Locklin on science

Golden age experimental physics memories

Posted in Design, physics by Scott Locklin on March 26, 2019

I’ve given some hints of my tastes in experimental physics, and that my taste is experimental physics rather than impotent theoretical cargo cult wanking. I didn’t exactly work on project SLAM, but my early work kinda had this flavor. I caught the last fumes of the heroic cold war age in experimental physics.

 

My first big project was an experiment for observing something called the quantum breaktime, which I believe nobody gives a shit about any more. If you observe a quantum (in our case, chaotic) system for a short period of time, it should look semiclassical. If you wait around long enough, because quantum bound systems are a recurrence map, it will end up looking quantum. Anyway, nobody cares any more, as it turned out to be a fairly trivial thing and nothing important was observed. But at the time it looked important; Anderson won the Nobel for a related idea, and so we tried to build a crazy contraption to observe the thing. None of it was my idea, other than a few gew-gaws to make it go, as I was just some redneck kid who was good at making mechanical things work. I think the PI on this project is still alive, shooting at crows in Kansas or some such thing, and the senior grad student (who graduated) has gone on to more gentle pursuits. I totally lost track of the laser jockey. Names withheld to protect the innocent.

Proof this actually happened; and I used to have hair

The physical embodiment of the idea was to build a couple cubic meters worth of vacuum chamber filled with calcium vapor and shoot lasers at it. The problem with calcium vapor is at the partial pressures we needed it at, the chamber needed to operate at 400 degrees C. Oh yeah, we also needed to distill the crap so we were only using one of the isotopes, to avoid some fine structure nonsense that would have sunk the whole experiment, but as I never got that far, we’ll just pretend it didn’t matter. So, calcium is a reactive metal that wants to bind with anything resembling an optical opening that can withstand a 500 degree C bake out. So, there was another chamber within the chamber, with a set of calcium fluoride windows resting on knife edges that hopefully would keep most of the calcium out of the main chamber and away from the seals and the sapphire windows that kept the air out and let the laser pulses in. Did I mention seals? Yeah, seals and 500/600 degree C bakes (you need to cook all the volatile shit out of the chamber at higher than operating temperatures) don’t get on well. You can’t use viton which is the ordinary high vacuum seal. You sure as shit can’t use conflats and copper due to different coefficients of expansion of stainless and OFHC copper. The PI came up with this brilliant thing involving bolts under preposterous strain, shallow spring like knife edges, and a thick brand of aluminum foil. I think it was used in the Mercury program and promptly forgotten by everyone but the PI who was actually alive and sentient in those days. I won’t tell you what we used to seal the optics; it was similarly insane (and, unlike the aluminum trick, carcinogenic) and found by scouring the literature using INSPEC and paper indexes rather than the garbage you ninnies use on your nerd dildos. I tested both technologies, and to my minor amazement, they both worked  reliably at the design temperatures.

The pump on this thing was something called a diffusion pump. You pump on the chamber with a piston driven mechanical roughing pump to rough it out to 10^-3 torr or whatever, then you fire up the diffusion pump. Diffusion pumps boil some dense fluid which makes a spray through various trumpet like things in a big cooled metal tube, and it creates a pumping action which works sort of like how the shower curtain gets sucked inward when the shower is on. The dense fluid is sometimes mercury, which is why every experimental atomic physicist of a certain age has a mad hatter twitch, though in this experiment, we used some weird fluorodated oil made by Dow-Corning which we hoped wouldn’t explode when calcium vapor hit it. On top of the diffusion pump sits some water cooled baffles and a “trap” of liquid nitrogen, which catches any stray diffusion pump operating fluid molecules and prevents them from futzing up the vacuum too badly. Believe it or not, this kind of pump stack was dirt standard for 60s-90s atomic physics before turbo pumps and ion traps became cheaper. Probably still often used where you need high pumping power in a relatively small place.

Now, to do atomic physics, generally speaking, you also need lasers. The kinds of experiments we were doing you needed pump and probe stuff. This was mostly someone else’s responsibility, at least in the early days, but I was keenly aware of the laser systems as I had to observe proper safety procedures when the laser setup was being run in the same room with me. Our stack consisted of a UV excimer laser (which lived in the other room and ran on poisonous gas and high voltage electricity), an infrared YAG setup which fed a dye laser which I believe made green light when everything was working right. There was probably a KDP crystal or two in it somewhere, since momentum generally must be conserved, and since I remember the laser jockey blowing them up from time to time to powerful slavic imprecations. I don’t remember how many watts these things were, but you could light each other’s pantaloons on fire with some of the things. The dye laser setup used DMSO, a membrane penetrant used to deliver drugs through the skin, and a soup of carcinogenic and poisonous dye (I believe it was coumarin). A dye laser is basically a pump and high pressure hose with some optics around it, and it would occasionally spectacularly explode, shooting deadly DMSO dye goop all over the place. It never hit anyone important. Oh yeah, in case some of you don’t have laser safety training: green light, IR and UV; what do you use for safety goggles? I’ll tell you what you use: a  steel bucket on your head.

 

Remember how the excimer laser was in the other room? How do you think the laser light got into the magic show room of tremendous grad student danger? Well, I couldn’t tell you exactly how this happened, but there was a convenient hole in the wall. I heard a rumor someone rented an electric jackhammer and blew a hole in the (load bearing) wall over a long weekend. The past is a foreign country, and the late 20th century was different, I tell you.

 

There’s all kinds of interesting little details here; how do you build something to hold the vacuum chamber up while you’re baking it? It can’t be well thermally connected to anything or all the heat will bleed out where you don’t want it. It can’t expand or contract at much different rates from the vacuum chamber steel. Oh yeah, and since you have two chambers made of of stainless steel, and barely touching each other, you needed to thermally link them together with a big spring loaded bar of OFHC copper.  Finally, how do you make an oven which bakes the thing to those kind of temperatures? Turns out, rockwool blankets and big ceramic resistors I found in a junkpile fed by silica coated wires worked pretty good.  If I happen to die of mesothelioma, I’ve always harbored the view that rockwool can cause this as easily as asbestos -feel free to name it after me. I won’t even mention the microwave feed throughs and  high-Q niobium microwave cavity that was supposed to fit into the thing, as I never really believed it possible to do this. All of this was done using two line equations and graphing paper rather than the preposterous finite element analysis people waste time with now, and it worked just fine.  на коленки.

Finally an illustrative anecdote: at one point I was putting liquid nitrogen into the trap for a vacuum test, and did so too rapidly. Just like they said it might in the manual, the trap cracked from cooling it too fast, rendering it a leaky paperweight. I knew there was another trap of identical manufacture hooked up to a chamber in an abandoned lab across the hallway (physics departments in them days had all kinds of weird stuff across the hallway; punched tape CP/M machines, weird pumps, high voltage DC generators, farad tier high voltage capacitors with no internal resistance, depleted uranium bricks, etc). I considered just pulling it out of the other setup. I thought about it for a few minutes, and realized I should manfully admit my blunder to the PI first, because who knows what kind of bonkers shit was going on in that old lab across the hall when it was active. Well the PI was real understanding, as he had blown up a nitrogen trap or two in his day, and thought it was a swell idea to nick the nitrogen trap across the hall to save a few bucks and some leadtime on a new trap … oh wait a minute, that might have been the chamber they used for the atmospheric plutonium experiments. Here’s the stack of (60s vintage, probably slightly radioactive) safety sheets on plutonium, and go borrow the mica-window Geiger from Jimmy down in the other building.  I did my best on the safety front; I wore a HEPA dust mask, some gloves and a baseball umpire vest I found somewhere. I gingerly stuck the mica business end around the inside of the vacuum chamber with the matching nitrogen trap bolted onto it.  Plutonium is weird shit; I think it’s an alpha emitter. I know you have to get right on top of it with the counter or you can’t see it at all. Well, I found some plutonium all right; so much it actually shorted out the Geiger tube -you could hear it shorting out bzzz bzzz bzzz. I gingerly shut the thick plexiglass door and tried to never go into that abandoned lab again.

 

My experience wasn’t particularly dangerous or weird, but it was from a bygone era. I mean, pretty much everyone in that lab (including me at the time) smoked. In the lab. Next to the mercury diffusion pumps and poisonous shit. By the time I arrived at LBNL, a mere year or two later, I was doing nonsense like attending weekly safety circle, and signing up for  classes on how to safely use the sonicator and a beaker of acetone for cleaning UHV parts. LBNL had plenty of dangerous stuff around, and jerks would regularly create dangerous conditions; mostly because they were visitors and tragedy of the commons, so it was probably necessary. It felt oppressive though. You could tell it wasn’t always thus; I distinctly remember a photo of someone (probably Owen Chamberlain, though somehow I remember Segre or Luis Alvarez) smoking a pipe next to 1000 gallons of liquid hydrogen bubble chamber.

 

not the photo, but like it

I don’t know if there are lessons to be learned here. The project fizzled out a few months after I joined it because the Clinton administration were weasels who preferred to spend the “peace dividend” putting factory workers in prison while they outsourced the industrial base to China. Maybe the way we used to do things was ridiculously super dangerous and we’re all lucky to be alive. Maybe it is OK to play fast and loose with safety, because frankly time is more precious than a 2% higher probability of dying prematurely. All I know was it was fun living like this, just like it was more fun riding a bicycle before they made you wear a helmet.  The attitude was healthy, even if the environment objectively wasn’t. I am pretty sure people routinely do vastly more dangerous things in unsavory hobbies. I’ll probably never do experimental physics again; if I do it will be at least this ridiculously awesome.

12 Responses

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  1. Michel Dyakonov said, on March 26, 2019 at 10:59 am

    Scott, it was a joy to read this and plunge into the old time atmosphere of a lab! Although I became a theorist, I started by doing all kind of radio-technical stuff in high school, and later I have always enjoyed visiting labs and checking how the equations work in the real world of liquid Helium etc. I noticed the Russian term на коленки in your text, which is very familiar to me. However, it should be на коленкe (коленки is plural, it is legitimate to use plural, but then it should be на коленкax). Best wishes to you!

    • Scott Locklin said, on March 26, 2019 at 4:53 pm

      Thanks for the kind words and grammar correction; some day I will learn the vodka runes for real.
      Wish more theorists would work with experimentalists like you do; that’s where the magic happens.

  2. pindash91 said, on March 26, 2019 at 11:17 am

    Amazing! I had been wondering for a few years if you could combine quantum physics with chaos theory, specifically chaos theory suggests an extreme sensitivity to initial conditions and quantum uncertainty squishes the world down past a certain decimal place. Could you run a classically chaotic system for long enough to uncover what the underlying system looked like with more precision or is the point that the quantum effects interfere with the classical chaotic system?

    • Scott Locklin said, on March 26, 2019 at 4:57 pm

      Quantum smears out all the interesting fuzzy chaotic bits.
      I thought it was a big deal back in the day; how does this chaos arise? I still think it’s interesting, but not as fundamental as I thought. It has implications and should probably be taught as part of the regular curriculum, but physics is taking a long nap, so I doubt it will happen any time soon.

  3. Toddy Cat said, on March 27, 2019 at 9:55 pm

    A nice reminiscence from the days when we actually got things done.

  4. Quijibo said, on March 29, 2019 at 7:05 pm

    What do you think of the ER = EPR idea? Is this just wanking?

  5. Walt said, on March 30, 2019 at 2:42 am

    Scott,

    You look like you were deadlifting 500 lbs back in the day.

    • Scott Locklin said, on March 30, 2019 at 4:27 pm

      I didn’t start deadlifting until 10 years after this photo was taken. Healthy eating and left over kick boxing/karate physique from when I was a teenager.

  6. Senor DingDong said, on May 9, 2019 at 2:49 pm

    Are you Jewish at all? Not taking the piss, just asking.

  7. Cameron said, on May 16, 2019 at 3:52 am

    Here’s to hoping you post again soon, Scott. If you haven’t read this already, I think you’d enjoy it: http://nautil.us/issue/47/consciousness/the-kekul-problem

    Cameron Braun

  8. Jake Bowyer said, on October 14, 2019 at 2:16 am

    Mr. Locklin. Just wanted to say that you are one of my favorite writers. Been consuming your stuff since the glory days of Taki, 2009-2012. You were big inspiration in getting me writing. Thank you.

  9. Vince B Ho said, on February 18, 2020 at 12:40 pm

    Funny you used to ask me about mechanical watches and even attempted to get yourself into it. I was impressed. Mechanic watches are essentially obsolete when the tuning fork watches appeared on the market, then the quartz revolution, finally the kinetic watch which nail the mechanical watches’ coffin. Nowadays very few mechanical horological items are used for practical reasons. Usually they are used for military reasons so that they are always reliable despite magnetic problem or change. This applies to the Deck Watch of a ship jet fighter pilot’s wristwatch, etc.
    Wristwatch is not just about taste, nor even status symbols, they are subtle representation of what type and class the owner is. Rolex usually means “I made it!”, Patek Philippe means “I am a CEO”. Vacheron Constantin means “I am old money”, Jaegar Le Coultre means “I am a smart woman with class and taste”, and finally Breguet means “I am unique”.


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