Note: Thermally stable thin-film filters for high-power extreme-ultraviolet applications.
We investigated several types of thin-film filters for high intensity work in the extreme-ultraviolet (EUV) spectral range. In our application, with a peak EUV intensity of 2.7 W cm(-2), Ni-mesh-backed Zr filters have a typical lifetime of 20 h, at which point they suffer from pinholes and a 50% loss of transmission. Initial trials with Si filters on Ni meshes resulted in rupture of the filters in less than an hour. A simple thermal calculation showed that the temperature rise in those filters to be about 634 K. A similar calculation indicated that using a finer mesh with thicker wires and made of Cu reduces the temperature increase to about 60 K. We have exposed a Si filter backed by such a mesh for more than 60 h with little loss of transmission and no leaks.
Evidence Against Carbonization of the Thin-Film Filters of the Extreme Ultraviolet Variability Experiment Onboard the Solar Dynamics Observatory
In spite of strict limits on outgassing from organic materials, some spacecraft instruments making long-term measurements of solar extreme ultraviolet (EUV) radiation still suffer significant degradation. While such measures have reduced the rate of degradation, they have not completely eliminated it in some cases. For example, in five years, the aluminum filters used in the Extreme Ultraviolet Variability Experiment (EVE) instruments onboard the Solar Dynamics Observatory (SDO) suffered losses exceeding 40% at 30.4 nm. Comparing those losses with the negligible losses of nearby zirconium filters on the same instruments indicated that the problem was not due to carbonization on the Sun-facing side of the filter. To investigate whether the loss was due to carbon deposition on the downstream face of the Al filter, we exposed the backsides of Al and Zr filters to EUV in the presence of a volatile organic solvent in the laboratory and concluded that this could not be the cause. Given that the residual-gas composition in the SDO spacecraft likely has water vapor as well as organics, these findings suggest that the transmission loss in the Al filter originated with oxidation caused by UV-activated adsorbed water.
Magnetic plasma confinement for laser ion source.
A laser ion source (LIS) can easily provide a high current beam. However, it has been difficult to obtain a longer beam pulse while keeping a high current. On occasion, longer beam pulses are required by certain applications. For example, more than 10 micros of beam pulse is required for injecting highly charged beams to a large sized synchrotron. To extend beam pulse width, a solenoid field was applied at the drift space of the LIS at Brookhaven National Laboratory. The solenoid field suppressed the diverging angle of the expanding plasma and the beam pulse was widened. Also, it was observed that the plasma state was conserved after passing through a few hundred gauss of the 480 mm length solenoid field.