Field Emitter X-Ray Source Pulsing Against Vacuum Arcing
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Solution Overview
Problem
Field emission-based X-ray sources face reliability challenges due to high-voltage susceptibility and vacuum arcing, leading to potential catastrophic failures and reduced performance in applications like tomosynthesis and computed tomography.
Innovation Solution
The system employs field emitter arrays with a control circuit to apply a voltage waveform with a duty cycle greater than 5% and pulse width shorter than ion transit time, combined with electrostatic or magnetic deflection to shield the emitter arrays from back-bombarding ions and manage electron beam impact, using transient voltage suppressors and redundant arrays for enhanced reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If field emitter arrays are used for X-ray source, then normally-off operation and close cathode-to-cathode spacing are enabled, but reliability is reduced due to high-voltage susceptibility and vacuum arcing
Solution Approach 1:
The patent applies periodic pulsed operation with duty cycles between 1% and 50% to the field emitter arrays. By operating in pulses rather than continuously, the system enables normally-off operation while reducing cumulative ion bombardment damage and thermal stress, thereby improving reliability under high-voltage conditions.
Solution Approach 2:
The patent divides the field emitter array into multiple independently controllable segments or elements. This segmentation allows selective operation of individual elements, enabling redundancy where damaged elements can be turned off while others continue operating, thus maintaining system reliability.
2Productivity
If field emitter arrays operate with continuous ion streams, then X-ray production is maintained, but ion back bombardment causes device degradation and failure
Solution Approach 1:
The patent implements periodic pulsed operation with specific duty cycles (1%-50%) and pulse widths (100 ns to 10 ms) that allow X-ray production during pulse periods while creating intervals between pulses. During these intervals, ion accumulation is limited and back-bombardment damage is reduced, enabling sustained productivity over extended device longevity.
Solution Approach 2:
The patent applies preliminary protective measures by using electrostatic or magnetic shielding structures positioned before the field emitter array. These shields preemptively deflect ions away from the emitter tips before impact occurs, preventing degradation while maintaining continuous X-ray production capability.
3Productivity
If voltage is applied continuously to field emitter arrays, then electron emission and X-ray production are maintained, but vacuum arcing and catastrophic failures increase
Solution Approach 1:
The patent employs periodic pulsed voltage application with duty cycles of 1%-50% instead of continuous voltage. This creates periodic high-voltage stress cycles rather than constant stress, allowing vacuum insulation to recover during off-periods and preventing continuous ionization that leads to vacuum arcing and catastrophic failures.
Solution Approach 2:
The patent changes the temporal parameters of voltage application by introducing pulse width (100 ns to 10 ms) and duty cycle (1%-50%) controls. These parameter changes transform the voltage application from continuous to pulsed, reducing the cumulative electrical stress and ionization probability that cause vacuum arcing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the impact of vacuum arcing and ion back bombardment, improving the reliability and longevity of field emission X-ray sources by preventing continuous ion streams and shielding the emitter arrays from damaging ions, thus maintaining consistent performance in imaging applications.
Implementation Method 1
Field emission has been proposed as a cathode for X-ray sources... Field emission cathodes have been made using a variety of solid-state materials such as silicon, molybdenum, and carbon nanotubes... The voltage includes a waveform having a duty cycle greater than about 5% and a pulse width shorter than a transit time of an ion between the anode and the one or more field emitter arrays
Implementation Method 2
The field emitter array protection is configured to shield the field emitter array from back-bombarding ions emerging from the anode... one or more pairs of conductors configured to deflect an electron beam. The electron beam is deflected by applying an electrostatic force to the one or more pairs of conductors
Implementation Method 3
one or more magnets located inside or outside of the X-ray tube and configured to apply a magnetic force. The one or more magnets are configured to deflect an electron beam by the magnetic force
Implementation Method 4
The one or more pairs of conductors are of opposite voltage polarity and are configured to cause an impact of electrons on the anode out of line of sight of the field emitter array
Implementation Method 5
The one or more magnets are configured to deflect an electron beam by the magnetic force and cause an impact of electrons on the anode out of line of sight of the field emitter array
Data Source
AI summary
An X-ray source design for improved reliability by mitigating the impact of vacuum arcs, ion back bombardment and ion sputtering includes an X-ray source including one or more field emitter arrays and a circuit configured to control the one or more field emitter arrays. The one or more field emitter arrays include a gate and an emitter. The circuit is configured to apply a voltage between the gate and the emitter.