Wednesday, October 23, 2013

Highlights from the Last Few Weeks in Particle and Astro Physics News

It's been a roller-coaster month for many scientists. In the US, there was a government shut-down. And in the wider community, there have been a number of news article on some interesting, but inconclusive experimental finding. The goal of this post is to highlight the findings and give people links to the articles by Scientific American and New Scientist.

So, a list of some recent experimental findings:

(1) Dark Matter particles likely have rest mass between 8 keV and 14 keV
Horiuchi et al. recently published a paper that compares experimental measurements with dark matter theory suggests that the rest mass of dark matter particles is somewhere between 8 keV and 14 keV. Only in this range of values of the rest mass can the number of experimentally measured subhalo counts be predicted. (See Figure 2 and Table II from their paper below.) This appears to be strong experimental evidence against dark matter with rest mass values of MeV or GeV. I look forward to see more data collection and analysis along these lines.



Monday, October 14, 2013

The Hype this week from the National Ignition Facility

A number of blogs this week have been critical of the hype this week on BBC news that nuclear fusion researchers at the National Ignition Facility reached a "milestone."

The NIF is an exciting research facility because it allows us to understand nature better and because it helps us understand the D-T fusion process used for military applications. However, I'm afraid that what we've learned this week is that the science media (once again) goes after whatever can get hype.

So, let's be clear with what happened at NIF last month.

192 lasers generated photons that had 1.8 MJ of energy. (It should be pointed out that the NIF site consumed well more than 1.8 MJ of electricity to create the 1.8 MJ of photons. If this had been a semi-continuous event, the lasers would likely need at least 5 MJ to create the 1.8 MJ in photons.)

Of the 1.8 MJ in the photons, less than 14 kJ of energy reached the inside of the target as high energy X-rays. And 14 kJ of neutrons were generated from the reaction. Assuming that the neutrons are used to run a Rankine cycle power plant (same as for nuclear fission), then we are talking about roughly 5 kJ of electricity could be generated from the neutrons.

This means that the site spent ~5MJ of electricity to be able to perhaps obtain 5 kJ of electricity.

This means that NIF is three orders of magnitude away from "breakeven," and four orders of magnitude after from being "thermodynamically viable." This is far from a "milestone", and it is far away from what has already been achieved by the magnetically-confined fusion plasmas at JET.

I think that it's silly that NIF is trying to sell itself as an energy source of the future.

With that having been said, I want to point out that the idea of nuclear fusion is not a complete pipe dream. There is a possibly viable route to electricity production via magnetically-confined fusion plasmas, such as the still-being-built ITER experiment in Cadarache, France.

While this experiment is really expensive and there's still a chance that there's another plasma instability that will keep the system from reaching the real "breakeven" milestone (i.e. of generating more potential electricity from the neutrons than the electricity consumed to heat the plasma), I am proud that this facility is getting funding from world governments, including the US. The research at ITER is ground-breaking, and magnetically-confined fusion plasma is a potential energy source in the future if we can figure out how to control a few more of the instabilities have have appeared over the last ~60 years of research in this field.

I'd like to end this post by detailing some more information on some of the main engineering breakthroughs required before magnetically-confined fusion plasma can become "engineering" viable.

List of engineering breakthroughs required for magnetically-confined fusion plasma
(Also see slide 4 of the following presentation. The required engineering 'feats' or breakthroughs are well known. The required feats are all likely achievable...just really damn hard and require lots of upfront capital to do the research.)
(1) Controlling any instabilities that occur through alpha-heating  (i.e. there are likely to be instabilities due to the fact that the alpha particles emerge with energies on the order 4 MeV, but the core temperature of the plasma may only be 100's of keV.) The ability to control potential instabilities in nuclear fusion powered plasmas will be tested at ITER.
(2) Not-steady-state: Tokamak plasmas have a torodial electric field that must be applied by a time-varying magnetic field. This means that the process is inherently not-steady-state because you eventually need to change the direction of the electric field as you reach the maximum magnetic field that can be generated. This means that the plasma needs to be turned off (likely on a weekly/monthly basis), and then the current needs to be restarted in the opposite direction. An engineering 'feat' is required here to design a system that doesn't break during these scheduled start-ups / shut-downs (or a breakthrough is required in steady-state plasmas) and that isn't cost prohibitive. So far, the steady-state stellarators designs have been cost-prohibitive.
(3) The wall materials that can withstand high flux of ions, electrons, photons, and neutrons still need to be tested and proven to work. Also, the process for generating Tritium from Lithium needs to be demonstrated on a continuous basis.  (Note: there are plans to do this testing. I'm just point out that this has still been yet to demonstrated.)
(4) There are also a number of challenges associated with making cheap, super-conducting, high field magnets, with fueling the plasma, with removing heat, and with designing wall materials to withstand instabilities that release large amounts of energy to the wall while not releasing material from the wall that can end up cooling off the core of the plasma.

My overall conclusion (i.e. educated guess) is that magnetically-confined fusion plasma may be engineering-feasible sometime in the next 50 years, but it may not be economically competitive in the next 100 yrs. There's just too much uncertainty to known if magnetically-confined fusion will ever be economically viable against other sources of energy.

What can be stated with 99% certainty is that inertially-confined, laser-driven fusion is nowhere close to being engineering-viable or economically-viable. As a tax-payer in the US, I'd like to be able to vote for where my taxes goes. I would be willing to vote for magnetically-confined fusion plasma research, but I would not vote for my tax dollars to go to inertially-confined fusion research.

Sunday, October 6, 2013

A summary of why we need to globally reduce the emission of carbon dioxide into the atmosphere

What do coral reefs off of the coast of Australia, computer chip factories in Thailand, ski&snowboarding resort on the US east coast, and islands in the South Pacific all have in common? The answer is that all of these places are already feeling the negative impact of human-induced increases in the concentration of CO2 into the atmosphere.
The goal of this post is explain the science behind the effects of higher CO2 levels in the atmosphere, such as global warming, ocean acidification, and sea level rises. My hope is to explain in a somewhat less-technical manner the effects of higher CO2 concentrations in the atmosphere compared with the recent publication by the IPCC. There's nothing wrong with how the IPCC presents this information; it's just that I think that it's help for the information to be presented by the eyes of somebody who has no connection to those people who wrote the report or the papers cited in the report.
Unfortunately, the topic of CO2 emissions has become so politicized that the actual facts are easily swept under the rug of political ideology. Part of the problem is that environmental groups rarely discuss the actual science (and are quick to bash people who aren't alarmists), and the other part of the problem is clearly that there are people who refuse to accept that humans can affect the global climate, the ocean pH, or the sea level.  I consider myself a fairly moderate person and my goal here is to tell it as it is, regardless of how difficult it may or may not be to solve the problem of preventing major changes to Earth's climate, to Earth's average sea/ocean level, and Earth's average pH level in the seas/oceans.
So, before I get into the science, I'd like to state simply what the actual problem is that we face:
The problem:  Our global society is on pace to cause the temperature in Arctic and Antarctic to raise to the point at which we will likely see at least a 3 meter increase in sea levels. In addition, the higher concentration of CO2 in the atmosphere will cause lower pH levels in the ocean, which is harmful to major shell forming species, such as coral reefs. These are the straight-forward and indisbutable effects of higher concenrtations of CO2 in the atmosphere. There are also a number of other effects, of varying levels of certainty.

The Solution: The only realistic way to prevent major climate change, sea level change and pH change is to globally limit the emission of CO2 into the atmosphere. We can't "geo-engineer" our way out of this problem by throwing particulates into the atmosphere to scatter light from hitting the surface because this "solution" doesn't solve the fact that the pH of the ocean will continue to decrease if we were to continue to emit large amounts of CO2 into the atmosphere.