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

Jupiter Laser Facility Website

Me

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

Callisto Laser

http://jlf.llnl.gov

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

Titan Laser

http://jlf.llnl.gov

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.

Extra Slides

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