Design Modifications in RF Interaction Cavity of a 140 GHZ Gyrotron to Achieve Wide Tunable Bandwidth for DNP NMR Applications
Sivavenkateswara Rao V1, Muthiah Thottappan2, Pradip Kumar Jain3
1Sivavenkateswara Rao V*, Centre of Research in Microwave Tubes, Department of Electronics Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi, India.
2M. Thottappan, Centre of Research in Microwave Tubes, Department of Electronics Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi, India.
3Pradip Kumar Jain, Department of Electronics and Communication Engineering, National Institute of Technology, Patna, India.
Manuscript received on September 23, 2019. | Revised Manuscript received on October 15, 2019. | Manuscript published on October 30, 2019. | PP: 6465-6462 | Volume-9 Issue-1, October 2019 | Retrieval Number: A2241109119/2019©BEIESP | DOI: 10.35940/ijeat.A2241.109119
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© The Authors. Blue Eyes Intelligence Engineering and Sciences Publication (BEIESP). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Abstract: The tapered RF interaction cavity of 140 GHz tunable continuous wave (CW) gyrotron operating in TE0,3,q mode has been tailored with the aim of providing RF power over a tunable bandwidth for 212 MHz DNP NMR spectroscopy applications. Gyrotron device RF interaction cavity design, its beam absent RF characteristics as well as electron beam and RF wave interaction behavior, both analytical and Particle-in-Cell (PIC) simulation studies have been presented. Using linear analysis, the start oscillation currents and the RF field profiles for the various axial operating modes indices q = 1, 2, 3 have been determined. Suitable modifications in the interaction cavity have been incorporated for the enhancement of device tunable bandwidth by operating the gyrotron in the high order axial indices via magnetic tuning. Gyrotron beam-wave interaction behaviour explored using time dependent non-linear multi-mode analysis for various beam currents and magnetic fields and more than >15W of RF power over a tunable bandwidth of 400MHz has been achieved through magnetic field tuning. This tunable bandwidth gyrotron design will of immense use for enhancement of sensitivity of the DNP NMR spectroscopy.
Keywords: Beam wave interaction, CRM instability, DNP NMR applications, Tunable gyrotron oscillator.