pre-accelerated seed populations of energetic particles in the heliosphere
DESCRIPTION
Pre-accelerated seed populations of energetic particles in the heliosphere. N. A. Schwadron* and M. Desai Southwest Research Institute *Also, Boston University. Miracle occurs. Where do energetic particles and cosmic rays come from?. Plasma : Solar Wind, Coronal Plasma. - PowerPoint PPT PresentationTRANSCRIPT
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Pre-accelerated seed populations of energetic
particles in the heliosphere
N. A. Schwadron* and M. DesaiSouthwest Research Institute
*Also, Boston University
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Where do energetic particles and cosmic
rays come from?
Miracle occurs
Plasma: Solar Wind,
Coronal Plasma
Energetic Particles,
Cosmic Rays
Diffusive Shock
Acceleration
Suprathermal Ions Provide a Critical Link between bulk plasma
and EPs/CRs
Suprathermal ions have a leg up to overcome injection
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Is there an Injection Problem?
• Theorist’s answer - No– Multiply Reflected Ions, Shock Surfing, VxB drift– Cross-field diffusion
• Observer’s answer - Yes– EP composition reflects suprathermals, not bulk
plasma
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Example: Pickup Ions to ACRsPickup ionsborn withhigh energyand naturallypredisposedto accel. AtTerminationShock
Evidence: 1. Single-
charge of ACR species
2. Composition like neutral ISM Schwadron et al., GRL, 2002
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Injection at several shock types• Injection energy given by
– Einj = vinj2/2, ush/cos(BN) < vinj, but vinj < ush
~ ||/rg (here, take ~ 30)
Type Shock Speed BN Einj(BN) Einj()
Termination Shock
300 km/s 89.93 deg 0.3 GeV 1 MeV
FALTS 300 km/s 70 deg 4 keV 1 MeV
CIRs (3 AU) 300 km/s 88 deg (Std)
30 deg (Fluct)0.4 MeV
0.6 KeV
Debate (2 keV - > MeV)
Traveling IP Shocks
50 - 1000 km/s Varies (Tylka et al., 2005)
KeV-MeV Debate (2 keV - > MeV
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Higher rates of energy gain and harder spectra at quasi-perp shocksHigher rates of energy gain and harder spectra at quasi-perp shocks..
If a shock takes on a range of If a shock takes on a range of BnBn
values, high-energies will be values, high-energies will be dominated by particles produced at dominated by particles produced at
BnBn ~ 90 ~ 90o.o.
Shock Angle Bn (degrees)
Rat
e of
En
ergy
Gai
n (
nor
mal
ized
) Jokipii (1987)
Slid
e fr
om T
ylka
, 20
05
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Quasi-parallel vs. Quasi-perp Shocks?
• Quasi-parallel: – Lower injection threshold
– Larger flux of injected ions
– Longer time for acceleration to high energies
• Quasi-perp:– Higher injection threshold
– Faster ion acceleration
• Most shocks, even the termination shock, cannot be classified as quasi-parallel or quasi-perp– Injection best where quasi-parallel
– Higher energy acceleration where quasi-perp
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Where does the injection
begin?• Composition
change, beginning at suprathermal energies, marks the injection speed
• Suprathermal tail may control particle injection
Chotoo et al., JGR ,2000
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v’/Vsw1 0-4
1 0-2
1 00
1 02
1 04
1 06
1 1 0
H+
He+
He2+
CIR 1, F’
Where does the acceleration begin, what gets accelerated?
Chotoo et al. 2000. JGR, vol. 105; 23107Chotoo et al. 2000. JGR, vol. 105; 23107
He+ abundance enhanced 103-104
times the solar wind value
Injection appears at ~twice solar wind
speed
He+/He2+ ~0.17
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(adapted from Desai et al., 2001 and Kucharek et al., 2003)
Where does the acceleration begin, what gets accelerated?
He+ enhancement from PUIs3He from flares
He+/He2+ ~0.18
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Statistical Acceleration in Co-rotating Interaction Regions (CIRs)
Statistical acceleration through transit time damping of magnitude field fluctuations (magnetosonic waves)
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Where does the acceleration begin, what gets accelerated?
Spatial profile of He+/He++ provides strong constraints on the acceleration rate
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Suprathermal Seed Population
• The source population of energetic particles and cosmic rays• Pickup ions provide an important example• What causes the suprathermal tails?
– Statiscal acceleration (transit time damping) provides a likely explanation and explains pickup ion tails
• What causes suprathermal tails close to the Sun?– We see composition differences, I.e., enhancements in 3He– What fundamentally differentiates solar wind from sources of
suprathermal ions?
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Paths for Deposited Coronal Energy
Injected Electromagnetic
Energy
DownwardConducted Heat,
Radiation,Siphon flows
Bound
, clos
ed
struc
ture
s
Slow wind Fast wind
Open
field
Tra
nsiti
on??
Hot & Bright Cool & DarkIntermediate?Fluctuating?
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Paths of deposited Energy
Schw
adro
n an
d M
cCom
as, A
pJ, 2
003
• Solar Wind Scaling Law• Electron heat
conduction and radiative losses
Fast windCool, Dark
Slow windWarm,Brighter
Radiative LossHot, Bright
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A Constant Energy Source Sc
hwad
ron
and
McC
omas
, ApJ
, 200
3
The suprathermal seed population: Suprathermal Ions with speedsgreater thanescape speed fromenergetically bound bulkplasma
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Summary
• Suprathermal Ions Seeds of energetic particles and cosmic rays
• He+/He++ spatial profile .. A powerful technique for resolving acceleration rate
• Suprathermal tails from Sun show characteristic composition differences with solar wind - why?
• Possible that suprathermals escape from energetically bound bulk plasma