Title: What is Role of Proton Beams in Solar Radio Bursts? Jun-ichi Sakai Laboratory for Plasma Astrophysics University of Toyama, Japan
1What is Role of Proton Beams in Solar Radio
Bursts? Jun-ichi Sakai Laboratory for Plasma
Astrophysics University of Toyama, Japan
2Motivation
- It is believed that solar radio bursts like Type
III and Type II are generated from electrons
accelerated in the solar flare region or from
electrons accelerated near the fast magnetosonic
shock front. - It is recognized that some protons can be
accelerated by surfing mechanism near the fast
magnetosonic shock front. And also some protons
are reflected and accelerated near the shock
front, resulting in proton beams.
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4Contents
- Proton acceleration by shocks--Surfing
acceleration - Examples of shock formation
- Wave emission from proton beams
- Conclusions
5Simulation Model
Magnetic Field Line
Shock Wave
Model(2)qlt90
CME
q
90
v
Model(1)90
v
Solar surface
6Simulation Model
- Two-dimensional fully relativistic
electromagnetic Particle-In-Cell code. - System size Lx800, Ly10
- The free boundary condition in the x-direction,
and the periodic boundary condition in the
y-direction are imposed.
7Initial Conditions and Parameters
Model(1)
10
y
v
B0
0
Model(2)
10
x
0
200
800
Mass ratio mi64me Plasma beta ?0.05
(?ce/?pe0.632) ?ceElectron cyclotron
frequency ?peElectron plasma frequency Alfvén
velocity vA0.08c (clight
velocity)
B0 n4n0400 v3vA0.24c
BB0 nn0100 v0
EvB (EzvyBx)
8Parameter Runs
- Alfvén Mach (v/vA) 3, 2, 1.5
- Propagation Angle (q) 90, 80, 70
- (for
Mach3) - 90,
70, 40 - (for
Mach2 and 1.5) - Our simulation results are based on Alfvén Mach
is 3 and Propagation Angle is 80.
9Wave Emission Process
Shock region
Ex
Ex
x
(?pet0)
1.Some electrons are reflected behind the
shock front. 2.The reflected electrons behind
the shock front mix up with the in-coming
electrons due to the counter- streaming
instability. 3.Then there appear the electro-
static waves behind the shock.
vix/c
vex/c
x
(?pet90)
10Particle Acceleration
Shock region
By
By
x
(?pet0)
viz/c
Both electrons and ions are strongly accelerated
in the z- direction near the shock front through
the surfing mechanism.
vez/c
x
(?pet90)
11Surfing Acceleration byElectrostatic wave
propagating perpendicular to magnetic field
Equation of Motion
ExE0sin(?t-kx) ByB0
Solve for vz In moving frame
y
Ex
e
Acceleration Factor
x
z
12Spatial Distribution of Ex and Ez
(?pet66)
(?pet18)
Ex
Ez
x
x
Red arrow area (x70?326) are used to find the
dispersion relation of Ex. Blue arrow area
(x540?796) are used to find the dispersion
relation of Ez.
13Dispersion Relations of Ex and Ez
Elecrostatic Langmuir Waves (Z-mode) are
generated in the yellow contour line.
?/?pe
?/?pe
EM Waves are excited.
kc/?pe
kc/?pe
Ex
Ez
14Conclusions
- We found the wave emission process of Solar Type
II Radio Bursts associated with CME. - We also found that fast magnetic shock wave is
formed with both protons and electrons
accelerated by the surfing mechanism.
1. Some electrons are reflected behind the
shock front. 2. Reflected electrons generate
electrostatic waves. 3. They could be
converted to the extra-ordinary
electromagnetic waves through the Direct
Linear Mode Conversion.
151.Generation of magnetosonic shocks during
collision of two current loops
- PIC simulation
- Force-Free magnetic configuration
- JB 0
- Uniform density and uniform temperatur
- System size
- 900 900
- n0100
- Loop position (300, 300) (600, 600)
- Loop radius 100
Simulation System
y
x
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202.Generation of magnetosonic shock during
formation of current sheet
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24Emission of electromagnetic waves by proton beams
- The proton beams propagating to the low-density
region are forced to move, together with the
background electrons, to keep charge neutrality,
resulting in the excitation of electrostatic
waves - proton beam modes and Langmuir waves.
- In the early stage of electrostatic wave
excitation, both R and L modes near the
fundamental plasma - frequency can be generated along a uniform
magnetic field. - It is also found that, in the late stage, the
second harmonics - of electromagnetic waves can be excited through
the interaction of three waves. During these
emission processes, proton - beams can move along the magnetic field almost
without losing their kinetic energy.
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29Electron(solid line) and Proton(dashed line)
velocity distribution(a) t0 and (b) ?pet1500
30- Sakai and Nagasugi (2007) investigated the
dynamics of proton beams propagating along a
uniform magnetic field, as well as across the
magnetic field in nonuniform solar plasmas,
paying attention to the emission process of
electromagnetic waves to understand a new
solar-burst component emitting only in the
terahertz range during the solar flare observed
by Kaufmann et al.(2004).
31Proton beams propagating into high density region
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39- From the simulation where the proton beams
propagate along a uniform magnetic field into the
high-density region, it is found that strong
electromagnetic waves are generated behind the
proton beams. When the proton beams propagate
perpendicular to the magnetic field, the
extra-ordinary mode can be excited from two
electron Bernstein waves through three-wave
interactions. These simulation results could be
applied to the electromagnetic wave emission from
the solar photosphere during the solar flares.
40Conclusions
- 1.Protons can be accelerated by surfing mechanism
in shock front -
- 2.Proton beams play an important role for the
emission of electromagnetic waves
41- The role of proton beams reflected in the fast
magnetosonic shock front is also discussed for
the emission mechanism of the Type II radio
bursts.
42Shock formation and double structure(60 degree)
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45Time History of Ex and Ez
Ex
Ez
(Electrostatic)
(Electromagnetic)
Fundamental
Second harmonic
wpet
wpet
Parameters Red line w/wpe1.3 ?1.6,
kc/wpe0?2.5 Black line w/wpe1.5 ?2.0,
kc/wpe0?3.0 Blue line w/wpe2.5 ?3.5,
kc/wpe0?4.0
They are obtained by Inverse Fourier
Transformation using the data of dispersion
relations.