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 80.15 mm 5.16 mm 28 286.5 mm 4.817 T Magnetic compression ratio ( f m ) 23.96 Beam current ( I o ) 88 A 389
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 () 0.147 mm Magnetic field at cavity (Bo) 4.817 tesla Cathode slant length (Ls) 5.16 mm velocity spread 3.17% Magnetic field at cathode (Bc) 0.201 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-0.1 - - - - Ls-0.05 - - - - Ls-0.025 - - - - Ls 1.48951 17.64 0.14743 3.17007 Ls+0.025 1.49312 17.63 0.14772 3.21297 390
Ls+0.05 1.49099 17.63 0.14756 3.12042 Ls+0.1 1.49113 16.92 0.14777 3.23091 Ls+0.2 1.47883 17.64 0.14771 3.34229 Ls+0.5 1.45258 17.59 0.14714 3.76728 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 = 5.16+ 0.5 mm. (ii) Change in slant angle of cathode (θ) Table 4: Optimized value of slant angle with tolerance θ (28º) θ-1.0% 1.4485 17.71 0.1464 3.25672 θ-0.5% 1.4675 17.61 0.1469 3.36702 θ 1.4895 17.64 0.1474 3.17007 θ +0.5% 1.4784 17.42 0.1462 3.04312 θ+1.0% 1.4958 17.58 0.1468 2.83449 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 -0.2 1.4955 17.66 0.1476 3.32863 Dac -0.1 1.5115 17.65 0.1478 3.36610 Dac -0.05 1.5006 17.65 0.1475 3.18644 Dac 1.4895 17.64 0.1474 3.17007 Dac 1.4851 17.62 0.1473 3.08084 +0.05 Dac +0.1 1.4827 17.63 0.1473 3.05633 Dac +0.2 1.4965 17.63 0.1476 3.25555 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
Distance between anode and cathode (Dac) with tolerance = 5.961 ± 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-1.00 1.5976 17.57 0.1485 2.86697 Rc-0.75 1.5592 17.61 0.1481 2.95857 Rc -0.50 1.5785 17.59 0.1477 2.68309 Rc -0.25 1.5089 17.64 0.1475 3.05363 Rc 1.4895 17.64 0.1474 3.17007 Rc +0.25 1.4595 17.64 0.1470 3.39241 Rc +0.50 1.4895 17.64 0.1463 3.56450 Rc +0.75 1.4296 17.66 0.1446 4.79387 Rc +1.00 1.4247 17.70 0.1447 4.61799 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-1.00 1.4826 17.60 0.1466 3.3716 z-0.75 1.4767 17.59 0.1467 3.4263 z-0.50 1.4858 17.61 0.1470 3.3880 z-0.25 1.4909 17.63 0.1467 3.0876 Z 1.4895 17.64 0.1474 3.1700 z+0.25 1.5040 17.62 0.14644 3.4622 z+0.50 1.5088 17.67 0.1486 3.2966 z+0.75 1.5042 17.62 0.1473 3.1299 z+1.00 1.5396 17.65 0.1488 2.9551 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
%) Bc-30 guass 1.4229 17.50 0.1464 4.6635 Bc-20 guass 1.4579 16.90 0.1473 4.4159 Bc-10 guass 1.5015 17.65 0.1482 3.3603 Bc 1.4895 17.64 0.1474 3.1700 Bc+10guass 1.5196 17.66 0.1476 3.0163 Bc+20guass 1.5160 17.63 0.1471 2.7627 Bc+30guass 1.5289 17.67 0.1473 2.3796 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% 1.5084 17.62 0.1487 3.4039 Bo 1.4895 17.64 0.1474 3.1700 Bo+0.5% 1.5041 17.60 0.1464 3.3688 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, 1986. [2] M. V. Kartikeyan, E. Borie, and M. Thumm, Gyrotrons High-Power Microwave and Millimetre Wave Technology. Germany: Springer, 2004. [3] Thumm, M., High power gyro-devices for plasma heating and other applications," Int. J. Infrared Millim. Waves, Vol. 26, 483{503, Apr. 2005.}. [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{521 1977. [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, 2010. 393