Wednesday, October 17, 2012

Lunar Dust Returns Home (sort of)

(February 11, 2012) After over 16 years of experiments, awe, and admiration, our Apollo 17 lunar dust, generously loaned to us by the wonderful people at NASA, is on its way home (to NASA, that is, not the moon). Every time this lunar soil came out of the safety of its hiding place, a crowd inevitably gathered. Always so much ado for such a little pile of dirt! In our defense, how many people can say they have handled, or even looked at a real piece of the moon, besides in a museum or through a telescope. Lunar material is so rare and scarce that there is an entire industry dedicated to creating lunar simulants. In fact, we have buckets of lunar and martian simulants, but nothing beats the real thing!

Update: Forgot to add in, this is what the dust looks like up close! (ShuA2)

Actual lunar dust seen under a scanning electron microscope

Wednesday, August 8, 2012

High School Plasma Success!

But wait! there's more! (from the highschoolers.)

So, despite the title of our last post, we youngins are here once again to celebrate having finally gotten the plasma generator in the student office to work, at least rudimentarily.

(our first plasma; isn't it cute?)

As evidenced by the above picture, and those below, we've managed to generate a reasonably bright plasma; however, it is not ideal because of the striations visible along the axis of the tube, which we will hopefully be able to correct before we try to make any measurements on the properties of the plasma. Our eventual goal will be to use the plasma generator and included langmuir probe to measure the density and temperature under various pressure and voltage conditions.

(the Langmuir probe which we use to measure plasma properties. Inside the tiny glass tube is an even smaller wire (which the camera won't focus on.)

For now however, we are happy to have overcome some of the challenges that have slowed our progress so far. Included among these set backs are the difficulty we had creating a proper seal between tube components with the original plastic gaskets and, ironically, a leaky leak valve. Neither of these problems were particularly difficult to solve but they both required ordering replacement parts, which cost us quite a bit of working time.

Finally however, we've gotten a working set-up; so listen my children and you will hear science-y details of our (ok, it's a bit of a lame rhyme.). Anyway, the method we're using to generate plasma consists  of emitting electrons and establishing an electric field (along the axis of the tube) to accelerate the electrons until they hit a passing neutral atom, hopefully with enough energy to ionize said atom. This method has a few limiting factors, however. First, in order for the average free electron to have enough energy to reliably ionize the gas, they have to have some room to accelerate before colliding with atoms, meaning that the pressure (and therefore atom density) of the gas must be low. Second, not all gasses have the same breakdown voltage at the same pressure. To illustrate, we have a picture of the Paschen curves of several gasses, including atmospheric gasses and Argon, which we're using.

As you can see, Argon (in red) has a much lower breakdown voltage on average than does Nitrogen, hence our use of Argon. The plot also illustrates the pressure dependence of breakdown voltage , which, for argon, has a minimum around .6 Torr cm; since our tube has a length of approximately 50cm, our ideal pressure is around 12 mTorr.

To generate free electrons we're using a thoriated tungsten filament (red circle & first close up), heated until almost white hot (~900 C). Then we use the anode on the right (green & second close up) to produce an electric field along the axis of the tube. Below that we have a pump to keep the pressure low (blue & third close up). On the left (yellow & fourth close up) we have our bank of power supplies; the black one provides power to the fillament (averaging about 15 amps) and the two grey ones produce the voltage between the tube anode and cathode. Lastly, we have a tank of argon (purple. two guesses which close up) and the replacement for the leak valve, to supply and regulate a flow of argon.

 Overall setup. and a fan. which Keith paid 4 (thanks, Keith!).

Filament: shiny.

The anode is on the right.

Ye olde pump.

Power supplies. the left one is a beast.

 The argon feed and tank. and a delightfully functional leak valve.

And now, as a reward for sitting through the science, it's time for some pretty pictures of glowing argon.


Monday, July 30, 2012

Final Intern Update

We're wrapping up our summer jobs at CCLDAS. We would like to thank Andrew,  Mihaly, Anthony, Paige, Anna, Evan, Addie, Tobin, Mark, Keith, Chris, and Spenser. This experience was truly invaluable and we all learned a lot.

Our last week at the lab was busy, as always. We began by helping install the UHV chamber in the beamline. First, we disconnected LEIL from the beamline and moved it aside. Next, we moved the UHV chamber into place, only to realize that the wheels  put the chamber too high. We eventually removed the wheels from the UHV assembly  in order to lower it to the correct height. The chamber is now properly in place and is currently in use for Andrew's neutral gas generation experiment.  In the process of installing the new chamber, we learned tons about high vacuum systems. Andrew taught us about flange installation techniques, cryogenic pumping, chamber alignment, and more.  Look below to see  pictures of the installed UHV assembly!

The newly installed UHV chamber

To our chagrin, the dust particles never hit the target, suggesting a misalignment. However, after disassembling the beamline, we were able to determine that the alignment was actually correct. This has brought about many concerns for Andrew's experiment. 

After the UHV was installed, we wrote a Matlab program for Paige. This program can be used to find peaks in the charge values recorded by the LeCroy oscilloscope for the Dust Coordinate Sensor, ultimately allowing us to determine a dust particle's position as it travels down the beamline. 

We then made a program for Spenser's Database project, which provides an organizational platform for data taken for various accelerator experiments. Our program puts LeCroy waveforms into a LabView friendly format  and posts them to the CCLDAS database. 

As a bittersweet ending to the week, we had to say goodbye to our fellow high schoolers from the lunar rover LEGO®  Mindstorms camp. They brought youthful energy to our workspace, and we will miss them as they continue on their journeys in high school.  Check out their awesome Lunar rovers in action below!

Rovers navigate the obstacle course

We all enjoyed our time at the lab. Thanks again to everyone at CCLDAS!


Wednesday, July 18, 2012

High School Intern Update

 It’s been an interesting week for the high school intern team. We began by creating a successful NXT robot to navigate the course created for the resident summer camp, a 3-week Lego Mindstorms lunar rover challenge. You can see our robot tackle the course in the video below!

As you can see, we have kept ourselves busy with various coding projects: 
Jordan modifying NXT code
Nick creating a Fourier series program
Sean solving a statistics coding challenge

Several weeks ago, the pyrex tube on the plasma machine shattered. Now that we received a replacement part, we have redirected our attention toward this project.  Jordan and Nick designed a Plexiglas shield for safety, and Sean helped to install it.After that, we reassembled and evacuated the tube. Unfortunately, the O-Rings that we were using failed to create a viable seal, so we made new ones from sheet rubber. With the new ring in place, we got the tube down to 15 mTorr, but unfortunately the required breakdown voltage was too high for us to safely generate a plasma. The next day, we went at it again, but this time using Argon gas, since it has a lower breakdown voltage. However, this lead to a new problem. The leak valve on the Argon gas cylinder prevented us from lowering the tube pressure below 150 mTorr, so we are currently awaiting a new leak valve.  We hope to begin experiments, using the LabView code  that Emily has written, in the near future. 

Working on the plasma tube
We have also been assisting students from Professor Scott Robertson’s lab with the stepper motors project. These motors will be used for both the LEIL table in the beamline, and Professor Robertson’s lunar wheel experiment. You can see our current setup in the picture below. Until next week… 

The stepper motor setup

Friday, April 27, 2012

Focused Ion Beams

Hi Everyone,

Platinum deposition and cutting of my name into a
Silicon wafer (notice the scale bar is 3 um)
0 degree view of a crater that has been cut for cross
section view.

A quick update, I just finished training to use the Focused Ion Beam yesterday so I am now fully capable of micro machining!  You can do a lot of cool stuff like writing your name into a sample, marking a sample so you can find your targets again and more relevant to my thesis, cut craters in half and see the crater profile.

Platinum deposition helps to protect the sample you want to see a cross section of and helps to bring out the contours of craters.  In parallel with this work, I'm working with Yancey Sechrest, another grad student working for Tobin on a plasma turbulence problem, to create a program that can take a stereo pair (2 images of the same crater at different angles) and recreate a 3D model of the crater.  Hopefully I'll have a post soon with the results of that project

25 degree view of a crater that has been cut.  The white stuff
is a layer of platinum deposited to make the crater edge more

Monday, April 23, 2012

Scanning Electron Microscope Pictures

Hi Everyone,

Sorry again for taking so long.  I've been away for a while (in Heidelberg, Germany playing with their accelerator) and working hard at getting scanning electron microscope (SEM) pictures of the craters I'm making with the accelerator.  So without further ado, here's some of the pictures I've taken.  I'm trying to get images of craters and then tilting the image to make a stereo pair and reconstructing a 3D model of the crater.  Enjoy!

Embedded iron particle in Polyvinylidene Fluoride (PVDF) 
Crater in PVDF
Also I'll be doing training to be able to use the Focused Ion Beam (FIB), which is essentially the same thing at the SEM but it can also cut samples and build up structures!
Image of a crater taken in a FIB

The same crater as above but with a cross section cut out