Half a croissant, on a plate, with a sign in front of it saying '50c'
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Synchrotron Projection TV

A long-lasting bright light source
  [vote for,

The biggest problem I know of, for a projection-TV system, is the fact that the light bulb is very bright and gets very hot and has a relatively short lifespan. We need a more energy-efficient source of bright light!

One quite-efficient way to generate light is to cause an electrically charged particle to experience an acceleration. And one way to do that is to force such a particle, travelling at high speed, to follow a curved path.

It is an odd fact of Physics that an object moving at a constant speed, but following a curved path, is nevertheless experiencing "acceleration". That's because the definition of "acceleration" is "ANY change in a velocity" --and the definition of "velocity" encompasses both "speed" and "direction". So, if we change the direction an object is moving, even if its speed is constant, the object can be said to be experiencing acceleration --ANY change, either in speed or direction, suffices.

In various scientific instruments popularly known as "atom smashers" and more accurately known as "cyclotrons" or "synchrotrons", electrically charged particles are accelerated to high speed following a curved path, and they do indeed emit light in the process. One reason modern particle accelerators are built large (the newest one, the Large Hadron Collider, is 8.6 kilometers in Diameter) is because the gentler the curvature that the charged particles travel, the less energy they emit. Obviously it can be difficult to create a high-energy particle beam if most of the energy is lost while simply traveling in a circle! (The lost energy is known as "synchrotron radiation".)

There are some particle accelerators that have been purpose-built specifically to generate synchrotron radiation. That's because, after more than 60 years of development, we can manipulate charged particle beams very precisely, and synchrotron radiation can be a very "pure" light source. It is almost as pure as laser light, but it is easily a great deal brighter, and also is very much more energy-efficient in the way the light is produced, than any laser can yet manage. Not to mention that a synchrotron light source can accomodate an extremely wide range of frequencies, including hard Xrays, which no laser at all can currently do.

See the link. A synchrotron Xray source is quite a large machine, and certainly isn't something you want in your living room for a projection TV! However! The energy of a single Xray photon can be many thousands of "electron volts", and that alone is the main reason a synchroton light source tends to be large. It simply takes a large machine to "pump up" charged particles to the point where it is possible for them to radiate such large amounts of energy.

Photons of ordinary visible light possess approximately 2 electron-volts of energy (not 2 thousand or 2 hundred, just plain 2). This means that a synchrotron light source, designed to create visible light, could actually be a rather small device (on the order of a half-meter, and maybe less)!

I'm envisioning the core of this unit to be triangular-shaped. Each straight tubular section is surrounded by a magnetic field coil, and contains a fairly simple electrostatic acceleration zone for the charged particles in our circulating beam (probably ordinary electrons). Each curved section uses more magnetic fields to force the particles to emit light. We accelerate the particles to slightly different energies in each of the three straight sections, so that red light emerges from one curved section, green light emerges from the second curved section, and blue light emerges from the third curved section (blue light at about 2.5 electron-volts of energy is about twice as energetic as red light). We then combine the beams of colored light appropriately, either before or after modulating them with a TV signal, and project them toward our home theatre screen.

Note that because we use the same circulating electrons over and over and over again, to generate light, this can indeed be an extremely long-lasting light source. The magnetic fields are constant-strength, and the electrostatic acceleration fields are constant-voltage. There is almost nothing changing that can wear out!

(Upon further thought, it appears to be necessary to add some changing electrostatic fields in the vicinity of the curved sections, to ensure the electrons, after following the curve, don't reverse course. Still, this can be electronically controlled, and if not overpowered can still last a long time. <rant>I hate that lots of modern electronics seems deliberately to be operated at such a high power that lifespan suffers. Did you know if you "underclock" the CPU in your computer by maybe half-a-gigahertz the machine likely will last three times as long?</rant> Not to mention any circuit prone to failure can be modularized for easy replacement.)

Vernon, Dec 21 2009

National Synchrotron Light Source http://www.nsls.bnl...machine/parameters/
As mentioned in the main text [Vernon, Dec 21 2009]

STFC Daresbury Laboratory http://www.srs.ac.uk/srs/
World pioneer [8th of 7, Dec 21 2009]

US2007273262 http://v3.espacenet...=2007273262A1&KC=A1
Light Source with Electron Cyclotron Resonance [xaviergisz, Dec 21 2009]

Fluorescent Lighting http://hyperphysics...ctric/lighting.html
Some scientific details, for anyone interested. [Vernon, Apr 20 2018]

Wikipedia: Microtron https://en.wikipedia.org/wiki/Microtron
Mentioned in my anno. A type of particle accelerator [notexactly, Jun 11 2019]

The Museum of Unworkable Devices: Stevin's principle https://lockhaven.e...work.htm#stevinprob
Mentioned in my anno. Also, check out the rest of this site if you haven't seen it before—it's about how all sorts of perpetual motion machines don't work [notexactly, Jun 11 2019]

Wikipedia: Garter spring https://en.wikipedi.../wiki/Garter_spring
Mentioned in my anno. A coil spring bent and joined into a toroidal shape [notexactly, Jun 11 2019]

Advanced Certificate in Powder Diffraction on the Web: Properties of Synchrotron Radiation http://pd.chem.ucl....pdnn/inst2/prop.htm
Mentioned in my anno. The page that told me synchrotron radiation is unsuitable for these applications [notexactly, Jun 11 2019]

Wikipedia: Undulator https://en.wikipedia.org/wiki/Undulator
Mentioned in my anno. Spectrally pure light source powered by an electron beam, and the core of a free-electron laser [notexactly, Jun 11 2019]


       Surprisingly, this appears to work [+]
BunsenHoneydew, Dec 21 2009

       All projection television (as indeed all television) seems to be based on the same idea - scanning a spot (either an electron beam, or a refresh scan, or whatever) rapidly across a screen in front of the viewer. However large the screen, the viewer's eyes condense the image onto the retina, where it is smaller than a postage stamp.   

       Therefore, it strikes me that there is a more ergonomic and economic solution. Simply modulate the intensity of three fixed lasers (blue, green, red), all of which are aimed at the eye of the viewer.   

       Then, use an electromagnetically actuated head-clamp to scan the viewer over the image in synch with the modulation.
MaxwellBuchanan, Dec 21 2009

       [MaxwellBuchanan], I do think the laser approach is under active development. Note it is a personal-viewer device, even if it appears to be widescreen. So, every member of a group would need the device to see a particular video. The advantage of a general projection unit is that you only need one to let the group see the video.
Vernon, Dec 21 2009

       I agree with your points, Vernon. It's just that I'd like to build a machine which could fire three lasers into the eyes of people watching Big Brother, whilst shaking their head back and forth at a 60Hz scan rate.
MaxwellBuchanan, Dec 22 2009

       How efficient would this be as a source of ordinary lighting in a room? Would it be better than conventional electric lamps?
nineteenthly, Dec 22 2009

       [nineteenthly], see the patent that was linked by [xaviergisz]. I sort-of-think the answer is "yes and no", for a couple of reasons. First, the basic light output (quite efficient, yes) is just-one-color, unless specially designed to emit multiple colors (as in triangular version described in main text) --and then the colors need to be mixed with appropriate mirrors and/or lenses, if you want white light. Second, the light will be emitted as a beam more than as a glow. You'll need add more mirrors and/or lenses to be able to illuminate a whole room with it at once. I suspect the price tag will be too high for this purpose.   

       The price of projection-TVs is easily high enough to allow research into developing this variant for that purpose, though.
Vernon, Dec 22 2009

       //as indeed all television) seems to be based on the same idea - scanning a spot//
I'm pretty sure this is not how my LCD TV works.
AbsintheWithoutLeave, Dec 22 2009

       I think it still scans, in the sense that pixels are refreshed dynamically, perhaps row-by-row.
MaxwellBuchanan, Dec 22 2009

       Though i can see the price would initially be high, i wonder if it might pay for itself. I personally would be happy with monochrome light towards the blue end of the spectrum. I used to use that anyway, the only problem being that it makes a lot of people uncomfortable so it's not conducive to family life or having friends.   

       What about Cherenkov radiation?
nineteenthly, Dec 22 2009

       It is extremely inefficient to generate Cherenkov radiation. It only occurs when some particle, moving through some medium other than a vacuum (like water), moves faster than the speed of light in that medium. So, in a device specifically intended to do this, you first have to boost the speed of a lot of particles to tremendous velocity (probably in a vacuum), inject them into the relevant other medium, in which the emission of Cherenkov radiation is the mechanism by which they lose energy and slow down to less than the speed of light in that medium -- and then you have to somehow filter them out of the medium so you could accelerate them again. The main energy-wastage will occur after they stop emitting Cherenkov radiation, and lose all the rest of their energy as heat, due to friction-equivalent interactions with particles of the medium.
Vernon, Dec 23 2009

       Sad. Ah well, stick with synchrotron then. However, presumably that means that transparent media are all very slightly luminous because of the neutrinos.
nineteenthly, Dec 23 2009

       Sorry, I should have specified "charged" particles. Neutrinos don't qualify
Vernon, Dec 23 2009

       Really? I'll go on Wikipedia in a sec to be comfortingly misinformed, but i've always thought of it as analogous to a sonic boom, applying to anything which moves particle-wise.
nineteenthly, Dec 23 2009

       I'm pretty sure some sort of interaction with the medium is required. Neutrinos mostly just don't interact, passing through solid matter, so there is no reason for them to slow down. Meanwhile, the vacuum of space is full of "virtual particles" of ALL sorts, including things that neutrinos are practically guaranteed to interact with (if actually encountered). That suffices to ensure any hypothetical FTL neutrinos would quickly become STL neutrinos, via sonic-boom-equivalent interaction mechanism.   

       Otherwise I'd expect a fair amount of heating to take place in our bodies, due to all the sonic booms of all the Solar neutrinos passing through them --and this is not reported, so.....
Vernon, Dec 23 2009

       This is a pretty great idea [+]   

       You say a synchrotron for X-rays is quite large… how small do you think it would be possible (for me) to make one? How about for gamma rays? For a few years I've wanted to build a portable synchrotron to use as a high-brilliance X-ray/gamma ray source… to be used responsibly, of course.   

       // How efficient would this be as a source of ordinary lighting in a room? Would it be better than conventional electric lamps? //   

       It would be very efficient, but it would have a CRI near zero. However, I think you could modulate the emitted wavelengths by modulating the bending fields, and thereby scan the visible spectrum. If you did that rapidly enough, you could achieve a persistence of vision-integrated CRI near 100. I don't think that would reduce the efficiency much, either.
notexactly, Apr 19 2018

       [notexactly], for gamma rays you would almost certainly have to accelerate protons in your synchrotron, instead of electrons. Fortunately for you, lesser acceleration of protons can yield X-rays.   

       You will still need a significantly-sized power source. Remember, **each** photon of ordinary visible light carries maybe 2 electron-volts of energy, while an average X-ray photon might carry a thousand times as much energy, and an average gamma photon might carry a million times as much energy. If you can't supply the power, you can't get a lot of the desired photons.   

       With respect to ordinary room lighting, I'm going to suggest that if we want to use a synchrotron as the primary light-source, it might be simplest to tune it to emit ultraviolet light (about 5 electron-volts per photon; see the link), and then use fluorescence to change that to white light.
Vernon, Apr 19 2018

       Are there such things as electrons?
Ian Tindale, Apr 20 2018

       Something has been named and the mesh frame of facts as a model works unbelievably extremely well. So yes. But then a single uncovered fact can show a whole new perspective.
wjt, Apr 20 2018

       With a sufficiently powerful and focussed synchrotron beam, it should be possible to write directly to the visual cortex, eliminating the bulk and clutter of TVs, lighting and other paraphernalia.
MaxwellBuchanan, Apr 20 2018

       Ah, a picture, a tan (maybe, stain) and a blinding smile. In 2 seconds flat.
wjt, Apr 22 2018

       [+] neat... I'm trying to get a handle on this : so,   

       electrons are accelerated linearly, then their path is bent enough to emit a photon(s) - tangentially or radially ? - out of the device onto a cinema screen, assumedly losing speed in the process. They then hit a conductive plate (out of the photon escape path), where they're recycled, their remaining energies averaged out. Rinse and repeat. Yes ?   

       So the beam would go through a magnetic field which determines its vertical angle (scanline), then through a horizontal field which determines its horizontal angle and also does the photon-release bending.   

       3 slingshots, one for each colour. hmm... could you get that down to one ?
FlyingToaster, Apr 22 2018

       [FlyingToaster], the electrons are not stopped; they move continuously through a triangular loop. The sides of the triangle slowly accelerate them to an appropriate energy; the sharp corners strongly accelerate them to make them emit photons. At any single corner all the electrons emit the same color of light. But every electron emits all three colors as it travels around the overall triangle and pass through the three corners. We want the triangle to contain electrons all around its perimeter, so that light is emitted continuously from the three corners.   

       The light has to be collected with mirrors. A rotating mirror can be used to make the continuous beam scan.
Vernon, Apr 22 2018

       Alternatively, it could use an SLM (such as a DMD (such as TI's DLP) or LCD (such as the common 3LCD arrangement)) for each color, similarly to existing projectors and RPTVs. It could even—given the monochromaticity of the light source—use a MOEMS beam steerer (such as a GLV) in place of the scanning mirror(s).   

       // the vacuum of space is full of "virtual particles" of ALL sorts, including things that neutrinos are practically guaranteed to interact with (if actually encountered) //   

       What things are those? Could they or similar things be harnessed and concentrated to enhance neutrino capture for the purposes of an improved neutrino detector/receiver?   

       // [Synchrotron radiation] is almost as pure as laser light, but it is easily a great deal brighter, and also is very much more energy- efficient in the way the light is produced, than any laser can yet manage. Not to mention that a synchrotron light source can accomodate an extremely wide range of frequencies, including hard Xrays, which no laser at all can currently do. //   

       Except free-electron lasers. But those use synchrotron radiation to do it.
notexactly, Jun 09 2019

       A TV, really. A moon beacon or emergency daylight , I suggest is more fitting. Though, if the money comes from the TV.
wjt, Jun 09 2019

       [This annotation is pretty much all wrong—see the last paragraphs, after the bracketed note. I'm posting it anyway because I think it's still interesting and potentially inspiring, and some bits of it are still accurate AFAIK. It's probably worth reading.]   

       In your idea, you imply that it's the acceleration, and thereby the electrons' kinetic energy, that determines the wavelength of synchrotron radiation emitted in the bend. In my anno a year ago, I implied that it's the bending magnetic field strength instead. Upon thinking about it the other day (after my previous anno), I realized it does make more sense the way you were talking about it. It seems to me that the wavelength emitted does indeed depend on an electron's kinetic energy rather than how hard it is accelerated around the curve, while the rate at which it emits photons is what is dependent on that acceleration (curvature). Also, it seems to me that the nonzero spectral linewidth of the synchrotron radiation is due (at least in part) to the electron's kinetic energy decreasing slightly as it goes around the bend, due to emitting photons as it does so; previously, I had been thinking the spectral broadening was due to the necessary nonuniformity of the magnetic field.   

       But you could still accomplish the spectral scanning for CRI improvement I described, by the analogous method of varying the acceleration in each side of the triangle rather than the bending field in each corner. (Of course, it doesn't have to be a triangle if you don't specifically want three wavelengths simultaneously.)   

       You could even vary the multiple wavelengths being emitted from the multiple bends in a multiphase sinusoidal manner. Things generally prefer to oscillate sinusoidally, so that (or close to it) would probably be the easiest modulation waveform for the accelerators (which I'm presuming to the typical RF cavity type, so this would be frequency modulation applied to their drivers). The more phases (i.e. the more bends and the more accelerators), the denser your spectral– temporal coverage, and the better the CRI for a given modulation frequency. But I expect that even with only two or three phases, probably even with only one, you could modulate it fast enough that human eyes would perceive good CRI. The other thing about this is that sine waves are "denser" (spend more time) in the region around the peaks and troughs than in the region around the middle. So, if this causes bad CRI, you could compensate by modifying the waveform, or by running different phases on different spectral ranges. Simple examples: multiple phases all centered at the same wavelength but with different spectral excursion (modulation amplitude), or multiple phases with the same spectral excursion but offset center wavelengths. You could even have the different bends trade roles, or cycle roles around the ring, in such a scheme, if that helps with, say, efficiency by allowing you to resonantly circulate the modulation around the ring, or something.   

       I just had a thought: the synchrotron lamp could be quite good for spectrophotometry! No need for a monochromator or a linear CCD with a diffraction grating. Just a single broad-spectrum photodetector, and have the synchrotron lamp scan its output wavelength. It would be faster than a monochromator in scanning, and it would be optically "faster" than either conventional type because the lamp would be brighter than an incandescent lightbulb or a deuterium arc lamp (and, importantly, would be much more brilliant and therefore much more efficiently couplable to the input of the optical system). Due to that much greater amount of light going through the sample, you might be able to get away with a cheaper detector than a photomultiplier. OTOH, the increased amount of light might damage or affect the properties of the sample. Synchrotron radiation goes all the way to hard X-rays, too, much shorter than the ultraviolet produced by a deuterium lamp, though you might need a different detector there.   

       And I had another thought just now (after I wrote the immediately above paragraph, as I started to write the one above that): you could get the three wavelengths needed for the display application without using one corner of triangle for each wavelength, and it might even be preferable to not do it that way. I mean that, by modulating the acceleration, you could use only a single bend to get all three wavelengths, sequentially. That (sequential RGB light, or sometimes more than three wavelengths) is the usual input to a DMD, so that would make integration with existing display technology easier. You could even use a circular synchrotron, if you could somehow accelerate in the same region as bending without any conflict between the two. (If attempting that, I suggest to take inspiration from synchrotrons designed before the discovery of strong focusing.) A microtron [link] or cyclotron might be better for a continuous-bending version, actually, though you might have more difficulty controlling the outward spiral of the electrons in those designs. With any of these continuous-bending variants, the synchrotron radiation would be emitted uniformly outward in the plane of the device, and could be collected and concentrated by an annular concave mirror, possibly with some sort of annular lens or diffraction grating to remove the tangential component of the light. (Hmm… that feels illegal. I feel like there's some kind of geometric equivalent of Stevin's principle of virtual work [link] for optics that prevents this radialization of tangential light. It also feels like an etendue violation: tangential light approaches being radial as the distance from the source to the observer approaches infinity, so to make the light radial at close range feels like it would be a free lunch.)   

       It also has occurred to me that your idea as written is already a pulsed light source, just by using a synchrotron, which by definition accelerates discrete bunches of particles, so maybe you might as well do it that way, unless you want to use three accelerators and optimize each one for a given amount of kinetic energy. OTOH, the synchrotron's bunch frequency is probably a lot higher than the wavelength alternation frequency you'll want to use for a DMD.   

       Another thing I just thought of, while proofreading the above paragraphs: compact packing of the synchrotron. AFAIK, most or all existing synchrotrons (and circulating particle accelerators in general) are built in the shape of flat rings, because that's the shape that has the least severe bends and therefore the least loss of power to synchrotron radiation. But in these applications, we want bends, and we also want to keep the overall size of the apparatus down. Therefore, you could overlap the accelerators in the Z axis and make something like a figure-eight or a trefoil knot, allowing you to use the space in the middle of what would normally be an empty ring. You could even orient the accelerators parallel to the Z axis, forming a ring or nested rings around the Z axis, with bends at the ends of the bundle. It would look like a kind of spring that I can't find a picture of right now, which is basically a garter spring [link] extended axially with straight sections. In such a configuration, it might be feasible to share the bending field between all of the bends at each end, using a toroidal magnetic field somehow.   

       [Here's where I discover I was wrong in most of the above.]   

       Hmm… I just looked up some more info on synchrotron radiation [link] and it turns out that it's actually not monochromatic at all! If you want to make a spectrophotometer, you still need to use a monochromator to filter the synchrotron radiation. The main advantage for that application is that it's very spectrally smooth over a very wide bandwidth, which is pretty much the exact opposite of what I was assuming when I wrote all of the above. (Another advantage is the high brilliance—even though the monochromator throws away most of the light that enters it, more of the light enters it in the first place—the entrance slit is effectively more efficient.) That broad spectrum also completely invalidates original synchrotron video projector idea here, AFAICT. But it's still good for a high- CRI lamp, actually even better because it doesn't need any of the wavelength scanning I described.   

       I hope that page I found is wrong, but I doubt it. Maybe some modification to the bending field could make it work the way we want, but I don't know at the moment what that might be.   

       A currently known technology that can produce narrow-band radiation from an electron beam is the undulator [link], which uses a static transverse magnetic field that alternates in direction over a linear region, causing the electrons to follow a sinusoidal trajectory. Presumably they are not exhausted and can continue circulating around the ring after exiting the undulator. The wavelength of monochromatic on-axis output is dependent on the spatial frequency of the magnetic field. It isn't dependent on the electrons' kinetic energy/speed, so you can't modulate that to control the output wavelength. Presumably, you could arrange three of these (RGB) and one accelerator in a square or doubled line, using bending magnets at the corners/ends but not using their synchrotron radiation. Also, an undulator does produce a lot of other-wavelength sidelobes, which are usually cut off by its enclosure because they aren't useful. Both of these factors will reduce efficiency.
notexactly, Jun 11 2019


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