Transcript Making Gamma-Ray Burst in the Laboratory: Ultra-intense Positron and Gamma-Ray Creation using the Texas Petawatt Laser PI: Edison Liang, Rice University Co-PI: Todd Ditmire/Manuel.

Making Gamma-Ray Burst in the Laboratory:
Ultra-intense Positron and Gamma-Ray Creation using the
Texas Petawatt Laser
PI: Edison Liang, Rice University
Co-PI: Todd Ditmire/Manuel Hegelich, UT Austin
Rice Team Members: Devin Taylor, Taylor Clarke, Alexander
Henderson, Steve Zhou, Petr Shagin, Xin Wang. Xinyi Cen
UT Team Members: Gilliss Dyer, Kristina Serratto, Nathan Riley,
Michael Donovan
Work Supported by DOE DE-SC-000-1481 and Rice U. FIF
Many new >100J-class PW lasers are coming
on line in the US, Europe and Asia
Omega laser facility,
Univ. of Rochester
FIREX
Omega
laser
Gekko
Omega-EP
ILE Osaka
The National Ignition Facility
LLNL
TPW
ARC
Two unique features of relativistic outlfows:
gamma emission and e+e- pair domination
Pulsar wind
jets
Gamma-Ray Bursts: High G favors an
e+e- plasma outflow?
Woosley & MacFadyen,
A&A. Suppl. 138, 499 (1999)
e+e-
e+e-
Internal shocks: What is primary energy source?
How are the e+e- accelerated?
Hydrodynamic
How do they radiate?
Poynting flux:
Electromagnetic
Ultra-intense Laser is the most efficient tool to make e+e- pairs
In the laboratory
BetheHeitler
MeV e-
e+e-
e
Trident
Sample Laser Numbers
1 PW = 1 kJ / 1 ps =100 J /100 fs
1 PW / (30 m)2 = 10 20 W/cm2
22
10 W/cm /c ~ 3.10 erg/cm ~ 2.10
20
2
16
3
e+e- /cm
3
Solid Au ion density ~ 6.1022 /cm3
n+/ne ~ 4.10 -3
In reality, the max. achievable8 pair density is
Bequipartition ~ 9.10 G
probably around 1019 - 10 20 cm -3
Early laser experiments by Cowan et al (1999) first demonstrated
e+e- production with Au foils. But copious pair production was
only demonstrated at LLNL in 2009 by Chen et al.
Cowan et al 1999
Chen et al 2009
Sample Titan data
1
1
2
e+/e- ~ few %
Monte Carlo
simulations
MeV
Qu i c k T i m e ™ a n d a
Gra p h i c s d e c o m p re s s o r
a re n e e d e d to s e e th i s p i c t u re .
The Team: Dyer, Henderson, Liang, Clarke, Taylor, Riley
(Not in picture: Serrato, Shagin, Zhou, Donovan, Ditmire)
TPW Performance for the first 67 shots of run
1. E = 81 -130 J , <E> ~ 100 J
2. DT = 128 - 245 fs, <DT> ~ 160 fs
3. P = 450 - 800 TW, <P> ~ 650 TW
4. %E in 10 m circle = 40 - 80%, <%E> ~ 65%
5. Peak I = 3x1020 - 1.9x1021 W.cm-2, <I> ~ 7x1020
25% of shots had I ≥ 1021 W.cm-2
Au Target Parameters
1. Flat Disks: 0.2 - 4 mm thick
2. Thin Rods: 2-3 mm diameters, 4 mm - 1cm long.
3. Angles between laser and target normal: 25 -45 degrees
e+e- Magnetic Spectrometers
1. 10 inch magnet: 2 MeV - 130 MeV
2. 6 inch magnet: 2 MeV - 55 MeV
3. 4 inch magnet: 0.4 - 6 MeV
Gamma Detectors
1. Filter-stack spectrometers: up to 1.5 MeV
2. Forward Compton spectrometer: 2 - 50 MeV
3. 30 dosimeters per day: up to 40 MeV
TPW Performance for the first 67 shots of run
1. E = 81 -130 J , <E> ~ 100 J
2. DT = 128 - 245 fs, <DT> ~ 160 fs
3. P = 450 - 800 TW, <P> ~ 650 TW
4. %E in 10 m circle = 40 - 80%, <%E> ~ 65%
5. Peak Intensity I = 3x1020 - 1.9x1021 W.cm-2, <I> ~
7x1020
25% of shots had peak I ≥ 1021 W.cm-2
Summary of Major Results
Major Results
1. Of the first 67 TPW shots , over half show detectable e+ signals
in one or more magnetic spectrometers.
2. Emergent e+/e- ratio shows nonlinear rise with thickness..
4. All thin targets (≤0.5mm) show narrow e+ peaks at ~ 10 - 22
MeV, much higher than the proton sheath energies.
5. Maximum inferred emergent e+ density lies in the range
~1014 - 1015/cm3, higher than previous experiments.
6. Long narrow rods show higher e+/e- ratios than disks. The
ratio increases with rod volume.
Diagnostics and target setup of the 2012 run.
TC1 with
f/3
mirror
Qu i c k T i m e ™ a n d a
T I F F (U n c o m p re s s e d ) d e c o m p re s s o r
a re n e e d e d to s e e th i s p i c t u re .
laser
detector
target
normal
We used 3 magnetic e+e- spectrometers: 1 low-E (<7 MeV), 1 mediumE (2-50 MeV) and 1 high-E (1-120 MeV), calibrated with LSU e-beams
12”
Bmax~0.6T
Qu i c k T i m e ™ a n d a
T I F F (Un c o m p re s s e d ) d e c o m p re s s o r
a re n e e d e d t o s e e t h i s p i c tu re .
Typical e+e- Image Plate images after conversion to PSL
positron spectra
proton spectra
y
e+ plates
x
Low-E plates
electron spectra
High-E plates
e- plates
Positron signal is mostly a few percent of electron signal
Proton signal measures target sheath potential (1.5 - 4 MeV)
Because the e+ signal is << background, we need to construct a
very accurate, robust background model to extract the e+ signal.
After many trials and errors, we adopted a 2D moving-window
5th-degree polynomial fit to construct the background model.
Advantages: 1. Gives null signals to Al, Cu and other non-e+ shots
2. Produces smooth deconvolved spectra
3. Maximizes R2 and other statistics in most cases
Method: Remove pixel data along a 4 - 5 mm wide strip where e+ signal
is concentrated. Fit the residual <PSL(x)> vs y profile inside moving
window with 5th-degree polynomial to construct background model.
moving
y
4 -5 mm strip removed
window
e+signal
<PSL(x)>
x
background model
y
Sample e+e- Signal + Background Profiles for Au Shots
e+
e-
PSL
y
y
e+
e-
PSL
y
y
Red Line is best 5th-order polynomial fit to background
with central pixels removed
The above procedure applied to Al and Cu shots gives null results
for any e+ signal above background. These fits also provide an
estimate of the systematic error for this method.
PSL
QL
Cu
Al
y
y
Red Line is 5th-order polynominal fit to data with central 4 mm
wide pixels removed
Vertical spread due to laser and detector angle variations
2012 TPW Data (averages for all shots)
2009 LLNL Titan Data
Vertical spread
mainly due to
Incident and Detector
Angle Variations
Outliers ~ correspond
to detector angle
> laser incident angle
Yield spread mainly due to angle variation: No trend vs. thickness
At fixed angle, yield is almost constant vs. thickness ≥ 0.5 mm
GEANT4 simulations suggest that e+ yield /incident
hot electron peaks at around 3 mm and increases with
hot electron temperature at least up to ~15 MeV
Emergent positrons/incident electrons (log)
1.00E+000
1.00E-001
e+/e- (10MeV)
e+/e- (5MeV)
1.00E-002
1.00E-003
0
2
4
6
Thickness (mm)
8
10
12
We also explored using long narrow rods to optimize
emergent e+/e- ratio by maximizing gamma-->pair
optical depth along rod axis, with encouraging results.
laser forward
to DETECTOR
LASER
target normal
maximize
gamma flux
along rod
axis
Detector needs to be positioned so as to maximize solid
angle of entire rod visible by the detector pinhole
Clear Evidence of
Nonlinear Scaling
of e+/e- Ratio with
Rod Volume
But No Evidence of Yield Scaling vs. Rod Volume
Sample deconvolved e+ spectra from the low-E (<7 MeV) spectrometer
e+ peaks at 6-10 MeV and e- peaks at 10-20 MeV. note the absence of low energy electrons
e+
80000
70000
e-
1800000
1600000
1400000
60000
1200000
50000
1000000
40000
Series1
Series1
800000
30000
600000
20000
400000
200000
10000
0
0
2
4
6
8
10
12
MeV
0
0
12000
400000
10000
350000
20
30
40
50
MeV
60
300000
8000
250000
6000
Series1
4000
200000
Series1
150000
100000
2000
50000
0
-2000
10
0
0
2
4
6
8
10
0
10
20
30
Sample deconvolved Spectra From High-E Spectrometer
40
50
All thin targets (≤ 0.5 mm) show narrow e+ peaks at 11 - 22 MeV,
while TNSA proton energies are only ~ 1 - 3 MeV
I=6.6e20Wcm-2, 162fs, 0.35mm target
Raw IP data showing small
e+ bump above background
After background subtraction,
deconvolved e+ spectrum
of above data shows a
narrow peak at ~ 22 MeV
Magenta= 0.35mm; red=0.5mm, blue=1mm; black=4mm
e+ peak energies are ~ 10 times higher than TNSA proton energies
For Thick Targets, More Gamma-Rays Emerge than Hot Electrons,
reaching 50% of Incident Electron Energy (~15-20% of laser energy)
Laser-created gamma-ray beam
opening angle and energy distribution
are both suitable to study GRB
interaction with environments.
GEANT4 Sim.
Gamma Ray Bursts (GRBs)

The photon density on emergence from the target is ~
1011-1013 ergs/cm3


The same parameter in the region around GRB
sources is approximately 1012 ergs/cm3.
The photon fluence on emergence is ~1010-1012
ergs/cm2.


The fluence of a GRB at 30 parsecs (pc) is about
1011 ergs/cm2.
We may be able to study the effects of GRBs on the
Interstellar Medium using these.
Low-Energy Gammas Are Measured with Filter-Stack Spectrometer
S h ot 2 3 5 7, De te c t o r 2
High-Energy Gammas: Need to use FCES
Plastic filterConverter
6 mm
Incident
Gamma Rays
6 mm
Magnet
Image plate (over gap)
Magnet
High-Z
Optional Teflon collimators
Gamma Collimator
-Image plates on both sides detect positrons and electrons.
-The effects of pair production can thus be subtracted.
-Converter materials include plastic, Al, Cu, and Sn.
Compton Electron Gray Value
5000
4000
3000
Simulated Counts
(Scaled)
Calibration Gray
Value
2000
1000
0
0
5
10
15
20
25
30
Energy (MeV)
•An x-ray beam line at LSU MBPCC was used for
calibration.
•The peak location is off: the source spectrum or
alignment may be off. Further study is needed to resolve
this.
Au Target
Compton Electron PSL Value
Forward Compton Electron Spectra from TPW Expt
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
10
20
30
40
50
60
Energy (MeV)
 Red is FCES data, blue is simulation using the
measured electron spectrum as input.
 The FCES used a combination of plastic and Sn.
 Additionally, teflon blocks with holes in them were used
to reduce the acceptance angle.
Deconvolved -Spectra shows we can measure gamma-ray continuum out to > 50 MeV
1.00E+009
Gamma Rays Detected
1.00E+008
1.00E+007
1.00E+006
1.00E+005
1.00E+004
1.00E+003
1.00E+002
1.00E+001
1.00E+000
2
12
22
32
42
52
Energy (MeV)
 Red is FCES data, blue is simulation using the
measured electron spectrum as input.
 The FCES used a converter consisting of plastic
followed by copper.
Assuming that the conversion of laser energy to hot electrons
is ~ 30 %, and the hot electron temperature is ~ 10 -20 MeV,
our results suggest that the maximum positron yield is
~ 1012 e+ per kJ of laser energy
when the Au target ~ 4 - 6 mm
The emergent e+ density could reach > 1017/cm3
The peak e+ current could reach > 1024/sec
(This current is 1010 higher than conventional schemes
using accelerators and accumulators)
relativistic shear boundary layer/shocks may be studied by
injecting laser-created relativistic e+e- jet into a low density gas
(adapted from picture courtesy of Wilks)
n>1019/cc,G~40
low density gas
~mm
shear boundary
layer
shock
For Astro applications,
Needs n> 1018/cc for skin-depth to be < 10-2 of jet dimension
2D model of a pair-cloud of Cygnus X-1 surrounded by a thin
accretion disk to explain the MeV-bump
The Black Hole gamma-ray-bump can be interpreted as
emissions from a pair-dominated MeV plasma with n+ ~ 1017cm-3
logL(erg/s)
Pair-dominated
kT limit
T/mc2
Can laser-produced pair plasmas probe the pair-dominated temperature limit?
Double-sided irradiation plus sheath focusing may provide
astrophysically relevant pair “fireball” in the center of
a thick target cavity: ideal lab for GRB & BH -flares
diagnostics
high density “pure”
e+e- due to coulomb
repulsion of extra e-’s
PW laser
PW laser
3-5mm
3-5mm
diagnostics
Thermal equilibrium pair plasma and BKZS limit may be replicated
if we have multiple ARC beams staged in time sequence.
Medical Applications
Narrow-Band 10-20 MeV Positron Beams may be useful for
Cancer Therapy since the 511 keV Annihilation Line can
help pinpoint the endpoint of energy deposition as in PET.
A Dose of 1011 e+ per shot should be plenty for cancer therapy.
Physical effects of ultrashort ultraintense e+ pulse on biological
systems need to be first studied. This may open up a new field
Of medical physics.
E = mc2
1 gm of e+e- annihilates into
9x1020 ergs
= 25 GWHr
= 21 kTon of TNT
The LBL Bela Laser
claims to fire a 40 J PW laser
once per second. If 1 J of e+
is created/second, a
microgram of e+ can be
created in 3 years, equal
to the escape energy of 1 kg
from earth. A 1 ton payload
would need the e+ from
a 1 Hz 40 kJ PW laser
operating for 3 years.
Most Other Applications need slow (< keV) e+
Key advantages of laser produced positrons are short pulse (< ps),
high density (>1015/cc) and high yield efficiency (>10-3).
To convert these multi-MeV positrons to slow positrons using
conventional techniques, such as moderation with solid noble gas,
loses the above inherent advantages.
We are exploring intense laser cooling, using photons as “optical
molasses” similar to atomic laser cooling, to rapidly slow/cool
MeV pairs down to keV or eV energies.
e+/e-

no
42no
In a strong B field, resonant scattering cross-section can become
much larger than Thomson cross-section, allowing for efficient
laser cooling: analogy to atomic laser cooling
To Compton cool an unmagnetized
>MeV electron, needs laser fluence F
~mc2/sT ~ 1011J.cm-2=10MJ for
____~ 100m spot size.______
But resonant scattering cross
section peaks at fsT, f>103, F is
reduced to 10MJ/f < kJ. However, as
in atomic laser cooling, we need to
“tune” the laser frequency higher
as the electron cools to stay in
________resonance. How?_________
. For B=108G, hwcyc=1eV
res=1m
f>103sT
sT
Idea: we can tune the effective laser frequency as seen by the
e+ beam by changing the laser incident angle to match
the resonant frequency as the positron slows.
to
t1
e+

B
cyc = laser(1-vcosq)
t2
t3
Idea: change the incident angle by using a mirror
and multiple beams phased in time
to
t1
t2
e+

B
cyc = laser(1-vcosq)
We are developing a Monte Carlo code to model this
in full 3-D. Initial results seem promising
(Liang et al 2013 in preparation)
t3
High density slow e+ source makes it conceivable to
eventually create a BEC of Ps at cryogenic temperatures
(from Liang and Dermer 1988).
A Ps column density of
1021 cm-2 could in
principle achieve
a gain-length of 10
for gamma-ray
amplification via
stimulated annihilation
radiation (GRASAR).
(from Liang and
Dermer 1988).
Such a column would
require ~1013 Ps for
a cross-section of
(1 micron)2.
1014 e+ is achievable
with 10kJ ARC beams
of NIF.
Ps annihilation cross-section with only natural broadening
Porous silica matrix at 10oK
1021cm-2
Ps column
density
ps pulse of
1014 e+
sweep
with
204 GHz
microwave
pulse
1 micron diameter cavity
Artist conception of a GRASAR (gL=10) experimental set-up
Summary
1. We succeeded in creating ultra-intense positron and
gamma-ray sources at TPW in 2012, with e+ density >1015/cc
and gamma-ray density ~ cosmic GRB source density
2. We confirmed that e+/e- ratio increases nonlinearly with
target thickness > 4 mm, with potential to reach tens of percent.
3. We confirm the scaling of e+ yield with laser energy and
laser intensity: a 10 kJ PW laser can create > 1013 e+ per shot.
4. We discovered narrow-band 10-20 MeV positrons using thin
targets, ideal for medical applications.
5. We measured the gamma-ray spectrum using Forward Compton
Electron Spectrometer, and confirmed the gamma-ray yield.