SAFIRE Project update - Apr 2017
SAFIRE Phase Two – Update
OTF Conference Apr 2017
Certainly a pleasure to be here, representing the SAFIRE team. Some of you might have seen the update talks last summer at the EU conference. Preparing for that conference was a real push to get the new chamber built and fire up the plasma. Since then we have been working long days and weekends to commission the instruments and synchronize data collection.
Figure 1 Core team welcomes the new chamber
Here is the core team, standing proudly by the main chamber when it arrived in lab. We found this chamber sitting in someone’s back yard not too far from here, actually. Then transported it several thousand miles on flatbed back to eastern Canada. I will review our various roles at the end of the talk.
Figure 2 chamber design - side view
Here is a design view of the chamber. That center cylinder is about as big as a car. When you are standing next to it your head is about level with the middle of the chamber.
Figure 3 Chamber design - top view
Here is looking down from above. You can see the main cylinder, surround by instruments, vacuum pumps, power supplies, etc. There are over 40,000 parts here.
Figure 4 Cryo-pump
The chamber is like a fractal, seems when you look up close things are just as complicated as when you are standing far away. Here for example is our cryo-pump, which allows the chamber to get down to very low pressures. It’s pretty amazing to be sitting next to something that is just a few degrees above absolute zero.
Here is the control room. Given that we have optical spectroscopy, mass spectroscopy, Langmuir probes, UV cameras, IR cameras, high-speed video, radio antennas, pressure, voltage & current control, and real-time changes of geometry, you can imagine we have put in a lot of work into data collection and instrument control.
Figure 5 SAF-con
Let’s jump right into plasma physics and astrophysics.
Figure 6 Plasma discharge on sphere with dipole magnet
Here is a picture of a discharge in our chamber. The center ball is a magnetized metal sphere. Here is a sketch of the magnetic field lines. I drew the center electrode as a yellow circle. North-South runs a little towards us at the lower left, and points a little away from us at the upper right.
Figure 7 overlay sketch of the magnetic fields
The alternating light and dark shells you see are electric double layers. You will be hearing a lot more about DL in astronomy over the coming years. While well known to plasma physicists in non-astronomical settings, the electric DL has had a very difficult time getting traction in astronomy. This is because for most of the 20th century, most influential astrophysicists have considered large electrical structures impossible in outer space. Yet, everywhere in space we have put a satellite we have found these electrical structures, so it is time to modify our theoretical foundations in cosmic settings. One of the jobs for SAFIRE is to systematically study DL, so that astronomers can have a better tool box, and start looking for DL instead of being surprised to find them.
Figure 8 drawing of an electric double layer
An electric double layer is similar to a battery or a capacitor in the sense that it is a separation of charges. DL have excess positive charge on one side, and excess negative charge on the other side, and an electric field in between. DL store energy, because it takes energy to create them. They can transport energy. For example, we see a steady stream of DL travelling out from the Sun. DL transform energy, as for example in a planet’s magnetosphere DL step up the energy of injected electrons from kilovolts to megavolts. DL can also release energy, as when they explode. I think that exploding DL is another name for magnetic reconnection. I would appreciate it if someone in the audience could help work out those details. The whole explanation of magnetic reconnection is based upon mathematical idealizations so extreme as to no longer describe anything real. We need to reformulate those descriptions into terms of real, physical quantities like electric charges which are moving and hence creating magnetic fields. DL also emit broadband electromagnetic radiation. DL produce the aurora kilometric radiation from Earth, as well as the Decametric radiation from Jupiter’s magnetosphere. So, as I said, DL are ubiquitous astronomical phenomena.
Here then is adding DL to the sketch accompanying the discharge.
Figure 9 Adding electric double layers
Notice in the spherical case, there is a particular relationship between the magnetic fields and the electric double layers. In the left hand image the light and dark shells you see are the double layers. Each of those light and dark bands are regions where electric charges have been separated. You see the bright glow because charged particles are accelerated through those electric fields, and excite atoms in the plasma, causing those excited atoms to emit radiation.
Coming back to this diagram, you can imagine this wrapped into a half-sphere. And further imagine several of them stacked next to each other. Multiple double layers are Nature’s usual solution to dealing with large changes of voltage. In the Earth’s magnetosphere electrons are stepped up in energy from kilovolts to megavolts. The mechanism eluded for many years because astrophysicists did not have the idea of DL in their tool box.
The theorists were constrained to explanations involving shock waves, plasma acoustic waves, and magneto-hydro-dynamic explanations. The solutions were complicated, and required unlikely initial conditions of the starting electrons. In 2013 a satellite flew through the portion of the magnetosphere where electrons were being stepped up in energy, and measure thousands of electric double layers, which were traveling 3,000 km/s. My point, just to be really clear, is that if the NASA and ESA theorists had studied DL in graduate school, they probably would have gone looking for the DL rather than being surprised to find them.
In our initial experiment we have a magnetized sphere, analogous in some ways to the Earth and its dipole field. We change the electrical potential of the surroundings relative to the model planet, and right away, right out of the box you might say, SAFIRE is producing astronomical features that were, until recently, highly controversial. If we had done this experiment back in the 1980s, and seen that electric double layers form above the poles and accelerate charged particles into and out of our model planet, we could have suggested the satellite missions above the Earth’s pole go looking for these structures, instead of them stumbling upon them.
This potential of cosmic structures informing our experiments, and our experiments informing astrophysical explanations is the main purpose of SAFIRE. For example, in addition to DL traveling through the magnetosphere, there are also DL above the north and south poles, closer to the surface of the Earth. These DL accelerate particles which cause the aurora borealis.
[movie of aurora]
Do these DL move also? Are the required conditions for DL formation here different than in the outer magnetosphere? Do DL always accelerate particles or do they also slow them down? Are DL only DC linear accelerators, or do they also operate in an alternating current mode? It is time for some experimental evidence.
As we run our experiments, I will be referring to what are called MRB – Magnetospheric Radio Bursts, This is the term used to describe energetic bursts that come from a planet’s magnetosphere. They are observed from Earth, Juptier, Saturn, Uranus, and Neptune. This diagram here shows where the emissions come from. It also shows that many times the emissions are localized along the Birkeland current that flows between a planet and its moons. These are sometimes called Decameter radio burst (DAM), those from Jupiter are detectable from Earth in the 10-40MHz range. Most papers one reads about these say the origins of the radiation is unclear. A very few papers make reference to the fact that electric double layers emit radiation over a broad range of frequencies. This is known from laboratory experiments. But how are the frequencies related to the attributes of the electrical environment, the number of DL, the average potential drop of each DL, are the DL moving, is the radiation emitted when DL form and disappear? The scientific community is very shy on details. Putting all this together is going to take much more than expanding Magneto-hydro-dynamic theories – it is going to take a whole lot of experimental observation. I am determined to make certain the SAFIRE team makes major contributions to all those questions.
Once we can determine experimentally how the electrical environment affects the nature of the radiation emitted, then we can learn a tremendous amount about all those places we cannot send a satellite, like into a solar flare,
or to a pulsar, or an active galactic nucleus.
We have to view these from a distance – we have to observe the radiation they emit. This is why I have been designing our experiments to look closely at radiation emitted from DL in our chamber. This summer we will be running experiments to characterize the types of radiation emitted by DL. We can then take that knowledge and re-examine existing data from solar flares, pulsars, active galactic nuclei, and also give suggestions on what our telescopes need to be looking for in the future.
A good example is Fast Radio Bursts, which are millisecond burst of energy measured by radio telescopes. There is no agreement about what produces these bursts. The signal has a high dispersion measure, which means that the light has travelled through a lot of plasma. They could originate very far away, and travel through intergalactic space, hence going through a very great distance of very low density plasma. Or, the bursts could be originating quite close, and be coming from a region of very high density plasma, hence traveling a short distance through very dense plasma. The dispersion measure alone cannot tell us which it is. The FRB are usually assumed to be very far away, which means they must be incredibly powerful. To account for them in the gravity models we must of course assume some enormous train wreck, like a neutron star colliding with a black hole while both are on fire and falling off a cliff. But since there are probably about 10,000 FRB per day such unlikely cataclysms do not seem like a very good explanation. However, if we assume the FRB are phenomena like known emissions from planet’s magnetospheres, then we can easily explain why we would see repeated FRB coming from the same locations in space.
And finally, we need to do better at incorporating DL into cosmic electric circuits. Something as practical as a circuit diagram has been difficult to find in astrophysical journals.
Here is our existing understanding of the electric circuits around the Earth. As complicated as this is, it is notably missing capacitors, resistors, inductors, etc. And, on the flip side, you will not find any DL in a traditional EE course, because you don’t get plasma DL with wires. It is time for the two worlds to come together - our circuit diagrams need to incorporate DL and our astronomy analysis need to include circuit diagrams. If you are looking for one book to read about how to think about electricity in space, there is a recent edition of Anthony Peratt’s book, “Physics of the Plasma Universe”
What I will speak of right now comes largely from there. Since double layers form in electrical currents, the double layer itself can be considered an element within the complete electrical circuit. This diagram depicts a simple series circuit in which a current flows. We have the elements: generator, motor, resistance, inductance, and a double layer.
Figure 10 From Peratt, 5.10 Basic Properties of Double Layers p.191, Series circuit containing a voltage source, resistance, inductance, motor, and double layer. Circuit energy in the “motor” is used to accelerate the plasma
If the electrical potential in the circuit is increasing, we have a generator transferring plasma power into the circuit. If the electrical potential of the circuit is decreasing, we have a motor transferring circuit energy into kinetic energy of the plasma, or in electromagnetic radiation being emitted. The circuit also has a resistance R which dissipates power into heat, and an inductance L in which circuit energy is stored.
In most cosmic plasma situations, the individual circuit elements must be replaced with elements that are distributed over cosmic distances. Such as the well-known electric currents between Jupiter and its moon Io. Thus, even the conducting “wire” itself, connecting the circuit elements, must be replaced by a transmission line representation of the current-carrying, field-aligned, plasma conductors.
Every circuit that contains an inductance L is intrinsically explosive. The inductive energy can be tapped at any point of the circuit. Any interruption of the current results in the transfer of the inductively stored energy to the point of interruption. By its nature, this point is most often a double layer which then releases energy at a rate proportional to the current and potential in the circuit. This energy is used for accelerating charged particles, the generation of noise, and emission of broadband radiation.
This role of DL to store, and explosively release, energy will be central to interpreting the wealth of new data coming back from infrared telescopes. The galaxy is filled with filaments, like the one in this image from the Herschel telescope, looking at the constellation Taurus. Star formation along filaments was strictly forbidden in models that only consider gravity and thermal energy. But in order to correctly interpret such new cosmic data, we need a much better understanding of how DL behave and their role in cosmic electrical circuits. This again, is where SAFIRE comes in, where we can study these phenomena in a controlled environment.
Figure 11More of the team
In closing I want to make sure everyone realizes that this is a team effort. Tracey Childs, who is not in the photos, does an amazing job keeping the business side of things sailing smoothly. (Laser point…) Monty Childs has been leading the project, and in addition to doing most all the design, has also gotten us through some pretty difficult times. Lowell Morgan brings about 50 years of experience in plasma physics, electrohydrodynamics, and nuclear processes. Paul Anderson is a chemist and expert in high energy reactions as well as statistics and design of experiments. Jano Onderco heads up the instrument control and data collection. Jason Lickver turns Monty’s blueprints physical devices. Leighton MacMillan is a machinist who also handles electric control. Jim Ryder has decades of experience leading large aerospace projects. He shares his vast knowledge of existing and future satellite missions, and constantly gives guidance that keeps SAFIRE on the right track, Scott Mainwaring has provided years of financial support to the project, and is responsible for SAFIRE getting off the ground in the first place. Bruce Mainwaring gives financial support, and has for many years been promoting better understanding of the role of electric currents in earth science.
The team is currently writing up our second paper and taking data for the next. If all goes well this should be a very exciting year for laying down new foundations for the astronomical community. Thank you.