Light Beamer | Phase

In order to test the feasibility of the system, the case of a meter-scale sail was examined. For example, to focus the light beam on a 4mX4m sail across an acceleration distance of 2x106 km requires a focusing angle of 2 nano-radians (0.4 milliarcseconds), which is the diffraction limit for a kilometer-scale light beamer operating at a wavelength of 1 micron.

Interferometry with the Event Horizon Telescope has already been demonstrated across the Earth, achieving sub-nano-radian precision at a 1mm wavelength. This is an encouraging benchmark on the way to achieving the required precision of the optical system for a kilometer-scale array on the ground.

Nov 05, 2016 03:16 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE"
"Sep 01, 2016 14:54michael.million@sky.comPosted on: Centauri Dreams
Perhaps if we had a number of FEL linacs/undulators arranged in a circle arrangement with a mirror at the end of each unit with a hole in it so electrons can make their way through to the next linac/undulator unit. The electrons can be kept in constant motion around the 'circle' reducing losses significantly as they don't need to be slowed down or stopped. Each mirror is then used to deflect the produced laser light upwards to propel the craft."

RE:
"Sep 04, 2016 17:59michael.million@sky.comPosted on: Centauri Dreams
We could build a test scalable FEL model of modest power built for a low price. 
I am thinking of three linac/undulators arranged in a triangle with a mirror/prism near towards the apex with a hole in them. If we bend the electron beam with large magnets before each mirror and into the next linac/undulator system and so on we can improve the efficiency quite a bit by recycling the electrons. With the hole in the mirror/prisms we can use some of laser light as a seed via a reflection prism into the next linac/undulator unit and so on which would again aid the efficiency of the system. This test model could be built in the Nevada desert (mentioned earlier) where the altitude is high, but importantly it would have access to the power grid or at least some decent mobile electrical generators."

Answer:
These are good approaches that need to be investigated. FEL should certainly be considered, but keep in mind that we need over 50GW of laser light in the final system.

- Avi Loeb, Breakthrough Starshot

Nov 18, 2016 11:16 michael.million@sky.com Posted on: Centauri Dreams

FEL lasers can certainly deliver that power in bursts, TW's even, since there is no medium to be heated they can be very powerful, they will need the electron re-cycling issue resolved though to be effective.

Dec 06, 2016 18:13 Breakthrough Initiatives Posted on: Breakthrough Initiatives

"Nov 18, 2016 11:16 michael.million@sky.com Posted on: Centauri Dreams

FEL lasers can certainly deliver that power in bursts, TW's even, since there is no medium to be heated they can be very powerful, they will need the electron re-cycling issue resolved though to be effective."

Answer:

We intend to consider using electron recycling at least in the early portion of the thrusting phase of the flight.

- Avi Loeb, Breakthrough Starshot

Jan 05, 2017 08:22 michael.million@sky.com Posted on: Centauri Dreams

We could have standard FEL modules installed over time, if say we had the FEL's arranged in a circle with the bending magnets in an articulated arrangement so the circle of FEL's just gets bigger by adding FEL units or can be arranged in smaller circles. This arrangement will improve the recyclability efficiency of the electrons enormously, just need to keep them going through the FEL's and they will only need to be dumped or decelerated at the end of a powered phase. This arrangement also allows us to stack the FEL beam systems so multi-channels can be used, i.e. the first top FEL's electrons are deflected into the next FEL by magnets and the laser light is reflected upward after going through a small channel. The next lower laser beam has a slightly longer channel with a mirror at the end of it and so on, each channel slightly further out. This arrangement allows us to share RF power circuits and/or drift tubes and magnet sets lowering the cost of the system significantly. We can start small and just get bigger over time but it also allow us to use small parts of the overall system as and when or the application requires.

Jan 21, 2017 16:37 michael.million@sky.com Posted on: Centauri Dreams

It may be better to have a central electron generator and conditioner and then lines of FEL going outwards from it like spiders legs. The lines of stacked FEL's will zigzag to allow the laser light out and allow for the bending of the electrons into the next FEL and so on, they could be built on rail lines to aid installation and repair. Although the electrons can't circulate to improve efficiency there are tricks to recover energy from the electron beam in a line and further as the lines of FEL's get longer the end losses get less in proportion to the whole system. In this configuration the number of FEL's can be changed more easily to suit each mission as well.

Feb 02, 2017 18:56 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE:
"Jan 05, 2017 08:22 michael.million@sky.com Posted on: Centauri Dreams
We could have standard FEL modules installed over time, if say we had the FEL's arranged in a circle with the bending magnets in an articulated arrangement so the circle of FEL's just gets bigger by adding FEL units or can be arranged in smaller circles. This arrangement will improve the recyclability efficiency of the electrons enormously, just need to keep them going through the FEL's and they will only need to be dumped or decelerated at the end of a powered phase. This arrangement also allows us to stack the FEL beam systems so multi-channels can be used, i.e. the first top FEL's electrons are deflected into the next FEL by magnets and the laser light is reflected upward after going through a small channel. The next lower laser beam has a slightly longer channel with a mirror at the end of it and so on, each channel slightly further out. This arrangement allows us to share RF power circuits and/or drift tubes and magnet sets lowering the cost of the system significantly. We can start small and just get bigger over time but it also allow us to use small parts of the overall system as and when or the application requires."

Answer:
Thank you for your consideration. Our biggest problem is trying to achieve coherence of an infinite number of lasers. The level of coherence we are shooting for is lambda over 10. Of course our next biggest consideration is cost.

- Pete Klupar, Breakthrough Starshot

Feb 02, 2017 18:57 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE:
"Jan 21, 2017 16:37 michael.million@sky.com Posted on: Centauri Dreams
It may be better to have a central electron generator and conditioner and then lines of FEL going outwards from it like spiders legs. The lines of stacked FEL's will zigzag to allow the laser light out and allow for the bending of the electrons into the next FEL and so on, they could be built on rail lines to aid installation and repair. Although the electrons can't circulate to improve efficiency there are tricks to recover energy from the electron beam in a line and further as the lines of FEL's get longer the end losses get less in proportion to the whole system. In this configuration the number of FEL's can be changed more easily to suit each mission as well."

Answer:
Thank you for your consideration. Our biggest problem is trying to achieve coherence of an infinite number of lasers. The level of coherence we are shooting for is lambda over 10. Of course our next biggest consideration is cost.

- Pete Klupar, Breakthrough Starshot

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