Free Electron Laser Energy Spreaders Suppress Microbunch Instability
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Solution Overview
Problem
Current free electron lasers face challenges in achieving high power output due to microbunch instability, which is exacerbated by low initial energy spread in electron bunches, leading to reduced output power in EUV lithography applications.
Innovation Solution
The implementation of a free electron laser design that includes a reversible energy spreader before the bunch compressor and another before the undulator, along with a washout step to smear out density and energy fluctuations, to avoid microbunch instability and enhance output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the initial energy spread of electron bunches is kept low, then the beam quality is improved, but microbunch instability is exacerbated leading to reduced output power
Solution Approach 1:
The patent applies preliminary action by introducing a controlled energy spread in advance (before the undulator) through energy spreaders. This pre-conditioning of the electron beam prevents microbunch instability from developing, allowing the system to maintain both low effective energy spread at the undulator and high output power by suppressing the instability mechanism that would otherwise occur with low initial energy spread beams
2Power
If energy spread is increased to suppress microbunch instability, then output power is improved, but energy spread increases leading to reduced beam quality
Solution Approach 1:
The patent applies local quality by creating different energy spread conditions in different regions of the beam path. Energy spreaders are positioned to introduce controlled energy spread locally at specific points (before and after the bunch compressor) rather than uniformly throughout the system. This allows suppression of microbunch instability in critical regions while maintaining low energy spread at the undulator entrance, thereby preserving beam quality while improving output power
3Productivity
If recirculating beam is used to increase power, then throughput is improved, but beam instability increases
Solution Approach 1:
The patent introduces energy spreaders as intermediary devices between the electron source and the undulator, and between beam recirculation passes. These intermediaries condition the beam by introducing controlled energy spread that suppresses microbunch instability, allowing the recirculating beam system to operate at high throughput while maintaining beam stability through the mediating effect of the energy spreaders
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 increases the output power by a factor of 2 or more while maintaining a narrow energy spread, effectively suppressing microbunch instability and improving the performance of EUV radiation sources for lithographic systems.
Implementation Method 1
a linear accelerator system configured to accelerate the upstream electron beam
Implementation Method 2
a bunch compressor configured to compress the upstream electron beam
Implementation Method 3
an undulator configured to convert the compressed upstream electron beam into coherent radiation
Implementation Method 4
a first energy spreader operable to impart a reversible change to the energy distribution of bunches of electrons
Data Source
AI summary
A free electron laser FEL comprises an undulator 24 generating coherent EUV radiation receiving an upstream electron beam EB2 and emitting a downstream electron beam EB4 and at least an electron source 21a, 21b operable to produce an upstream electron beam EB1, EB2 comprising bunches of electrons. A beam path is configured to direct the upstream electron beam through: a linear accelerator system (LINAC) comprising at least a first and a second linear accelerators 22a, 22b, a bunch compressor 28b, and said undulator 24. The downstream electron beam EB3, EB4 that leaves the undulator 24 recirculates through the second linear accelerator 22b in parallel with the upstream electron beam with a phase such that the downstream beam is decelerated by the second linear accelerator 22b and then recirculates through the first linear accelerator 22a in parallel with the upstream electron beam with a phase such that the downstream beam is decelerated by the first linear accelerator 22a; and to direct the downstream beam to a beam dump 100. At least a first energy spreader 50a, 50b, 50c imparts a reversible change to the energy distribution of bunches of electrons and is located at a position in the beam path before the bunch compressor 28b and so that it is only passed through by the upstream electron beam EB1. A second energy spreader 50d reverses the change to the energy distribution of bunches of electrons imparted by the at least one first energy spreader 50a, 50b, 50c, the second energy spreader 50d being located at a position in the beam path before the undulator 24 and so that it is only passed through by the upstream electron beam EB2.