David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 1

Damage ConsiderationsDavid Fritz

FEL Source Propagation Absorbed Energy DoseDamage Processes in SolidsDamage ThresholdsFLASH ResultsSummary

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 2

Comparison to Synchrotron Sources

Parameter APS LCLS

Repetition Rate 6,500,000 Hz 120 HzPulse Length 70 ps 0.25 psAverage Power 1,000 W 0.25 WPeak Power 2.2 MW 8,000 MW

Average heat load is not a concern but instantaneous energy deposition must be considered

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 3

FEL Source Propagation

2/12

0

1)(

zzzW

2

00

Wz

DistancerangeRayleigh

waistbeamGaussian

0

zzW

A diffraction limited Gaussian source is assumed

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 4

Peak Fluence

densityphoton Peak

densityPhoton pulse ain photons ofNumber

)(2)(

2)()(

),,(

)(),,(

2

2

)(2 2

22

peak

photon

peak

peak

photon

zwyx

peakphoton

A

N

zwNzA

zwzA

dydxzyxN

ezAzyx

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 5

Radiation Dose per Atom

photoionpeakphoton AEDose section crossron photoelect Atomic

energyPhoton

photoion

photonE

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 6

Solid State Damage Processes

Thermal meltingPresure effects

SpallationShear

AblationNon-thermal melting

Multi-pulse fatigue effectsThermomechanical stressChemical Phase transition

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 7

Thermal Damage Thresholds

M

R

T

TTM dTCD QdTCD

M

R

T

TM

Heat Capacity - Energy required to raise the temperature of one gram of a substance by 1° K.Enthalphy of Transformation (a.k.a. Latent Heat) – the amount of energy released or absorbed by a substance during a change of phase.

meltingofheatLatentetemperaturMelting

etemperaturRoomheatSpecificmelttoDose

etemperaturmeltingreachtoDose

QTTCDD

M

R

M

TM

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 8

Thermal Damage Thresholds (2)

Beryllium Silicon

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 9

Thermal Damage Thresholds (3)Material Dose to Tmelt

† Dose to Melt † Dose in NEH3 † * Dose in FEH1 † *Be 0.34 0.42 0.0002 0.00004

B 0.54 1.06 0.0005 0.0001

Al 0.19 0.30 0.03 0.007

Si 0.37 0.89 0.04 0.01

Ti 0.50 0.65 0.24 0.06

Cu 0.31 0.45 0.15 0.03

Ge 0.29 0.68 0.12 0.03

Mo 0.93 1.32 0.36 0.08

Ag 0.41 0.43 0.56 0.13

Ta 0.98 1.36 0.72 0.16

W 1.24 1.78 0.76 0.17

Pb 0.09 0.14 1.17 0.26

* 8265 eV Photon Energy, 1.1 x 1012 ph/pulse† Units of eV/atom

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 10

FLASH Results

32.5 nm wavelength25 fs pulse duration5.5 μJ pulse energyB4C, C, Si, SiC were exposed to focused FLASH FELUp to 2.2 J/cm2

Threshold for surface damage is on the order of the fluence required for themal melting

S. Hau-Riege et al., Applied Physics Letters 90, 173128 (2007).

David Fritzdmfritz@slac.stanford.edu

LUSI DOE Review July 23-24, 2007Damage Considerations 11

Summary

Instantaneous energy deposition must be consideredHigh melting point, low-Z materials will be most resistent to damageThermal model predicts that some materials can be safely placed in the NEH and FEH beam at normal incidenceFLASH damage results are consistent with the thermal model