5:15 PM - 6:30 PM
[PEM17-P04] Virtual collective Thomson scattering measurement of foreshock instabilities in collisionless shock experiment at ILE
Keywords:Collisionless shock, Non-equilibrium plasma, Collective Thomson scattering
In space collisionless shocks are ubiquitously observed. Dissipation
mechanism at a collisionless shock is highly complex and has not been
well understood. Recently, collisionless shocks have been successfully
reproduced in a laboratory by using high power laser facilities. We have
performed the laboratory experiment on collisionless shocks by using
Gekko XII high power laser in collaboration with the Institute of Laser
Engineering (ILE) at Osaka University. To measure the local plasma
quantities in the shock transition region, collective Thomson scattering
(CTS) measurement is utilized. The CTS is the scattering of low
frequency incident electromagnetic waves by collective oscillations of
plasma electrons. The spectrum of the scattered waves enables us to
infer the local plasma quantities like electron density, electron and
ion temperature, valence of ions, etc, as a function of local position
along the path of the incident probe laser light. If a plasma is nearly
in equilibrium, scattered wave spectrum typically has two types of peaks
called electron and ion features. The electron (ion) feature is produced
when the incident waves are scattered by Langmuir (ion acoustic) waves.
On the other hand, the CTS theory in a non-equilibrium plasma has not
been established. In the foreshock region a back streaming plasma is
often observed as a beam by which beam instability is easily generated.
Although the electron feature is usually too weak to be detected in an
equilibrium plasma, it is possibly enhanced by the beam instability in
the foreshock. Therefore, electron feature measurement is planned in the
ILE experiment.
Numerical simulation greatly helps to interpret the experimental
results. PIC (Particle-In-Cell) simulation is regarded as a first
principle simulation of a collisionless plasma. It can reproduce a
variety of non-equilibrium plasma phenomena in a self-consistent manner.
However, the time resolution usually assumed in a PIC simulation is not
enough to reproduce the CTS with realistic parameters. In this study we
construct a simulation system of virtual CTS for realistic parameters in
the ILE experiment. A foreshock beam instability is reproduced by using
a PIC simulation. Then, the time-series data of electron density
obtained from the PIC simulation is used to solve a wave equation of the
scattered waves separately with much higher temporal resolutions. We
performed this virtual CTS simulation for a parameter set typical in the
ILE experiment and confirmed that electron feature is strongly enhanced
through an electron-beam instability in a foreshock. In the meeting we
will discuss characteristics of virtual CTS spectra for a variety of
beam-plasma systems.
mechanism at a collisionless shock is highly complex and has not been
well understood. Recently, collisionless shocks have been successfully
reproduced in a laboratory by using high power laser facilities. We have
performed the laboratory experiment on collisionless shocks by using
Gekko XII high power laser in collaboration with the Institute of Laser
Engineering (ILE) at Osaka University. To measure the local plasma
quantities in the shock transition region, collective Thomson scattering
(CTS) measurement is utilized. The CTS is the scattering of low
frequency incident electromagnetic waves by collective oscillations of
plasma electrons. The spectrum of the scattered waves enables us to
infer the local plasma quantities like electron density, electron and
ion temperature, valence of ions, etc, as a function of local position
along the path of the incident probe laser light. If a plasma is nearly
in equilibrium, scattered wave spectrum typically has two types of peaks
called electron and ion features. The electron (ion) feature is produced
when the incident waves are scattered by Langmuir (ion acoustic) waves.
On the other hand, the CTS theory in a non-equilibrium plasma has not
been established. In the foreshock region a back streaming plasma is
often observed as a beam by which beam instability is easily generated.
Although the electron feature is usually too weak to be detected in an
equilibrium plasma, it is possibly enhanced by the beam instability in
the foreshock. Therefore, electron feature measurement is planned in the
ILE experiment.
Numerical simulation greatly helps to interpret the experimental
results. PIC (Particle-In-Cell) simulation is regarded as a first
principle simulation of a collisionless plasma. It can reproduce a
variety of non-equilibrium plasma phenomena in a self-consistent manner.
However, the time resolution usually assumed in a PIC simulation is not
enough to reproduce the CTS with realistic parameters. In this study we
construct a simulation system of virtual CTS for realistic parameters in
the ILE experiment. A foreshock beam instability is reproduced by using
a PIC simulation. Then, the time-series data of electron density
obtained from the PIC simulation is used to solve a wave equation of the
scattered waves separately with much higher temporal resolutions. We
performed this virtual CTS simulation for a parameter set typical in the
ILE experiment and confirmed that electron feature is strongly enhanced
through an electron-beam instability in a foreshock. In the meeting we
will discuss characteristics of virtual CTS spectra for a variety of
beam-plasma systems.