Department of Electronics and Communication Engineering Shrinathji Institute of Technology & Engineering, Nathdwara (Raj.)

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1 Sensitivity and Misalignment Analysis of MIG for 120 GHz, 3MW Gyrotron Manoj Kumar Sharma 1, Mahesh Kumar Porwal 2 1 M Tech-IV Semester, 2 Associate Professor Department of Electronics and Communication Engineering Shrinathji Institute of Technology & Engineering, Nathdwara (Raj.) Abstract: The magnetron injection gun is the very sensitive part of Gyrotron small change in the position of subpart of MIG can affects the beam-wave interaction which leads to the change in the output power completely so after finalized the design of 120GHz, 3MW Gyrotron we perform sensitivity analysis using EGUN software to calculate the tolerance of different parts, effect of misalignment and position of different parts on the output power and different gun parameters. Keywords: Gyrotron, MIG (Magnetron Injection Gun), EGUN Software. I. INTRODUCTION The microwave tubes have lot of applications and the range of microwave frequency is from 3GHz to 300GHz and higher frequency gyrotron is used for the heating, material processing and ceramic sintering [1,2]. The gyrotron is based on the cyclotron maser interaction between the electromagnetic wave and the gyrating electron beam [3].In the Gyrotron, there are different subparts but among them magnetron injection gun (MIG) is a the most important and it is the source of electron beam, which is interaction with rf field in intersection section called cavity. The efficiency of gyrotron depends on the design of magnetron injection gun or source electron beam. Therefore, for getting desired power at desired frequency depends on the electron beam properties at the interaction region. So that success of any Gyrotron design is completely depends on the design of magnetron injection gun. and little bit if variation of dimension and position can completely change the beam parameters and it further affect the electron beam interaction and the power generated at the output can completely change. II. FINALIZED DESIGN The different parameter and dimension of different sub parts of 120GHZ, 3MW Gyrotron has been calculated using equations derived by Baird and Lawson [4,5] and final analysis is done by simulation using EGUN software. Finalised value of different parameters are given below. Table1: Final MIG Dimensions and parameters Parameters Optimized Cathode radius ( r c ) Slant length of emitting surface ( l s ) Cathode angle ( ) c Distance between centers of cathode and cavity ( d cc, ) Magnetic field at interaction region ( B ) o mm 5.16 mm mm T Magnetic compression ratio ( f m ) Beam current ( I o ) 88 A 389

2 Beam voltage ( V ) o 95 kv Modulating anode voltage ( V ) a 88 kv Operating mode TE0,3 Output power (P0) 3MW III. SENSITIVITY ANALYSIS OF MIG Sensitivity analysis is the study of how the variation (uncertainty) in the output of a device can be attributed to different variations in the input parameter. Put another way, it is a technique for systematically changing variables in a model to determine the effects of such changes. In any budgeting process like gyrotron, there are always variables that are uncertain. During the fabrication and operation of the device, it is very difficult to maintain the MIG operating parameters fixed. A small change in the MIG parameters affects the beam-wave interaction which leads to the change in the output power. Thus, it is necessary to analyze the effect of the variation of the various gun input parameters, namely- slant length (Ls), cathode angle, distance between cathode and anode (Dac), cavity magnetic field (Bo), cathode magnetic field (Bc), Beam misalignment with cathode position, Radial shifting of magnetic coil and axial shifting of magnetic coil. After simulating with egun software, we found that according to geometry of MIG our final beam parameters, cathode dimension and magnetic field at cathode & cavity are approx. same as we obtained in synthesis program. Our finalized parameters of MIG obtained after simulation which are used for sensitivity analysis are as follows Table 2: Finalized parameters of MIG obtained after Simulation Beam radius () 17.64mm, Transverse to axial velocity ratio 1.48 Larmour radius () mm Magnetic field at cavity (Bo) tesla Cathode slant length (Ls) 5.16 mm velocity spread 3.17% Magnetic field at cathode (Bc) tesla Distance between anode and cathode (Dac) 18.0mm IV. TOLERANCE IN MIG (i)change in slant length of cathode (Ls): Table 3: Optimized value of slant length with tolerance Ls (5.16mm) Ls Ls Ls Ls Ls

3 Ls Ls Ls Ls Above table shows that slant length of cathode (Ls)can attain a maximum increase in length of 0.5 mm but there will not be any decrease in slant length of cathode (Ls). Reason for not going in negative value of slant length is that beam emission is not possible. According to table 4.3, we conclude that Slant length of cathode (Ls) with tolerance = mm. (ii) Change in slant angle of cathode (θ) Table 4: Optimized value of slant angle with tolerance θ (28º) θ-1.0% θ-0.5% θ θ +0.5% θ+1.0% above table shows that how much % of tolerance is possible for cathode angle so that our beam pattern and output parameters should not change to the great extent. θ =300 is the best possible angle at which our beam parameters are set to design but according to table a little change is almost possible that helps in fabricating of device. So, according to table 4.4 we observe that Slant angle of cathode (θ) with tolerance = 300 ± 1.0% (iii)change in distance between anode and cathode (Dac) Table 5: Optimized value of distance between anode and cathode with tolerance Dac (18mm) Dac Dac Dac Dac Dac Dac Dac Above table, we can see that all the results are fulfilling our criteria without being much change in our beam parameters and output parameters. According to table 4.5, we observe that 391

4 Distance between anode and cathode (Dac) with tolerance = ± 0.2 mm (i)cathode misalignment radially V. MISALIGNMENT STUDY OF MIG Table 6: Optimized value of cathode misalignment radially (upward or downward) Rc (22.15 mm) Rc Rc Rc Rc Rc Rc Rc Rc Rc Cathode misalignment radially (upward or downward) = R c ± 1.0 mm (ii) Cathode misalignment axially Table 7: Optimized value of cathode misalignment axially (forward or backward) z (31 mm) z z z z Z z z z z VI. BEAM MISALIGNMENT WITH RESPECT TO MAGNETIC FIELD (i)cathode magnetic field(bc) Table 8: Optimized value of change in magnetic field at cathode (Bc) Bc (0.201 T) spread( 392

5 %) Bc-30 guass Bc-20 guass Bc-10 guass Bc Bc+10guass Bc+20guass Bc+30guass Misalignment of Cathode magnetic field = Bc ± 9 gauss (ii)cavity magnetic field Table 9: Optimized value of change in magnetic field at cavity (Bo) Bo (4.817T) Bo-0.5% Bo Bo+0.5% Misalignment of Cavity magnetic field = Bc ± 0.5 gauss VII. CONCLUSION In this paper, the sensitivity analysis and misalignment analysis of magnetron injection gun of 120GHz, 3MW Gyrotron are presented. This analysis are very important after successful design of MIG because during implementation of design little bit of error is possible so in that case tolerance of every aspects are required and during that limit beam parameters of MIG and output power is not affect so much. ACKNOWLEDGMENT Authors are grateful to HOD (ECE) and Director, SITE, Nathadwara, for permission to publish this paper. Also Thanks to Dr. Hasina Khatun, Scientist C CEERI from CEERI Pilani and my friend s for continuous support and encouragement. REFERENCES [1] A. S. Gilmour Jr., Microwave Tubes. Boston: Artech House, [2] M. V. Kartikeyan, E. Borie, and M. Thumm, Gyrotrons High-Power Microwave and Millimetre Wave Technology. Germany: Springer, [3] Thumm, M., High power gyro-devices for plasma heating and other applications," Int. J. Infrared Millim. Waves, Vol. 26, 483{503, Apr }. [4] G. Dammertz, E. Borie, C. T. Iatrou, M. Kuntzee, B. Piosczyk, and M. Thumm, 140 GHz gyrotron with multimegawatt output power, IEEE Trans. Plasma Science, vol. 28, no. 3, 2000 [5] Baird, J. M. and W. Lawson The gyrotron Magnetron injection gun (MIG)" IEEE Trans. Microwave Theory Tech., Vol. 25, No. 6, 514{ [6] U. Singh, A. Bera, R. R. Rao, A. K. Sinha, Synthesized parameters of MIG for 200 kw, 42 GHz gyrotron, Journal of Infrared Millimetre and Terahertz wave, vol. 31, pp. 533,