2 research outputs found
EUV Debris Mitigation using Magnetic Nulls
Next generation EUV sources for photolithography use light produced by
laser-produced plasmas (LPP) from ablated tin droplets. A major challenge for
extending the lifetime of these devices is mitigating damage caused by
deposition of tin debris on the sensitive collection mirror. Especially
difficult to stop are high energy (up to 10 keV) highly charged tin ions
created in the plasma. Existing solutions include the use of stopping gas,
electric fields, and magnetic fields. One common configuration consists of a
magnetic field perpendicular to the EUV emission direction, but such a system
can result in ion populations that are trapped rather than removed. We
investigate a previously unconsidered mitigation geometry consisting of a
magnetic null by performing full-orbit integration of the ion trajectories in
an EUV system with realistic dimensions, and optimize the coil locations for
the null configuration. The magnetic null prevents a fraction of ions from
hitting the mirror comparable to that of the perpendicular field, but does not
trap any ions due to the chaotic nature of ion trajectories that pass close to
the null. This technology can potentially improve LPP-based EUV
photolithography system efficiency and lifetime, and may allow for a different,
more efficient formulation of buffer gas
Ideal relaxation of the Hopf fibration
Ideal MHD relaxation is the topology-conserving reconfiguration of a magnetic
field into a lower energy state where the net force is zero. This is achieved
by modeling the plasma as perfectly conducting viscous fluid. It is an
important tool for investigating plasma equilibria and is often used to study
the magnetic configurations in fusion devices and astrophysical plasmas. We
study the equilibrium reached by a localized magnetic field through the
topology conserving relaxation of a magnetic field based on the Hopf fibration
in which magnetic field lines are closed circles that are all linked with one
another. Magnetic fields with this topology have recently been shown to occur
in non-ideal numerical simulations. Our results show that any localized field
can only attain equilibrium if there is a finite external pressure, and that
for such a field a Taylor state is unattainable. We find an equilibrium plasma
configuration that is characterized by a lowered pressure in a toroidal region,
with field lines lying on surfaces of constant pressure. Therefore, the field
is in a Grad-Shafranov equilibrium. Localized helical magnetic fields are found
when plasma is ejected from astrophysical bodies and subsequently relaxes
against the background plasma, as well as on earth in plasmoids generated by
e.g.\ a Marshall gun. This work shows under which conditions an equilibrium can
be reached and identifies a toroidal depression as the characteristic feature
of such a configuration