Theory, design, and demonstration of a new microwave-based undulator
- Synchrotron Light Sources and Free Electron Lasers (FEL) oﬀer great applications in the ﬁelds of metallurgy, biology, chemistry, and archeology etc., by providing a radiation probe for extremely small structures (like molecules, DNAs) and small durations (like timescale of chemical reactions). In these experimental facilities, electrons are accelerated to relativistic energies and then passed through an undulator or wiggler to generate the radiation. The undulator, which is the backbone of such a light source, is conventionally a series of permanent magnets with a strong magnetic ﬁeld, constant in time but alternating in space. These undulators, however, provide limited control over the properties of the generated radiation. Moreover, it is very challenging to scale the magnetic undulators down to smaller undulating periods -- a useful feature to generate shorter wavelength radiation by spending lesser energy in the acceleration of the electrons. Such scaling will also require strict limits on the maximum electron beam aperture, ﬁeld strength, and consequently the radiation brightness. To overcome these shortcomings of the magnetic undulator technology, we have designed a novel short-period microwave undulator and have demonstrated its successful operation at NLCTA, SLAC. This microwave undulator is essentially a Thomson scattering device that has yielded tunable spontaneous emission and seeded coherent radiation. It is about 1 m long axisymmetric, corrugated, copper cavity, resonant at 11.424 GHz with an undulator period of 1.39 cm. The undulator deﬂection parameter (K) of this microwave undulator is tunable and has achieved a value as high as 0.7 (the equivalent ﬁeld strength is 0.55 Tesla). Given the availability of a high power rf source, K = 1 could also be achieved without breakdowns due to high surface ﬁelds in the undulator cavity. Moreover, the design of this undulator is conveniently scalable to smaller undulator periods as the required size of the electron beam aperture does not reduce as sharply as it does for the magnetic undulators. The undulator ends were designed to have tapered ﬁeld to minimize transverse drift and kick induced in the electron beam. For future generation light sources, this device promises shorter undulator period, large aperture, and fast dynamic control. We have also presented a new Finite Element Method (FEM) based implementation that can eﬃciently calculate electromagnetic ﬁelds in general axisymmetric cavities.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Electrical Engineering.
|Lee, Thomas H, 1959-
|Lee, Thomas H, 1959-
|Statement of responsibility
|Submitted to the Department of Electrical Engineering.
|Thesis (Ph.D.)--Stanford University, 2014.
- © 2014 by Muhammad Shumail
- This work is licensed under a Creative Commons Attribution 3.0 Unported license (CC BY).
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