Imploding cone-in-shell
capsule
2.7 mm
15-MeV proton backlighter
Imaging detector
Protons per unit area on detector
protons
Proton Radiography of Electromagnetic Fields in Laser-Produced High-Energy-Density Plasmas
HEDLP Workshop Washington DC August 08C. K. Li MIT
MITMIT
SummaryTime-gated, monoenergetic proton radiography provides unique measurements of E+B fields in laser-produced HED plasmas
• Radiography of laser-foil interactions:
Observation generations of ~106 gauss B field and 109 V/m E field Observation of decay dynamics and instabilities of MG B field Observation of field topology change due to magnetic reconnection
• Radiography of direct-drive cone-in-shell/spherical implosions:
Observation of radial, filamentary structures with complex striations and bifurcations, of B field magnitude 0.6×106 gauss
Observation of radial E field of order 109 V/m and its direction reversal
• Radiography of laser-irradiated gold hohlraums:
Observation of ~106 gauss B field and its evolution Observation of ~109 V/m E field and its evolution
LLE-UR
R. BettiJ. DelettrezV. GoncharovJ. KnauerF. MarshallD. MeyerhoferV. Smalyuk
Collaborators
MIT
F. SéguinJ. FrenjeR. PetrassoM. Manuel (G)D. Casey (G)N. Sinenian (G)
LLNL
P. AmendtO. LandenJ. RyggR. Town
GA
C. BackJ. KilkennyA. Nikroo
The proton source is a laser-driven glass capsule filled with D2 and 3He gas
0 10 20
6×108
0
(MeV)
protonsMeV
source spectrum
3% FWHM
3×1018
0
(ns)
protonss
0 0.5 1
source emission
130 psFWHM
14.7 MeV protons
D + 3He → 4He + p (14.7 MeV)
Heating of the gas during implosionleads to nuclear fusion production:Source
Emission of 14.7 MeV D3He protons is pulsed, monoenergetic, and isotropic
PRL 2006
Radiographs of laser-generated plasma bubbles on opposite sides of a foil prove that deflecting fields are B rather than E
OMEGA shot 46535
dBξ pvpm A
a)-qa(A
a
A
Petrasso et al APS 2007
Data and LASNEX simulations are similar with the laser on, but diverge afterwards
Interaction laseron for 1 ns
5mm
Outer bubble Burn-through hole
0.3 ns 0.6 0.9 1.2 1.5 1.8 2.3 3.0 ns
0
500
0 1 2 3
Time (ns)
0
0.6
La
ser
po
we
r (T
W)
0
2000
0
0.6
La
ser
po
we
r (T
W)
Meanbubbleradius(µm)
(a)
(b)
RMS bubble
asymmetry(µm)
0
250
0 1 2 3
Time (ns)
0
0.6
La
ser
po
we
r (T
W)(c)
Bdℓ (MG-µm)
2D code LASNEX produces credible simulations of the hydrodynamics and field growth as long as the laser was on, failing only when 3D instabilities appeared.
LASNEX+LSP by R. Town
PRL 2007a
0
200
0 1 2 3 4 5
Position along lineout (mm)
Magnetic reconnection has been observed and quantified
5 mm
Bdℓ(MG-µm)
0.31 ns 0.51 ns 0 .69 ns 0.97 ns 1.24 ns 1.72 ns 2.35 ns
5mm
0.04 ns 0.67 ns 1.42 ns
Bdℓ(MG-µm)
0
200
0 1 2 3 4 5
Position along lineout (mm)
> 95% field strength was reduced in the region where bubbles overlap
PRL 2007b
Face-on 15-MeV radiographs show the evolution from “corrugated” to cellular structures
0 1 2 3Time (ns)
Drive laser
~0.6 MG fields in these cellular structures with cell size ~ 120 μm
Position (µm)
P-P amp. ~ 18%
Position (µm)
P-P amp. ~ 5%
Diameter = 2.5 mmThickness = 20±1 mModulation ~ 120 mP-V modulation ~ 0.5m
“ linear” (2D)
Petrasso et al APS 2007
0
100
200
300
400
500
0 0.5 1 1.5 2 2.5
r(m)
t (ns)
envelope of high shell density
proton arrival (a.u.)drive pulse
Radiography of a cone-in-shell capsule implosion reveals field topology and capsule compression
Fluence
Energy
14 kJ laser drive
filamentary field structures
radial focusing E-field
capsule compressedby a factor of two
cone shadow
Rygg et al Science 2008
Time-gated proton radiography of direct-drive ICF spherical implosions provides the spatial structure and time evolution of E+B fields
0 0.5 1 1.5 2Time (ns)
Drive laser
3 mm
Fluence
Seguin et al APS 2007
The reversal of proton fluence focusing indicates the direction change of a self-generated radial E field
0.8 ns 1.2 ns 1.4 ns
1.6 ns 1.9 ns 2.1ns
1015
1010
105
0
-105
-1010
-1015
0 1 2 3
Time (ns)
E
(V/m)
Data
Simulation
PRL 2008
2mm 7mm
Radiograph E+B fields generated inside Au hohlraums with protons (DD and D3He) and with alphas (D3He)
B
B
before reconnection
after reconnection
OMEGA-Scale 1.5
10 beams (1ns-square,SG4+SSD) from Cone 3 drive the hohlraum
21 beams drive the backlighter
Fields are very important for :•understanding ignition experiments at the National Ignition
Facility. •laboratory astrophysics of plasmas with lower β (~1)
0
0.4
0.8
0.0 0.5 1.0 1.5 2.0 2.5
Distance (mm)
Protons μm-2
2.6 mm
t = 0.52 ns
Observation of ~106 gauss B field and ~109 V/m E field and their temporal evolution have been made
LASNEX+LSP simulation by R. Town
MITMIT
SummaryTime-gated, monoenergetic proton radiography provides unique measurements of E+B fields in laser-produced HED plasmas
• Radiography of laser-foil interactions:
Observation generations of ~106 gauss B field and 109 V/m E field Observation of decay dynamics and instabilities of MG B field Observation of field topology change due to magnetic reconnection
• Radiography of direct-drive cone-in-shell/spherical implosions:
Observation of radial, filamentary structures with complex striations and bifurcations, of B field magnitude 0.6×106 gauss
Observation of radial E field of order 109 V/m and its direction reversal
• Radiography of laser-irradiated gold hohlraums:
Observation of ~106 gauss B field and its evolution Observation of ~109 V/m E field and its evolution