Posted by Paul LaViolette
October 23, 2016
Update: October 25, 2016
In this update the October 21st test video was redone to include a clip of a second DC test which was inadvertently not included in the previous version of the video. This clip shows the coil pendulum moving in the direction of its wider end by 9 mm, hence in a direction opposite to what was predicted. I have accordingly modified below the discussion of the Oct. 21st test.
Earlier this year we had conducted a crowd funding campaign to raise money in order to conduct a test of the Nassikas thruster II propulsion device (https://www.indiegogo.com/projects/superconducting-levitation-thruster#/). The coil was wound by Superpower Inc. (Schenectady, NY) in early October and tests were completed this past week at the Superpower facilities. They were attended by Dr. Nassikas and myself and Superpower technicians. Sadly, I report here that the test results showed no evidence whatever that the conical superconducting coil we had made produced any axial thrust.
October 17th Test
Based on computer modeling of our conical coil previously carried out at Superpower, we had predicted that the coil (with its 3 degree taper) should have produced an axial thrust of 66 kg when energized with a current of 30 amperes. In our tests we instead energized the coil with up to 60 amperes, which should have produced a magnetic field strength twice as great as previously planned (i.e., ~0.4 Tesla) and thrust four times greater than previously estimated, i.e. 265 kg of force. A force this large, about a quarter of a ton, should have slammed the coil against the wall of its liquid nitrogen container and propelled the entire assembly across the room. In actuality, we observed no axial displacement of the coil in the direction of its narrow end, as had been predicted.
The first test of the coil was conducted on October 17th. The coil was suspended in pendulum fashion using a set of plastic ribbons 1.36 meters in length. Our intention was to look for any sign of lateral displacement. Our pendulum test setup was capable of indicating a lateral displacement of as little as 1 mm. To make this minimal displacement, our coil assembly which weighed 3.2 kg would have had to generate a force of 2 grams. But we saw no displacement at all in the October 17th tests. So we can conclude that, if the coil was generating any force at all, it would have had to be less than 2 grams, or about 120,000 times less than we had expected.
In one of our coil thrust tests we ramped up the current to the 60 ampere maximum in the span of one minute. In a second test we ramped up the current to 60 amperes in 6 seconds. This was as rapid as we could go without damaging the coil. Pulsing was not a possibility. In each case current flow was DC. No thrust was seen in either case. A video of the October 17th test is presented here:
Prior to conducting the test we had noted that the outer layer of coil windings did not have a uniform progressive 3 degree slope, but in some areas the coil surface appeared to have a zero inclination (approaching a cylindrical shape) and in some small end sections the surface even had a slight opposite slope. This was due to the difficulty of forcing the superconductor tape to conform to the intended 3 degree slope, which it did not always do as a result of periodic kinking. There were a total of 400 turns, and hence many consecutive layers that would have propagated any developed unevennesses towards the surface. So all of the windings of the coil did not have the ideal 3 degree inclination. But even if half had this intended inclination, we should have observed at least 150 kg of force, and yet none was observed.
One thought we had was that the magnetic field was not floating free of the coil but had attached to the superconductor through a phenomenon known as pinning. In such a case, any axial Lorentz forces developed by the coil would only have produced an axial stress in the coil and no displacement. We surmised that if pinning was present in our tests that it could be avoided by energizing the coil with a 60 cycle AC current. Even though the current reverses every sixtieth of a second, so also does the produced magnetic field, with the result that the Lorentz force should always be in the same direction, and any resulting axial force. We imagined that repeatedly reversing the magnetic field would prevent it from pinning to the superconductor coil structure. This test was carried out on a different date (October 21st) because first a 20 amp power source for the coil needed to be put together. We also decided to remachine the coil’s conical plastic support form with an 8 degree inclination and rewind the coil on this new form. A quick check determined that an 8 degree inclination was feasible for winding the superconductor tape.
The October 21st Test
Particular attention was paid to winding the coil so that the tape conformed to the form’s 8 degree inclination. But even so, unevennesses developed in the windings and the result was that on its outer surface the coil indicated an average inclination of only 2 degrees. As you see in the photo below some of the outer windings on the left of the coil actually had an inclination opposite to the intended inclination. Although it was difficult to determine what was the overall slope of the windings, probably a reasonable guess is that they had a net slope of 5 degrees relative to the coil’s axis. All the windings were insulated with a thin layer of Kapatan tape to prevent winding-to-winding shorting during the AC test.
The photo below shows how the coil was suspended in pendulum fashion. In this case a single plastic ribbon was used giving a length of 1.525 meters from the fulcrum to the coil’s axis and 1.34 meters from the fulcrum to the ruler gauge.
We decided to first begin with a DC test. Two tests were done in which the current was increased linearly to 60 amperes over the span of one minute, held for one minute, and then decreased over the span of one minute. In a third test the current was increased to 60 amperes in the space of 10 seconds. In neither case did we see any displacement of the coil towards it narrow end. In the first DC test the coil displaced by 9 mm for a short space of time, but in the direction of its wide end. In the second DC test there was a short space of time in which the coil displaced by 2 mm, but again in the direction of its wide end. I attribute this to a number of possible causes:
- The displacement could have been due to turning of the coil as it oriented itself relative to the geomagnetic field (its north end was directed toward magnetic north),
- The displacement could have been due to nitrogen bubbles in the vessel creating an asymmetrical pressure on the coil.
- The displacement could have been due to liquid nitrogen currents circulating in the cooling vessel. As seen from the movement of ice on the surface of the liquid nitrogen, these currents were quite rapid and we had not put any baffles around the coil to act as shields from these currents.
In the case of the AC test, the coil was powered by a 60 cycle AC current which was rapidly increased up to 19.5 amperes and held there for about half a minute. Again, no movement of the coil was observed. A video of the October 21st test is presented here below:
We also had on hand a piezoelectric digital balance for measuring any developed force up to 75 kg and another balance capable of measuring up to 2 kg of force. But due to the negative results of the pendulum test, these scales were not put to any use except to check the weight of the coil.
Discussion of the Test Results
We do not fully understand why the above test results were negative. Here are two possible explanations.
• One possibility might be that the magnetic field was pinning itself to the coil structure even in the AC test which had been designed to minimize this effect. As mentioned earlier, if the magnetic field had pinned itself to the coil structure, it would have created no net axial movement of the coil, only an axial stress on the coil windings. But no axial movement of the windings within the coil was observed.
• Another possibility may be that the force radially expanding the coil is not due to a Lorentz force, as commonly thought, but rather to an Ampere longitudinal tension which instead would be directed along the length of the coil windings rather than perpendicular to the windings. If the coil were in fact producing only an Ampere force, no axial force could develop, the Ampere force being directed along the axis of the winding inclination, rather than perpendicular to it.
When I speak here of Ampere tension I am referring to the force that is observed to explode wires longitudinally when they are energized by a strong current. For Lorentz forces not to be present, this would imply that the coil’s magnetic field was unable to penetrate the surface of the superconductor tape to interact with the supercurrent circulating within. In fact it is known that superconductors tend to expel magnetic fields from penetrating their surface. We had assumed that some fraction of the magnetic field would have succeeded in penetrating sufficiently to interact with the current flowing within. But we may have been wrong, and actually no Lorentz forces were being generated.
However, I just communicated with a GE Engineer who is the inventor of the superconducting generator and he says that strain gauge measurements have been made on superconducting coils which confirm that the coil expanding force is perpendicular to the wire, hence a Lorentz force. If so the Ampere force theory would not be a valid explanation of the absence of an effect.
The Ampere force, on the other hand, would nonetheless have been present in the superconductor since it exists within all conductors whenever a current is flowing through them. Standard theory of superconducting coils assumes that it is the Lorentz force that is responsible for distending the coil’s windings. If this is not so and the force is actually due to the coil’s longitudinal Ampere forces, then this demands that the superconductor coil industry entirely rethink its theory as to where this coil-expanding force comes from. I consulted with one physicist who confirmed that the longitudinal Ampere force scales according to the square of current. So too does the Lorentz force. The Ampere force is not as well studied by the physics and engineering community and could perhaps have been overlooked as the true cause of the coil distending force.
In view of the present findings, we are not encouraged to conduct a liquid helium test of the coil. Although, magnetic field pinning is not observed in low temperature superconductors such as tin-niobium alloy operating at liquid helium temperatures. So if pinning were the reason why a positive result was not found in the test of the REBCO tape coil, this factor would not be present in a low temperature superconductor test coil. However, such low temperature superconductors are in the form of wire (circular cross section), rather than tape (rectangular cross section). So it seems to me that it would be difficult to establish a specific inclined plane for its super current and hence a resultant axial force. The only possibility might be to build a conical coil with a low temperature superconducting tape to be tested at liquid helium temperatures, if such a tape superconductor can be found. But if Lorentz forces were actually not present in the REBCO tape coil, it is also unlikely that they would be present in a low temperature superconductor coil.
With the present discouraging results, I feel that time is better spent if Dr. Nassikas concentrates his efforts on conducting low temperature tests of his first thruster invention which has already been shown to work at liquid nitrogen temperatures. Even if one were to believe that the temporary 9 mm displacement were due to some intrinsic force generated by the coil itself, this still amounts to only 21 grams, which implies a thrust to weight ratio of only 0.0067, which is half of what was indicated by Dr. Nassikas’ first thruster invention. Also there is the concern that a similar displacement was not seen in the majority of the tests. This fact alone would point to random actions of the environment acting on the coil.
Both Dr. Nassikas and I greatly appreciate the help of those who donated to make this experiment possible. We regret that the experiments did not have positive results. Whether they may point to a flaw in the standard theory of the force that causes superconducting coils to expand when energized needs to be determined.