Ion Suppression Grid for Microchannel Plate Photomultiplier
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Solution Overview
Problem
Ion feedback in microchannel plate photomultiplier tubes (MCP-PMTs) degrades photocathode sensitivity and reduces device lifetime due to positive ions generated during operation, which existing techniques partially address through material engineering, vacuum processing, and physical barriers but with complexity and performance drawbacks.
Innovation Solution
A photomultiplier tube design incorporating an ion suppression electrode in the form of a conductive grid positioned between the photocathode and the electron multiplying device, with a source of electric potential configured to provide voltages that effectively neutralize positive ions before they reach the photocathode, using a chevron or Z-stack configuration of microchannel plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If material engineering and vacuum processing techniques are used to reduce ion feedback, then photocathode sensitivity degradation is reduced, but device complexity and manufacturing cost increase
Solution Approach 1:
An ion suppression grid is introduced as an intermediary component between the photocathode and the MCP pore inputs. This grid acts as a mediator that selectively blocks positive ions while allowing electrons to pass through, thereby protecting the photocathode without requiring complex material engineering or vacuum processing techniques.
Solution Approach 2:
The ion suppression grid utilizes voltage parameter changes to control ion feedback suppression. By applying a voltage to the grid that exceeds the MCP output voltage, the system dynamically adjusts the electric field to repel positive ions away from the photocathode, providing a controllable and adjustable solution rather than relying on fixed material properties.
2Object-generated harmful factors
If physical ion barriers are formed in MCP geometry or deposited on external surfaces, then ion feedback is reduced, but device complexity and performance are adversely affected
Solution Approach 1:
The ion suppression grid serves as a separate intermediary structure positioned in the electron optics space between the photocathode and MCP. This approach avoids modifying the MCP geometry itself or depositing barrier films on MCP surfaces, thereby maintaining the original MCP structure while still achieving ion feedback suppression through the external grid.
Solution Approach 2:
The ion suppression function is segmented as a separate, independent component (the grid) rather than being integrated into the MCP structure itself. This segmentation allows the grid to be independently positioned, adjusted, and optimized without affecting the MCP's internal pore geometry or requiring modifications to the MCP fabrication process.
3Object-generated harmful factors
If ion suppression electrode is positioned between photocathode and electron multiplying device, then ion feedback is suppressed, but device complexity increases
Solution Approach 1:
The ion suppression grid is constructed as a thin, flexible structure with conductive material arranged in a grid pattern. This thin-film approach minimizes the physical presence of the suppression electrode, allowing it to be positioned in the limited space between the photocathode and MCP without significantly increasing overall device complexity or volume.
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
Significantly reduces the rate of positive ions reaching the photocathode, thereby extending the life cycle of the device and improving performance by effectively neutralizing ions deep within the MCP pores when the suppression grid voltage exceeds the MCP output voltage.
Implementation Method 1
A source of electric potential connected to the second electrode and to the ion suppression electrode provides a first voltage to the second electrode and a second voltage to the suppression grid electrode that has a magnitude equal to or greater than the magnitude of the first voltage
Implementation Method 2
photons are detected by their absorption and the subsequent ejection of photoelectrons from a semi-transparent photocathode
Implementation Method 3
electron stimulated desorption (ESD) from the surfaces of the MCP pore channels
Data Source
Figure 1~2
Figure 3~4B
Figure 5~6
AI summary
A photomultiplier tube having an ion suppression electrode positioned between a photocathode and an electron multiplying device in the photomultiplier tube is disclosed. The ion suppression electrode includes a grid that is configured to provide sufficient rigidity to avoid deformation during operation of the photomultiplier tube. The photomultiplier tube also includes a source of electric potential connected to the electron multiplying device and to the ion suppression electrode to provide a first voltage to the second electrode and a second voltage to the suppression grid electrode wherein the second voltage has a magnitude equal to or greater than the magnitude of the first voltage. A method of making the photomultiplier and a method of using it are also disclosed.