Highly Efficient Micro Cathode

Busek Company, Inc. proposes to develop a micro thermionic cathode that requires extremely low power and provides long lifetime. The basis for the cathode is a Barium impregnated dispenser cathode. The innovation will be the heating technique. We are proposing to heat the cathode to emission temperatures through radio frequency induction heating. The current state of the art micro cathodes utilize a resistive heater typically operated by passing a DC or AC current through a small refractory wire, heating the wire through ohmic heating. This requires significant sized wires and mechanics that create a heat sink through the leads, greatly increasing the power required to heat the cathode. Alternative development programs for micro cathodes have proposed utilizing lasers to heat the backside of the cathode. The drawback for this method of heating is the low power efficiency of state of the art lasers. In support of our proposed concept, Busek has recently developed an innovative RF generation circuitry that leads to applications like the proposed. The circuit is highly efficient and load variant tolerant. During Phase I we will design, build and test a model cathode with integrated induction heater coil and RF generator. Phase II will optimize the design and develop a commercial cathode for applications such as sensors, traveling wave tubes or micro ion engines.

Potential applications of the micro cathode are abundant, though the likely first and highest NASA interest will be for very high frequency TWT microwave generators. As the frequencies of these sources increase, the size (diameter) of the electron feed beams needs to decrease. NASA could also have interest for this low power, micro cathode for scientific sensor such as probes for measuring electric fields in earth orbit is by measuring the ExB electron drift. This requires small beam spot and as spacecraft shrink in size and power, the exceptional low power of the proposed cathode will be needed. Another potential application for the proposed cathode is for use as a neutralizer and plasma initiation electron source for our micro RF ion engines. Developing a thermionic cathode that emits on the order of 1mA for 100mWatt input would eliminate on critical hurdle for efficient micro ion engine utilization for space propulsion. We currently have a field emission cathode that can emit this current, but has difficulty starting the plasma. The proposed cathode should be able to be overdriven for a fraction of a second to deliver multiple mA of current. The cathode can be scaled larger for the larger ion engines if needed.

Non-NASA applications mirror the NASA applications plus there is significant interest in developing the necessary equipment to enable the use of the extremely high frequency (EHF) band for military and commercial applications. For the armed services, realization of millimeter wave amplifiers enables Gigabit rate point-to-point satellite communications, as well as access to currently unused spectrum. Furthermore, millimeter wave radio communications enable reduced antenna size and increased signal directionality, increasing effective signal gain to the target. Commercial applications for EHF amplifiers tend to focus on atmospheric science, in particular monitoring upper atmospheric temperatures.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.