proton conversion efficiency using erbium hydride coatings interview for postdoctoral research...
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Proton Conversion Efficiency Using Erbium Hydride CoatingsInterview for Postdoctoral Research Position at Sandia National Laboratory
Dustin OffermannGraduate Research AssociateDepartment of PhysicsThe Ohio State UniversityColumbus, Ohio 43210
People and AcknowledgementsThe Ohio State UniversityThe Ohio State University - L.D. Van Woerkom, R.R. Freeman, E.
Chowdhury, A. Link, D.T. Offermann, V. Ovchinnikov
Lawrence Livermore National LaboratoryLawrence Livermore National Laboratory - M. Key, A. Mackinnon, P. Patel, A. MacPhee, Y. Ping, J. Sanchez, N. Shen, H. Chen, M. Foord, W. Unites, D. Hey
University of California, San DiegoUniversity of California, San Diego - F. Beg, T. Bartal, J. King, T. Ma, S. Chawla
Massachusetts Institute of TechnologyMassachusetts Institute of Technology - C. Chen
General AtomicsGeneral Atomics - R. Stephens, K. Akli
University of AlbertaUniversity of Alberta - Y. Tsui
Sandia National LaboratorySandia National Laboratory - L. Espada
This work performed under the auspices of the U.S. Department of
Energy by Lawrence Livermore National Laboratory under Contract
DE-AC52-07NA27344.
About Me Degrees
BS in Physics, Seattle University, Seattle, WA, 2002 MS in Physics, The Ohio State University, Columbus, OH, 2005 PhD in Physics (pending), The Ohio State University, Columbus, OH
Graduate Research Experience The Ohio State University, LVW Short Pulse Laser Lab
Ti:Sapphire CPA laser system (1TW) Multi-photon ionization experiments
Sandia National Laboratory, ZBL 100TW Experiments in Collaboration with Sandia, UCSD and Ohio State
Lawrence Livermore National Laboratory, JLF Callisto and Titan Lasers Proton Conversion Efficiency Experiments Support for Numerous Titan and Callisto experiments
Motivation
Proton Fast Ignition Requires * (Fuel Density 400g/cc, d=1mm) Protons Focus to a 30μm Diameter Spot Slope Temperature ≈ 3MeV For These Parameters an Enclosed Geometry is Needed Total Beam Energy of 15kJ
(15% Conversion Efficiency for 100kJ Laser)
* S. Atzeni, M. Temporal, J.J. Honrubia, Nucl. Fusion 42 (2002) L1–L4
Ultra Intense Laser
Thin Foil
e- Sheath Field
H+, C+, C+2, … Ions
H+, C+, C+2, … Ions
TNSA Model
d
How To Improve Conversion Efficiency
Better Conversion to Hot Electrons Optimization of Laser Conditions (Pre-pulse, etc) Target Materials with Good Coupling
Thin Foils Experiments Show 1/L Scaling Requires Very Low Pre-Pulse
Coated Rear Surfaces More Protons Available More Protons per Non-Hydrogen Atom If Non-Hydrogen Atoms are High Mass Then the Fraction of Energy Carried
by the Protons Will be Greater
* 2
exp2
eiei
sei
kTQ
E
kTEQL
tcN
dE
dN
eisei
totali kTtQcLNdEdEdNEE )/(,
* P. Mora, Phys. Rev. Lett. 90, 185002 2003.* P. Mora, Phys. Rev. E 72, 056401 2005.
** E. A. Williams et al., Phys. Plasmas 2, 129, 1995.
Length Debye
State ChargeIon
ThicknessTarget
eTemperaturElectron Hot
ElectronsHot ofNumber
** Speed Sound )//( 2/12
D
i
e
e
iiies
Q
L
kT
N
QmQkTc
From the Solution to the Isothermal Model
Dstc ifOnly
Valid Vacuum theinto
Expansion Plasma D-1
for Model Simple
Theory and Motivation
LSP model show for high-Z hydrides like Er and U, conversion efficiency to protons approaches that of pure hydrogen.
Semi-empirical model from the simulated data, where M = masshydride/massproton N = # of protons per
hydride Q = Charge of hydirde
0
10
20
30
40
Hydrides
BC
Pro
ton
co
nve
rsio
n e
ffic
ien
cy (
%)
H LiH CHn
MgH2
CaH2
CsH ErH3
UH3
CH4
CH2
CH
HZ
ZHn
Thot=880keV5 m Au + 1000 ZH
n
17.1
1
MN
Qfb
Experiments Seek to Observe This Region
Contaminants
M. Foord, A. Mackinnon, P. Patel, et al, J. Appl. Phys. 103, 056106 (2008).
LSP Model of Callisto Targets
Er+10
Hf=0.40
H
C+4
O+4
f=0.30H
C+6
O+8
f=0.21
LSP simulation shows for protons above 3MeV, erbium LSP simulation shows for protons above 3MeV, erbium hydride improves conversion efficiency by hydride improves conversion efficiency by 22%22%
Time (ps) Time (ps) Time (ps)
J/cm
2
J/cm
2
J/cm
2
LSP simulations were run until total ion energies vs run time became asymptotic.
The number f is the fraction of beam energy in protons above 3MeV Three cases are shown: ErH3 - CHO Fully Ionized - CHO Ionized to +4
5μm Au-Er+10 3H+ 5μm Au-C+6H+O+8 5μm Au-C+4H+O+4
Erbium Hydride Experiments
Compared 3 Conditions: Contaminants on foil ErH3 not cleaned (contaminant layer still present)
Cleaned ErH3
5 or 14 micron Au 5 or 14 micron Au substratesubstrate
200nm ErH3200nm ErH340Å Oxide40Å Oxide
10Å Contaminants10Å Contaminants
Cleaned Cleaned using Ar-using Ar-
ion ion EtcherEtcher
Element Atom %
(aelement)
Carbon 50
Nitrogen 1
Oxygen 37
Fluorine 1
Erbium 11
X-ray Photoemission X-ray Photoemission Measurement of Measurement of
Contaminant CompositionContaminant Composition
322103)22(
)22(
cm
maamama
aaN
HOcErErcc
OCa
Assume Contaminant Density of 1g/cc and Carbon and Oxygen from data are CH2 and H2O.
Proton Source Diameter ≈ 200μm. * Approx. 1x1012 Protons in Contaminants.
* P. Patel, A. Mackinnon, M. Key, et al, Phys. Rev. Lett. 91, 125004 (2003).
Estimation of the number of protons in contaminants
Do these give the same result?
Expected to Improve C.E. by factor of 1.22
Removing the Contaminant Layer
Setup for Measuring the Etch RateSetup for Measuring the Etch Rate45 deg
Argon Ion Sputtering Gun Etching System Positioned 15cm behind TCC and inclined 45 degrees in Callisto. Positioned 15cm behind TCC and inclined 39 degrees in Titan. Etcher beam diameter approx 3cm. Hydride thickness reduction rate measured to be ~15nm/min.
Microprofilometer Scan
Removes 15 nm per minRemoves 15 nm per minScan Length (μm)
Radiochromic Film Pack (Primary Diagnostic) Purpose: RCF packs are the tried
and tested means to measure proton conversion efficiency, slope temperature, and beam properties.
Energy Range: from 3.8 to 40 MeV Typical Dose: up to ~180 krad Dose Uncertainty: 20% *
Callisto Type Pack
Titan Type Pack
Titan: 5-7 cm from TCCCallisto: 2.5 cm to TCCProton Beams are f/1 from flat foils
Tit
an
Pack P
roto
n
Ran
ge
* D. S. Hey, Laser-Accelerated Proton Beams: Isochoric Heating and Conversion Efficiency. PhD thesis, University of California, Davis, 2007.
Calibration Curves
Nikon Scanner Capable of Resolving Nearly 3 Orders of Optical Density
RCF Dose Measurement
www.nikonusa.com
Super Coolscan™ 9000
Film was calibrated using a 64.5MeV proton beam from the Crocker Nuclear Laboratory Cyclotron at University of California, Davis.
The Absorbed Energy was Computed From SRIM (www.srim.org) Stopping Powers.
RCF Exposed at CNL proton Cyclotron
Scan of Step Wedge ND Filter
Rippled 25μm Cu with CH Coating
Ripples on Cu-CH (3μm Repeat) made by General Atomics
12th layer film 34.5 MeV approx 125μm source diameter
Virtual Source
Ripple Surface Target
to RCF
14μm Gold Foil with Contaminants
3.8 MeV 4.9 MeV 5.9 MeV 6.8 MeV
7.6 MeV 8.3 MeV 16.7 MeV 22.1 MeV
26.7 MeV 30.6 MeV 34.2 MeV 37.5 MeV
40.6 MeV
Sample Fit (Un-Etched Gold)Sample Fit (Un-Etched Gold)
Energies computed from stopping powers determined using SRIM.
(www.srim.org)
Thomson Spectrometer Distance to TCC – 13/37 cm
(Callisto/Titan) View - Target Rear Normal Voltage - 4000 V Peak Magnetic Field - 6.0 kGauss Pinhole Diameter - 250/200 microns Minimum Proton Energy - 1.0 MeV Detector - BAS-TR/SR image plate
Carroll, D.C., et al. Central Laser Facility Annual Report 2005/1006
FFBB
FFEE
HH++
CC++
CC+2+2 CC+3+3 CC+4+4
RCF
Thomson Spectrometer
Imaging Lens to Interferometer
13cm
2.5cm
800nm
Probe400nm
28°To Single Hit
Experimental Setup
TCC
RCF
(Callisto: 25mm from TCC
Titan: 65mm from TCC)
Thomson Spectrometer
(Callisto 13cm from TCC
Titan: 36.7cm from TCC)
Diagnostics Radiochromic Film Pack Thomson Spectrometer Side-on Interferometer Single Hit CCD
Callisto Thomson Data
Bright lines are CBright lines are C+4+4 and H and H++ Bright lines are HBright lines are H++ and some Cand some C+5+5
Contaminants NOT removedContaminants NOT removedWithout ErHWithout ErH33 With ErHWith ErH33
Cleaned ErHCleaned ErH33 Target Target
HH++
CC++
CC+2+2
CC+3+3
CC+4+4
HH++
CC++
CC+2+2
CC+3+3
CC+4+4HH++
CC++
CC+2+2
CC+3+3
CC+4+4CC+5+5 CC+5+5
CC+5+5
Contaminants show H+ and C+4 as the dominant ions LSP simulations with this assumption predict a 22% increase in proton
C.E.
Callisto Hydride RCF Results (5μm Au)
Improvement from Improvement from Erbium Hydride is Erbium Hydride is
(25±19)%(25±19)% for for protons above protons above
3.4MeV3.4MeV
From Contaminants From Contaminants C.E. = (0.12 C.E. = (0.12 ± 0.006)± 0.006)%%
From Erbium Hydride From Erbium Hydride C.E. = (0.15 C.E. = (0.15 ± 0.016)± 0.016)%%
Au With Contaminants
Au-ErH3 Cleaned
Raw Data Processed
Hole and off-edge represent 5% of dose
Preliminary Results for Titan
Target ELaser
(J)
# H+
1012
C.E. > 3MeV
Etched Au-ErH3 149 4.2 3.4%
Un-Etched Au-ErH3 143 5.6 5.7%
Un-Etched Au 137 3.0 2.5%
Etched Au 136 0.6 0.3%
Cleaned Au-ErH3 improvement in
C.E. of 36%36%. Au-ErH3 improved C.E. by 128%128%!!! Analysis of the contaminant layer
suggests proton depletion at 10101212 protons
More Shots Needed for Statistics!!!
Preliminary
Affect of Etching Gold
Light ions removed Heavy ion acceleration efficiency improves *
The gold was ionized up to +18, Erbium has similar ionization potentials Calculated traces of ions plotted over data.
Thomson Spectrometer Fujifilm™ IP with close-up look at Au ion signal
Laser: 136 J at 0.5 ps, tight focus (f/3).
Target: 14μm Au foil 3.8 MeV 4.9 MeV 5.9 MeV
6.8 MeV 7.6 MeV 8.3 MeV
* M. Hegelich, S. Karsch, et al., Phys. Rev. Lett. 89, 085002 (2002).
Conclusion
Erbium hydride DOES improve conversion efficiency. In Callisto the mechanism is that of the model
predicted by LSP simulations from Mark Foord, et al.
In Titan, depletion of hydrogen in the contaminant layer is the likely explanation.
Future Efforts
Though results from this experiment do not reach the goal of 15% conversion efficiency, 5.7% offers hope
With a density of 7.6g/cc, ErH3 targets can be made thinner than CH and still provide enough hydrogen to avoid depletion
A study of laser pulse length effects with 5μm Au-ErH3 hopes to demonstrate a factor of 3 improvement this summer on Titan.
Titan Thomson Data
Multiple sources due to edge effects
Contaminants NOT removedContaminants NOT removedWithout ErHWithout ErH33 With ErHWith ErH33
Cleaned ErHCleaned ErH33 Target Target
HH++
CC++
CC+2+2 CC+3+3 CC+4+4
HH++
CC++
CC+2+2 CC+3+3 CC+4+4
HH++
CC++
CC+2+2 CC+3+3 CC+4+4
Single Hit
Single hit spectra for the 5 Titan shots on gold are each similar in yield. Black inverted line is a copper spectrum for reference.
Probe
Because of curled edges on the target, most probe data was obscured on several shots.
These two shots are the exception, however self-emission was also too bright.
Un-Etched AuUn-Etched AuUn-Etched Au-ErHUn-Etched Au-ErH33
Converting Pixel Values to Dose
First 6 layers of filmFirst 6 layers of film
Box and Whiskers show pixel values from data Curves are the calibrated film response
HD810HD810 MD v2 55MD v2 55
1515th th LayerLayer
77thth-14-14th th LayerLayer
Affect of Ionization on HydrideskT = 3MeV Carbon Erbium f(Er)/f(C) f(Er)/f(C)
ne (cm-3) Zavg Zmax Zavg Zmax From avg From max
1e19 3.32 4 4.91 13 1.28 1.24
1e20 3.67 4 9.79 16 1.26 1.18
1e21 3.62 6 17.4 31 1.09 1.11
1e22 5.09 6 24.4 40 1.14 0.91
1e23 5.15 6 35.0 53 0.91 0.69
1e24 3.48 6 42.7 58 0.62 0.63
17.1
1
MN
Qfb
Table showing how the ratio of proton conversion efficiency changes as the sheath E-field increases with the root of the hot electron density. Here I compare ErH3 with CH2
As the electron density goes up, the electric field strength goes up.
Ionization by Barrier Suppression is the dominant ionization mechanism.
Erbium can easily ionize to higher charge states than Carbon and because of the Q1.7, the ratio turns around.
nkTn
E he ˆ2/1
0