- Physics world. - Hello and welcome to the
Physics World Weekly Podcast. I'm Hammi Johnston. In this episode, I'm in conversation with an accelerator
engineer who's written a fascinating book that
describes how the cryogenic superpowers of super fluid
helium have made possible some of the most important scientific
discoveries in physics. But first, a word from our sponsor. We'd like to thank Pfeiffer Vacuum for sponsoring this podcast. The company is one of the
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precisely tailored to the needs of scientists and customers. Find out more@pfeiffervacuum.com. The effects of quantum
mechanics are all around us, but the quantum properties of matter are generally only apparent at the microscopic level. Super fluidity is an exception, and some of its bizarre
characteristics can be seen with the naked eye. What's more super fluids
have found several important applications in science and technology, and are used in multi
ton quantities today. To talk about super fluids,
I'm joined down the line by John Wisened, who is senior accelerator
engineer at the European Inspiration Source, an adjunct professor at
Lund University in Sweden. He's a specialist in
cryogenic engineering, and I've just read his
new book, super Fluid, how a Quantum Fluid
Revolutionized Modern Science. Hi, John, welcome to the podcast. - Hi, Hamish. Thank you for
having me. I'm glad to be here - And and congratulations on your book. Uh, John, I really enjoyed it, um, and I've also, uh, reviewed
it, uh, for Physics world and at the end of the podcast,
I'll, uh, I'll tell people where they can read that review, but yeah, I, I I thought
it was a fascinating book. Uh, so yeah, thanks for writing it. Very - Happy to hear that. - So, um, as you do in
the book, John, can, can you start off with a,
a, a simple description of what a super fluid is. - So the, the material that I talk about in the
book is super fluid helium and super fluid helium, or as it's sometimes called helium two is the second liquid phase of helium. So if you take, uh, helium gas
and you cool it to 4.2 kelvin and atmospheric pressure,
it becomes a liquid. If you further cool it down to 2.2 kelvin and below, it has a second liquid phase. This is known as helium two. And while helium one, the,
the first liquid phase behaves like a standard fluid and is, it doesn't really
have any unusual properties. The second liquid phase, helium two or superfluid helium does have
very interesting properties among which are, uh, the ability
to flow through small holes without any pressure drop and, and exhibiting what we
call zero viscosity. So that, uh, is what's
known as supra fluidity, and thus we call this
this second liquid phase of helium two, uh, superfluid helium. Um, it's a, uh, it has other properties that is a very efficient,
uh, heat transfer mechanism that's not seen anywhere
else in the universe. Uh, it, uh, has things called
quantized vortices in it that explain rotation and, and potentially, uh, useful
model for turbulence. It would only be
interesting scientifically, but as it turns out, uh,
the properties of SLU helium have very important and useful, uh, technical applications
principally in the cooling of superconducting magnets,
superconducting RF cavities, and, uh, infrared astronomy. And so because of these
practical applications, it's widely used, uh, in
the scientific world, uh, and is responsible for some of the largest scientific instruments currently in existence. - And, and John, in your book, you, you talk about something
called the two Fluid Model of Helium two. And, and, and that was
something I, I suppose that as a condensed matter
physicist really intrigued me. It's, um, it it provides a very useful way of understanding some of these
very useful properties of, of the super fluid. Can can you describe this model? - Sure. Uh, the, the physics or the quantum physics behind
the existence of Helium two or superfluid helium is
that a certain fraction of the atoms in the helium
have undergone something known as Bose Einstein condensation. They've condensed down to
the ground state of the, of the ground quantum state. And this means that the, um, those atoms or that fraction of
the helium are the ones that are zero viscosity and zero entropy. And what the two fluid model
does is it says, let's imagine that that helium two is divided
into two completely mixed together fluids, one that we'll call the
normal fluid component, which has finite viscosity
and finite entropy, and one called the SLU component,
which is zero viscosity and zero entropy. And each of these fluids, um, will have their own velocities, and each of them will
have their own densities. And with this as a
background, you can then write the conservation of mass momentum and energy equations for
each of the two fluids, and you can add terms into these equations that discuss the interaction
of the two fluids together. Um, and from that, you
can do a very good job of explaining transport
properties such as heat transfer. Uh, you can just explain,
uh, the existence of things like second sound and the fountain effect,
uh, without having to go through the rigorous, you know, quantum mechanical, uh, model. There is a more rigorous model, which is really this really
thought of as the, um, true microscopic model of Helium two. And that was developed by Lev Landau. Um, but that model requires a
much deeper understanding of, of quantum mechanics, and
quite frankly, harder math. The two fluid model allows people to really understand the
transport properties as well as, uh, use those properties
to design practical, uh, uh, uh, behaviors. So whenever we do this
in large scale cryogenics or in in accelerated accelerated
design, things like that, we use this two fluid model. We don't use the more fundamental model. - And, and one thing
that struck me about, um, about the super fluid
state of helium is that it, although it does have these,
you know, sort of wondrous, um, properties like the ability
to to flow uphill it, it also in, in, in a, in a
sort of practical way, behaves as a fluid in the sense that you can, you can have it flow along
a pipe to where you want it to go, um, in a, you know,
in, in an application. So it's, it, it, it, it,
it seems, it struck me that it was almost like a,
a perfect material in a, in a sense, uh, to, to work with. - Yeah. That, that that's true. I mean, sometimes the universe is kind. Um, one of the things that was
developed as people started to move from simply looking at Helium two into practical applications
was exactly this question. If you have this material that has zero viscosity under
certain conditions, um, can you do useful things with it? And research done in, in
a number of laboratories and universities worldwide,
mainly in the seventies and eighties, showed that
while superfluid helium, if you look at it in, in bulk and, and you're not pushing
it through very small holes in porous media, for
instance, or in very thin films, but if you look at it in bulk, the fluid mechanical property
mechanical properties are basically the same
as a conventional fluid. And this goes back to the
explanation for this is that the quantized vortices that exist
in the super fluid component interact with the viscosity of the normal fluid
component in such a way that the whole fluid, the bulk fluid looks like
a conventional fluid. And this is tremendously helpful because it means not only can
we do practical things of it, but we also can use
practical scaling laws. So the, the law that we
use in, in engineering to discuss the pressure drop of a fluid through a pipe applies
completely to helium two, you just have to use the right density and the right temperatures. Uh, same is true with, uh,
sizing of pumps, uh, sizing of valves, all these sort of
practical things that have standard engineering rules
still apply to helium two. Where this breaks down is if
we're doing anything about transferring heat or if
we're doing things in small porous media or, or thin films. - And, um, and it is, it is
the transfer of heat, isn't it, at very low temperatures where, where Helium two really comes
into its own, um, it, it, it's an incredibly good
conductor of heat, isn't it? Uh, and I think the, the
two fluid model has a, a very beautiful
explanation of why that is. - Yes, that's true. Um, the
Helium two has a very, uh, uh, unique mechanism for heat transfer. It's actually the only
material that we know that does this though, I think
heal the super fluid phase of, of Helium three also does this, but in, in Helium four, uh, the way this works is
it has something known as internal convection. And this is not standard convection, and it's not conduction. In fact, what happens
is there's an interplay between the superfluid component and the normal fluid component. And so if you imagine a tube
with a heated wall on one end and a cooled bath on the other, and it's filled helium
two, what will happen is that the normal fluid component
will flow away from the heated wall carrying heat, and it will be replaced by super fluid component flowing
in the opposite direction, uh, towards the heated wall,
which then eventually heats up and becomes normal fluid. And so you have the circulation, and this is an extremely efficient, uh, it is under certain conditions,
a thousand times better, uh, than pure copper under those conditions at the same temperatures. So it's, it's a very, very efficient way. And it has another function as a result of being very efficient. It means that you don't
really get boiling in the body of Helium two, if you
have a bath of Helium two and you apply heat to it under, as long as you keep it in the Helium two state, the heat will be transferred
to the surface, uh, by internal convection, and then it will evaporate
quietly off the surface, but it won't boil and have
bubbles in the surface. And then that has very important
technical, uh, advantages, uh, particularly in the
area of cooling Sr uh, superconducting cavities. - Actually, there, there is
one, one thing that I wanted to ask you about, um, about this in internal convection process. It, it, are the, is the
material actually moving or is it sort of converting
from one, uh, component to another in, in that situation? - So y yeah, it, it, it
is not moving in bulk. So if you were to have internal,
if you did the experiment that I just mentioned and
you put a flow meter there, you would not see any
movement of the helium. Uh, what the two fluid model does, and remember it's only a
phenomenological model, is it assumes that the
normal fluid as a velocity and the super fluid as a velocity and the moving in opposite directions. Okay. Um, but, but that's just the
model, the actual physics, the physical reality is that the, the, the fluid is not moving. You wouldn't see a, a flow in a flow meter end of those conditions. - Okay. And, and that's the thing that makes it very efficient. The, uh, mm-hmm,
. Right. Okay. And, um, another, uh,
sort of phenomenon that, that I think has, has proved
useful is this idea of a, of a, a fountain, a super fluid
fountain where you can pump, uh, a super fluid without
any mechanical parts. How, uh, and that, that also
can be explained elegantly using the, the two fluid model, can't it? - Yes. Uh, in that model, what you have a, a super fluid pump typically
will have a ho media of a sort of micron sized holes in it
and helium on both sides of it, and then a heater at one side of it. And so when you turn the
heater on, what will happen is that the super fluid
component, uh, will move because it can move through
the porous media towards the heater, and thus become
normal when it gets heated up. But the normal fluid
component can't go back through the porous media
because it has finite viscosity. And so what you wind up doing
is building up a pressure, uh, where the heater is. And so this allows you to pump helium at, at fairly high rates. You just have to build the pump
big enough, uh, uh, to, um, uh, without any mechanical components. And this is particularly
useful in space applications where people are always very worried about mechanical reliability. And, and, uh, this eliminates yet another moving part
at low temperatures. - And I think in, in the
book you did mention that, that this was done successfully in space. - Yes. There was a, uh,
uh, project called Shoot, which was space, which was super fluid
helium on orbit transfer. And it was a, an experiment
flown on the space shuttle, um, in the, uh, late eighties, early nineties. And what they did was
they had two doers of, of superfluid helium, and connecting between them was a, uh, a line, a transfer line. And in that transline are
actually in one of the doers, there was this super
fluid, uh, fountain pump. So they moved helium from
one doer, uh, to the other and back again, uh, while
they were in, uh, zero G. And the motivation for this
was that in those days, they thought that they would be in a mold where they would bring super
fluid helium up to, say, a satellite that used it or to an experiment on the space station, and they'd wanna refill the helium. Uh, what what's developed in
the, as time has gone on, is that it turns out that's
not actually the most practical thing to do. It's actually better to simply
build the doer big enough and reduce the heat load and have the, have it do it that way and not try to refill it. Because the mission to refill
it is as expensive typically as buying a new instrument. So that tends to be the better approach. But this experiment was,
was very impressive, and it validated a lot of useful practical things
about using Helium two in space and Helium two in general. So it was a useful
experiment in that sense. You know, the spinoffs are quite useful. - And, and in the book,
you, you do spend, um, some time talking about
applications in space. Um, so, so what was the
first mission that, um, successfully used Helium two? The first, - The first real mission that
used Helium two in space was a, uh, infrared space
telescope called Iris, uh, that was launched in the, in the eighties. It was a joint US uk
uh, Netherlands project. And it was really the first
satellite that did a, a, um, sky wide survey of the
universe in the infrared bands. And in order to look in the infrared, you have to do two things. You have to get above
the Earth's atmosphere or most of the Earth's atmosphere because the Earth's atmosphere
will absorb IR radiation. And you have to be cold enough so that the sensors can detect the cold objects in space
you're trying to look at. Uh, and it turns out that, uh, helium two, if you operate these sensors
at about 1.8 K to 2K, they can get, they can then see most of the universe's dark, uh, material. And so when Iris flew,
it was a watershed sort of ob set of observations. No one had really seen the universe in these wavelengths before. And so they were able to
see through dust clouds, they were able to see
darker, uh, uh, astr, uh, astronomical objects. Um, and, and so it led to a series of, of telescopes flown in space,
uh, cooled with Helium two and the James Webb telescope,
which was just launched also, um, operates, uh, principally
in the infrared band. Um, though it does not
use Helium two to do that, it doesn't get quite as cold as some of the o earlier telescopes. And it has some mechanical
cryo coolers, uh, that can get down to the
temperatures it needs. - And in the intro, I I
mentioned, uh, you know, the fact that super fluid is used
in multi ton quantities, and I I'm guessing that the bulk of that is in particle
accelerators. Is, is that right? - That's correct, yes.
It's used in two places in particle accelerators. It's used to cool superconducting magnets. And the reason you would
cool a superconducting magnet to two Kelvin or so, 1.8 Kelvin, is that the principle
superconducting material that we use these days is opium titanium. And it performs better. It has higher current density and higher field strength
at these lower temperatures. So that's one reason to do it. So it's used all the magnets
at the CERN experiment are almost all the magnets
at the CERN experiment and at CERN at LHC are
cooled by super fluid helium. And then the other thing that's done that's become more common
in the last 10 or 15 years, and actually is used in more and more places, is the use of, uh, cooling super fluid helium,
uh, using super fluid helium to cool, uh, superconducting RF cavities. So these are, again,
superconductors, they're made out of pure niobium, and they will, they're used
to accelerate particles, uh, charge particles in accelerators. And they also perform
better at two kelvin. They are, are less lossy, um, because it's a radio
frequency superconductivity, there's still some losses,
but the significantly less so you need less power to
run them at two Kelvin. And then the other big
thing that Helium two does, and though that
application is, I mentioned that there's no boiling in bulk helium two and boiling around the
cavities can cause the cavities to lose their tuning 'cause
they're resonant devices. And so the fact that you are
surrounding them with a coolant that can't boil is another big
advantage, uh, to using it. So while CERN is the single
largest user of Helium two, the bulk of helium two used
in laboratories now I think is close to becoming, uh, this application in
superconducting RF cavities. 'cause these accelerators
are used for many things, including free electron lasers and, uh, uh, proton accelerators and, and neu that derive neutron
sources like my home institute and, and other things. So that's the, the other big application. - So at, at the European
Inspiration source, um, which ultimately CR creates
neutrons, you, you, you use, um, helium two as a coolant, or are you - Planning on your seal? Right. We have a, the way we
create neutrons at s at the European installation source
is we have a proton linac that we use to accelerate
protons to very high energies. Those protons then strike
a metal tungsten target, and there's a interaction
at the, at the nuclear level that essentially, if you
will, boils off neutrons. And those neutrons are then sent out, uh, to scientific instruments. But the accelerator, uh, uses
is about 400 meters in length. And 90% of the acceleration
is done by, uh, superconducting RF cavities
operating at two kelvin. So we have a very large,
uh, uh, about three kilowatt cooling, uh, helium refrigerator that operates at two Kelvin. - Right. And you, you
mentioned that a, a lot of the early work for,
um, magnets for, uh, helium two cooled magnets
was actually not done in, in, in the, in the realms of particle physics. It was, um, it was for, uh, magnetically confined fusion
experiments. Is that right? - Yes, that's right. The
first, the first real sort of application of, of helium
two in, in an industrial sense occurred at the to Supra tomac, which was built in Ash
France back in the eighties. And their motivation,
there was twofold There. It was, it was designed
to be the first, uh, tomac or fusion experiment that used superconducting magnets. I mean, they all do now, but back then, this was the first one
because they wanted to go to longer plasma pulses, and they couldn't really do
that with conventional magnets. And at the same time, uh,
they decided that the Zina of this decided that the
advantage would be to use, uh, superfluid helium. So again, the magnets
would be stronger, uh, at these lower temperatures. And it really became a,
a very useful validation that you can use super fluid
helium in large quantities. And they had to work
out the people in France that designed it from Grenoble. And Ash really had to help work
out the practical aspects of how you both, um, handle helium two. And, uh, the, um, people that provided the refrigerator for
this, which was airly keyed, had to develop a piece of technology known as a cold compressor that
would allow them to efficiently and reliably get down to these helium two, um, uh, temperatures. And so those two developments
have now been, uh, seen in all the fu all the later work. - E earlier on you, you
mentioned that, um, for example, in some space applications,
mechanical cryo coolers are, are now being deployed instead
of super fluid based ones. And, and I suppose in general,
there is a worry about, um, uh, sort of a, a shortage of helium because it is, uh, a finite resource. Um, do, do, do you think we're,
are, are we at sort of peak helium two cooling at the moment and, and in the future, people will
be developing maybe new ways of, of getting down to those temperatures? Or is is super fluid, uh, helium two here to stay for a lot of, - I, I, I don't, I think, I
think it's probably fair to say that we're getting close to
peak, peak usage, if you will. There's a number of large, uh, accelerator projects on the
books now that are being, uh, uh, built, uh, principally in China and in the United States
that do use Helium two. So it's not going anywhere anytime soon. Uh, but you are right in that one of the other technical
trends of the last 30 years is the development of
reliable, uh, um, uh, mechanical coolers that can get down. They typically can't get down
to helium two temperatures, but they can get down to below 4.2 K. Um, uh, and, and that is useful in that
you don't have to have, uh, large amounts of helium
and you don't have, and you can just
recirculate what you have. Uh, this is really driven
by the reliability of these. It was really driven by the space and the military that wanted
to use these things for, for infrared detection. But now that that's done, it's
relatively straightforward to go into a laboratory and cease one operating at
say, 20 Kelvin, a chemist or a, or a biologist. And they don't have any liquid helium. They simply have a mechanical
refrigerator that they turn on and gets them to those temperatures. And so, yes, I think that,
you know, as time goes on, we should see more and more of that. The limit at the moment is the capacity of these devices at the
very lowest temperatures. They tend to only be a,
a few watts at 4.2 K. Um, so for big applications
that, that develop, that, that need lots of, uh, heat removal, we're probably still gonna look at at, at liquid cryins, at least for a while. But the trend certainly,
I think is that way. - And, and what about, you know, developments in new
superconducting materials, new magnet designs? Is that, um, could that
something that affects, um, the use of super fluid? I suppose it - Does. Yes, I think so. And I
think in terms of just, uh, the way in which you do things as, uh, in general in cryogenics, you know, high temperature
superconductors were first discovered in the eighties, um, and it's taken a very long time. It's not surprising. It's a
very complicated material, and it actually mirrors
the amount of time it took to develop practical low
temperature superconductors after they were discovered in the early part of the 20th century. Um, but now they're
beginning to develop more and more of these device, these conductors and understanding how to use
them so that we're seeing them, uh, in more and more, uh, applications. Uh, and I think that's
something that will go on. And then you're sort of able
to operate at kind of the 50 to 60 Calvin level, and that really is sort
of also the sweet spot for these small crowd coolers. So a combination of development of super, of high temperature superconductors and small crowd coolers, again, I think is a longer term
thing that'll happen and, and will reduce the sort of the need to operate at, at these temperatures. - I see. And, um, I, I mean,
I would've thought that the, the, the incredible efficiency and, you know, the fact that, that the, the substance doesn't form bubbles, that that must be a huge
advantage, um, when you're, when you're trying to cool something. But is that offset by the
extra expense of having to get another two kelvin out of your cryogenic system? System is - That's a huge expense. It's, it's actually offset by that. And there's, there's
two things that happen. Um, the, uh, first of all, the,
the first question I ask is what temperature I need,
do I need to operate at? And, and for the magnets and the SRF cavities that we've
talked about, um, it's, it's true that the additional
cost to cool things down a couple more degrees is well offset by the improved performance that you get. Um, in the case of
superconducting RF cavities, it's actually dependent on
the frequency of the rf. It turns out, uh, because the material responds differently at different frequencies. So if it's a very low
frequency system, sort of in the 80 megahertz range of RF and of RF frequency, it
actually turns out that that calculation doesn't hold. It's the mally better to
operate at say, 4.5 k, though you still now
have the bubble problem. And, and that may also mean that you would operate at 2K anyway, uh, but at higher frequencies,
you know, 300 megahertz and higher, it definitely,
you definitely went by going down to two Kelvin. And so that plus the removal
of bubbles really drives that as a, as the right thing. I think that what one
might see in the future is, and people are working
on this, is the idea of cooling these, um, cavities, not by immersing them in the liquid helium, but by rather attaching
them to a cryo cooler, uh, that has its own challenges. The cavities are susceptible to vibrations and cryo coolers are
mechanical devices, uh, but there are people that are, that are working, working on that. Hmm. I also think the other
place that we'll still, so we'll still see helium two,
uh, uh, being used in a lot of places for the next, um,
with the guess 20 years or so. Uh, but I also think that
the technological trends are, are going sort of more
away from that, uh, simply because there are other ways
to achieve what you wanna do. - Hmm. And, and John, as I was reading your
book, it dawned on me that, um, there are several Nobel
prizes for physics that are, I suppose, made possible
by the use of Helium two. Do, do you have a favorite
out of those prizes? - Yes, I do actually. Um, uh, Lee Ooff and Richardson, uh, won the Nobel Prize for discovering super
fluidity in Helium three. This is the other isotope
of helium. Mm-Hmm. Now helium three is not a boon. And so the mechanism by which
it becomes a super fluid is not Bo Einstein condensation. It's rather something much more similar to what you see in superconductors
where it's more of a, a cooper pair kind of a thing. It only occurs at about
below about 2.7 milli Kelvin. Uh, but what I like about
their, their discovery was that they weren't really looking for this. They were looking for something else. They were doing fundamental
measurements in helium, in the helium three isotope. And as a part of those
measurements, they saw a phenomenon that they were able then to describe that they were able then to
describe as superfluidity and as and a superfluid, uh,
phase in helium three. And in fact, there are three
superfluid phases in helium three, uh, because helium three is also
a, has a magnetic moment. And so magnetism, putting a magnetic field on
it also affects the phases. Um, so there discovery was, uh, really a case of serendipity. And, and I really like that. I like the fact that someone
was looking for some one thing, and in the process of
looking for something, found something entirely
different and, and interesting. And I think some of the most exciting scientific
discoveries you get are those that occur in that manner
where it's not, I'm looking for X and I've found X,
it's I'm looking for X, and oh, what is this over here? And in many cases, that's the far more interesting, uh, thing. So I think that's my favorite one. - And the, so, so the
two different types of, well broadly different
types of super fluid, the, the two different isotopes, are
they, are they both used in, in a dilution fridge or is it, does that
not have anything to do with, with super fluid? - Uh, well, yes. I mean, because of the
temperature levels in a dilution fridge, typically there is a, a pot that operates at about two Kelvins, so that has super fluid helium in it. They don't really take advantages of the superfluidity of that at all. It's really just, but they do
have the advantage that the liquid in that vessel at
two Kelvin is isothermal because of the high heat
transfer and heat helium two. And they do have to worry
about some design features to prevent, for instance, the helium from crawling up the
wall, the container and, and into the pumping
line and, and being lost. Uh, in the case of the helium three part of the dilution fridge,
they don't operate well. They actually, that's not true. They might operate cold
enough that some of that will become super fluid, but I, I don't think that that has much of an effect on the
design or the use of it. - And so, so at the
moment we, you know, we, we associate super fluidity with helium. Is it, is it possible that there are any other
super fluids out there that we haven't seen? Possibly we haven't gone
cold enough to see them. - I, I mean, I, you, you never wanna say never in
these sorts of questions, so I, I think it's entirely, it
could be entirely possible. I think it's somewhat unlikely. You know, one of the features of Helium is that it's the coldest liquid we have. So any other element is,
is becomes a solid long before it gets down to these,
down to these temperatures. Uh, so it seems to me that it might, that it's probably unlikely,
but I, I won't say no. I, I will say that there have
been experiments using, uh, that have created other b
Einstein condensates using lasers and, and I think rium gases,
uh, it's, it's a different sort of a, it is truly a b
Einstein condensate, and it's, but it operates at a, it
operates at a very cold, nuclear molecular temperature, I think. Mm. Uh, but it's not a
bulk of fluid at all. - Well, th thanks, John. That was a, a, a fascinating conversation. And John's book is called Super
Fluid, how a Quantum Fluid Revolutionized Modern Science, and it's published by Springer. And you can read my review
on the Physics World website, just look for the
headline, super Fluidity, the Mysterious Quantum
Effect that became a backbone of Experimental Physics. Thanks for being on the podcast, John. - Thank you very much, Amy.
It was nice to be here. - I'm afraid that's all the time we have for this week's podcast. Thanks to John Wisen for joining me today and to our producer, Fred Isles. And a special thanks to our
sponsor, Pfeiffer Vacuum. We'll be back again next week, but in the meantime, do
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an orchestral trip through the moons of our solar system. Thanks again to Pfeiffer Vacuum for sponsoring this
episode of the podcast. Pfeiffer Vacuum provides all
types of vacuum equipment, including hybrid and magnetically levitated,
turbo pumps, leak detectors, and analysis equipment, as well as vacuum chambers and systems. Besides, they offer products that have been specially developed for accelerator applications. You can explore all of its products@pfeiffervacuum.com, - Physics world.