K-Shell Spectroscopy of Au Plasma Generated with a Short Pulse LaserCalvin Zulick[1], Franklin Dollar[1], Hui Chen[2], Katerina Falk[3], Andy Hazi[2], Karl Krushelnick [1], Chris Murhpy[3], Jaebum Park[2], John

Seely[4], Ronnie Shepherd[2], Csilla I. Szabo[4], Riccardo Tommasini[2]

[1] Center for Ultrafast Optical Science, University of Michigan[2] L-472, Lawrence Livermore National Laboratory

[3] Clarendon Laboratory, University of Oxford[4] Space Science Division, Naval Research Laboratory

Experimental Setup and Background: The

Titan laser, part of the Jupiter Laser Facility

at Lawrence Livermore National Laboratory,

was used to deliver a 350 joule, 10 ps, 1054

nm laser pulse to a Au target. The

absorption of laser energy by the resulting Au

plasma results in the production of

suprathermal (“hot”) electrons which

propagate into the target. The high energy

electron beam knocks inner shell electrons

from their orbit leaving vacancies which can

be replaced by higher energy electrons. The

energy released as electrons relax into inner

shell vacancies is given off as x-rays

(commonly referred to as K-alpha and K-beta

radiation) which differ in energy depending

on the original shell position of the electron.

Summary:

•The cylindrically bent crystal spectrometer provides an effective way of measuring

K-alpha and K-beta x-rays from short pulse laser-matter interactions.

•The presence of a nanosecond pulse on the rear surface of the gold target

increased the K-alpha to K-beta ratio.

•The plasma conditions inferred by the K-shell x-rays may provide some insight into

the production of positrons.

Cylindrically Bent Crystal Spectrometer: A hard x-ray spectrometer

was used to time-integrate x-ray spectra and prove intensity and

energy data. The spectrometer utilized a cylindrically bent quartz

crystal to “focus” Bragg diffracted x-rays through a lead slit. The

dependence of the Bragg angle on the x-ray energy introduces

spatial separation in the x-ray energies which are then resolved on

image plate.

References:

[1] Kneip, S. et al. HEDP 4 41-48 (2008)

[2] Jiang, Z. et al. Phys. Plasmas 2 5 1702-1711 (1995)

[3] http://www.nist.gov/physlab/data/xraytrans/index.cfm

[4] Chung, H. et al. http://nlte.nist.gov/FLY/ (2008)

Electron Shell Diagram

Titan Experimental Chamber

This work performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344 and was funded by LDRD #10-ERD-044

Simulation: FLYCHK[4], an atomic NLTE code designed to provide ionization and

population distributions, was used to simulate the K-alpha and K-beta spectra for

Au targets with varying temperatures and ionization states. Temperature and

ionization estimates were calculated with HYADES (a 1-D hydro-code).

Image Plate showing Eu Spectra

K-Shell Spectra: K-Alpha1,2 and K-Beta1,2 transitions were observed over a

series of 40 shots with varying target and laser conditions. The observed

spectra were consistent with tabulated energies[3] for both cold Au and Eu

targets.

0

0.02

0.04

0.06

0.08

30 40 50 60 70 80 90 100

Inte

nsi

ty (A

rb)

Energy (keV)

Eu Shot

Line Kev

Kα2 40.9

Kα1 41.5

Kβ1 47.3

Kβ2 48.3

Tabulated Values (NIST)

Line Kev

Kα2 66.9

Kα1 68.8

Kβ1 78.5

Kβ2 80.3

Tabulated Values (NIST)

The axial symmetry of the spectrometer allows duplicate

information to be recorded on each side of the image plate,

providing additional signal and information about the

background noise. Second order Bragg peaks from the K-

alpha signal are also evident in this image.

Higher Energy

Spectrometer in the Titan target chamberCAD drawing and schematic of the spectrometer

The spectrometer was designed with a

60cm stand off distance which

corresponds to a collection angle of

approximately 50 mrad.

We performed a series of shots in which the backside of the target was pre-

heated and pre-ionized with a long pulse laser (3 nanosecond, 1-10 joule). We

observed an increase in the ratio of K-alpha to K-beta signal with increasing

short pulse laser energy.

Abstract: The production of x-rays from electron transitions into K-shell

vacancies (K-α/β emission) is a well known process in atomic physics and has

been extensively studied as a plasma diagnostic in low and mid Z materials[1-2].

Such spectra from near neutral high-Z ions are very complex and therefore

difficult to describe with analytical models. In this experiment a high Z (gold)

plasma emission spectrum was measured with a transparent cylindrically bent

quartz crystal spectrometer with a hard x-ray energy window ranging from 17

to 102 keV.

Using these estimates, FLYCHK was used to establish a better estimate on the

plasma conditions by matching the simulated spectra to the observed intensity

ratios. Ultimately, this information will be used to establish a connection

between the plasma temperature and ionization states and the production of

positrons.

Kβ1 Kβ2

Kα2 Kα1

0

20

40

60

80

100

120

60 65 70 75 80 85 90

Inte

nsi

ty (A

rb)

Energy (KeV)

Au Shot

2.5

3

3.5

4

4.5

5

5.5

6

6.5

0 2 4 6 8 10 12

Rat

io

Joules

Au Kα/Kβ

area

Peak

3

3.5

4

4.5

5

5.5

6

1 10 100 1000

Rat

io

Joules

Eu Kα/Kβ

Area

Peak

0

0.1

0.2

-0.005 0 0.005

Thickness [cm]

Ke

V

Electron Temperature

10

30

0 0.01

Thickness [cm]

Z b

ar

Ionization Level

2x1021

4x1021

-0.02 -0.01 0 0.01 0.02 0.03

Thickness [cm]

Ele

ctr

on

s p

er

cm

3

Electron Density

1018

1019

1020

1021

1022

1023

-0.02 -0.01 0 0.01 0.02 0.03

Thickness [cm]

Ion

s p

er

cm

3

Ion Density

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

60000.00 65000.00 70000.00 75000.00 80000.00 85000.00 90000.00

No

rmal

ized

Inte

nsi

ty

Energy (eV)

K-alpha / K-beta strengths for various Au conditions

Neutral

100eV 10+

10eV 5+

50eV 10+

75eV 10+