. tf.3 iwaito'jia 1 co1;;/ -o psrrnii the broadest possible avail- ability. FINAL REPORT MILLIMETER WAVE STUDY PROGRAM u by H.R. JORY, E.L. LIEN and R.S. SYMONS ft, 0 {I Order No. Y-12 11Y-49438V j November 1975 report prepared by Varian Associates Palo Alto Microwave Tube Division 611 Hansen Way o Palo Alto, California 94303 under subcontract number 11Y-49438V ; for ' ' r>4 OAK RIDGE NATIONAL LABORATORY * ° Oak Ridge, Tennessee 37830 operated by UNION CARBIDE CORPORATION for the nrsTKIUUTiON 01? 'ijl;.;?!---''--^-'.^-^''' UNLLMIT DEPARTMENTS ENERGY FINAL REPORT MILLIMETER WAVE STUDY PROGRAM by H. R. Jory, E. L Lien and R, S. Symons - NOTICE- Urn report Mas piepated as an account, of worl; sponsored by die Untied Stales Government. Neither Die United State* not the United States Pepastment of l.nergy, tiar any of1 their employees, nnr any of then contractors. subcontractor or their employees, makes any warranty, express or implied, or assumes any legal liability oi responsibility for tlie accuracy, completeness of usefulness of any information, apparatus, product or process disclovd. or represents that its use would not mUmfe pnvately owned npjits. Order No, Y-12UY-49438V November 1975 « 0 " report prepared by Varian Associates Palo Alto Microwave Tube Division 611 Hansen Way Palo Alto, California 94303 K< under subcontract number 11Y-49438V for OAK RIDGE NATIONAL LABORATORY Oak.RitJge-J'ennessee 37830 c.-..operatedjby U N 10N CARBiDE^G0RP0RATI0N, o <J>c l . DERARTMEWJ'O'F ENERGY TABLE OF CONTENTS Section - 9 " , ' „ Page No. 1. INTRODUCTION. ....... o . ... 1-1 ' // 2. WAVEGUIDE DESIGN . 0 " . , . 2-1,, 3. WINDOW DESIGN 3-1 4. LINEAR BEAM AMPLIFIERS >< . 4-1 > i 4.1 Introduction ,4-1 4.2 TWT Amplifiers •<....".•;.„ 4-3 4.3 Harmonic Amplifiers 0 v. ; 5. PERIODIC BEAM DEVICES ...;...... 5-1 o 5.1 Introduction ............ 5-1 5.2 Ubitron ' .. 5-1 5.3 Periodic Beam TM Interaction 5-4 6. CYCLOTRON RESONANCE DEVICES . q. 4 6-1 6.1 General Description of'Device Alternatives . 6-1 6.2 Analysis of Cavi,ty Losses in Cyclotron Resonance Devices 6-12 < 6.3 Gyrotron Giui Design . - ,6-16 6.4 Axis Encircling Beam . 6-22 f6t. 5 Gyrotron Interaction Theory ' • " 6-33 6.5.1 Introduction and Summary , e , . = 6-33 6.5.2 Review of Russian-Theoretical Work . 6-35 • 6.5.3 Analogies Between Klystrons and Gyroklystr.ons 6-42 6.5.4 Determination of Performance Parameters Using Numerical Methods 6-48 6.5.5 Ballistic Trajectory Analysis Code. 6-58 7. CHOICE OF APPROACH ..." 7-1 o 8. DESIGN CALCULATIONS FOR THE PREFERRED APPROACH 8-1 v. 8.1 General Description .J 8-1 8.2 Microwave Circuit Design . 8-3 8.3 Electron Gun Design. ~ . .. 8-10 8.4 Foe using'Solenoid 8-11 £r .8.5 Collector and Water Cooling Design . t8-12 8 .6 Waveguides and Windows xr- „. • 8-12 t? • (x sr ° 8.7 Summary of Design Parameters .... , 8-13 o iii TABLE OF CONTENTS (cont'd) Section « Page No. 9. CONCLUSIONS 9-1 10. REFERENCES 4 ,,10-1 „ O• ' M , • , APPENDIX A APPENDIX B , „ 'll LIST OF ILLUSTRATIONS Page No. Attenuation Due to Copper Losses in Circular Waveguides o at 120 GHz Assuming.a Skin Resistance of 0.09 ohms. 2-4 Measureo d Window-Loss as a Functio11 n of Transmitter Power. '" 3-5 f) I _ Dimensions of a Disc-Loaded Waveguide Designed for Forward Wave, Operation at, S-band at a Voltage Level of 200 kV. 4-5" W-/S Diagram for the Disc-Loaded Waveguide Circuit f/ • Described in Figure 3. ' t ' 4-6 0 & •> , l' ' " ^ • Measured Impedance for'the Disc-Loaded Waveguide at a Radius Equal to 0.84 Times the Beam Hole Radius. " 4-7 Modified Applegate Diagram Showing'the Phase of>sthe Various Disc-Electrons vs ^Distance Along the Tube." '' ' '' "ij -- i u Fundamental Component of Beam Current Along the Tube ' " Together with Gap Voltages. '' is 4-10 (j ' " As 'V, II . , Average Valuecof Radial Factor of Beam Coupling Coefficient .for Uniform Density Beam ^Partially Filling Gap. « " 4-12 Phase" vs Distance for Electrons in Output Section of Tapered ^Impedance TWT with.Output Power of'110 kW. \ 4-17 ' RF Beam Current and Cavity Voltages of Tapered Impedance • ,t n-i^T7rn'x vv j. ;WJ.U 1 illifui 1-Titv»vr v_/UlpUtrtii^nf. " fr^jlv"? oi o Phase vs Distance with Impedance and Velocity Tapers and 207 kW Output of-20 a ' " Beam Currents ancrCavity Voltages with Impedance.and Velocity Tapers and 207 kW Output... ° 4-21 0 0 Output Circuit with Tapered Impedance. „ » <=> 0-4-22 o Modified Applegate Diagram Showing Performance on,a Tube >. , 0 with Cavities Spaced and Tuned as Shown in Table VTEP « 4-27 _ , , ' - <1 , • n Development of the Fundamental, Second Harmonic and Fourth Q ^ Harmonic Components of Current; «, : 4-29 a * v. 3 0 « , a tP Kf-Ps & • a • LIST OF ILLUSTRATIONS (cont'd) Figure Page No. 16 Schematic Drawing of V-bancl TJbitron Amplifier 5-3 is « 17 Gyrotron Configuration (after Zaytsev). " „ - 6-3 " O te „ 18 " Cross Section for 02I Gyrotron. 6-5 i'l o H 19 Cross Section for TE „ Gvr.otron. w •6-7 ^ nn231 " <"-' „ i) 20 Drawing of Experimental Gyrotron and"the Axial Distribution » of the Magnetic Field (after Kisel1) . " 6-10 i, « v!l Raclial Variation of E . for TE „ Cylindrical Cavity. cp " n,\l, 1 ^ 6-11 ' a \\ CI - 252±; Figure of Meriffor TE- • Modes. ' - 0,m,l 6-15 CI I Figure of Merit for TE , , Modes. ' „ 6-17 II 24 Posisible'fElectron'Orbits in Hollow Beams Useful in 5ssi. » U 6-23 TE „ jDevices, ° Ml i'. o 25 Beam Envelope with Magnetic Reversal. 6-25 26 Coordinate System for Electron off Axis. 6-27 <P 27^ Locus'of. Allowed Solutions with Magnetic Reversal. ,6-28 " i, =28 Electron Trajectories Through Simple Magnetic Reversal 6-30,. 29 O " Electro° n Trajectories Throug'h Compensated Magnetic Reversal 6-?A I- 30 Electric Field for Optimum Efficiency for Osc illatbr"Analyzed 6-40 tby Rapoport, et al. o < -u 31 Model Showing Power Flow in the Amplifier. 6-49 32 tt 100 kW, 120 GHz Gyroklystron. 0 S - 33 Electron Energy vs Time with 'Synchronous Magnetic Field. 8-7 '1 j o 34 Electron Energy vs Time with Magnetic Field\Set for 4.5% Slip. 8-8 • o '." - 9 vi V ft * LIST OF TABLES u a TABLE PAGE NO. Diameter/Wavelength'for TEnm Mode Cutoffs in( Cylindrical Guide. 2T2 II Diameter/Wavelength for TM^ Mode Cutoffs" in Cylindrical Guide. <t 2-2 m Data for Various Commercially Available Window Materials at X-Band. VI Window Test Results Summarized. 3-4 V Voltage-Dependent Parameters of One-Megawatt Beams. 3-11 VI Brillouin Focusing Field and Area Convergence for Various One-Megawatt Beams of Different Energy and Size.,, (\ 4-13 •o VII Parameters of Selected One-Megawatt Beams. 4-15 . " <tO 'vm Characteristics of Possible TWT Amplifiers 4-23"' Jo 3 u IX Characteristics of 120 GHz Output Circuit with Impedance and •Velocity Taper. ' 4-24 '0 ° x Cavity Tuning for Harmonic Amplifier. 4-25 XI Parallel and Peroendicular Energy for Rotating Beam, 6-33 i, XII Tentative Design Parameters. 8-14 u a o 'if \V v^5 0 vii 1. INTRODUCTION rW:- The purpose of this program was to study the various approaches to \ " ' " - II building an amplified to produce 100 kW or more cw power at 120 .GHz to decide on an optimum approach, and,to perform design calculations. The stuc .y has led Q to the conclusion that a cyclotron resonance amplifier (gyrotron) is the optimum approach for 100 kwland that this type of interaction offers the best possibilities o 1 ;i • P for going to still"higher power levels. ! This report includes discussion in depth of all"the topics and approaches ! . ° 1 considered in the study. Sections 2 and 3 deal with output waveguide and window ' | " c • >. ' " O "I •• o designs. The fourth section discusses linear-beam amplifiers. The fifth section . o. It „ . II .considers periodic-beam (other than cyclotron resonance) devices. !! I ,. 0 si • ii - i Some readers may wish to bypass"these early sections of the report and i' I iv begin with Section 6 which considers cyclotron resonance devices in detail, or • 1 Section 7 which summarizes the. arguments leading to the choice of the gyrotron r as the optimum approach= ". Section "8 contain' s design calculationn s for a 10ii 0 kW \ (I gyrotron amplifier based on the background and theory presented in Section 6. , 6 (j e •fi c 4> 4 l-l • 2. WAVEGUIDE DESIGN ' ; ' o • • v • / " A single-mode, rectangular TE waveguide, 0.080 inch wide by 0.040 inch high, has an attenuation of about 4.3 dB/meter at 120 GHz1 assuming ri skin " 'n .• • • resistance of 0.. 11 ohms per square for copper. This is more realistic than the « w ^ dc based value of 0.09, although when surfaces are not htghly polished (electro- polished for example) skin resistance can easily reach double the dc base d 11 value. Even if this attenuation were acceptable, the power density on the waveguidu e surface 2 ' " at 100 kW would be a 1.6 kW/cm which would require heroic cooling measures, " and the electric field would be about 70,000 V/cm. For"this application, 'therefore, it would seem that there is little choice other than a multimode waveguide.
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