SuperCool: High-Temperature Superconducting Solenoid Punch
Friday, May 14, 2004
Our final presentation is up. Please be aware that this file is about 5 MB in size, and once you scroll to the movie slide, you must wait for the 1.5 MB movie to download before proceeding.
Final Presentation (PPT)
Tuesday, May 11, 2004
After a little bit of freaking out, I managed to get the PDF to print properly so I think everything should work now. What might be useful is to send Hao both the PPT and PDF files, in case the printer prefers one of them.
Final Project Poster (PPT)
Final Project Poster (PDF)
Monday, May 10, 2004
We finally got our testing done yesterday, and are currently working on the final presentation/poster.
Thursday, May 06, 2004
While our solenoid clearly works, because we can feel a force on the iron core, we are running into difficulty at the moment with quantitative tests. Issues include Kevlar string falling off and the magnetized core sticking to the power leads.
Tuesday, May 04, 2004
Monday, May 03, 2004
Last Thursday, our group visited David Bono in the undergraduate laboratory in order to conduct magnetic field measurements. He was surprised to see that we were using an apparatus rather than a plain liquid nitrogen dewar. However, because of our setup, we were able to use a regular magnetometer rather than the magnetometer that David Bono had created for us. Our preliminary results indicate that we are able to get higher than the 30 amps of current that we had expected. However, we still need to analyze the data that we have collected.
Wednesday, April 28, 2004
calculations:
using 30 m of tape we can theoretically get 30 N of force and 1200 gauss field.
calculations will be shown in our presentation.
we wound 160 loops of superconductor onto our PVC tube. We did this by placing the tube on a lathe and and allowing the tape to wrap around it as the tube rotated. We also seperated the layers with Kapton tape.
Before we began wrapping, we placed two copper squares on the tube. We soldered one end of the tape to one copper squrare, and then proceeded with the wrapping. The other copper squre was shaped into a Z, so that it can be attached to the other end of the superconducting tape, which was about 4 centimeters away from the pvc tube, after the wrapping.
Using a gaussmeter I measured the field inside our solenoid at 1 amp (1.2 V) at room temperature, and found the maximum field to be 25 gauss. Since we will be running our solenoid at approximately 30 amps (because of self field problems) our maximum field will be approximately 750 guass, which is much less than our expected 1200.
This is not very disappointing since we are intrested in the gradient of the field and not the field itself.
David Bono helped me construct a little device that could hold our gauss meter and move it into the solenoid at controlled lengths. On thursday we will use this device to record that field at different points in our solenoid so that we can determine the gradient of the field. We can use the found gradient to ammend our force calculations.
In addition, we will again be performing current tests on our solenoid. We can couple our current and magnetic field gradient tests to determine the best operating conditions for our punch.
Pictures should be posted soon!
Thursday, April 15, 2004
Chris and I finished soldering the copper power leads to superconducting tape. This time we used a propane torch to get the copper cap hot enough, and it took no time to do so. We unfortunately scorched some of the PVC and a bit of electrical tape, but it doesn't look like anything catastrophic happened. We screwed down the leads with guides and used tape to hold them to a larger PVC pipe extension to secure them and make sure they don't twist during handling. Everything worked this time.
We tried testing the apparatus, but found that the magnetic field generated was not strong enough to cause the iron core to move. We tried using a screwdriver to manipulate the position of the iron core, thinking it my have been out of the field's strongest influence, but it remained stationary. However, we did notice that the screwdriver was magnetically attracted to the iron rod, and that the attractive force varied qualitatively with the current through the HTS tape. We estimate that our critical current is around the same as it was during testing, since the change in magnetic field for current less than 80 A was substantial, whereas the difference between 100 A and 120 A was not qualitatively noticeable.
We believe that the final solenoid, which will have many more turns, should generate sufficient field to move the iron core.
Today we split up into teams and accomplished a few small goals.
Dave and I went to find/calculate equations describing the magnetic fields along the axis of the solenoid.
We found an excellent book titled "Solenoid Magnet Design" by Montogomery that stepped us through the derivation of the field equations.
In a previous presentation we had used the eqaution for the field in the center of a loop.
Now, treating this loop as an element of a larger coil, we integrated over a current sheet of elements and found the field at the center of that current sheet solenoid. To find the field at a point z along the axis of a solenoid of length L, we partitioned the solenoid into two subsolenoids of length 2z and 2(L-z). Summing the two central fields from these subsolenoids gaves us the field at the point z in our actual solenoid, since the end field of any coil is half the central field of a coil of twice the length. We used this equation to determine the maximum force for our punch. We found that the force has a linear dependance on position z. We also found that force increased as solenoid height decreased. So, we are comfortable with the height of our prototype at its current 3 inches and we do not need to make it larger. We will continue working with this equation, so that we can decide whether we reallly need 50 m. of tape.
An important assumption in our calculations was that the solenoid has no thickness. We might have to revise our equation later, since a short solenoid would require many layers of tape.
Additionally, we found an equations describign the axial and radial components of the fields in spherical coordinates, but they involved power series of Legnedre polynomials......
Meanwhile, Chris and Andy successfully attached the power leads to our coiled HTS tape! Andy or Chris, will probably post about this.
Today we split up into teams and accomplished a few small goals.
Dave and I went to find/calculate equations describing the magnetic fields along the axis of the solenoid.
We found an excellent book titled "Solenoid Magnet Design" by Montogomery that stepped us through the derivation of the field equations.
In a previous presentation we had used the eqaution for the field in the center of a loop.
Now, treating this loop as an element of a larger coil, we integrated over a current sheet of elements and found the field at the center of that current sheet solenoid. To find the field at a point z along the axis of a solenoid of length L, we partitioned the solenoid into two subsolenoids of length 2z and 2(L-z). Summing the two central fields from these sub-coils gives us the field at the point z in our actual solenoid, since the end field of any coil is half the central field of a coil of twice the length. We used this equation to determine the maximum force for our punch. We found that the force has a linear dependance on position z. We also found that force increased as solenoid height decreased. So, we are comfortable with the height of our prototype at its current 3 inches and we do not need to make it larger. We will continue working with this equation, so that we can decide whether we reallly need 50 m. of tape.
An important assumption in our calculations was that the solenoid has no thickness. We might have to revise our equation later, since a short solenoid would require many layers of tape.
Additionally, we found an equations describign the axial and radial components of the fields in spherical coordinates, but these involved power series of Legnedre polynomials......
Meanwhile, Chris and Andy attached the power leads to our coiled HTS tape. Andy, will probably post about this.
Wednesday, April 14, 2004
Rough prototype presentation is posted.
It might be noted that not only did we get a kink in the wire, it plain just broke the superconducting tape.
Tuesday, April 13, 2004
On monday, Dave and I went to the hobby shop to finish milling. We made the central hole 15/16" and the iron slug a few thousandths of an inch smaller. Dave did a great job!
Later in the day the group met up to test our prototype. The first thing we had to do was attach the power leads to our superconductor, which proved to be much more difficult than we expected. Basically one soldering iron does not provide enough heat for our copper connectors to melt solder. We went to the Edgerton center, and with the assitance of Ed Moriarity, tried some "extreme" soldering techniques. We used a blowdryer, a stove, and multiple soldering irons in conjuction. With much persistence and patience we were able to tin and solder one connecter , but as were were trying to work on the other lead, the first one kinked, due to the weight of the 2 gage wire. So now, we have to cut off the piece of superconductor where the kink is and redo the connection further in. Ed gave us some gaffer's tape which helped secure the power leads better and he helped us come to the conclusion that the only way to solder such a large piece of copper is to torch the copper and then touch it with solder. Hopefully during our next lab class, we will have more success attaching the power leads.
Valuable lessons learned about heat conduction....
Saturday, April 10, 2004
Friday, April 09, 2004
While Dave and Andy worked on milling, Chris and I twisted the remaining meter and a half of superconductor tape around our 2" diameter PVC tube. It took 1.5 meters of tape to cover 2 inches, without overlap. When we construct our actual solenoid, we will have to figure out how to wrap the wire about itself without kinking when the overlap occurs. Also, we now have an idea of how many insulative layers we will need for a 50 meter wire. The spacing was not even at the extereme edges because that would have caused kinking.
After this, we put connectors on our 2 gage power leads. This will enable us to attach the power leads to the superconducting tape with greater ease. We considered some ways to attach the power leads to our device, but chose not to try any until we could consult with Andy and Dave. Yin-lin has informed us that our pipes have arrived.
Thursday, April 08, 2004
Today we presented our second update to the class, and then returned to the Hobby shop to finish milling our aluminum. Dave and I ended up spending 5 hours in the Hobby Shop (until 8 PM), trying to mill the aluminum. We struggled for a while with finding the edge of the cylinder before we finally prevailed. The milling went slowly, because each rotation only removed thirty thousandths of an inch, and was preceded by an application of oil, which further hindered the process. When our initial trough was milled, we attempted to use the side of the bit to expand the walls of the trough. However, we didn't figure that the drill would cause a rotational "kick-back" which then completely misaligned the entire cylinder. consequently, after trying different alternatives, we were forced to use the same top-down process, which enabled us to finish the milling, but which also gave us an inner diameter that was too small. Before next Tuesday, we need to drill the hole for the iron core, but should otherwise are done for our rough prototype. Hopefully the supplies for the final prototype will finally arrive.
Making something by hand is incredibly rewarding. It's not often that you get this opportunity.
Thursday, April 01, 2004
As Andy mentioned, we will most likely have to weld the apparatus (2 Al pipes and a toroidal bottom). Towards that end, we have ordered the two pipes (5" and 1.25" diameters). We also contacted Toby Bashaw for help with the welding. We have to decide whether to weld a disk to the bottom and then cut a hole to form the toroidal bottom, or to make a toroid out of the disk and then weld it to the aluminum pipes.
In addition to running into problems with milling, we are having some difficulty in finding better ways to cool our apparatus. Neon is the only gas that is safe to use, and will give us better cooling than nitrogen. We were warned though, that Neon might be prohibitively expensive. I am trying to contact Air Liquide, and BOC to get prices. We also decided to study the feasibilty of constructing a dewar with a jacket. The dewar would hold the helium and jacket would hold the nitrogen. The jacket might in effect be a bath in a bucket, but this might hinder our ablity to perform measurements and actually use the device as a punch. We will also consider finding a device to measure our low temperatures.
Our immediate goal is to weld the apparatus as soon as possible, hopefully by Tuesday.
We've run into a bump regarding milling our apparatus. Our container will be 6 inches deep, but there are no drill bits in the Hobby Shop of that length that would allow us to remove all that aluminum. What we're trying to do now is to assemble the part from aluminum tubes and fitted pieces with the large solid aluminum cylinder we had. We're barely on schedule right now, if not slightly behind; we forgot to incorporate the assembly of the large solenoid, though we had planned (and skipped) making a smaller solenoid.
Friday, March 19, 2004
We went to the hobby shop yesterday and discussed with Ken Stone the possibility of machining out our apparatus. While he didn't have the mills set up at the time, he said he'd be able to do it shortly. Additionally, he gave us some perspective and we now think that using a CNC mill may not be necessary, since we're not going for high precision. David will be renewing his Hobby Shop dues, and the rest of us may also join, if we can make the orientation times.
Our nitrogen tank has arrived, and we had to spend some time testing out different pipes that would allow us access to the liquid. We will also be meeting next week with Professor Vander Sande regarding the 50 m of tape and Makoto Takayasu for cooling options to give us a higher critical current.
Tuesday, March 16, 2004
Today we also took care of ordering our raw materials. We ordered a foot long rod of aluminum with a 5" diameter, as well as two foot long iron rods, one with a 1" diameter and the other with an 1 1/4" diameter. We will use the Al rod for our apparatus; the iron rods will give us two different punch sizes to test. We ordered the parts from McMaster-Carr, which has an excellent distribution network, so we should receive our supplies tomorrow.
Today we got better results because we used solder to connect the leads of the voltmeter to our HTS tape. At 2.5 inch diameter the critical current is around 80 amps. In our previous runs we thought the critical current was around 30 amps, so we see that we can get stronger magnetic fields at the size we want to build our solenoid. On thursday we will look into other cooling methods (neon, argon, increasing pressure on liquid nitrogen).
After talking to David Bono, we were allowed to keep the power supply that he dug up for us; additionally, he showed us his own setup for measuring the voltage drop across the HTS tape. We found out that indeed solder does work. We had previously come up with that idea, only to scrap it without giving it a try first because we thought thermal property mismatch would cause the solder to come off the silver tape. A good example of why you should try something out first, especially if it doesn't require too much effort or resources to implement.
Data, pictures, further comments, and perhaps even a movie to come...
Saturday, March 13, 2004
Tuesday was another frustrating day, as we weren't able to reproduce the results we had gotten previously. Our reading would range anywhere from .01 mV to .1 mV, which is still one or two orders of magnitude away from the .003 mV we had been able to get. The culprit seems to be the electrical contact between the voltage meter leads and the superconducting tape, but we suspect that the flat-toothed alligator clamps don't do a good job of clamping at very low temperatures. Ideally we would use C clamps like we do for the power leads, but we aren't able to find small enough clamps that would still allow us to fit everything into our foam pot. We eventually had to move the leads from opposite sides to adjacent positions, so the tube would fit all the way into the pot. We are constantly fighting volume limitations due to the pot, but at the same time getting a bigger insulated pot is surprisingly difficult and would require even more liquid nitrogen than the copious amounts we're using now.
Thursday was the final design presentation, whose link I have posted.
Tuesday, March 09, 2004
Sunday, March 07, 2004
Currently thinking of a site redesign, so that visitors will have an easier time navigating the site.
Friday, March 05, 2004
Finally! A kink in our voltage vs. current data!
Finally, we got a kink in our data taken on Thursday. We wrapped the superconducting tape around a PVC pipe with 60 mm outer diameter and took measurements. The critical current occurred between 30 A and 40 A, as you can see in our data: 0304_VvsI_60mm_straight_good_x1.xls. I've tried to show clearly the key change we made with our testing design. We used small toothless alligator clips to make a tight physical contact between our copper lead tape and the superconducting tape. However, when we used the same change on our straight tape test, we found that though the current held steady below ~108 A as it should, higher amperage actually caused the voltage to decrease rather than increase. We're still trying to figure out why that occurred.
We also attempted to use a larger diameter PVC pipe, but ran out of time as initial measurements were in the high tenths of a millivolt range, which according to our previous experience meant bad contact between the copper tape and the superconductor.
Thursday, March 04, 2004
pro-e tap / ncl files
i asked my boss yesterday at work if i could use pro-e files on a solid works mill. he said all that mattered was the ncl file and the tap file. the tap file is processed from the ncl file; giving machine specific instructions. the good news is he said that our mill uses an industry standard language, so i could post-process the ncl file to a tap file for our machine and it should work on mit's mills with very few or no modifications.
i plan to go in on sunday and whip up a design for wrapping and cooling our coil.
Tuesday, March 02, 2004
Better voltage (resistance) measurements!
We conducted another test of the straight HTS tape, just to see if our results matched. The data, both good and bad, can be found here: 0302_VvsI_straight_x2.xls. The graphs of voltage vs. current show much better voltage drop for the "good" data, but do not show a definite kink that would indicate a precise critical current.
We began our test of a bent HTS tape (wrapped around PVC pipe), but ran out of time and liquid nitrogen right before testing. It would be helpful as well to find C-clamps of slightly smaller size so the entire assembly could fit better in our foam pot. Some pictures are shown below:
We also discussed the design of the final punch. We would like to machine a container that would allow liquid nitrogen to fill a torus-shaped container to cool the wound HTS solenoid, and in the center of the "donut" would be a hollow area for the magnetic punch to operate. We guessed that aluminum would be a good candidate, for its machinability and its non-magnetic properties.
Friday, February 27, 2004
We presented our first progress report today (permanent link on the right).
We almost encountered full frustration today, after trying new electrical contacts. Our previous lab session's measurements didn't come close to literature data values, so this time rather than clipping alligator clips directly onto the superconducting tape, we connected the alligator clips to copper tape that was in contact with the HTS tape. However, the copper tape had an adhesive side, and that seemed to be completely hindering our measurements. We finally came up with a setup that avoided the adhesive side and used silver paint to help secure connections.
Photos of the final setup below:
There is some frustration over the slow going and hit-or-miss experience we're having so far. Unfortunately, no one can meet outside of lab hours at least over this coming weekend.
Wednesday, February 25, 2004
Well, I finally figured out how to move files into the 3.082 group locker, and managed to set up Blogger.com to secure FTP the blog into the locker.
Should be putting up our initial presentation shortly.
