DavidPace.com

Plasma Parameters Widget

Thu, 10 Jul 2008 04:56:26 +0000

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Introduction

Required Apple Statement

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This is the permanent web page for the Plasma Parameters Widget. I previously made a new page for each iteration of the widget, but that seems unnecessary since there are so few changes between them.

Introduction

This is a Dashboard widget that calculates an assortment of relevant plasma parameters given user inputs of basic characteristics. For example, the user provides the background magnetic field and the widget displays the electron cyclotron frequency. Most of the equations used to calculate these parameters are taken directly from the Naval Research Laboratory's (NRL) Plasma Formulary, a source that has been vetted by the plasma physics community over the past few decades. Some parameters, including the Bremsstrahlung radiated power, are taken from sources provided by plasma physicists since this widget was first made public.

Status and Download

Latest Version: 4.1 (first to include radiated power parameters)
Download: Directly from DavidPace.com, From Apple

How it Works

Widget screenshot demonstrates the equation pop-up that appears when the cursor is held over a label. In this case the cursor is held over the text "fce".

This is a simple javascript-based calculator. You provide input values relating to the most basic properties of the plasma and then various length, frequency, and velocity parameters are output. The figure to the right is a screenshot of the widget illustrating the default display with a help window. The area above the “Calculate” and “Choose Preset...” buttons is for the input parameters. These input parameters and their required units are,

Bo: Magnetic Field [Gauss]
μ: Ion Mass Factor [unitless], the ratio of the ion species mass to the mass of a proton
Z: Charge Factor [unitless], atomic number of the ion species
γ: Adiabatic Index [unitless]
ne: Electron Density [cm-3]
Te: Electron Temperature [eV]
Ti: Ion Temperature [eV]
ln(Λ): Coulomb Logarithm [unitless], a collision parameter
R: (secondary display) Tokamak Major Radius [m]
a: (secondary display) Tokamak Minor Radius [m]

You are not required to provide a value for each input. All of the parameters that can be calculated from the values that have been provided will be displayed. Any other output will return “NaN” to signify “Not a Number”. Using one of the preset input sets will provide decent values that you might want to use as the value for inputs you do not know for certain.

The output parameters and their units are,

fce: Electron Cyclotron Frequency [Hz]

fci: Ion Cyclotron Frequency [Hz]

fpe: Electron Plasma Frequency [Hz]

fpi: Ion Plasma Frequency [Hz]

νe: Electron Collision Frequency [Hz]

νi: Ion Collision Frequency [Hz]

re: Electron Gyroradius [m]

ri: Ion Gyroradius [m]

vthe: Electron Thermal Velocity [m/s]

vthi: Ion Thermal Velocity [m/s]

δe: Plasma Skin Depth [m]

Cs: Ion Sound Speed [m/s]

vA: Alfén Velocity [m/s]

λD: Debye Length [m]

β: Beta [unitless]

ι: Ion Inertial Length [m]

ftr: Trapped Particle Fraction (Toroidal Geometry) [unitless]

Pbr: Bremsstrahlung Radiated Power [W/m3]

λe: Electron Mean Free Path [m]

Prec: Recombination Radiated Power [W/m3]

λi: Ion Mean Free Path [m]

Pline: Line Radiated Power [W/m3]

Placing the cursor over any of the parameters labels causes a help window to pop-up. This window displays the equation used to calculate the parameter. This is the example shown in the screenshot.

Preferences

The information side (reached by clicking the “i” button in the lower right hand corner) allows you to set preferences. The checkbox labeled, “Show Tokamak Side as Default” determines which output parameters are visible by default. The screenshot shown previously displays the primary parameters. Holding the cursor over the infinity button at the bottom of the widget will cause this primary screen to disappear and the “Tokamak Side” to display. The tokamak pane includes the radii input and the mean free path and radiated power output parameters. Placing a check in the aforementioned box causes the tokamak (secondary) panel to display by default. If this is set, then placing the cursor over the infinity button causes the primary parameters to display.

The rollover help only works for the default display. If you have the primary parameters as the default, then you cannot place the cursor over the secondary parameters in order to view the help window. This will be obvious when you move the cursor away from the infinity button and witness the disappearance of the displayed parameters before being able to view their help windows.

Default values for the major and minor radius can be set in the appropriately labeled areas. These will appear in the input display automatically. Entering a number in the preference areas sets the default, there is no need to press .

The remaining input areas on the information side allow for you to create a preset. These will serve as the “My Set” collection provided by the drop down button on the front side. Typing values into the text areas on the information side will set them as the preference.

Customizing

It is possible to alter the expression of any output parameter by modifying the javascript code used for the calculations. To view the relevant code, browse to Library\Widgets\plasmaParams4-1.wdgt in Finder. This is in the Library folder of your personal user account (not the system-wide Library). Control-click, or right click, the widget file and select “Show Package Contents”. A new Finder window will open and display all the files of the widget. The file with the equations for calculating the output parameters is named plasmaParams.js

Open this file with the text editor of your choice. Find the line (probably line 186) that reads,

function calcParams(event)

This is the function in which the parameters are calculated. Change it as you see fit, save it, and then try the widget anew. It is probably a good idea to copy the entire widget to a new directory and then attempt to change it. Also, you can always contact me to suggest changes and improvements.

Acknowledgments

The following acknowledgments section can be found on the information side of the widget.

This widget is primarily based on the Plasma Formulary published by the Naval Research Laboratory (NRL). The NRL provides hard copies of the Formulary for free, and I also thank them for that service.

Additionally, I would like to extend my gratitude to the following people for their help.

Joe Huba (NRL): for allowing me to include the official formulary link and suggesting that space plasmas receive better treatment in the output. He further suggested the inclusion of the ion inertial length, ι, and provided the expression for it.

Aaron Roberts (NASA): for providing Solar Wind parameters and suggesting better handling of space plasma parameters.

Melvyn Goldstein (NASA): for providing Solar Wind parameters and seconding the request for better handling of space plasma parameters. He also demonstrated the usefulness of including the adiabatic index as an input parameter.

Thomas Pedersen (Columbia University): for pointing out errors in some of the calculations.

Frank J. Wessel (University of California, Irvine): for suggesting the inclusion of radiation emission power and providing the necessary reference. The expressions for radiation power are taken from page 234 of “Fusion Plasma Analysis” by Weston M. Stacey, Jr. (© 1981, John Wiley and Sons, Inc., Reprinted with corrections in 1992).

UCLA Plasma Physics Group: Brian Brugman, Troy Carter, Neal Crocker and Anne White all helped with the initial development of this widget by troubleshooting and making suggestions for useful calculations.

Required Apple Statement

"Mac OS X 10.4 Tiger is required. If youre using Safari, click the download link. 
When the widget download is complete, show Dashboard, click the Plus sign to 
display the Widget Bar and click the widgets icon in the Widget Bar to open it. If 
youre using a browser other than Safari, click the download link. When the widget 
download is complete, unarchive it and place it in /Library/Widgets/ in your home 
folder. show Dashboard, click the Plus sign to display the Widget Bar and click the 
widgets icon in the Widget Bar to open it."

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Colonel Mustard, in the Kitchen, with the Poison Gas

Mon, 07 Jul 2008 03:48:45 +0000

Over the holiday weekend we had a family dilemma. Everyone wanted to play Clue, but no one wanted to go out in the holiday traffic to purchase the game. Fortunately, we found two people willing to walk to a nearby store, but of course, that store did not have the game. They did, however, have enough of an office supply and toy selection to make it possible to create a homemade version of Clue. Our home version is easily as enjoyable as the store bought one and it allows for customization, as you will see.

Professor Plum: Has his lifelong obsession with solving magnetically confined fusion finally pushed him over the edge and made him a murderer?

For those who may not know, Clue is a “crime fiction board game” with a lengthy history. It inspired at least one funny movie and possibly a few other enjoyable ones. The official rules can be found online (PDF). I had never played it prior to this weekend, but it is easy to learn (even though other people will be sure to take advantage of the least experienced player).

Sure, we could have just played cards, or someone could have volunteered to go find the game, but that would not have been as enjoyable as creating a homemade version. The game was put together from the following items.

Large poster board: As large as you are willing to draw on.
Package of Index Cards: Draw the playing cards on one-half of one side, fold, and tape to prevent other players from being able to see through the cards.
Dice: Only need a die, but it is useful to have two dice for a faster game.
General Paper: Any basic paper can be used to make items representing the players.
Action Figure with Weapons: This is key, the toy weapons of the action figure serve as the icons for the game weapons. This is why Colonel Mustard used poison gas instead of a candlestick.

The map is drawn on a large piece of poster board.

This can actually cost less than the official game. It depends on how expensive the action figure is, though there is usually a very cheap (i.e., generic) one available. The toughest part of putting this together is probably going to be drawing the map on the poster board. As seen in the image to the left, the routes can get skewed. A ruler and patience will make this better, but as long as there is some semblance of a clear path it should be possible to follow it. Beware of ill-defined squares because they encourage creative counting on the part of players seeking to reach a room quickly.

A benefit of taking the time to create your own game is that it motivates the addition of new items. While we started with the simple task of changing the weapons based on what was available, this quickly morphed into the addition of an entire new class of item: the motive.

The motive is the fourth aspect of the murder that must be correctly determined to win the game. The standard aspects are murderer, weapon, and location. As someone not particularly familiar with the game prior to this weekend, I do not understand how the location can still be a matter of debate. Regardless, requiring players to figure out the motive increases the difficulty of the game while also making it all the less likely that someone will get lucky early on.

Alligator: A failed motive card becomes a dangerous new weapon.

Representing the motives by graphics on their cards took longer than drawing the full map. The motives are: greed, insanity, jealousy, revenge, self-defense, and accident. An alligator served as the representation of accident, but it just did not look correct. In the end, we added alligator as a weapon and used the red cross for the accident card. Now imagine winning the game by determining that Mrs. Peacock committed the murder in the library using an alligator in self-defense.

I definitely recommend this as a family activity. Most homes probably have enough material to create the game set without buying anything new. It's even easier if you have any remnants from an older version of the game. Why buy replacement parts when you can make them?

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The solution, without motive, is clear.

What's This? - Number 4

Fri, 27 Jun 2008 16:52:20 +0000

What's This is not to be confused with the original and star, Bob Park's What's New.

The Obsolete Scientific Method:
The editor in chief of Wired, Chris Anderson, has written an article that claims the scientific method is becoming obsolete as researchers develop the ability to collect, store and process petabytes of information. You see, the only reason we needed the scientific method and its slow procession from hypothesis to testing to refinement to repeating, is that we have never been able to collect a truly complete data set! I am sure plenty of people will point out the absurdity of this claim; two of my favorite sites already have. I humbly add today's edition of What's This to the growing collection of such criticism.
But What Will Happen Next Time?
Anderson suggests that with enough data it is possible (nay, required) to “throw the numbers into the biggest computing clusters the world has ever seen and let statistical algorithms find patterns where science cannot.” Then, we simply review these computed correlations and enjoy the scientific progress. We don't need models when we have a complete data set. One problem, however, is that we can never collect data from the future. Models are used to provide predictive capability. A petabyte of data regarding the motion of the planets, even the plutoids, will surely allow an “analyzer” to describe their motion to incredible detail and precision. Where will these objects be in one year? What about 100 years, 1,000 years? An analyzer doesn't care about the future because their job is to analyze up to the present, which is why I didn't call that person a scientist. Assuming that the behavior up until now accurately predicts that of the future is to also assume that the system exhibits no non-linear behavior. Reviewing the behavior of some chaotic systems will demonstrate that measurements of the past and present cannot always lead to accurate predictions of the future.
Mainstream Contradiction:
Anderson cites the Cluster Exploratory supercomputer as an example of how this new thinking about science is going “mainstream.” It will have a lot of processors and a lot of hard-drive space so it must be a completely new paradigm of performing research. He then notes that an early project of the machine will be to simulate the brain. Simulations are computer implementations of models! Supercomputers do not typically analyze data (though I would be happy to receive correspondence of counter-examples). We only collect as much data as needed to vest a model. Models are continuous while data, regardless of the resolution or total amount, are discrete. Not even Google, the idolized soothsayer of Anderson, can collect so much data that models and the scientific method become obsolete.
Maybe He's Right:
I am forced to admit a successful application of Anderson's highlighted method. My research question is: “Is society developing a heightened inability to understand modern science?” The old way to proceed with this research issue is to construct some models of society and the act of understanding and then to begin fitting data points (people) to this model. But why cling to these old ways! My usage of the new science allows me to let the cloud present a bunch of examples that allow me to conclude: “Yes, a lot of people do not understand how science operates.” If I can get a project approved for the Cluster Exploratory, then maybe I can harness the 1,600 processors to scour the web and find a petabytes worth of examples, thereby proving my argument conclusively.

The opinions expressed in this article are not those of a Ph.D. physicist, but they will be.

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Technorati Tags: wired, scientific method, media criticism

New Discussion Forum and Removal of Comments

Fri, 06 Jun 2008 18:33:32 +0000

I have set up a Forum to encourage visitor participation. The forum is intended to replace the comment form that used to appear at the bottom of every content item. Eventually, every content item will have its own thread in the forum and links to the relevant thread will appear in the items.

My motivation for making this change is two-fold. First, some of the comments (especially on the items in the EM Topics section) were long and full of questions that are best covered in a forum format that makes it easy for multiple to participate. Second, I am attempting to make this website more efficient from the server perspective and this is helped by removing the commenting routines. If you visited this site six months ago you have noticed that it loads much faster today. The performance improvement has resulted in page load times that are under three seconds, compared to the more than eight seconds it took back then. I'm going to write more about that at some point in the future.

About the Forum

I am aware that commenting is something that is available on just about every blog in the world. The suggested evolution of blog commenting involves using standard forms from third party vendors and I appear to be doing exactly the opposite. In order to make the forum more like the ubiquitous comment form there is no registration required. Visitors can post to the forum without making their own account. If you make an account, then your posts will be displayed without review. Anonymous posts will be moderated. Hopefully, this is an agreeable balance between ease of use and spam protection.

Just in case you are wondering, the separate forum is not a performance hit for the website because it is hosted separately from the main site.

Here's the forum discussion link that will eventually appear on every content item,

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