Internship at Princeton Plasma Physics Lab {PPPL}

We have decided to move away from the triangulation project for a bit, and work on something similar but possibly more valuable for visualization purposes. Instead of triangulating each plane, and rendering them separately, we are going to draw line segments along the magnetic field lines and interpolate the value between adjacent points. This will demonstrate the fluid spiraling motion of the field. The data files I’m reading in contain a value that quantifies the twisting of the field as an index offset to change by in each iteration. This is rather hard to explain, so a movie of the finished product is above. Through development of this dataset, I realized that some time steps are duplicated in the data file, and so the actual number of steps is 702, not 721. This changes a couple things, but for the most part, the data is just more representative now!

Additionally, we decided to compute most of the data locally on the new work station that came in! On that note, I get to use the new work station. It has two massive monitors (like unbelievably large computer monitors), and about 2 TB of local storage. This allows the output files of my code to be stored locally, which means i can run VisIt locally as well, and reading the local files is far faster than reading over the network. And as if that wasn’t great enough, the computer also has 8 cores, and 16 GB of ram, allowing for a decent amount of parallel processing.

This new assignment was to approach making a smooth cross section of φ in a different manner. My mentor suggested using a program called Triangle, which preforms very accurate Delaunay Triangulations. This essentially turns a polygon into a grouping of triangles of all roughly the same size.  The mesh structure of the data I am reading in per cross section of the NSTX is in concentric non-circular rings. Each ring has a different amount of points, and each point has a φ value for each time step. For creating the structure I can simply create a 2D ring by turning to adjacent rings into a ring-like polygon. Then I run Triangle over this file. I can repeat this for all adjacent rings, and then compile all the triangulation into one file that contains thousands of triangles. If done for each of the 60 rings inside each of the 32 planes, I can descibe the geometry of the entire data set. And then I can append φ data corresponding to the points based on any requested plane and time step to create a clean rendering of the plane with a heat map like coloration (pseudocolor plot) for φ. This worked well but needs a little work for next week.

This week I also was given an RSA key chain. Without going into too much detail, this key chain, in combination with a program locally on my laptop allows me to securely connect to the network at the lab over the internet using a VPN (Virtual Private Network). After connecting to the network, I can use Cygwin as a POSIX terminal to ssh to any computer on the network. This will allow me to do work and access and file or program at the lab at anytime (as long as I have internet).

Further work was done this week in constructing another Elliptical Torus, except with Python. This yielded a result by the end of the day, and is primarily all I worked on this week.

I finally finished my Elliptical Torus Model!! I used the area below a parabola and above an ellipse, swept about an axis to create the shape. It came out better than I expected and pretty much puts a close on this assignment, at least for now. The code for generating the file was written in C++, and partially in bash; however my mentor has requested that I write future code primarily in python. Development should be faster that way, and it will be far easier for other people to read my code! 

I also assisted in another lesson on main campus, but this time for the python module numpy. I think the lesson went even better than last week's, and I can't wait for a third lesson about VisIt and it's applications in the future!

It was a really great experience teaching on campus (a short drive from the lab), and I got to meet some great people who are part of PICSciE.

We also spent some time preparing for the PICSciE (Princeton Institute for Computational Science and Engineering) presentations that we would be acting in as TA's for in the following weeks. The first two (the next week and the one after) will be an Introduction to Python Programming and an Introduction to NumPy respectively. I can't wait to help in these classes next week!

I was also given an assignment to produce a spherical torus shape as accurately as possible in a rectilinear grid. I wasn't able to finish this week but I will work over the week!

One of the file formats we learned the most about is the VTK format.  This file format is extremely versatile and I can tell it's going to be very useful. VisIt renders this file format particularly well (it's the internal file format), and my mentor spent time explaining how the graphical constructs that the file represents work. Additionally, he pointed us to some material he has made and hosted online explaining how to use VisIt with VTK files, and other formats as well.

We first toured the lab a bit and met some of the staff, and then we went to administration to get employee badges. We signed some employee agreements and then took a computerized safety exam. Finally I registered my car and got a parking pass for the employee lot. There wasn't time for anything after that, but I can't wait to get started next week!