Graduation Year

2010

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Alex Volinsky, Ph.D.

Committee Member

Nathan Crane, Ph.D.

Committee Member

Delcie Durham, Ph.D.

Keywords

Thin Films, Thermal Mismatch, Slope Error, Free Electron Laser, Uneven Heating

Abstract

A novel, no-contact approach to X-ray mirror bending control is presented here,

proposed for use on the beamlines of the European X-ray Free Electron Laser (XFEL)

project. A set of mirrors with tunable bending radii are desired, that will maintain their

optical properties even as the beam incidence causes local heating. Various mechanical

bending mechanisms have been proposed and used on other beamlines, which can take up

a lot of physical space, demanding more vacuum power, while using expensive high

precision servomotors. Rather than bend the mirror by mechanical means, it is proposed

to heat the mirror to produce the desired bending. This could work two ways. One

scenario calls for a finely tunable heat lamp to irradiate the back surface of the mirror

while the X-ray laser heats the front side. With appropriate tuning, simulations show that

this approach can keep the mirror flat, and perhaps produce a circular profile. The

second scenario is similar to the first, but a thin film of tungsten is added to the back of

the silicon mirror. This scenario calls for the temperature of the mirror to change

homogenously to affect the desired bending, and in this case the profile should be

cylindrical. In both scenarios the uneven nature of the incident radiation causes

distortions that may be undesirable. Both scenarios are simulated and it is shown that the

stress produced by a metal film may minimize this distortion. The response time of the

mirror and configuration of both the heating and cooling mechanism are also considered.

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