Engineered-material exposure in Dragonfire – Progress Report Farrokh Najmabadi, Lane Carlson, UC San Diego HAPL Meeting, UW Madison October 22-23, 2008

1. Current arrangement of Dragonfire

Experimental Setup Sample Heater halogen lamp ~500˚C base temperature Sample manipulator electronics Sample manipulator xy translation external control located closer to window In-situ microscopy <25  m resolution Thermometer head 2-mm field of view QCM Laser path

Several PPI “nano-engineered” samples were exposed ID # SubstrateTungsten Material Nominal Size (LxWxH)mm Feedstock Powder Nominal Thickness (µm) V Steel25x25x5Fine W2000 V LAF Steel25x25x5Fine W100 V Steel25x25x5Coarse W100 V Steel50x50x5Coarse W860 V LAF Steel25x25x5W-2Re100 V Steel19x19x5 Topcoat: NanoW 50 Undercoat: Coarse W 600 V *Removed43x9x0.55 Topcoat: NanoW 50 Undercoat: Coarse W 500 Exposed Samples  Sample 171 was not uniform (e.g., substantially different peak temperature for the same laser energy at different locations on the sample.) Results are not reported here.

Exposure of PPI engineered samples – Thermal Response

Thermal response of the PPI samples is quite different from Power-Met samples Sample 152: “Fine” W powder deposited on Steel substrate (nominal thickness of 2000  m)  Lower Thermal Diffusivity: For a fixed laser energy, the peak temperature is considerably higher.  Considerable “hysteresis” in “T vs E” response. For a fixed laser energy, the peak temperature is substantially “reduced” after some exposure. Impurities “boiled” off? Sharpe edges, “loose” pieces were removed by the laser?  Lower Thermal Diffusivity: For a fixed laser energy, the peak temperature is considerably higher.  Considerable “hysteresis” in “T vs E” response. For a fixed laser energy, the peak temperature is substantially “reduced” after some exposure. Impurities “boiled” off? Sharpe edges, “loose” pieces were removed by the laser?

Thermal response of PPI non- engineered sample (nano-W V ) evolves under laser irradiation  The sample temperature evolves for the first minutes.  Is the peak temperature a good parameter for characterization of sample response?  The sample temperature evolves for the first minutes.  Is the peak temperature a good parameter for characterization of sample response?  Substantially lower thermal diffusivity: For a fix laser energy, the peak temperature is considerably higher.  Substantially larger “hysteresis” in “T vs E” response: for a fixed laser energy, the peak temperature is substantially “reduced” after exposure.  Substantially lower thermal diffusivity: For a fix laser energy, the peak temperature is considerably higher.  Substantially larger “hysteresis” in “T vs E” response: for a fixed laser energy, the peak temperature is substantially “reduced” after exposure.

Exposure of PPI engineered samples – Micro-structure Response  As samples start with irregular features, evolution of surface morphology is difficult to ascertain.  Powder-Met samples as a point of reference: For T < 2500 K, no major visible damage (e.g., cracking) occurred. Sample surface “roughness” increased rapidly in the first thousand shot and remained constant afterwards.

There is some evidence of damage to W layers starting at high rep-rate (appear to start at ~2500k) Pristine 152A-H: 150 mJ, T~2200K, 10 5 shots 152A-C: 200 mJ, T~2500K, 10 4 shots 152A-F: 200 mJ, T~2500K, 10 5 shots Sample 152: “Fine” W powder deposited on Steel substrate (nominal thickness of 2000  m)

There is some evidence of damage to W layers starting at high rep-rate (appear to start at ~2500k) Sample 152, Pristine 152A-H: 150 mJ, T~2200K, 10 5 shots 152A-C: 200 mJ, T~2500K, 10 4 shots 152A-F: 200 mJ, T~2500K, 10 5 shots

At higher temperature, micro-structure is disappearing rapidly with increased no. of shots Sample 152, Pristine 152A-D: 275 mJ, T~3000K, 10 4 shots 152A-Iii: 275 mJ, T~3000K, 10 5 shots 152A-I: 275 mJ, T~3000K, 3x10 5 shots 152A-I: 275 mJ, T~3000K, 10 3 shots

“Fine” structure on nano-engineered samples disappear as laser energy is increased even at low no. of shots (10 4 ) Sample 443, Pristine 443-B: 150 mJ, T~ K 443-C: 200 mJ, T~ K 443-F: 250 mJ, T~ K 443-G: 100 mJ, T~ K Sample 443: “Fine” W topcoat (50  m) on “coarse” W undercoat (600  m) deposited on Steele substrate

Cracks appear in the undercoat with increased no. of shots Sample 443, Pristine 443-F: 250 mJ, T~ K, 10 4 shots 443-E: 250 mJ, T~ K, 10 5 shots 443-D: 150 mJ, T~ K, 10 5 shots Sample 443: “Fine” W topcoat (50  m) on “coarse” W undercoat (600  m) deposited on Steele substrate 443-B: 150 mJ, T~ K, 10 4 shots

Summary  Thermal response of “nano-engineered” samples evolve during laser irradiation. Possibilities include: Fine-scale structure may be disappearing Impurities may be removed.  Thermal stability of these sample is a major issue.  For a fixed laser energy, the peak surface temperature is considerably higher than achieved for power-met sample ( ~ a factor of 2 lower thermal diffusivity). This has major implications for maximum power density on the wall.  Thermal response of “nano-engineered” samples evolve during laser irradiation. Possibilities include: Fine-scale structure may be disappearing Impurities may be removed.  Thermal stability of these sample is a major issue.  For a fixed laser energy, the peak surface temperature is considerably higher than achieved for power-met sample ( ~ a factor of 2 lower thermal diffusivity). This has major implications for maximum power density on the wall.  Guidance from The Material Working Group is Needed: As samples start with irregular features, evolution of surface morphology is difficult to ascertain. How should we define a simulation experiment when sample response evolves for the first minutes? Is the peak temperature a good parameter?  Guidance from The Material Working Group is Needed: As samples start with irregular features, evolution of surface morphology is difficult to ascertain. How should we define a simulation experiment when sample response evolves for the first minutes? Is the peak temperature a good parameter?

Thank you, Any Questions?

Small changes in sample when maximum temperature < ~2500K shots 10 5 shots 10 4 shots 14A, 150mJ, RT, Max: 2,500K (~2,200K  T) 11A, 200mJ, 773K, Max: 3,000K (~2,200K  T)  It appears that material response (powder metallurgy samples) depends on the maximum sample temperature and not on temperature rise

An image relay optical train was to used to obtain an accurate thermometer field of view  The thermometer field of view is controlled with the size of the aperture.  A CCD camera was used to verify the theoretical calculation of the spot size.  The thermometer field of view is controlled with the size of the aperture.  A CCD camera was used to verify the theoretical calculation of the spot size. Aperture PMT Head Image of calibration lamp filament 280  m image M=0.2  All results reported are based on a 1-mm aperture (2 mm thermometer field of view)  Reported temperatures are heavily weighted toward “hot spots” because of T 3 dependence of radiation.  All results reported are based on a 1-mm aperture (2 mm thermometer field of view)  Reported temperatures are heavily weighted toward “hot spots” because of T 3 dependence of radiation.

Spatial profile of sample temperature is obtained  The objective of the thermometer head is mounted on a translation stage which would allow sweeping the thermometer spot over the laser beam spot and measure temperature profile of the target in real time.