TST, Vol. 11, No. 1, PP. 1-20
(Invited paper) Design studies and analysis of operational limits of 0.24-THz gyrotrons for DEMO
M. Thumm 1, 2*, K. A. Avramidis 1, J. Franck 1, G. Gantenbein 1, S. Illy 1, J. Jin 1, P. C. Kalaria 1, I. Gr. Pagonakis 1, S. Ruess 1, 2, C. Wu 1 and J. Jelonnek 1, 2
Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany
1 Institute for Pulsed Power and Microwave Technology (IHM)
2 Institute of High Frequency Techniques and Electronics (IHE)
* Email: manfred.thumm@kit.edu
(Received March 06, 2018)
Abstract: Electron Cyclotron Heating and Current Drive (ECH&CD) systems using gyrotrons as RF sources play a key role in present controlled thermonuclear fusion plasma experiments and are also planned for the future European DEMOnstration power plant (DEMO). Following the development of 1 MW continuous wave (CW) 140 GHz and 170 GHz gyrotrons for the W7-X stellarator and the ITER tokamak, respectively, the conceptual designs of tubes with frequencies up to approximately 270 GHz are ongoing at KIT. Along with a 237.5 GHz, 2 MW coaxial-cavity gyrotron design, a 236 GHz, 1 MW hollow-cavity approach is under investigation, as backup solution. In both cases, operating modes have been selected considering multi-frequency operation at around 170 GHz, 204 GHz, 237 GHz and 270 GHz for multi-purpose applications and fast-frequency tunability in steps of 2-3 GHz within the frequency range of ±10 GHz around the operating center frequency for plasma stability control.
At 237.5 GHz, a coaxial-cavity design for the TE49,29-mode (eigenvalue ~ 158) has been found and optimized using realistic electron beam parameters with quite promising 1.9 MW output power and 33% interaction efficiency at a maximum cavity wall loading of 2 kW/cm². At 203.8 GHz, oscillating in the TE42,25-mode (eigenvalue ~ 136), the same cavity could deliver 1.9 MW output power with 32% interaction efficiency at reduced maximum cavity wall loading of 1.7 kW/cm². For 170 GHz operation in the TE35,21-mode (eigenvalue ~ 113), the corresponding parameters would be 1.8 MW, 31% and 1.3 kW/cm².
In the case of a TE43,15-mode (eigenvalue ~ 103) hollow-cavity gyrotron operating at 236.1 GHz, again considering realistic electron beam parameters in the cavity (rms velocity spread: 6%, radial width: λ/4) and a realistic conductivity of the anticipated cavity material Glidcop, the results suggest stable output power of 0.92 MW with an interaction efficiency of 36% at a maximum cavity wall loading of 2 kW/cm². For the TE37,13-mode (eigenvalue ~ 89) at 203.0 GHz and the TE31,11-mode (eigenvalue ~ 74) at 170.0 GHz the corresponding values are 1.15 MW and 1.55 MW and 35% and 33%, respectively, at the same wall loading.
The development of magnetron injection guns (MIGs) with high electron beam quality and of multi-stage depressed collectors (MDCs) for energy recovery is necessary to achieve the required total gyrotron efficiency of > 60%.
Keywords: DEMO, Electron cyclotron heating and current drive (ECH&CD), Multi-frequency gyrotrons, Frequency step-tunable gyrotrons, Coaxial-cavity gyrotrons, Mode selection, High-order modes, Magnetron injection gun, Quasi-optical mode converter, Broadband synthetic diamond Brewster and tunable windows.
doi: 10.11906/TST.001-020.2018.03.01
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TST, Vol. 11, No. 1, PP. 21-27
(Invited paper) Study of gene transcription and bio-molecular information by terahertz waves
Mingxia He 1*, Liyuan Liu 1*, Pengfei Wang 1, Jinwu Zhao 1, Yuefei Wang 2, and Lijie Dong 3
1 Center for Terahertz Waves, School of Precision Instrument and Optoelectronics Engineering，Tianjin University, China
2 State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, China
3 Tianjin Medical University Eye Hospital, China
* Email: lyliuma@tju.edu.cn; hhmmxx@tju.edu.cn
(Received December 26, 2017 )
Abstract: Terahertz (THz) technologies have shown great potentials for biomedical applications such as THz radiation effects on cells and spectroscopy of water studied in terahertz range. Water’s strong absorption to THz wave restricts the acquisition of high frequency information, promoting the development of THz attenuated total reflection system (THz-ATR). Besides, the advances in terahertz applications have stimulated renewed interest regarding the THz bio-safety, which results in development related to biological effects studies of terahertz radiation.
Keywords: Terahertz spectroscopy, Protein, Hydrating water
doi: 10.11906/TST.021-027.2018.03.02
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TST, Vol. 11, No. 1, PP. 28-33
(Invited paper) Global gene expression in human skin tissue induced by intense terahertz pulses
Cameron M. Hough 1, 2*, David N. Purschke 2, Chenxi Huang 2, Lyubov V. Titova 3, Olga Kovalchuk 4, Brad J. Warkentin 1, and Frank A. Hegmann 2
1 Medical Physics Division, Department of Oncology, University of Alberta, Edmonton, AB T6G 1Z2, Canada
2 Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
3 Department of Physics, Worcester Polytechnic Institute, Worcester, MA 01609, USA
4 Department of Biology, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
* E-mail: chough@ualberta.ca
(Received March 10, 2018)
Abstract: Terahertz (THz) radiation has been gaining increasing interest for medical applications due to the potential of pathological contrast for diagnostic applications. However, the interaction mechanism with biological systems implies that intense THz pulses can induce significant non-thermal biological effects, and these have been observed at the molecular, cellular, and tissue level of organization. To investigate the biological processes that are dysregulated by exposure to intense THz pulses, the global differential gene expression profile in skin tissue models was measured. Furthermore, gene ontology analysis identified biological processes that are significantly over-represented by the set of THz-affected genes. In total, 1,681 genes were found to be differentially expressed by exposure to intense THz pulses, and the down-regulated genes were significantly associated with several biological processes related to epidermal differentiation, suggesting the potential for THz exposure to dysregulate/inhibit differentiation or skin function in exposed tissue. The intensities required for the onset of potentially dysregulatory effects are much higher than intensities currently utilized in technologies for diagnostic medical applications.
Keywords: Terahertz, Gene expression, Bioinformatics
doi: 10.11906/TST.028-033.2018.03.03
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