Re: Quick question about a STL trip - and another...

On Aug 23, 5:45 pm, "n...@xxxxxxx" <Alien8...@xxxxxxxxx> wrote:
On Aug 23, 8:43 am, IsaacKuo <mech...@xxxxxxxxx> wrote:

The basic acceleration mechanism is simple absorption/scattering.
The X-ray acceleration laser is tuned to the k-edge transition of
Tungsten (this is very short wavelength and allows for an
extremely long ranged laser).  About a third of the x-rays get
absorbed by the chip's tungsten while two thirds gets randomly
scattered.  The x-rays mostly pass through the carbon parts.
The result of this is acceleration almost perfectly away from the
laser.

  Chip velocity WRT laser? Doppler frequency shift puts laser
wavelength where?

The doppler shift is a concern. The X-ray laser can be tuned
to a large degree, but there will plausibly be a need to swap
out wiggler segments a few times. The zone plate will also
need to be swapped out a few times. While a simple binary
zone plate wouldn't need to be swapped out, it's only half as
efficient as a sinusoidal zone plate. A sinusoidal zone plate
depends upon partial transparency, so the absorption rate in
the zone plate material is critical. This is similar to the problem
of chromatic distortion in traditional lenses. Using two layers
of different materials can compensate and allow for a wider
sweet spot, but at some point you'll want to swap out for a
different zone plate.

On the other hand, it's not strictly necessary to keep the laser
tuned to the k-edge transition of tungsten on the laser sails.
The laser sail chips will function as long as the tungsten base
absorbs more of the photons as the carbon semiconductor
electronics.

  Chip deceleration rate = ? Alters absorption how?

Chip deceleration rate? What would cause the chips to
decelerate?

  How are you producing the X-ray beam? Could an X-ray FEL (no idea
how to build one, sorry) be frequency-agile enough to make the above
irrelevant?

The type of laser I assume is a SASE X-ray FEL which is
focused by a sinusoidal zone plate spaced far away from
the main laser. In principle, this type of laser can be up to
50% efficient because the zone plate absorbs half of the
incoming light while focusing the other half. However, it's
doubtful that the XFEL will be anywhere near 100% efficient.
A more plausible number would be maybe 2% to 10%,
halved to maybe 1% to 5%.

Isaac Kuo
.

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