Broadband Amplification of Low-Terahertz Signals Using Axis-Encircling Electrons in a Helically Corrugated Interaction Region

Experimental results are presented of a broadband, high power, gyrotron traveling wave amplifier (gyro-TWA) operating in the (75-110)-GHz frequency band and based on a helically corrugated interaction region. The second harmonic cyclotron mode of a 55-keV, 1.5-A, axis-encircling electron beam is used to resonantly interact with a traveling TE_{21}-like eigenwave achieving broadband amplification. The gyro-TWA demonstrates a 3-dB gain bandwidth of at least 5.5 GHz in the experimental measurement with 9 GHz predicted for a wideband drive source with a measured unsaturated output power of 3.4 kW and gain of 36-38 dB. The approach may allow a gyro-TWA to operate at 1 THz.

High power wideband gyrotron backward wave oscillator operating towards the terahertz region

Experimental results are presented of the first successful gyrotron backward wave oscillator (gyro-BWO) with continuous frequency tuning near the low-terahertz region. A helically corrugated interaction region was used to allow efficient interaction over a wide frequency band at the second harmonic of the electron cyclotron frequency without parasitic output. The gyro-BWO generated a maximum output power of 12 kW when driven by a 40 kV, 1.5 A, annular-shaped large-orbit electron beam and achieved a frequency tuning band of 88-102.5 GHz by adjusting the cavity magnetic field. The performance of the gyro-BWO is consistent with 3D particle-in-cell numerical simulations.

High-pressure injection of dissolved oxygen for hydrocarbon remediation in a fractured dolostone aquifer

A field experiment was completed at a fractured dolomite aquifer in southwestern Ontario, Canada, to assess the delivery of supersaturated dissolved oxygen (supersaturated with respect to ambient conditions) for enhanced bioremediation of petroleum hydrocarbons in groundwater. The injection lasted for 1.5h using iTi's gPro® oxygen injection technology at pressures of up to 450 kPa and at concentrations of up to 34 mg O₂/L. A three-dimensional numerical model for advective-dispersive transport of dissolved oxygen within a discretely-fractured porous medium was calibrated to the observed field conditions under a conservative (no-consumption) scenario. The simulation demonstrated that oxygen rapidly filled the local intersecting fractures as well as the porous matrix surrounding the injection well. Following injection, the local fractures were rapidly flushed by the natural groundwater flow system but slow back-diffusion ensured a relatively longer residence time in the matrix. A sensitivity analysis showed significant changes in behaviour with varying fracture apertures and hydraulic gradients. Applying the calibrated model to a 7-day continuous injection scenario showed oxygen residence times (at the 3mg/L limit), within a radius of 2-4m from the injection well, of up to 100 days. This study has demonstrated that supersaturated dissolved oxygen can be effectively delivered to this type of a fractured and porous bedrock system at concentrations and residence times potentially sufficient for enhanced aerobic biodegradation.