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We propose an advanced active current-control (ACC) unit composed of two cascade transistors for extremely stabilizing field emission currents. The upper transistor connected to the cathode modulates high voltages for field emission while the other one regulates emission current stably. Using the ACC unit developed, very stable emission currents were achieved from the fully vacuum-sealed x-ray tube...
We developed a field emission nano-focus x-ray source using carbon nanotube (CNT) emitters and electron beam (E-beam) focusing modules, which could be used in the applications requiring the high-resolution x-ray images. For the nano-size focusing of E-beam from CNT emitters, we designed special focusing modules consisting of electrostatic and magnetic lenses. The geometries and operating conditions...
We developed a fully vacuum-sealed carbon nanotube (CNT)-based field emission x-ray tube with commercial-level performance for dental imaging application. The CNT x-ray tube was designed in a triode configuration with the focus-functional gate and had a compact size, much smaller than the conventional hot-cathode tubes. The small size of CNT x-ray tubes along with no cathode heating enables us to...
We describe reliable CNT x-ray tubes and their digital properties such as easy modulation of x-ray dose, high-speed operation, and low-voltage and low-power consumption control with an active-current control unit (ACCU) developed. The simple and advanced ACCU was found to shorten the response time of CNT x-ray tube down to sub-microsecond along with stable and reliable operation. The fast digital...
We have optimized the aging process of fully vacuum-sealed carbon nanotube (CNT) X-ray tubes in terms of an anode voltage, a cathode current and pulse on-time. Degradation and electrical arcing have been monitored and severely suppressed during the aging process. The completely aged CNT X-ray tube with an outer diameter of 15 mm and a length of 60 mm shows a cathode current of 3 mA at an anode voltage...
The advanced active-current control with a push-up voltage source is proposed for the fast operation of a carbon nanotube (CNT) field-emission X-ray tube while maintaining the advantages of improved stability and reliability. The push-up voltage source, composed of a resistor and a voltage supply, was found to reduce the response time of CNT X-ray tubes down to sub-microsecond.
We have designed and fabricated a novel electrostatic lens module composed of a micro- and macro-focusing lens in carbon nanotube field-emission electron guns for energy-variable X-ray sources maintaining their focal spot size. The effective focal spot was observed to be small and isotropic by the micro-focusing lens to suppress the divergence of an individual electron beam and the elliptical macro-focusing...
The advanced active-current control with a push-up voltage source is proposed to operate a carbon nanotube (CNT) field-emission X-ray tube rapidly with maintaining the advantages of improved stability and reliability. The push-up voltage source, comprising of a resistor and a voltage supply, strongly reduced the response time of CNT X-ray tubes down to several μs.
We analyzed the failure mechanism in miniature x-ray tubes with a gated carbon nanotube (CNT) field emitter. The miniature x-ray tube even with a small leakage current of field emission from the CNT emitters to the gate electrode has some distortion of the electron beam trajectory from the cathode to anode passage, causing a charging at insulating parts. The charging at the insulator spacer would...
We, for the first time, developed fully vacuum-sealed X-ray tubes with carbon nanotube field emitters. The specially designed brazing process has been adopted for the vacuum sealing of the X-ray tube. The fabricated two types of X-ray tubes showed a good operation with a high stability and long lifetime.
We have designed and fabricated a highperformance carbon nanotube (CNT) field emitter for a vacuum-sealed X-ray tube by a brazing process. The developed high-temperature endurable CNT emitters were vacuum-sealed in the diode and triode configurations, showing little degradation upon the brazing process and a good cold cathode of X-ray tube.
The CNT emitter on metal tip (CNT-on-Tip) cathode can provide high-brightness electron beams due to its point-like electron emission sites. The triode type emitter with a gate electrode is prerequisite to an intensity-controllable X-ray. We simulated the trajectory of the emitted electron beams in the triode CNT-on-Tip and optimized the configuration to obtain ideal triode properties. Consequently,...
We have fabricated a high-temperature endurable carbon nanotube (CNT) emitter for a cold cathode X-ray tube. The ball-milling was used in the CNT paste procedure for effective material dispersion. After a high-temperature annealing process for vacuum sealing, a negligible change was observed in the surface morphology of CNT emitters. The developed CNT emitter maintained outstanding field emission...
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