D. Bowes
University of Strathclyde
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Featured researches published by D. Bowes.
Physics of Plasmas | 2009
H. Yin; A. W. Cross; W. He; A. D. R. Phelps; K. Ronald; D. Bowes; C. W. Robertson
Experimental studies of the production and propagation of an electron beam from a multigap pseudospark discharge are presented. From a three-gap pseudospark, a beam up to 680 A was measured at the anode at an applied dc voltage of 23 kV. This beam can propagate downstream as far as 20 cm in a gaseous environment with no guiding magnetic field, which confirms that the transport of the electron beam was based on the neutralization of the space charge of the electron beam due to the ionization of the gas molecules by the beam itself. The beam is of very small size of 1-3 mm in diameter and is ideal to drive high frequency radiation. Higher energy electron beam pulses were generated using a 14-gap pseudospark discharge powered by a cable pulser capable of producing 120 ns duration and 170 kV voltage pulses. The beam measured had a current of up to 110 A. Interactions between the produced beam and a Ka-band Cherenkov maser and a W-band backward wave oscillator slow wave structure were simulated and designed. Millimeter wave pulses were detected from the Cherenkov maser and backward wave oscillator beam-wave interaction experiments.
Applied Physics Letters | 2015
W. He; L. Zhang; D. Bowes; H. Yin; K. Ronald; A. D. R. Phelps; A. W. Cross
This paper presents for the generation of a small size high current density pseudospark (PS) electron beam for a high frequency (0.2 THz) Backward Wave Oscillator (BWO) through a Doppler up-shift of the plasma frequency. An electron beam ∼1 mm diameter carrying a current of up to 10 A and current density of 108 A m−2, with a sweeping voltage of 42 to 25 kV and pulse duration of 25 ns, was generated from the PS discharge. This beam propagated through the rippled-wall slow wave structure of a BWO beam-wave interaction region in a plasma environment without the need for a guiding magnetic field. Plasma wave assisted beam-wave interaction resulted in broadband output over a frequency range of 186–202 GHz with a maximum power of 20 W.
Journal of Physics D | 2013
G. Liu; W. He; A. W. Cross; H. Yin; D. Bowes
Backward wave oscillators (BWO) are promising high-power portable radiation sources in the terahertz frequency range. A G-band (140–220 GHz) sheet beam BWO based on a double staggered metallic rod array as the slow wave structure (SWS) has been designed and presented in this paper. The novel SWS allowed extension of the interaction area for the sheet beam with a uniform electric field if the height of the rod array is properly chosen. This could alleviate beam instability problems in the sheet beam transportation and potential parasitic oscillations. Moreover, a relatively broad bandwidth can be achieved due to its special dispersive properties. Particle-in-cell simulation had predicted that the G-band sheet beam BWO with the improved non-uniform double staggered metallic rod array can achieve output power of over 110 W in a continuous frequency tuning range of 186.3–227.2 GHz (relative bandwidth 20%) with a maximum electronic efficiency of 2.8% by using a 200 mA sheet beam and adjusting the beam voltage from 20 to 40 kV.
IEEE Transactions on Plasma Science | 2014
D. Bowes; H. Yin; W. He; K. Ronald; A. D. R. Phelps; Defeng Chen; Peng Zhang; Xiaodong Chen; D. Li; A. W. Cross
A pseudospark (PS)-sourced electron beam of 3-mm diameter has been experimentally investigated. Emission of X-rays was detected during a PS discharge and clear X-ray images were formed using the PS-sourced electron beam impacting on a 0.1-mm-thick molybdenum target at an applied voltage of 46 kV. Using a phosphor-coated scintillator, the beams cross-sectional profile and surrounding ion channel were also observed. These results confirm the presence of an electron beam.
NEW DEVELOPMENTS IN NONLINEAR PLASMA PHYSICS: Proceedings of the 2009 ICTP Summer College on Plasma Physics and International Symposium on Cutting Edge Plasma Physics | 2009
A. W. Cross; H. Yin; D. Bowes; W. He; K. Ronald; A. D. R. Phelps
The production and propagation of an electron beam from both a multi-gap and a small-scale single-gap pseudospark discharge are investigated. From a three-gap pseudospark, a beam up to 680 A was measured at the anode at an applied dc voltage of 23 kV. This beam can propagate downstream as far as 20 cm in a gaseous environment with no guiding magnetic field, which confirms that the transport of the electron beam was based on the neutralization of the space-charge of the electron beam due to the ionization of the gas molecules by the beam itself. The beam is of very small size of 1-3 mm in diameter and is ideal to drive high frequency radiation. Higher energy electron beam pulses were generated using a 14-gap pseudospark discharge powered by a cable pulser capable of producing 120 ns duration and 170 kV voltage pulses. The beam measured had a current of up to 110 A. A Ka-band Cherenkov maser and a W-band backward wave oscillator from the produced beam were simulated and experimentally studied. Millimeter wave pulses were detected successfully from both devices. In an effort to show the effects of scaling down the size of the pseudospark discharge on beam performance, a single-gap 1mm aperture pseudospark electron beam experiment was conducted, based on which a 206 GHz microklystron was designed and simulated.
Proceedings of SPIE, the International Society for Optical Engineering | 2010
T. Schuhmann; Jonathan M. Protz; David James Fields; H. Yin; A. W. Cross; W. He; D. Bowes; K. Ronald; A. D. R. Phelps
High performance terahertz (THz) radiation sources hold great promise for a variety of military and space applications. With micro-electro-mechanical systems (MEMS) fabrication techniques, it is possible to attain the smaller, more precisely machined resonant structures required by Vacuum Electronic Devices (VEDs) to function in these frequencies. The research presented here proposes a design and fabrication process for a micro-klystron with a targeted operating frequency of 200 GHz; being developed jointly by Duke University, the University of Strathclyde, UK, and Logos Technologies. It also analyzes the use of a pseudospark (PS) discharge as a novel electron beam source to drive the klystron. Dimensional tolerances are investigated using both analytic and numeric techniques. The incorporation of alignment structures into the fabrication process that utilize kinematic and elastic averaging effects, along with clever stacking techniques, allows submicron alignment tolerances yielding an expected power output of approximately 5W per klystron with an overall efficiency of 20%. The device proposed here, with a volume on the order of 0.01 cc, should be capable of output power densities of up to 1kW/cc. A fabrication run recently completed at MITs Microsystems Technology Laboratories yielded promising results and 32 silicon die were successfully bonded into a stack 1.4cm tall. Difficulties remain, however, in controlling surface roughness and integrating a klystron with alignment features for parallel processing. Several alternative fabrication schemes have been proposed and another fabrication run based on these modifications is currently underway.
international conference on plasma science | 2012
A. W. Cross; H. Yin; D. Bowes; W. He; K. Ronald; A. D. R. Phelps; D. Li; Xiaodong Chen
Summary form only given. High frequency radiation sources in sub-terahertz frequency range (0.1–1 THz) are currently very attractive for both research and technical applications. To generate the high frequency radiation, a pseudospark (PS)-sourced electron beam is ideal because of its scalability accompanied with high intensity and high quality beam generation [1, 2]. The propagation of a PS electron beam is aided by an ion channel formed by the beam front resulting in no need for a guide magnetic field, which brings great simplicity and flexibility. Most recently, PS-sourced electron beam experiments were performed with beam diameters in both the millimeter and micro meter range. The 3mm beam was also diagnosed with a beam produced x-ray image. The PS beams have been applied in radiation sources from Ka to W bands [3, 4]. For further radiation generation, a klystron at 94 GHz is designed because the klystron is an ideal choice for higher frequency operation due to its operation mechanism, efficiency and robustness as well as the fact that it may be easily scaled in size as well [5].
international conference on infrared, millimeter, and terahertz waves | 2010
D. Li; Xiaodong Chen; H. Yin; D. Bowes; W. He; A. W. Cross; K. Ronald; A. D. R. Phelps
The Terahertz band of EM spectrum has received considerable research interests recently. A micro-klystron has the potential to meet the requirement of high power and compact terahertz source in many applications. The micro-klystron needs a very thin electron beam with sufficient current density. A pseudospark discharge cathode has the ability to provide high current density with small diameter electron beam (<1mm).
international vacuum electronics conference | 2009
H. Yin; A. W. Cross; W. He; D. Bowes; K. Ronald; A. D. R. Phelps; Jonathan M. Protz; M. Verdiel; M. Reynolds; T. Schuhmann; Xiaodong Chen; D. Li; J. Zhou
Based on previous experimental investigations on pseudospark (PS) discharges, a small-scaled PS electron beam source was conceived to drive a 200GHz microklystron. Recent PS e-beam experiments producing a beam of 1mm in diameter and klystron interaction simulations will be presented. The microklystron will be fabricated using micro-electro-mechanical systems (MEMS) construction techniques.
2016 IEEE 9th UK-Europe-China Workshop on Millimetre Waves and Terahertz Technologies (UCMMT) | 2016
A. W. Cross; W. He; L. Zhang; H. Yin; D. Bowes; K. Ronald; A. D. R. Phelps; D. Li; Xiaodong Chen; Yong Yin; Guoxiang Shu; G. Liu; Jun-Wu Zhao
High quality intense electron beams play an important role in high power millimeter-wave and terahertz radiation generation. To this end, the pseudospark-sourced electron beam has been investigated with their applications in different beam-wave interaction structures. Different structures have been designed and modelled using the particle-in-cell codes MAGIC and CST Particle Studio. The experimental demonstration of the PS-sourced electron beams of submillimeter diameter and the coherent millimeter wave radiation generated from PS-sourced electron beams in different beam-wave interaction structures will be presented.