Author Topic: EM Drive Developments - related to space flight applications - Thread 7  (Read 1680692 times)

Offline TheTraveller

These are typical optical cavities:



it is misleading to be confusing such an optical cavity with an EM Drive:



The concave-convex optical model is, as I understand it, the end plate configuration of the Demonstrator and Flight Thruster EmDrives. With both Rs at the vertex of the cone / frustum

I suggest the confocal arrangement would help to eliminate most end plate alignment issues. Rs of both end plates would be very large, maybe 50x to 100x length. Very shallow concave curve in each end plate.
« Last Edit: 03/11/2016 09:01 pm by TheTraveller »
It Is Time For The EmDrive To Come Out Of The Shadows

Offline rfmwguy

  • EmDrive Builder (retired)
  • Senior Member
  • *****
  • Posts: 2184
  • Liked: 2704
  • Likes Given: 1124
EMDrive speculation to the year 2035 - An interesting and perhaps accurate prognostication on EMDrive development for entertainment and diversion only (love the 2035 entry):

(snip)

2032: Emdrive applications trickle down to civilian and terrestrial uses. Sophisticated 3D nagivation and spacial awareness technologies allow for cars to be fitted with Emdrive thrusters for vertical lift- the first true example of a 'hover car'. The Emdrive however still loses thrust with acceleration, and so hydrogen thrusters provide lateral propulsion, as per Shawyer's original demonstrator vehicle design from 2009.

Late 2032: Planetary Resources launches a staging post to lie at the Lagrangian point between Earth and the Moon; the beginning of a space station that will serve mining vessels performing operations on Near Earth Asteroids. Future vessels will be built on Earth and sent to the Lagrangian station with materials to expand the station itself (largely through additive manufacturing).

2034: On behalf of all on Earth, the first human steps foot on Mars. Due to huge improvements over the past twenty years to the efficiency and thrust potential of the Emdrive, his/her trip has been a relatively short one. On top of this, the Emdrive has made it possible to transport large amounts of equipment and materials into Earth orbit and ultimately onto the Mars-bound craft, making it capable of also carrying the necessary starter-kit for a colony, with the knowledge that whoever stays there will have the ability to return to Earth in a brief time period. Humanity, thanks to the Emdrive, is now a multi-planet species.

2035: The physicist Sean Carroll upgrades his view of the Emdrive's thrust from 'impossible' to being 'improbable'.

Original posting: http://tinyurl.com/jbjyexd from a friendly, open-minded subreddit about 9 months ago ;)
« Last Edit: 03/11/2016 09:04 pm by rfmwguy »

Offline Monomorphic

  • Full Member
  • ****
  • Posts: 1725
  • United States
  • Liked: 4366
  • Likes Given: 1404
Radius=8.835cm
theta 30.7199

Radius? I just need the height (in cm). This is a flat-end frustum. Want to see how it compares to what I found.
« Last Edit: 03/11/2016 09:07 pm by Monomorphic »

Offline X_RaY

  • Full Member
  • ****
  • Posts: 852
  • Germany
  • Liked: 1146
  • Likes Given: 2479
Radius 8.835cm*2=17.67cm

Radius? I just need the height (in cm). This is a flat-end frustum. Want to see how it compares to what I found.
SORRY I meant the height!  17.67cm
« Last Edit: 03/12/2016 11:11 am by X_RaY »

Offline tchernik

  • Full Member
  • **
  • Posts: 274
  • Liked: 315
  • Likes Given: 641
The disappointment simply comes from unrealistic expectations about the speed of the experiments and the validation process required to change opinions. People seemed to expect we would see hyper-strong Emdrives in a short while, while all replications have been showing very tenuous forces at best.

Which would still be a very big deal, because we should be seeing none at all or just those caused by a equivalent photon rocket.

This is still a highly speculative and controversial potential physical phenomenon, which hasn't left the stage of experimental anomaly reported by a few.

It needs a lot of work of many people, working on improving the experiments, models and ruling out sources of error, to finally enter into the stage of "somewhat verified phenomenon".

And that can take a lot of time, with its related frustrations, enduring mocking criticisms and mustering the required perseverance from the part of those actually doing experiments and measuring something.

I have resigned myself to the very likely fact that, in the best of worlds, we won't ever see a flying car out of this, but that we might eventually see some revolutionary propellentless satellites or probes treading the Solar System in 20 or 30 years, after this finally gets out of the NASA TRL or anything equivalent in other space agencies.

Which would be completely fine and actually, an astounding result.

Or simply, nothing will come out of it, except the amusement of discussing what-ifs.

Offline rq3

  • Full Member
  • **
  • Posts: 240
  • USA
  • Liked: 281
  • Likes Given: 42

The situation is worse: Monomorphic has accepted that he is aiming for a tolerance of only 1 mm.  There is no way that a resonance is going to be achieved at optical frequencies that have a wavelength 200,000 times smaller than the frequencies of a typical EM Drive.

There is no way that you are going to have reflection and resonance, with well-formed standing waves with a tolerance of only 1 mm at optical frequencies.

How can one have resonance in a cavity having 1 mm tolerance, with an optical wavelength of 0.0006 mm ???



  As far as I understand, Monomorphic stated that his microwave frustum will have a tolerance (better than) 1mm, not the optical one.
  Most likely, the optical one will have optically aligned mirrors.
  Optical cavities can easily have Q of several millions, see:

     https://www.rp-photonics.com/q_factor.html

  Therefore, if we are to take Shawyer's theory as guide, it makes total sense that the thrust of an optical system with:
   -input power ~ 10W
   -quality factor > 1e6
will be easily measurable.

  Like RonM, I too think that the optical EmDrive is a legitimate path to explore, at least in light of what we know so far.
  Of course, there might be other arguments against an optical EmDrive, in this case, let's hear them.

Which brings up the fascinating fact that the Q of a standard, say 6 inch long, HeNe (helium neon) laser tube is infinitely high, because the cavity exhibits gain, not loss. So back to ammonia filled frustums with maser gain?

Offline rq3

  • Full Member
  • **
  • Posts: 240
  • USA
  • Liked: 281
  • Likes Given: 42
Actually, you can create a concave-convex optical cavity in the shape of a frustum. In fact, the cavity length (5cm) is dictated by which concave and convex mirrors are available for purchase at specific diameter and radii.

As pointed out by Dr. Rodal, the huge difference is the modes in an optical cavity will be much higher order.

NOTE: Side walls are also mirrored, they are only shown clear here so you can see the interior of the frustum.

In fact, from the historical perspective, this is why the laser was not actually built until 1960, when it could easily have been done as early as the 1920's. Everyone ASSUMED that standing wave resonance would be required in the optical cavity, but that is obviously not so.

Offline rq3

  • Full Member
  • **
  • Posts: 240
  • USA
  • Liked: 281
  • Likes Given: 42
...
Consider these points.

I wondered when RFPlumber's test when he first ran his tests he deformed the large plate from heating.

I also wondered how a TE012 mode could provide the thermal profile on the large plate to warp it. It didn't match his COMSOL sim of a TE012.

...

Shell, I noticed you keep mentioning that the large plate in my tests has been deformed from heating, I am not sure what makes you think so. I recall the exchange when someone asked whether the end plates on my frustum were flat or warped and I measured it and replied that they were maybe 1 mm warped in the center. My assumption back then was that the question referred to the quality of construction, and not to any deformation caused by the actual test. And my reply was also with an implicit assumption that this 1mm warping has been there from the start, and it was not the result of RF heating. I doubt one can cause any real warping on the plates with only 30W of energy (where a portion of it is then further leaking out as plain RF).

Also, if I were to get any non-trivial amount of induction heating inside the frustum, I would have most likely witnessed "thrust" from all the hot air escaping through the gaps around side walls. It is possible that some of the thermal force I am attributing to the RF amplifier hot plate air convection could be coming from said hot air escaping from the frustum, but again, 30W is hardly enough to make any lasting deformation on the 0.5mm copper plates.

For perspective, the average hobbyist soldering iron is about 30 watts.

Offline rq3

  • Full Member
  • **
  • Posts: 240
  • USA
  • Liked: 281
  • Likes Given: 42
Cavity metal: Believe it was Aluminum

It was copper.  0.5mm thick

For perspective, 0.5mm is about 0.020 inch, or about the thickness of 4 sheets of typing paper.

Offline Rodal

  • Senior Member
  • *****
  • Posts: 5911
  • USA
  • Liked: 6124
  • Likes Given: 5558
Actually, you can create a concave-convex optical cavity in the shape of a frustum. In fact, the cavity length (5cm) is dictated by which concave and convex mirrors are available for purchase at specific radii.

As pointed out by Dr. Rodal, the huge difference is the modes in an optical cavity will be much higher order.


Thanks for the picture and the discussion.

Does this have side-walls ? if so, what material is used for the side walls?


I updated my post. The side walls are shown clear here so we can see the interior. They would be of the same material as the end-plate mirrors. Glass and vapor deposited aluminum or dialectric mirror.

At optical frequencies, I don't think that one needs the side walls, and actually the side walls will be detrimental to the effect being pursued.


Quote
The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to the literal cavity that would be employed at microwave frequencies in a maser. The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in the medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially.

At optical frequencies, your side walls are never going to be accurately straight and parallel to the optical ray and they are never going to be sufficiently smooth.  They don't serve any useful function and worse, they are detrimental.  It would be better not to have anything that can either reflect or refract the optical rays on the conical sides.  Better leave it open. (Of course, do wear eye protection).

SUGGESTION: Test it both A) with sidewalls and B) WITHOUT side walls




« Last Edit: 03/12/2016 02:40 am by Rodal »

Offline FattyLumpkin

  • Full Member
  • **
  • Posts: 279
  • Boise ID
  • Liked: 71
  • Likes Given: 0
Dr. Rodal, would minimal arc (concave) in the large reflector be beneficial? The mirrors below might do well?  FL

Offline SteveD

  • Full Member
  • ***
  • Posts: 312
  • United States
  • Liked: 83
  • Likes Given: 10
Actually, you can create a concave-convex optical cavity in the shape of a frustum. In fact, the cavity length (5cm) is dictated by which concave and convex mirrors are available for purchase at specific radii.

As pointed out by Dr. Rodal, the huge difference is the modes in an optical cavity will be much higher order.


Thanks for the picture and the discussion.

Does this have side-walls ? if so, what material is used for the side walls?


I updated my post. The side walls are shown clear here so we can see the interior. They would be of the same material as the end-plate mirrors. Glass and vapor deposited aluminum or dialectric mirror.

I don't think that one needs the side walls, and actually the side walls will be detrimental to the effect being pursued.


Quote
The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to the literal cavity that would be employed at microwave frequencies in a maser. The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in the medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially.

At optical frequencies, your side walls are never going to be accurately straight and parallel to the optical ray and they are never going to be sufficiently smooth.  They don't serve any useful function and worse, they are detrimental.  It would be better not to have anything that can either reflect or refract the optical rays on the conical sides.  Better leave it open.

SUGGESTION: Test it both A) with sidewalls and B) WITHOUT side walls


Bae, in his photonic laser thruster research, found that putting a gain media in the resonance cavity will cause the resonance to become highly resilient to misalignment of the reflectors (he had an Oh Sh*t moment when he held one of the mirrors in his hand and the thing remained in resonance).  I'm not sure what adding a solid gain medium would do for an EMDrive, but it might be worth a shot to see if it can alleviate the need for extremely precise alignments. 

Offline TheTraveller

Dr. Rodal, would minimal arc (concave) in the large reflector be beneficial? The mirrors below might do well?  FL

Telescope mirror coating would need to be 10x skin depth thickness. 1x skin depth for Aluminium at 2,450MHz is 1.66um.

http://chemandy.com/calculators/skin-effect-calculator.htm

Rf penetrates 5x skin depth. So the mirror coating needs to be at least 16.6um thick and pin hole free..

Next issue is the end plates (mirrors) need to be in very good, continuous around the rim, electrical contact with the side walls to stop Rf leaks and potential arcing. Not an easy job but could maybe work if the Alum or Silver coating were thick enough.

BTW I once hand ground & polished telescope mirrors, so know them well.

Interesting though is using 2 in a long confocal arrangement might reduce the amount of eddy current losses in the side walls and if so, increase Q quote a bit. Or not?

The shorter the focal length, the higher the phase distortion introduced upon each reflection.

Phil
« Last Edit: 03/12/2016 01:53 am by TheTraveller »
It Is Time For The EmDrive To Come Out Of The Shadows

Offline RFPlumber

  • Member
  • Posts: 97
  • Redmond, WA
  • Liked: 155
  • Likes Given: 119
...
Were the measurements inside or outside of the frustum?


The dimensions are supposed to be for the inside diameters, and w.r.t. COMSOL simulations this is definitely the case (as COMSOL does not even require wall thickness). The actual frustum was measured with a tape measure where the error is easily on the order of (at least) +-0.5mm, so even though I was measuring the inside dimension, for a 0.5 mm wall it almost does not matter...

Simulated sensitivity of the resonance frequency to the change in diameter (at either end) was about 5 MHz per mm give or take.

P.S. Hanging around as I am very curious to see how the next experimenter is going about convincing herself/himself and others that the observed force is not the result of hot air.  :)

Offline RotoSequence

  • Senior Member
  • *****
  • Posts: 2208
  • Liked: 2068
  • Likes Given: 1536
P.S. Hanging around as I am very curious to see how the next experimenter is going about convincing herself/himself and others that the observed force is not the result of hot air.  :)

Have you considered re-testing your experiment? Using FEKO, Monomorphic believes that your setup was ~15 Mhz off of establishing any mode shape, but would achieve the targeted resonance mode at 2.323 GHz.

Offline rq3

  • Full Member
  • **
  • Posts: 240
  • USA
  • Liked: 281
  • Likes Given: 42
Dr. Rodal, would minimal arc (concave) in the large reflector be beneficial? The mirrors below might do well?  FL

Telescope mirror coating would need to be 10x skin depth thickness. 1x skin depth for Aluminium at 2,450MHz is 1.66um.

http://chemandy.com/calculators/skin-effect-calculator.htm

Rf penetrates 5x skin depth. So the mirror coating needs to be at least 16.6um thick and pin hole free..

Next issue is the end plates (mirrors) need to be in very good, continuous around the rim, electrical contact with the side walls to stop Rf leaks and potential arcing. Not an easy job but could maybe work if the Alum or Silver coating were thick enough.

BTW I once hand ground & polished telescope mirrors, so know them well.

Interesting though is using 2 in a long confocal arrangement might reduce the amount of eddy current losses in the side walls and if so, increase Q quote a bit. Or not?

The shorter the focal length, the higher the phase distortion introduced upon each reflection.

Phil

Phil, I don't know where you get your "mirror coating would need to be 10x skin depth thickness", or "Rf penetrates 5x skin depth". Skin depth is an engineering convenience, and nothing else, based on 1/e, ( inverse natural logarithm) of energy depletion of an electromagnetic wave in a conductor. In other words, the wave rapidly depletes within the conductor to the point that its field strength becomes effectively negligable.

Dielectic mirrors required for (example , Helium Neon) laser gain most definitely violate the conditions you state. Can you provide some source of confirmation for your declaration?

And "The shorter the focal length, the higher the phase distortion introduced upon each reflection" isn't quite necessarily true, but you're treading into quantum mechanics territory with that statement. At distances less than a wavelength, true. At distances greater, not. This is why recent advances in optics (optical, x-ray, ultrasonic, and others) that "violate" the Raleigh limit are of interest.

Are they Emdrive applicable? No one knows; that's why we're all here. But I beg you to not make unsubstantiated statements without at least a modicum of verifiable reference.
« Last Edit: 03/12/2016 02:52 am by rq3 »

Offline rq3

  • Full Member
  • **
  • Posts: 240
  • USA
  • Liked: 281
  • Likes Given: 42
Actually, you can create a concave-convex optical cavity in the shape of a frustum. In fact, the cavity length (5cm) is dictated by which concave and convex mirrors are available for purchase at specific radii.

As pointed out by Dr. Rodal, the huge difference is the modes in an optical cavity will be much higher order.


Thanks for the picture and the discussion.

Does this have side-walls ? if so, what material is used for the side walls?


I updated my post. The side walls are shown clear here so we can see the interior. They would be of the same material as the end-plate mirrors. Glass and vapor deposited aluminum or dialectric mirror.

I don't think that one needs the side walls, and actually the side walls will be detrimental to the effect being pursued.


Quote
The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to the literal cavity that would be employed at microwave frequencies in a maser. The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in the medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially.

At optical frequencies, your side walls are never going to be accurately straight and parallel to the optical ray and they are never going to be sufficiently smooth.  They don't serve any useful function and worse, they are detrimental.  It would be better not to have anything that can either reflect or refract the optical rays on the conical sides.  Better leave it open.

SUGGESTION: Test it both A) with sidewalls and B) WITHOUT side walls


Bae, in his photonic laser thruster research, found that putting a gain media in the resonance cavity will cause the resonance to become highly resilient to misalignment of the reflectors (he had an Oh Sh*t moment when he held one of the mirrors in his hand and the thing remained in resonance).  I'm not sure what adding a solid gain medium would do for an EMDrive, but it might be worth a shot to see if it can alleviate the need for extremely precise alignments.

Whoa, whoa, whoa!!! I thought this thread was about investigating whether Roger Shawyer's claims were physically realizable? To whit, an easily obtainable microwave oven magnetron, when launched into a "closed" resonant cavity, will develop thrust in reference to its environment, due to reaction against fields which can be incorporated within known Einstein/Newton physics? And as the Q increases, so does the thrust. Period.

Again, why has no one TUNED THE SOURCE TO THE FRUSTUM??? Rather than spend EONS TRYING TO TRIM COPPER TO MATCH A RESONANT CAVITY TO AN UNMATCHABLE MICROWAVE SOURCE???
 
Some experiments and theories are getting way out of bounds, me thinks. Optical replications of an effect that has NEVER been replicated in its original configuration are beyond pointless.
« Last Edit: 03/12/2016 03:56 am by rq3 »

Offline SteveD

  • Full Member
  • ***
  • Posts: 312
  • United States
  • Liked: 83
  • Likes Given: 10
Whoa, whoa, whoa!!! I thought this thread was about investigating whether Roger Shawyer's claims were physically realizable? To whit, an easily obtainable microwave oven magnetron, when launched into a "closed" resonant cavity, will develop thrust in reference to its environment, due to reaction against fields which can be incorporated within known Einstein/Newton physics? And as the Q increases, so does the thrust. Period.

Again, why has no one TUNED THE SOURCE TO THE FRUSTUM??? Rather than spend EONS TRYING TO TRIM COPPER TO MATCH A RESONANT CAVITY TO AN UNMATCHABLE MICROWAVE SOURCE???
 
Some experiments and theories are getting way out of bounds, me thinks. Optical replications of an effect that has NEVER been replicated in its original configuration are beyond pointless.

TheTraveller is running tests with a tuneable rf source and has mentioned initially positive results (8 mN I believe, plus some interesting subsequent observations).  The hackaday EMDrive team is also using a tuneable source.  Shell . . . actually is working on the extremely tight tolerances need to tune the frustum to the source and think the random fluctuation from the magnetron might have something to do with the effect.  I'm not really sure what rfmwguy is up to.  I've heard about attempting to work in brass or to utilize some non-standard shape. 

As for an optical EmDrive, I think there are people out there that would find it easier to believe the effect existed if it involved lasers and not microwave emitters.   

Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2442
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 3186
  • Likes Given: 2708
Actually, you can create a concave-convex optical cavity in the shape of a frustum. In fact, the cavity length (5cm) is dictated by which concave and convex mirrors are available for purchase at specific radii.

As pointed out by Dr. Rodal, the huge difference is the modes in an optical cavity will be much higher order.


Thanks for the picture and the discussion.

Does this have side-walls ? if so, what material is used for the side walls?


I updated my post. The side walls are shown clear here so we can see the interior. They would be of the same material as the end-plate mirrors. Glass and vapor deposited aluminum or dialectric mirror.

I don't think that one needs the side walls, and actually the side walls will be detrimental to the effect being pursued.


Quote
The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to the literal cavity that would be employed at microwave frequencies in a maser. The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in the medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially.

At optical frequencies, your side walls are never going to be accurately straight and parallel to the optical ray and they are never going to be sufficiently smooth.  They don't serve any useful function and worse, they are detrimental.  It would be better not to have anything that can either reflect or refract the optical rays on the conical sides.  Better leave it open.

SUGGESTION: Test it both A) with sidewalls and B) WITHOUT side walls


Bae, in his photonic laser thruster research, found that putting a gain media in the resonance cavity will cause the resonance to become highly resilient to misalignment of the reflectors (he had an Oh Sh*t moment when he held one of the mirrors in his hand and the thing remained in resonance).  I'm not sure what adding a solid gain medium would do for an EMDrive, but it might be worth a shot to see if it can alleviate the need for extremely precise alignments.

Whoa, whoa, whoa!!! I thought this thread was about investigating whether Roger Shawyer's claims were physically realizable? To whit, an easily obtainable microwave oven magnetron, when launched into a "closed" resonant cavity, will develop thrust in reference to its environment, due to reaction against fields which can be incorporated within known Einstein/Newton physics? And as the Q increases, so does the thrust. Period.

Again, why has no one TUNED THE SOURCE TO THE FRUSTUM??? Rather than spend EONS TRYING TO TRIM COPPER TO MATCH A RESONANT CAVITY TO AN UNMATCHABLE MICROWAVE SOURCE???
 
Some experiments and theories are getting way out of bounds, me thinks. Optical replications of an effect that has NEVER been replicated in its original configuration are beyond pointless.


Again, why has no one TUNED THE SOURCE TO THE FRUSTUM??? Rather than spend EONS TRYING TO TRIM COPPER TO MATCH A RESONANT CAVITY TO AN UNMATCHABLE MICROWAVE SOURCE???



You need to look at the other side of the same coin. You can do as you say and tune the incoming RF to the frustum or you can tune the frustum to the RF source.

If the RF source is an oven magnetron with a nasty power supply that causes the RF to be scattered all over a 30-50MHz bandwidth you stabilize it.

Everyone thinks that a magnetron is a widely spewing RF source with no real Fo but fail to realize that's because of three things that home makers of microwave ovens don't want to add into the cost of a microwave oven. It's also true that making the RF out of a magnetron   jittery helps to cook food.

Magnetrons are used in the Semiconductor industry and are high power, highly stable RF sources.

*The Power supply on a oven microwave is designed to output a 50% duty cycle to the magnetron and the voltage is not regulated. Causing jitter of the magnetron output signal.

*The cooling system of fins/fan just barely keeps the magnetron from overheating causing frequency drifting.

*The magnetron heater will cause sputtering if left on during operation.

If you address these issues with a magnetron power supply that removes these problems you will be left with a high power stable RF source. I've done that.

You then design the frustum to be tuned to the incoming RF and even when heating is observed in the frustum leading to thermal expansion you compensate for it. I've done that.

Tests up to now have been done at low power or the results that have been seen at high powered magnetrons lead to either a RF source so low as to not be able to take the system out of a error bar or using a RF magnetron source that splatters all over and heats up the frustum causing it to detune from any mode of operation.

This is cut and pasted from another site and should carry some weight in answering your question.

I was the very first builder to remove the magnetron off the frustum in a separate area that was shielded.
I am the only builder to use a Carbon Fiber Composite beam negating any issues of beam expansion from heat.
I was the only builder who said from the start that you needed a common ground system called a star ground to keep ground loops under control and also one of the first to talk about Lorentz issues and address them.
I was one of the first to detail out the thermal ballooning issues and provide a solution.
I was the first to redesign the power supply in for the magnetron to eliminate splattering and therefor excess heating.
I was the first to design waveguides into the frustum, antennas can cause issues.
I was the first to take a balance beam to measure not only pressure but using the same DUT and test stand measure acceleration.
I am the only one to design a frustum that negates the thermal expansion copper issues.
I am the only one to add ceramic plates to keep endplates from warping from thermal heat.
I'm the only one to thermally cool the magnetron to keep it from frequency drifting form heat.

Added: I also designed a fully enclosed frustum that vents any air jets away from the frustum causing measurement issues.


Offline Tcarey

  • Member
  • Posts: 45
  • Arlington, Tx
  • Liked: 18
  • Likes Given: 24
Actually, you can create a concave-convex optical cavity in the shape of a frustum. In fact, the cavity length (5cm) is dictated by which concave and convex mirrors are available for purchase at specific radii.

As pointed out by Dr. Rodal, the huge difference is the modes in an optical cavity will be much higher order.


Thanks for the picture and the discussion.

Does this have side-walls ? if so, what material is used for the side walls?


I updated my post. The side walls are shown clear here so we can see the interior. They would be of the same material as the end-plate mirrors. Glass and vapor deposited aluminum or dialectric mirror.

At optical frequencies, I don't think that one needs the side walls, and actually the side walls will be detrimental to the effect being pursued.


Quote
The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to the literal cavity that would be employed at microwave frequencies in a maser. The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in the medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially.

At optical frequencies, your side walls are never going to be accurately straight and parallel to the optical ray and they are never going to be sufficiently smooth.  They don't serve any useful function and worse, they are detrimental.  It would be better not to have anything that can either reflect or refract the optical rays on the conical sides.  Better leave it open. (Of course, do wear eye protection).

SUGGESTION: Test it both A) with sidewalls and B) WITHOUT side walls






This subject of an optical frustrum has me wondering about several things.

First, how would you inject light into the frustrum? I imagine that would require a hole in one of the end plates which would reduce the Q.

Second, if the end plates are optically flat and optically parallel wouldn't the light be reflected back to the input hole? If the injection beam is not perfectly collimated then it will spread out as it bounces back and forth so at some number of reflections it will impinge the frustrum sidewalls. That will of course happen because of imperfections in the mirrors and the alignment.

There was a comment about laser's having an infinite Q. I can't grasp that. Lasers have a continuous input of energy. If they had an infinite Q they would never put out any light at all.




 






Tags:
 

Advertisement NovaTech
Advertisement SkyTale Software GmbH
Advertisement Northrop Grumman
Advertisement
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1