Tip:
Highlight text to annotate it
X
Good morning and welcome to a virtual field trip of Jefferson Lab.
Today we're going to be showing you briefly how experiments are run here at the Lab.
My name is Joanna.
And I'm Steve.
And joining us today we have James Hillhouse High School in New Haven, Connecticut.
[Steve] Whoops! Wrong school! Sorry!
[Steve] There you are!
[Joanna] Hi and welcome!
[Joanna] And we also have the Governor's School of Southside Virginia,
located in Keysville, Virginia.
[Joanna] Hi and welcome! Thank you for joining us!
[Steve] Morning, guys!
[Students] (Indistinct noises of greetings)
[Joanna] I'd also briefly like to introduce our speakers.
[Joanna] We have Mike Epps, who is the Federal Project Director of the 12 GeV CEBAF Upgrade.
Good morning!
[Joanna] And we have David Lawrence, who is a staff physicist located in Hall D,
our newest experimental hall.
Hi!
[Steve] Hi, Dave!
[Joanna] And then we have Sandy Philpott, who is the Operating Manager for Scientific Computing.
Hello!
All right!
Now, before we begin, I would like to encourage you all to ask questions.
We're going to have a question and answer time after each speaker
and then, once again, at the very end.
And, for those of you who are joining us, who are watching us live,
you can also post questions to our Google+ Events Page or our YouTube page.
So, the first question we need to answer today is "What is Jefferson Lab?"
Now, if you are familiar with our YouTube page, you may think Jefferson Lab
is a place where Joanna and I take liquid nitrogen and throw it around and freeze things.
And, while it would be interesting if there were a lab that were dedicated
to that sort of purpose, that's not what Jefferson Lab is all about.
What Jefferson Lab is is a Department of Energy basic physics research facility.
And, it's our job to study particles called quarks and gluons which are inside of atoms.
That's actually not quite true.
Quarks and gluons actually get together to make other particles.
The ones you are probably most familiar with are protons and neutrons.
So, sense of scale...
A proton, if it were the size of my fist, the atom would be a couple of miles across.
The quarks within the protons and neutrons, if you make them the size of your fist,
the atom would then need to be about the size of the earth.
And that's what we study here at our lab.
Now, of course, these things are too small to see with your eye.
And, traditionally, you would think "Okay, small thing. I want to use a microscope or a magnifying glass."
That's not what we use here.
At our lab, we use a machine called an accelerator to study the quarks within the protons and neutrons.
And in our accelerator is Mike and he's going to tell us all about the accelerator.
[Steve] Take it away, Mike!
[Steve] We don't have good audio on you, Mike.
There!
[Steve] There we go!
Thanks!
My name is Mike Epps and I'm a physicist with the U.S. Department of Energy.
I'm currently the Federal Project Director for our 12 GeV CEBAF upgrade.
Before coming to DOE, I worked for about 12 years in the Accelerator Operations Department here at Jefferson Lab.
I'm currently standing about 25 feet underground in the main accelerator tunnel for our CEBAF machine.
CEBAF stands for Continuous Electron Beam Accelerator Facility.
It's a particle accelerator where we use electrons and accelerate them into fixed targets
in one of several nuclear physics end stations.
So, before we talk about that with one of our later speakers, let's talk about how this accelerator works.
Since electrons are negatively charged, they would interact with molecules in the air,
so, as you can see, we have multiple beam lines here, where the electron beam travels.
We can recirculate beam up to five times, with the lower energy beam being in the top
and the higher in the lower passes, and send them into one of four experimental end stations.
You'll also see large blue, and smaller red, structures on the beam line.
These are magnets.
Because electrons are negatively charged, so they would tend to repel each other,
we keep them controlled by using dipoles and/or quadrapoles to steer and focus the beam,
the same way you would use lenses and mirrors to steer and focus a beam of light.
We're in an active work zone, so we're going to allow some of our workers to pass.
As was mentioned earlier, the accelerator is racetrack-shaped,
which means we can send the beam around up to five and a half times,
coming out of our 180 degree arcs.
If we can pan down into the straight section...
this is where we actually do all of our beam acceleration.
It's called a LINAC, which is 'Linear Accelerator,' and in the straight portions,
on either side of our racetrack, we have the structures that we accelerate beam with.
They are 5- or 7-cell accelerating cavities.
We keep them in a large thermos bottle-type apparatus that's referred to as a cryomodule.
They have the property of being superconducting,
which allows them to lose all resistance at super-low temperatures.
So, our nominal operating temperature here at CEBAF is about 2 degrees above absolute zero.
Using these structures, we have over 330 accelerating cavities,
we can increase beam energy using electric fields up to 12 billion electron volts.
CEBAF is unique because it's the first large scale application of SRF,
or superconducting radio frequency technology, in the world.
At this point, if there are questions from the field, I'd be happy to field them.
[Steve] We do have one question.
[Steve] We're wondering why we have more than one level of magnet behind you.
I'm sorry, Steve. You said "Why do we have more than one...?"
[Steve] Yes, why there's separate sized magnets on the arcs.
So, the electron beam, as the energy increases,
you need more and more magnetic field to bend and steer and focus.
So, you'll see that, on the higher beam passes, where the energy is lower,
we have smaller magnets because we need a smaller field.
As you come down, you need larger and more magnets because the energy of the electron is higher.
[Steve] Great! And the Governor's School has a question as well.
[Steve] So, Governor's School, don't forget to take yourself off of mute.
Hey, so, you talked about you could run the electron beam, on average, like, five times around the track.
What limits the number times you can run the electron beam around the track?
You said, "How many times?"
[Steve] What limits.
So this is a... Unlike a storage ring, where you have countless times that you go around,
and you peel off chunks of electrons as you need them, this is a continuous beam.
So, once we go five and a half times around, we take the remaining electrons
and they're sent into a beam dump, for storage purposes.
So, this is not a continuous storage ring, but a recirculating LINAC.
[Steve] And, since every time you go around, you pick up more energy,
[Steve] you need different size magnets, so you need additional arcs for every trip around.
That's correct.
Until we get to our maximum energy at five and a half... uh, 12 billion electron volts.
[Steve] We also have another question.
[Steve] You said that the nominal temperature is about 2 Kelvin. What makes it that cold?
So, we use liquid helium here to maintain our cryogenic temperatures.
At any point, we have more liquid helium on-site than anywhere else on the planet.
[Steve] Cool! And, you also said you're underground. Why is that?
Underground gives us natural shielding from the earth above us.
We also have a tunnel made out of concrete.
It's about 13 feet across, 10 feet high and our walls are about 2 feet thick.
[Steve] Cool! Do we have any other questions from the schools?
[Steve] And, if not...
[Joanna] Alright! So, that has been a look at our accelerator.
And, as Steve and Mike had mentioned, it's a tool which scientists use,
but the actual experiments take place in our experimental halls.
So, now we're going to head over to Dave who is in Hall D,
one of our four experimental halls, to tell more about that.
[Joanna] Here's to you, Dave.
[Steve] Dave, you're on mute.
Okay, now can you hear me?
[Steve] Yes, we can.
Okay. Thanks, Joanna.
So, yeah, I'm over here in Hall D.
It's the newest experimental hall.
And this is the one where we are building an experiment to look for exotic hybrid mesons,
and I'll tell you what they are in just a second.
But, as Mike said, the accelerator's job is to produce this high energy electron beam,
and then they send it into the experimental hall and we use that to do experiments.
In this particular hall, we first create a secondary beam of high energy photons,
photons are just particles of light, and that's what we use for the experiments in Hall D.
The photons are going to come from very close to the viewpoint you're seeing right now from the camera.
It's actually set-up right near the beam line.
There's no beam on now. No beam has come into Hall D yet.
But it will come down in this direction and go into the center of that big red thing behind me.
If you can see that, that's a huge, superconducting, solenoidal magnet.
So, it's also kept at very low, cool temperatures in order to be superconducting
so we can run lots of current through it and create a very intense magnetic field.
So, we use that magnetic field because when the photons go in, we shoot them into a liquid hydrogen target.
Hydrogen has a single proton as its nucleus and so the reaction we're actually looking at
is a high energy photon interacting with a single proton.
And it will do a lot of different things, but there's a spray of particles that will come out,
that get created, and we want to look at the properties of those particles.
Some of the particles that get created, we believe, will be of this form, the exotic hybrid mesons.
And, without going into a lot of detail, if you know that, as Steve mentioned,
protons and neutrons have three quarks in them.
You can also make simpler structures, which are two quark structures,
actually a quark and an anti-quark, called mesons.
And, it's possible, we believe, and we have theory to back this up,
that you can create this in such a way that the glue that holds together these quarks can be excited.
It can be excited in a way, the best way to visualize it is like a jump rope spinning around.
And that glue then starts to contribute, because it's carrying some energy,
it starts to contribute to the properties of that particle.
Okay, this is kind of a different state of matter, has not really been seen,
but, if we see this and start mapping out the property and spectrum of these particles,
it tells us something about that glue that holds these together.
And that's what's really fascinating for us, because that is the same glue
that's holding together protons and neutrons and, therefore,
most of the matter in the universe is being held together by this strong force.
Okay, so, once we create one of these things, it actually does not live very long.
It only lives about 10 to the minus 20th seconds.
And then it decays into some other particles, which also live a very short time, and they decay.
And, after a couple of generations of this, you end up with four, five, six particles
in your final state, and we have detectors surrounding this target
that will see these things come flying out.
The magnetic field is used because the charged particles will, just as they do in the accelerator,
will curve or bend inside of that magnetic field.
And we can measure along the trajectory of that particle and see
what the curvature of that is and that tells you what the momentum of the particle is.
We also have other detectors.
Right now, we haven't go them all installed.
There's only one installed inside the magnet.
But if you see that black ring in the middle of the big red magnet,
that's the first detector installed inside the magnet.
And that's a calorimeter.
And it's job is to actually measure the energy of photons.
Photons are not bent in the magnetic field and, once they interact,
they kind of shower into many different particles and eventually get absorbed
and we have detectors that are very sensitive to those amounts of energy, that we can read out.
Okay, so, once the detectors that are in there, we have many more that will actually fill
that entire space inside there, and some downstream that you can't see from here,
once that we have read out the events into our electronics, we have a high speed trigger,
it's actually the electronics that will decide whether or not to record the event, if it's interesting.
When we're running at high luminosity, we're going to be having interactions at about 400,000 times a second.
And, our high speed trigger is going to cut away about half of those,
so that we only have about 200,000 events per second
that we will read out into lots of electronics.
And they'll be stored in racks like, if you can see black racks behind me,
they don't have the electronics in them yet, but we will have racks,
several sets of racks like this throughout the hall,
that will have digitizing electronics that will be able to take very small digital,
or very small electronic signals, make numbers out of them
that we can send over a network and store on a computer somewhere.
When we're running at high speed and high luminosity, we will be reading about
3 gigabytes a second off of our front end.
And we will send that upstairs to a small computer farm
that will then make a quick decision and throw away about 90 percent
of those events and keep the 10 percent that we actually think have something in it
and so we'll be writing about 300 megabytes a second to a disk there
and eventually then we will copy that through some fiber optic
over to the Computer Center where they will take care of it
for us until we get to the point of analysis on it.
The whole thing takes, as far as the experiment, how long it takes to do this...
The original discussions on this experiment, the GlueX experiment,
were done in 1998, I think they had their first meeting.
And, so, we're not actually going to be taking data till next year.
So, this is one of the longer term type experiments because it's large.
It requires not just building this hall, I mean, it's a facility upgrade.
We had to upgrade the energy of the accelerator, build a new experimental hall, outfit it with detectors.
A typical experiment that might come in that uses existing equipment in the existing accelerator
will still take 5 to 6 years to actually propose, put together,
go on the floor and then analyze the data and finally punish - publish a result.
Hopefully not punish the result.
But publish the result.
So, that's about the gist of what I have to say.
[Joanna] Alright! We actually have a question from our Google+ Events Page.
[Joanna] What do the research results indicate so far and how do experiments help us understand our world?
[Steve] And, we do understand that Hall D hasn't run any experiments, yet.
[Steve] But, if you could talk to the previous work you did in Hall B.
Ah! Okay, well... So, yeah, so, Hall D hasn't taken any data yet, and we won't for a little while.
There have been plenty of experiments, many, many experiments, actually, run here at Jefferson Lab.
I've been involved in a couple of them in one of the other experimental halls, as Steve mentioned.
One of them, I guess, more recently, I was involved with the PrimEx experiment,
which is looking for neutral pion production through the Primakoff Effect.
But, the main thing there is that that one had a very fundamental prediction from a theory.
And this is what, kind of the gist of all these experiments are.
We want to try to have a model or a theory on how these things work at a very low level.
And we make predictions and then we try to do experiments that will help prove or disprove that prediction.
Or, at least support that prediction from the theory.
And, so then, as you do these experiments, you start refining the theory,
because sometimes there are variables that go into the theory that are not very well known.
They're kind of coming from other experiments or other calculations.
And, so, these get refined over time.
So, in that particular experiment, it was a very precise experiment.
It was measuring the neutral decay width of the pi-zero through this Primakoff Effect
more precisely than it has ever been done before.
It was actually consistent with the theory that had predicted it,
which is actually very good, because it allows, it did actually allow the theorists
to kind of move forward, then, on trying to refine it to predict even other effects.
As far as just generally, the type of things we do here,
you might ask "Why do the GlueX experiment? What is important about it?"
This is basic research.
And, so, it's adding to the basic knowledge of mankind, about how things in our world and universe work.
One of the big questions that we actually have in nuclear physics right now is called the question of confinement.
Which means, when you have quarks, they can never be alone.
They always have to be with other quarks.
And the reason for that is the glue that holds them together.
If you start trying to pull it apart, you're putting energy in that glue and eventually that glue pops.
It breaks, if you think like a rubber band.
When it does that, it creates two new quarks and you're still stuck with quarks connected to quarks.
We want to understand the nature of that. Why is that?
And you have to do experiments about the glue that holds things together
to understand why these properties exist.
[Joanna] And new we have a question from the Governor's School.
I was just wondering, I know the Mike Epps talked about how the electrons went through about five and a half laps.
I was just wondering if that hall was kind of part of those laps.
If it went though that magnet and then came back out and then went around the laps again.
No, once it comes out of the accelerator, the beam is out of the accelerator.
It goes in a straight line.
They stop bending it and they send it in a straight line to us in the end stations.
And it goes through this and there's actually, on the other side of this thing,
in the wall, there's a small pipe that the beam will go into, that we call the beam dump.
And there's a bunch of earth piled up on...
This building is actually half underground.
And, so, it really is underground.
The beam is still underground at that point.
And it gets dumped into the earth and it dissipates the energy at that point.
[Steve] We're also wondering how big the detector is.
Well, if you can see, fortunately, there's a guy right over there now.
If you took out that black part in the middle of the big red magnet,
I could stand in there and it would be just about -
I'd be standing up and it would be just about at the top of my head.
So, it's about a six foot diameter magnet there.
So, from that, maybe you get a sense of the scale.
Downstream of that we have another calorimeter that's actually about almost as big
as the red part here because as photons go out, they'll spread out at an angle
downstream and we want to capture all of those.
[Steve] And when you're running experiments, are you in there watching it, or how does that work?
Ah, that's a good question.
The radiation environment in the hall -
Because, when the beam comes in and all these reactions are taking place,
you have lots of high energy particles flying around everywhere,
so there's a high radiation environment down here.
So, we cannot be in the hall while the experiment is running.
We have to control it from another room that's upstairs.
We call that the counting house because we're counting how many times certain things happen.
They have a very elaborate system, well, it's kind of elaborate,
but a system of double doors that are locked.
And, the accelerator actually controls that remotely with magnetic locks
to allow us in and make sure that we have training for radiation -
That we know to operate in a radiation environment and oxygen deficiency hazards and things like that.
When you do come in, if the beam is in -
If we're in operation where the beam could go on, everybody gets a key
from this little key thing that you put in your pocket and it's physically impossible
for them to turn on the beam as long as you have that key.
So, it's your kind of safety net to make sure they can't turn it on while you're in here,
until you go out and put the key back in.
[Joanna] Alright! Thanks for those great questions.
So, when I was in school, the -
We're getting a little bit of feedback from someone.
Not sure where that's coming from.
There we go!
I always liked doing the experiments.
So, it was always fun doing the experiments and, at least for me,
collecting the data and getting the apparatus to work.
What wasn't as fun, at least for me, personally was,
once you have the data, actually doing something with it.
Which, unfortunately, is actually -
The point of doing the experiment isn't to have fun doing the experiment,
is actually to learn from it.
And it would be insane for us to work through this stuff by hand.
Even if you have a room full of graduate students and an unlimited supply of pizza,
it's just not going to happen.
So, computers, right?
You have computers to crunch numbers for you and, in our Computer Center,
happily, we have Sandy, who's going to tell us all about computers at the Lab.
[Steve] Sandy!
So, hi everyone!
I'm Sandy Philpott and I'm the Scientific Computing Operations Manager here at Jefferson Lab.
It's my job to make sure that all the computers you see in this room
are up and running and are available to the scientists to actually analyze the data they took.
So, I'm standing in a room called the Computing and Data Facility.
We're about a half a mile away from the underground accelerator and experimental halls that you saw earlier.
We're in an office building on the bottom floor, so we're above ground,
but we do have a climate controlled room with locks
so that people can't just walk in and start using our computers.
We have a raised floor so that we can run cables underneath and all the connections we need.
We keep the room cold because, as you can imagine,
a room full of over a thousand computers that we have, can get very hot.
So, how are we connected?
David said that they have the counting room where they collect all of their data
and they only have a small amount of storage space there.
We take all of that data and ship it across the network to the computing facility here,
where the first thing we do is make sure we store it on tape.
It's very, very important that we don't lose any of the data that came off of the accelerator,
because that's what the scientists use to analyze their experiment.
So...
We have about 10,000 tapes now.
This is just a small tape cartridge.
We have about 10,000 of these that are storing data
that we've collected since the experiments have started running, back in the mid 90's.
So, the first thing that we have to make sure we do is write the data they collected onto tape.
And, it's actually so important that we write it onto two tapes
because we can't afford to lose the scientific data.
We take one copy and actually remove it from our tape library and store it in a room across the hall.
It's fireproof.
It's called our tape vault.
And, that way, we're always sure we have a copy of all the experimental data
that's been taken in the experimental halls by the scientists over the years.
So, right now, we have 10,000 of these tapes.
It's not an electron beam accelerator.
They're in a robotic tape library.
Now, how do we keep track of them all?
If you can see, they're bar coded.
So, if you can see the bar code on here, each tape has it's own bar code.
The tape robot knows how to go read these bar codes.
We keep all the data in a database so when a physicist asks for their data,
we say "Ah! That data's on tape number 600076."
We go tell the robot to get that tape and stick it into one of 14 tape drives that we have.
So, first and foremost, save the data.
Now, what do we do with all that data?
We have over 1,000 computers in the room.
I'm responsible for making sure they're all up, running, talking to each other on the network,
the software is up to date, the old computers go out, the new computers come in.
We get what we call a cluster, or a group of computers, sometimes once a year,
sometimes in funding years where the money's tighter, we don't.
So, we currently, out of these thousand computers, have 8 clusters that have different functionality.
or expect, what they think might happen and compare the simulated data
The main cluster for the experimental physicist are analyzing data,
so the physicist have special software that knows how to look at the events they captured,
to be able to take a look into that data and see what happened when they ran their experiment.
The other clusters are actually for our theoretical physicists.
So, in those clusters, scientists can actually run simulations and help predict,
to the actual data that they collected from the accelerator.
One really cool thing about our clusters is that we have our own accelerators.
It's a computing accelerator.
And, if you look closely, some of you may recognize this, for all of you video gamers out there.
We actually use graphics cards and the processors inside them -
Which, this one's not open.
This is an older model because all of our newest models are hard at work doing computation.
But, the processors inside these graphics cards are really good number crunchers.
And, just like they crunch numbers for you guys to do your video games,
our scientists can write code to program these graphics cards
to crunch the numbers they need for their simulations.
So, we think it's pretty cool that we have our own accelerators.
And, actually, with our newest cluster this year, and our newest graphics cards,
we were able to make the cluster look like one big supercomputer.
It was actually only 40 machines, each one with 4 graphics cards.
So, with that cluster, we were able to make it onto the top 500 supercomputing list.
So, we are probably the cheapest, or least expensive, cluster on that supercomputing list
because we're able to do our calculations on these really fast, graphics number crunchers.
We came in at number 363.
So, my background is in computer science.
I've been here at Jefferson Lab since before we had this big room full of computers.
And, over the years, I've watched the halls come on-line, taking the data, written it to tape,
stored it in the tape library, and managed these clusters of computers you see in the room
to help the physicists analyze and simulate their data to further science.
That's it in a nutshell.
[Steve] Great! So, you mentioned that the supercomputer is one of the least expensive supercomputers.
[Steve] How least expensive is it?
So, to make it onto number 363 out of 500, we did this for much less than a million dollars.
That might sound like a lot to you guys, but supercomputers themselves,
big machines, can cost tens and hundreds of millions of dollars, and more.
The key is that our scientists can use each individual machine to do a small job,
or, as I said, we can make the cluster act like one big machine,
one big supercomputer, and just run a single job.
So, we have a lot of flexibility in the way that the scientists are able
to use these calculators to be able to analyze their work.
[Steve] And, we were also wondering, if you happen to know,
[Steve] roughly how many computers you actually have in there.
We have over 1,000 computers grouped together in 7 or 8 different clusters, depending on how you count them.
But, each computer has anywhere from one to eight to up to thirty-two cores right now.
So, that, plus the graphics processors, which have hundreds of cores,
give us a lot of compute power in a small amount of space.
The room is actually outfitted so that we can add more computers but,
as it turns out, computers are getting smaller and smaller and smaller.
So, the more compute power we have, typically the smaller it gets.
Some of our racks aren't even full all the way to the top.
So, there's plenty of room to expand.
But, actually, computers are getting smaller each time we go out for a new procurement.
[Steve] So, when I use my laptop at home, I feel the heat on my lap.
[Steve] I notice you're wearing a sweater.
[Steve] If you're in there with a thousand computers, shouldn't it be, like, blazing hot in there?
Well, actually, we have to work with our Facilities Management group here at Jefferson Lab
to make sure the room stays cold enough.
There's actually chilled water around the site and some of that chilled water is pumped into this room.
You can imagine that if I go stand in the back of one of these racks,
that I'll have to take my sweater off soon because it gets upwards
of 80 or 90 degrees behind the racks.
And, so, we align the racks in hot and cold aisles.
We force cold air up through the floors through tiles that have holes in them
and then the computers get all the cold air, pump it out the back as they compute,
and it feeds into air conditioners behind the racks, which then recirculate,
make it cold, and keep things flowing.
So, it's very important that we work with the Facilities group to not only keep the room cold,
but to make sure we have enough power to run these machines.
We consume about a half a megawatt of power when we're running all these.
So, sometimes even in the summer, we've been asked to please shut our computing down
so that people at home can run their air conditioners and office space.
[Joanna] Great! Thank you so much!
So we can generate a lot of heat as these jobs run.
[Joanna] And Sandy, we received another question from our Google+ page.
[Joanna] "How long does the typical computing task take? Does it take minutes, hours, days?"
Well, we actually have the scientists break the jobs up so that they can run
in a matter of hours or days because there are certainly interruptions to the room,
like when we have to shut down the power or coolant.
So, while it may take months to analyze the data from one experiment,
the scientists break it down into manageable jobs that can run for typically eight hours a day,
and then they assimilate all the results and the end so that they're not having to make sure
the computers stay up for six months at a time to analyze their data with no interruption.
And they're very good about breaking their jobs up to be able to do that.
Thank you!
So this has been a cursory overview at how experiments are run here at the Lab.
In actuality, there's so many other groups and divisions that are involved to conduct an experiment.
When Steve and I do an experiment for the YouTube channel, it might take 5 or 10 minutes.
But, here at the Lab, it can take 5 to 10 years from the time a proposal
is approved to the time that results are published,
just to give you an idea of the scope or the magnitude of the experiments here at the Lab.
We'll have a general question period right now.
Again, the schools who are with us, again, if you actually do have a question,
please let us know through the group chat on the side.
But we do have a question for Dave, actually, so I'm hoping Dave is still out there and can still hear me.
[Steve] You had mentioned, well, Mike had mentioned that our accelerator accelerates electrons,
[Steve] but in your hall, you get photons.
[Steve] So, how does an electron accelerator that accelerates electrons shoot photons into your hall?
Ah, I'm glad you asked that.
There may be some background noise because there's a lot of work going in the hall here.
Hopefully, you can still here me.
Actually, there's about -
80 meters upstream, we'll have a thing called our photon tagger.
And, there we have a very thin diamond.
And, if you pass a charged particle through a material, as it comes close to a nucleus,
there's a chance that it can do a thing called Bremsstrahlung, which means 'breaking radiation.'
It's a German word.
That means it can emit a photon.
Then the electron is left with a little less energy and the photon goes basically straight forward.
We use a diamond, a thin diamond, because then we can do a thing called coherent Bremsstrahlung,
which gives a little enhancement in the energy.
Unfortunately, this Bremsstrahlung mechanism will create a lot of low energy photons
and very few high energy photons.
We really want just the high energy photons.
So by having it as a diamond crystal instead of just some plain material,
then we can get this enhancement in the energy, which we have it set-up on a very sensitive
tuning mechanism which just turns the angle.
And you turn that angle relative to the beam coming in, the electron beam coming in,
and you'll adjust where the energy peak is.
That's why it's so far away, actually, because then the guys that are really high energy
go straight down the beam line and the guys that, maybe less energy, energetic photons, will go wider.
And we have a, what we call a collimator, which is a big block of lead with a small hole in it.
It blocks everything except for what's going down the middle.
So, basically, just pass it through some material and you can create a photon that way.
[Steve] Very good. We also have a question for Sandy coming from Hillhouse.
[Sandy] Ask away.
[Steve] They're approaching the camera now.
My dad's a software engineer and he works at AT&T and I just wanted to know that,
I know sometimes when you have to transfer the data from one computer to another,
how do you do that, exactly?
Ah! Okay! So, I work with a lot of software engineers and developers
and we all make sure that our computers can talk to each other over our high speed network.
We have both Ethernet, which is like the kind of connection that you have maybe in your classroom or at the library,
but we also have a very high speed connection called InfiniBand
and all of our data is stored on a central file server called Lustre
and all of our computers can see the Lustre cloud system and all those files via this fast InfiniBand network.
So, for instance, when the hall takes the data, writes it up into the counting room,
we can copy it across the network using just standard copy commands.
We don't have to encrypt it.
We can just copy the data and move it across at very high speeds.
The connection between here and the counting house is 10 gigabits per second over this Ethernet fiber
And, within this room here, we have connections up to 40 and 56 gigabits per second.
So, we're able to move data around quickly by using standard Linux or Unix copy commands.
[Joanna] We have another question from the Governor's School.
My question is what kind of experiments have you guys done in the past?
[Steve] And, we'll give that to Dave.
[Steve] So, what kind of experiments were done in the past, Dave?
Well, let's see, we're got a number of them that have been done here.
I mentioned the PrimEx experiment where we were measuring the neutral decay lifetime of the pi-zero.
Also, let's see, try to think of other things that have been done in, umm...
We have this Q-weak experiment which I guess is looking for the weak charge in the nucleon.
We also have an add-on -
Another experiment that's been approved for Hall D, has not run yet,
is this one to measure the polarizability, electric, magnetic polarizabilities of the charged pion.
All of these tend to be ones that are looking at properties of nucleons
or mesons that have to do with how these things are connected together.
And that's the strong force.
In nature, there are actually, we say four, three or four fundamental forces,
depending on whether you count electric and weak force together.
But the strong force, the color force or strong force, is by far the strongest of all the forces,
much stronger than the electric force or electromagnetic force.
And that's the one that holds the protons and neutrons together.
So, we're really are focused on experiments that study excitation levels
or other properties of that glue that holds things together.
[Steve] Very good. We have a question coming in from the YouTube feed
asking how our accelerator and detectors compare to the LHC.
So, I'm hoping that Mike knows that information.
[Steve] And, you're on mute again, sir.
Hi, Steve, can you hear me?
[Steve] Yes, I can!
[Steve] So, they were wondering how the accelerator at CERN compares to the accelerator here.
So, the accelerator at CERN, the LCH, is a large hadron collider.
So, they use different particles, hadrons versus electrons here.
And, it's a collider, where you take two beams that are both moving
and you smash them together and you have your detectors in that location
to look at a shower of particles that will come out.
This is a fixed target linear accelerator, even though we're a racetrack shape,
we're linear because we do all of our acceleration in a straight part.
So, our nuclear physics targets are fixed. They don't move.
The electron beam is the thing that we accelerate and it comes in and hits the target
in a fixed location, as opposed to two beams coming together.
[Steve] And, as far as size, we're actually a much smaller accelerator.
The LHC, their track is about 27 kilometers around, ours is about 1.5 kilometers around.
[Mike] That's correct.
The energies are also much higher at the LHC.
They get up to about 4 TeV while we are around 12 GeV, once our upgrade is complete.
[Mike] We are a medium energy nuclear physics facility, that's correct.
They do high energy physics at the LHC.
[Joanna] And, Sandy, we have a question to you from YouTube.
[Joanna] What are the capacity of your tapes?
The tapes.
So, these are our newest, and they're going to hold 2.5 terabytes.
We don't have those in production, yet.
Most of the ones we're using now hold about a terabyte of data.
So, if you guys remember your bits and bytes, a bit is the very smallest piece of information.
A yes or a no. A one or a zero.
When you put those together in groups of eight, that's a byte.
A thousand bytes are a kilobyte.
A thousand kilobytes are a megabyte.
A thousand megabytes are a gigabyte.
A thousand gigabytes are a terabyte, and that's one of the tapes that we use now will hold.
And these are going to hold over twice that much.
So, we have about 10 petabytes worth of data.
A thousand terabytes is a petabyte, and we have about 10 petabytes stored on these 10,000 tapes.
[Steve] That's a lot of bytes!
That's a lot of bytes!
[Joanna] And now, we're heading over to Hillhouse.
[Joanna] You guys have a question?
My question is, why do the particles decay so fast?
[Steve] Okay, so I think, yeah, Dave had mentioned that the particles decay very quickly, the hybrid mesons.
[Steve] The question is "Why do they decay so quickly?"
Yeah, that's a good question.
I mean, it's really just, that is the scale at which things that are decaying through the strong force decay.
If you had things that are electromagnetically decaying -
So, particles can decay through these different forces of nature.
If it decays strongly, then it's about 10 to the minus 20 seconds.
If it decays electromagnetically, then it's about 10 to the minus 16 seconds.
And, things that are just weak decays will decay, even have longer decay times.
It's just the nature of the universe, I guess, is the real answer.
[Steve] And we're going back to the Governor's School for another question from them.
I know that David Lawrence was talking about quarks and mesons earlier.
I've never heard of a meson, but I've heard of quarks and leptons.
Really, what's the difference between a meson and a lepton?
Alright, so there are -
There are really two categories of fundamental particles.
Leptons, which the electrons belong to that family, are one group.
And, they're six of those. That also includes neutrinos.
There's electrons, muons, and taus and their associated neutrinos:
the electron neutrino, muon neutrino, tau neutrino.
And the other family are quarks, where we have the up, down, strange, charm, top, bottom quarks.
The quarks can combine together into these structures that are,
in fact, they have to combine together in these structures, and they can -
The type of structures have to be, without giving too much detail,
they have to be these colorless structures.
But you can, in fact, combine them into a quark and an anti-quark together to become a meson.
So, if there's really two quarks, it's a meson.
If there are three, then it's a baryon.
And three quark structures are like protons and neutrons.
[Steve] We have one more -
[Steve] wondering what your educational background is to do the job that you're doing.
[Steve] And, since we're on Dave right now, we'll stick with Dave.
Well, I went -
I'd say I grew up in Oklahoma, went to public school, and then I went to University of Oklahoma
for four years to get my Bachelor of Physics, then Arizona State University for about six years to get my Ph.D.
And then I went and did a postdoc position and there I stayed a little longer than usual,
about six years, before I got hired on as a staff member here at JLab.
[Steve] It's actually one question for all three people,
[Steve] And now we'll ask Mike the same question.
So, I grew up in Norfolk, Virginia.
I also went to public school.
I went to Norfolk State University where I got my degree, my undergraduate degree in physics.
I spent about six years in the Marine Corps.
After that I went to graduate school in Hampton University.
Then I came to work at the accelerator here.
Spent about twelve years working in accelerator operations.
And I spent the last four and a half years with the Department of Energy.
[Steve] And, to Sandy.
I also grew up in Norfolk and went to public school.
I left there and went to Virginia Tech. I'm a Hokie!
And, I got a Bachelor of Science degree in computer science.
I first started working in the area at Newport News Shipbuilding in their telecommunications department
and I kept hearing about this really cool place up the road that they were building, and it was called CEBAF.
And, I thought, "What is that?"
And, after quite a long time, I've been here -
I've been here half my life now, actually.
Now we're going to go over to Hillhouse, where we have a question?
My question, David?
My question is for David and I want to know why do you want high energy protons instead of low energy protons?
Yeah, that's a good question.
Well, the fact is that certain reactions won't happen -
You need -
We actually need the more energetic accelerator even to create these exotic hybrid mesons
we're trying to look for in Hall D.
Which is why Hall D was kind of motivated, or helped strongly motivate,
the upgrade of this accelerator to double its energy.
If you don't have enough energy, then you just don't have enough to create the particle.
You guys may have heard of this famous Einstein equation: E = mc^2.
The 'E' is energy and the 'm' is mass.
And the mass of the particle then dictates how much energy you need in order to create it,
because it's being created just out of the energy that's in the photon
when it comes and interacts with this proton which is essentially sitting still in the target.
The proton's basically just sitting there waiting for something to happen.
So, higher energy photons will allow you to create certain things and look at different things.
The question actually came up earlier about how are we different from LHC.
It's really kind of a matter of what type of microscope you have, what is the focus,
or the focal length of that microscope.
Somebody looking at a microscope, it's a very similar device as looking at a telescope in space,
but they are very different ranges, or scales, of the things you're trying to look at.
In order to look at the things at the scale that we want, we need photons of this energy.
[Steve] And we're going to take one, final question from the Governor's School.
Go Hokies!
I just wanted to ask, do y'all, by chance, have a picture, or a computer picture,
of what, exactly, is happening during all of these things, exactly?
I'd just really like to see an image of, possibly, the thing.
[Steve] Who wants that one?
[Dave] I'll take it.
I was just going to say, okay, so you can't actually see it, like -
The particles are so small, and because of the nature of how they interact with things,
we can't really see them with like a photograph.
What we do is, we do a lot of simulations and we render pictures, kind of a "What's happening in there?"
The whole point of the detector is to try to give us some detectionability
of these tiny little particles, which don't interact very much along the way.
Actually, the more you interact with them, the more you change their properties,
so you try to build a detector that's actually very thin and doesn't allow them to react much.
And you reconstruct, or redraw, the picture based on that little bit of information
you get from them as they pass through your detector on their way out.
So, it's not really possible to take a picture of the actual small interaction taking place.
We can only draw those.
Kind of CGI of something.
Alright! So, those have been some really great questions! Thank you!
If you have any additional questions, or if you think of some later,
this video is going to be posted on our YouTube page where you can
post any comments or ask any additional questions.
Before we sign out, a few housekeeping items.
This was a virtual field trip, but you can come here for real and actually walk around our accelerator.
You can't do it, like, at the drop of a hat.
But we do, roughly every two years, have an Open House.
The next one, we hope, will be in Spring of 2014.
Check our various social media outlets to see announcements about that.
Don't forget YouTube!
Right? Watch us on Frostbite Theater then you will again begin to believe
that Jefferson Lab is just a place where we throw liquid nitrogen around.
But, even though, now you've learned that it's far more than that.
Be on the lookout, also, for other Hangouts from other Department of Energy labs.
We're just one of the labs in the Department of Energy complex
and there are plans for other Hangouts at other labs.
We're more of a single purpose lab.
Other labs do a multitude of things so you can learn lots more,
in addition to what we've learned here, at those labs.
Again, be on the lookout of announcements for that.
I'd like to thank our schools for participating today.
Thank you to the James Hillhouse and the Governor's School of Southside Virginia
for taking time out of your schedule to join us.
Give yourselves a hand!
I'd like to thank Mike, Dave and Sandy for taking time out of their workday
and coming here early to do this event with us. Give them a hand!
I'd like to thank, also, the folks behind the scenes.
We have people roaming around here making sure our lights don't turn of by accident and fielding us -
Looking for the questions that come on-line.
And, thank you to everyone who is watching us on-line, for making this a very fun event for us to do!
Thank you so much!
Bye!
Bye!
(Chorus of byes)