PuK - Process Technology & Components 2024

Vacuum technology
Vacuum systems
gravitational wave hits the plane in
which the arms of the interferometer
lie, one arm (or both, depending on
the direction of incidence) is periodically
shortened and lengthened. This
changes the conditions for optical
superposition, i. e. destructive interference,
which produces a signal at
the so-called dark finge. This is what
makes the gravitational wave visible,
or rather audible. LIGO is based on
the same principle. At the two LIGO
sites in the US states of Washington
and Louisiana, great care is taken to
ensure that the highly sensitive mirrors
and their reflective properties
are not affected by dirt. Therefore,
only dry, hydrocarbon-free pumps
are used to create the necessary vacuum.
The pumping stations used consist
of dry screw pumps and magnetically
levitated turbopumps. This is
the only way to achieve the limit of
< 1 monolayer in 10 years on the mirrors.
In addition to cleanliness, low vibration
plays an important role.
To ensure that new and more
gravitational wave signals can be detected
in the future, continuous improvements
are needed to reduce
interference. Detectors on Earth are
limited in particular by the suspension
and regulation of the mirrors in a
vacuum. This suspension is necessary
to isolate the mirrors from disturbances
such as seismic waves. At the
same time, however, it must allow the
mirrors to be perfectly positioned. In
particular, the next generation of detectors,
such as the European Einstein
Telescope [5], will be even more sensitive
at lower frequencies and therefore
require mirror suspensions with
improved control and less noise. In
order to develop the necessary technologies,
smaller laboratories are trying
to simulate the environmental
conditions for the development of
better instruments and components
as accurately as possible, also in order
not to reduce the observation
times in the large detectors.
As part of the “Quantum Universe”
Cluster of Excellence (EXC2121:
German Research Foundation - project
number 390833306), the research
group headed by Prof. Dr. Oliver
Gerberding at the University of Hamburg
is working on improving optomechanical
sensors. Pfeiffer Vacuum the system, a second optical table is
GmbH is supporting the working mounted on a side wall of the vacuum
chamber and enables the trans-
group with a special vacuum system.
The vacuum system developed mission of laser light from the outside
to the inside via transparent
and manufactured within the project
“VatiGrav” (vacuum chamber with flanges in the same plane as both
seismic isolation of an optical test experimental tables. For easy access
platform, funded by the University of to the chamber and the experiment
Hamburg/State of Hamburg and the table inside, there are doors on both
German Research Foundation, DFG, sides of the vacuum chamber. There
project number 455096128) fulfills is a single large door at the front to
several functions at once with its size make the entire interior volume accessible
for experiments. This can
of approx. 1.5 m long, 2 m wide and
2.5 m high. The stainless-steel vacuum also be used to remove the internal
chamber with a free internal dimension
of 1.74 x 1.02 x 1.51 m (LxWxH) the vacuum chamber is divided and
optical table if required. The rear of
serves as a container for the experimental
setups of Prof. Gerberding’s via two separate doors.
allows access to the experiment table
research group. For this purpose, the In addition to the dual functions
vacuum chamber is equipped with of test chamber and vibration damping,
the vacuum system is responsi-
an optical table, which rests on passive
vibration dampers on the chamber
floor and on which the laser in-
are performed under vacuum condible
for ensuring that the experiments
terferometry experiments and the tions. For this purpose, two oil-free
pendulum systems can be set up. The ACP 40 multistage Roots pumps from
purpose of the passive dampers is to Pfeiffer Vacuum are installed in the
allow low-vibration experiments under
vacuum conditions. In addition, in an adjacent room of the laboratory
vacuum chamber. These are located
the vacuum chamber itself rests on and are connected to the chamber by
active vibration dampers that use internal
sensor and control technology The two pumps are used to gener-
approximately 4 m of vacuum piping.
to ensure that vibrations and oscillations
from the environment are sup-
Once the pre-vacuum pressure of
ate the pre-vacuum in the chamber.
pressed and do not affect the experiments.
Frequencies above 2 Hz are the ATH 3204 M turbomolecular
about 1e-1 mbar has been reached,
absorbed with over 90 % damping. pump located on the chamber ceiling
This isolation concept is based on can be switched on to achieve even
correspondingly more complex systems
at LIGO [6] and in other spe-
magnetically levitated turbomolecu-
lower pressures. The ATH 3204 M is a
cial laboratories around the world. To lar pump from Pfeiffer Vacuum and
couple experimental setups outside has a maximum pumping speed of
Fig. 2: Vacuum chamber with seismic isolation of an optical test platform
PROCESS TECHNOLOGY & COMPONENTS 2024
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