Week Ten: Big Finish and the Future

Hello internet!

This will most likely be my last post on this blog, and I want to first take a few sentences to thank everybody who helped me along this summer and who, if it weren’t for them, the summer wouldn’t have been a success. I’d really like to thank Professor Volpe and Max Roberts, a graduate student at the lab, for all the help both of them gave me over the course of the summer. Without their help and their vision for the project, I simply wouldn’t have had the opportunity to work at the lab this summer, and since this was my first research experience I really owe both a lot. Many of my friends from California and Columbia have given me their support over the summer as well, you all know who you are and I’m very grateful for your kind words.

I completed my circuit on Tuesday, and the final product is below. I was able to really good data out, and am overall very proud that I was able to take this from a theoretical concept to an actual circuit board.

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Also, I realized that I hadn’t posted a picture of the Collisionless Terrella Experiment (CTX), which is where my circuit will find application.

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It was an immeasurably fun experience to walk into work every morning and see this complex machine and think about all the work that went into it’s design.

That’s really all there is for me, and this summer. I’ll be giving a poster presentation at the SEAS undergraduate summer research symposium on October 7th, which I’m very much looking forward to, but until then it’s time to focus on a new academic year!

Bye bye internet,

Scooby Doo!

Lucs

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Week Nine: A Big Victory, and the Next Steps

Hello internet homies,

This will be my last post for some time as I’m headed to California on Tuesday until August 19th. I’ll return to work from the 25th to the 29th and by that time I hope to know whether or not I’ll be continuing to work at the Plasma Lab during the Fall semester. During this week I encountered lots of unforeseen trouble with getting the frequency controlled resistor set-up that I designed to work with the 90 degree shifter that I made. However, on Wednesday afternoon I was able to get data out for the first time, which was hugely encouraging for me as it meant that my project will function correctly once I figure out how to recreate this initial victory on the circuit board pictured in the last blog post.

I’m including the two plots in this post, the first shows the frequency response of the circuit with respect to frequency of the incoming signal, and as can hopefully be seen, it is a very flat response.
phase_v_freq

This phase response was something I had before, but what really made my day when I finally got it to work and pleased professor Volpe was the following graph of gain response versus frequency of the incoming signal.

gain_v_freq

While this should be as flat as the first plot, this response is much better than the response without the correctly functioning frequency controlled resistor that I programmed. With a little reprogramming, I am confident that I will be able to level out the higher frequency end of the second plot, bringing the goal of a circuit that has both flat phase response and flat gain response to incoming signals.

While professor Volpe was very pleased with these results, he also had some news that complicates the course that this project is going to take. He said that he realized only recently that the way I was setting up my circuit could only handle one signal at a time, while the signal that actually comes out of the plasma will have upwards of ten signals superimposed over one another. This makes the problem considerably more complex, and I’m going to have to find another method by which to isolate each of those signals and apply different resistances accordingly. I have some ideas about how to do this, but they definitely will not be ready by the end of the month, so that raises the issue of me working in the lab for the duration of the semester, which I would consider a great privilege. For this week though, a victory is a victory and the complicated nature of the next steps in this project will be something that I look into when I return from my glorious time off in California.

That’s all for now internet, stay beautiful

Lucas

Week 8: A breakthrough, and the end is in sight!

Hello internet friends!

This week was my eighth at Columbia University’s Plasma Physics Laboratory, and while my time in the lab this summer is drawing to a close next week, the circuit I’m building is tantalizingly close to working. I’m attaching a picture of the circuit and the box that I’ve put it in, so you all can see what the finished product will look like.

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The week started with my continuing struggle with programming the microcontroller I’ve been using to make a de facto frequency controlled resistor. By doing a lot of googling and reading through online forums, I was finally able to get the microcontroller working on Wednesday afternoon. This was a HUGE breakthrough for me, because I’ve been struggling with this, unsure if it would ever work since about the 5th or 6th week of this fellowship. It was an amazing feeling to turn a knob on my desk that controls the frequency of an incoming signal and see the corresponding drop in resistance that I need for my circuit to function correctly.

The next step was soldering in the new part of the circuit, which is composed of the three new chips into their proper place in the circuit. Once that was done, on Thursday morning, I ran into some issues that made both Thursday and Friday very frustrating for me. I had tested the circuit without the three new chips before I soldered them in and everything worked the way I expected it to, however once I put in the new chips, short circuits came up and I had to struggle to find the places where I had made bad connections. Compounding my frustration was my expectation that now that the hard part was over (the programming of the microcontroller) everything would be smooth sailing. One lesson that I’m definitely taking away from this fellowship is that the little things that aren’t supposed to be difficult are often those that take the longest. I shouldn’t let it get to me, but the circuit is so close to working and I’ve only got a week left before I go back to San Francisco, so I’d really like to get it done before I get on a plane and leave for two weeks.

I was able before the end of Friday to locate the source of the problems and fix them, but by then it was 5:30 and I wanted to go home. I should (should being the operative term) be able to go into the lab on Monday morning, hook up the new box, and test it. However, I will not be surprised if I end up trouble-shooting all day. My plan for Monday is essentially to go in and check all the connections in the circuit. If everything looks good, then I’ll go from there. Hopefully, I can get the circuit working the way I want it to, then generate some data to show Professor Volpe. This should be a very exciting week, and hopefully by the end of it, I’ll be able to test the circuit on the CTX (Collisionless Terrella Experiment). Which is one of the big machines in the laboratory.

That’s all for now,

Happy Saturday!

Lucas

Week Seven: Switches, coding, and the final step

Hello friends! It’s the end of my seventh week of work at Columbia University’s Plasma Physics lab and the end of the project is very much in sight. This week, since the part I needed to program the microcontroller did not come in until Thursday, I spent much of the week trying to create an array of inverters and mixers so that my phase shifting circuit could cover more of the angles in a circle. The original plan was to have it shift the incoming signal anywhere from 0 to -90 degrees, but with the array that I put together this week, it will be able to cover any angle in a circle through the use of three switches and four operational amplifiers.

I also soldered most of the circuit together this week, so the board has come together quite nicely. I’ll try to post a picture later in the week or definitely by the end of next week to show you all how I am progressing, but it is safe to say that a good portion of the circuit has been completed and is on an actual circuit board.

However, there still remains a significant final step to be taken. The voltage controlled resistor that I have been trying to make with a frequency-to-voltage converter, a microcontroller, and a digital potentiometer has not yet materialized. When the programmer arrived on Thursday afternoon I tried to upload the code I had written to the microcontroller and (big surprise), nothing happened. I have since tried two simpler versions of the code to no avail. This is the area of the project that I have the least experience in, so I’m not surprised that it’s not working yet. However I only have two weeks before I go home to San Francisco, and I’d like for the project to be done by then. I’d be lying if I said I didn’t feel any pressure, as this really has been my first research experience and I’d love to end it on a high note. However I’m confident that if I try hard and keep my focus, I’ll be able to figure out how to program this chip before I go home. If I don’t, I’ll have two weeks in California to let it stew, and then I have an extra week to work before I get back and school starts. I’d like it to not have to come to that, but you never know.

On Monday I hope to finish soldering the analog portion of the circuit and test it to make sure it works. Then all that will be left is the coding. Once that’s done, the circuit will be completed and hopefully I’ll get some good results.

That’s all for this week!

Scooby doo

L

Week 6: Stepping Stones

Hello internet friends, this week was my sixth working in Columbia University’s Plasma Physics Laboratory, and the project is definitely nearing completion. On Monday, I was able to get my frequency-to-voltage chip working the way I need it to, which means that for all the frequencies of the rotating plasma, a different voltage will be fed to the microcontroller, which will then tell a digital potentiometer what value to assume. This was a good start to the week, but on Tuesday I ran into a snag.

Somehow, I had missed a potentially harmful flaw in my previous design of the 90 degree shifter, which is essential for this circuit to work correctly and is the focal point of pretty much everything I’m doing this summer. The problem is that at higher frequencies, the signal drops off for some reason, meaning that rather than a pure cosine wave, the function starts to look like a constant is subtracted from the value of the normal function. Obviously, this would be a problem, but on Tuesday and Wednesday I was able to devise a solution through using another one of my frequency-to-voltage converters to compensate for the unexplained decrease in voltage. I also mapped out the resistances I need for a flat shift across the entire band of interest, and fitted that data to a curve.

Then it was back to the relatively unfamiliar territory of coding, where due to some help from one of Professor Volpe’s colleagues, I was able to write my own code for the microcontroller. The problem I then had to deal with was the minutia of getting the code to a point where it would be palatable to the microcontroller, but on Friday morning, the program that I wrote compiled successfully, which stunned me initially, because I foresaw this being much more of a drag than it ended up being. I am now ready to move forward with programming the microcontroller, which I will attempt to do once another part gets to the lab.

Tomorrow Professor Volpe returns from vacation, and I’m hoping to show him the prototype I made during the fifth week as well as show him my sketch of what the final circuit design may look like. Hopefully the part I need to program the microcontroller will come in soon, and I can be well on my way to completing the circuit on schedule. By the end of this week, I hope that I will be well on my way to testing the microcontroller with the frequency-to-voltage converter and the digital potentiometer, but a lot of that depends on the part I need getting here, so we’ll see. Hopefully tomorrow I’ll be able to show off my prototype, which in my opinion is a solid proof of concept, and the week will take shape from there.

That’s all for now,

Lucas

Week 5: Short Week (and my birthday!)

Hello internet friends! This week was the fourth of July, which also meant that my birthday (July 2nd), fell on Wednesday. During the time that I was in the lab this week, I spent most of my time trying to learn more about programming microcontrollers, which is the main task that I am going to have to accomplish during my remaining time in the lab this summer. I also spent part of the week corresponding over email with one of Professor Volpe’s colleagues who works at General Atomics in San Diego. The two of them co-authored a paper in 2012 that utilized a digital scheme similar to the one I am attempting to implement, so I was hoping that the code for the microcontroller that they used still existed, so that I could try it out myself without having to start from scratch.

I turned out to be in luck. On Thursday, Professor Volpe’s colleague sent me a large file with lots of helpful information that I will most likely spend a significant portion of this week sifting through in order to determine what is and isn’t going to be helpful for my project. The rest of my parts also arrived on Thursday, I’m excited to finally be working with something tangible and not just reading online tutorials which, while helpful tend to be dry and overly detailed to the point where I don’t feel like I am gleaning any helpful information by reading them.

Tomorrow (Monday), I’ll be attempting to get the frequency to voltage converter working correctly. The chip takes in alternating current at a particular frequency and outputs DC voltage that is (in theory) linearly proportional to the frequency of the incoming voltage. I need this DC output to vary from 0 volts to 5 volts across the 0.1 through 20 kHz band of interest for this circuit. This should be no problem at all, but as I’m learning, sometimes the tasks that shouldn’t take any time at all end up consuming way more time than you budget for. That’s why I’m giving myself all day tomorrow to get the chip working.

After that, I’ll need to take measurements on my 90 degree shifter again to determine the resistances that I need to program into the microchip. This will be both tedious and boring, but it needs to be done accurately if this whole circuit is going to function correctly. After that, the programming begins! Hopefully with the code sent to me by Professor Volpe’s colleague, the process will be exponentially less painless.

That’s all for now, I hope you’re smiling

Lucas

Week 4: A successful prototype and the end of the tunnel

Greetings to my hoard of internet friends!  My work at Columbia University’s Plasma Physics Laboratory this week mostly consisted of building my circuit on an actual board, testing it, and putting it in its own box.  A picture of the finished prototype is attached to this post,  and I’m very happy with the circuit so far.

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The phase shifter, after being properly tuned by those knobs you can see on the front of the box labeled “Cosine Amplitude” and “Sine Amplitude” does give a wide range of phase shifts, which means the concept itself that I have been working with is sound.  The problem is that this device needs to cover a wide range of frequencies (0.1 – 20 KHz), and the way the box is set up now, you have to specify the frequency it works at before you use it on the actual plasma machine (CTX or Collisionless Terrella Experiment).  This isn’t ideal, but the good news is that the only reason the box doesn’t work for all frequencies can be fixed by implementing the digital solution that I’ve spoken of in previous posts.

The Cosine and Sine amplitude knobs that are shown in the picture I’ve attached above are actually called potentiometers, which is a fancy way of saying that they are resistors that you can control by turning the knobs.  The idea that I’m going to be working on this week is to replace the “Cosine Amplitude” knob with a digital potentiometer, which will be able to adjust itself to the proper resistance based on the frequency of the incoming signal from the plasma within the machine.  It’s not going to be easy, mostly because I’m relatively unfamiliar with programming these digital components, but I’ve given myself enough time so that I believe that I can get it working before the summer is over.  On the plus side, after I get this digital business working, I should be very close to completing the project, which is very exciting and keeping me motivated!

I’m not sure what I expected when Professor Volpe gave me the job in April, but it certainly wasn’t a huge desk with huge measuring tools on it in a lab populated with a solid mixture of undergraduate and graduate students.  I’m attaching a picture of my desk so that you, my readers, can see where I work everyday.

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Those three big boxes, from left to right are a power supply, which I use to power various electrical components that I use during the day.  The second box is a function generator.  This one is important because it lets me feed signals of different frequencies to my circuit, which is important because this circuit is supposed to work for a pretty wide range of frequencies.  The last box is an oscilloscope, which I use to measure the signal that my circuit is outputting against the signal that the function generator is inputting.  Everyone at the lab has been very accommodating and, while I’ve never worked in a lab to compare this one to, I can say that I always feel like the myriad instruments, tools, and materials are well organized and readily available for anyone who wants to use them, which can’t be easy because there is a lot to keep track of!

So off I go, into the hinterlands of programming microcontrollers.  This should be a relatively low stress week, as my twenty-first birthday is on Wednesday, which means I probably wont be working the last half of the week.  However, I’m looking forward to trying out the digital solution, and am hopeful that it can produce the desired effects.

That’s all for now internet!

Scooby Doo!

Lucas

Week Three (the digital revolution is nigh)

Friends, Romans, Countrymen, and internet hooligans: the third week of my work at Columbia University’s Plasma Physics Laboratory has come to an end, and with it, my hopes of completing this circuit without doing any programming at all.  Last week I informed my cherished readers that I was hoping to utilize a scheme created by Iranian Electrical Engineers to make a frequency dependent resistor without using any digital components.  While I was (finally) able to make their design function the way they said it would, the circuit they proposed was fairly limited in its frequency range and didn’t give the resistance decay that I needed in my own design.  Long story short: I’ve ruled it out as a viable option.  I get my digital components in tomorrow, which is exciting because I’ll hopefully get to start looking at existing code and seeing for myself what needs to be done in order for this digital business to work correctly.  The idea was actually proposed by Professor Volpe, the principle investigator who I am working under and involves three components: a frequency to voltage converter, a microchip, and a digital potentiometer.

The frequency to voltage converter has a name that accurately explains its function.  The chip takes in voltage and determines its frequency and then spits out DC voltage that is directly proportional to that frequency.  Higher frequency incoming voltage gets you higher output voltage from the chip.  Next, the microcontroller digitizes the voltage and outputs a number to the digital potentiometer.  The digital potentiometer takes this incoming number and adjusts itself to a particular resistance, so effectively these three chips will (hopefully) give me a fairly accurate frequency dependent resistor when they are strung together and coded correctly.  I had a chance to talk with one of the graduate students who works with the lab about this and he said that the decision to go digital was most likely a good one, which made me feel a lot better as I’m getting into unfamiliar territory.  

My week took a different turn on Friday when Professor Volpe asked me to build a prototype for permanent use on one of the machines in the lab.  Even though the circuit isn’t functioning exactly the way we both want it to at this point, he’s still interested in the applications that could be observed when it gets tested out.  This means that I get to build something, which is pretty cool and that, even after I’m done this summer, something will stick around the plasma lab that I made.  Again, hopefully it will work a lot better than it does now, but the fact that Professor Volpe asked me to build something this early on indicates to me that he’s interested in my project and is happy with the work that I’ve put in so far.  My main plan for the beginning of this week is to produce, on a real board, the circuit that Volpe needs and get it to him by Tuesday, then begin working with my digital components on making the same design more broadband and more dependable.  That’s all for now lovelies, I’m off to enjoy what remains of my weekend.

 

Lucas

Second Week (during which I became Goldilocks)

Hello again!  As I’m sure my legions of internet fans will know, this past week was my second in Columbia University’s plasma lab, where I am designing a phase shifting circuit for use on the CTX (Collisionless Terrella Experiment).  My main challenge this week was to decipher a paper written by three Iranian scientists on how to construct a frequency dependent resistor for use on my circuit.  Unless I can get a signal that does not change in amplitude as my output for all frequencies that the experiment deals in, this circuit isn’t going to work.  This leaves me with two options, one of which is to find an analogue solution, one that deals only with basic circuit elements, which I have failed to adequately produce this week.  The other solution, which I am now leaning more in favor of, is to incorporate digitizing elements into my circuit and program a microchip to do exactly what I want to do in terms of getting the proper resistance.  This sounded like a sort of deus ex machina when my professor suggested it as a last resort, but since I have not programmed a microchip in a very long time, I want as much time as possible to fiddle with my digital components so that I don’t have to scramble at the end of the summer to get the device working.

I referenced Goldilocks in the title of this post because that is exactly what this week felt as I sat in the lab modifying my frequency dependent resistor circuit by testing it with different values of various components, looking for the configuration that was just right.  This process of trial and error was frustrating at times because the circuit proposed by this paper is complicated enough that to analyze it mathematically would be a significant waste of time, but the authors insist that by following a very precise procedure I should get the effect that I need.  I’m trying not to get discouraged (it is only my second week) but the fact that the paper I’m working with hasn’t gotten me the result I needed is not a very productive feeling.  I’m giving myself a couple more days of the Goldilocks routine, but if a significant amount of progress hasn’t been made by that time, I’m going to have to start considering the digital solution a little more seriously.

I should give the authors of this paper I’m working with a little more credit.  The circuit does exhibit a resistance that decays with frequency.  The problem is it introduces a phase shift that also varies with frequency, which is the worst possible thing for the circuit that I’m trying to design.  It also says in the paper that the circuit should not exhibit a phase shift, so I’ve been taking their word for it and just assuming that if I try enough configurations of the circuit with different components I will eventually obtain the desired effect.  By the end of this week, I hope to either be significantly closer to achieving the goal of decreasing resistance without a variable phase shift or to have prepared myself to start tackling the digital solution to this problem.

That’s all for tonight.  Goodnight adoring internet fans!

 

First Week

Greetings Internet!  It’s been a week since I started at Columbia’s Plasma Lab, and it was a fantastic time filled with new people, experience, and even a few victories.  The project that I’m working on has been almost completely elucidated and more than one method to get the circuit working has been proposed by my professor, so I’ve now got a few different roads to follow.  By reading one specific paper published by Volpe and a former student of his, I was able to get a thirty degree phase shifting circuit working that operated within acceptable limits in the 100Hz – 1kHz band.  This was good news for me, as it meant that I’m not too far from realizing one of the main goals of my project; a phase shifting circuit that is frequency independent.  However, the particular design has to be built around shifting an incoming signal a particular amount, which means I would have to build a wholly new circuit for each particular spot on the machine that it would be operating at.  This is not an ideal design, and instead I’m trying to make the angle adjustable, so the circuit is more fluid and can be applied at different locations around the machine simply by turning a dial to specify the actuator’s location.

Combining two different kinds of signal in a predictable way should accomplish this goal, but the problem of flattening the gain remains.  This is the problem that I will set myself to this week: the amplitude of the outgoing signal from every circuit I model in the lab decreases exponentially as the frequency gets higher.  This is an issue because the actuator that this circuit will be communicating with can’t function correctly if the incoming signal is too low.  To fix this problem, I need to find a way flatten the amplitude of the outgoing signal from my circuit.  I’m hoping that a frequency dependent resistor, proposed by Iranian scientists in a paper that Professor Volpe gave me to read, will help me with this goal, and that by the end of this week, I’ll have more an idea as to whether or not applying a frequency independent phase shift WITH constant gain is even possible.  I hope it is, otherwise I’ll have to go back to the drawing board.

I also got a chance to see a screening of “Particle Fever,” a documentary about the Large Hadron Collider and the scientists who work with it, on campus last Wednesday.  After the show, some scientists who were featured in the movie did a Q&A session and it was hugely inspirational to see people who were at the top of their game talk about the science that they were so obviously passionate about.  The screening really got me excited about doing science this summer; as I mentioned in my first post, this is the first time I’ve ever done any sort of research.  What really got to me was something that Nimah Arkani-Hamed and Savas Dimopoulos, two physicists featured in the movie, articulated both during the film and the Q&A session.  This was their opinion that science and art are more aligned than one might be inclined to believe, and that especially when it is pushed to it’s most abstract limit, the distinction between science and art is hard to draw because they really on people pushing the limits of traditionally accepted reality.  For me, sitting in a room with three graduate students with a machine behind be that makes a buzzing sound once a second all day long, this sentiment helped me return to working the next day with a new mentality about what I was doing.  Hopefully, this enthusiasm will carry on and I’ll be reporting back next week with more good news.  For now: I’m going to sleep.

L