1. RHEPP Materials Exposure: Recent Experiments Tim Renk and Tina Tanaka Sandia National Laboratories Beam Applications & Initiatives Department HAPL Program Workshop PPPL, Princeton, NJ October 27-28, 2004 Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. Supported by NRL by the HAPL program by DOE NNSA DP

2. Thresholds for Materials exposure to ions on RHEPP General exposure conditions: MAP nitrogen beam, 150 ns pulsewidth, single shot. Roughening threshold for graphite (matrix) is unknown, but probably below 0.5 J/cm 2 Roughening threshold for W for He beam is below that for MAP N Roughening threshold, unheated, for W25Re: 3.5 J/cm 2 Re: 1 J/cm 2 Pulsed Power Sciences, Sandia National Laboratories TJR 04/16/2004 0 Roughening threshold, PM W Plansee, unheated 1.3 J/cm 2 6 J/cm 2 Ablation threshold, W Melting threshold, PM W Plansee, 600C, SIM and expt 2.0 J/cm 2 ? Roughening threshold, Graphite 3 J/cm 2 Ablation threshold, graphites, BUCKY and expt

3. Heated PM W (600C) exposed to N beam at ~ 1.5 J/cm 2 - peak temp ~ 3300K General height change is UP. W25Re suffers similar but less dramatic effect SEMs of PM Tungsten (non-melt): appears stress cracking starts, then exfoliation, forming valleys Pulsed Power Sciences, Sandia National Laboratories TJR 04/16/2004 400 pulses 800 pulses 1200 pulses All images 2000X 1600 pulses

4. Heated W25Re (600C) exposed to N beam at ~ 1.5 J/cm 2 - peak temp ~ 3300K. Sample experienced short melt time SEMs of W25Re (short-melt): appears Similar but attentuated roughening compared to PM W Pulsed Power Sciences, Sandia National Laboratories TJR 04/16/2004 400 pulses800 pulses1200 pulses All images 2000X

5. PM W, Plansee, treated to near-melt, 1600 pulses: ‘Baklava’ structure to > 1 mm depth Pulsed Power Sciences, Sandia National Laboratories TJR 11/25/03 Photomicrograph, side view, 1600 pulses, surface temp to near-melt Grain structure here is horizontal- tending. This looks more serious than roughening

6. Comparison, treated W and W25Re, side view, 1600 pulses: ‘Laminated’ structure to 1mm depth on W, missing in W25Re Pulsed Power Sciences, Sandia National Laboratories TJR 11/25/03 Surface to near-middle (~ 0.8 mm) 0.8 mm to ~ 1.5 mm PM Tungsten: ‘Baklava’ effect’ W25Re Photomicrographs, side view, 1600 pulses, surface temp to near-melt Surface to near-middle (~ 0.6 mm) 0.6 mm to ~ 1.2 mm

7. W welding rod sample (vertical grains with ~ 1% La) was treated at ~ melting temp for 400 pulses Pulsed Power Sciences, Sandia National Laboratories TJR 04/16/2004 Treated WRod 600C (left) after 400 pulses - interface in middle SIM prediction: Ave fluence: 2.2 J/cm 2, high 2.8 J/cm 2, low 1.65 J.cm 2 2.8J/cm 2 : maxtemp 4159K, maxmelt 0.75 µm, duration 154 ns 1.65 J/cm 2 : maxtemp 3207K, no melting Dektak shows lumps ~ 20 µm apart, but can’t track deep ruts in surface.

8. Heated WRod topography looks different from PMW (Plansee) after 400 pulses: smoother, but deeper-looking rifts Pulsed Power Sciences, Sandia National Laboratories TJR 04/16/2004 PMW 600C after 400 pulses WRod 600C after 400 pulses Dektak shows WRod surface tending more towards valleys with cracks which cannot be tracked by Dektak tip

9. Plasma-sprayed W on Steel exposed to 400 Ion Pulses: Evidence of Mass-loss at low Fluence Pulsed Power Sciences, Sandia National Laboratories TJR 11/25/03 454 W on Steel Plasma-sprayed W on steel (unheated) exposed to 400 pulses MAP N at average 1.4 J/cm 2 SIM model prediction: 3000K max for surface temp Interface in middle, exposed at bottom Dektak measurements not definitive – both sides too rough Images indicate mass loss from treated side

10. New velvet material from Knowles exposed to 400 pulses: Good general survival, W melted on some tips Pulsed Power Sciences, Sandia National Laboratories TJR 04/16/2004 Velvet tips unexposedVelvet tips exposed: 400 pulses 2 J/cm 2 Velvet with sputtered W heated to 600C, exposed to 400 pulses MAP N beam at 2 J/cm 2 - melting threshold for W Velvet appears unaffected after treatment. SEM of tips (left) show some melting of W from the tips No W at base of velvet. Appears that W adhered to sides of velvet shafts

11. Summary Roughening may or may not lead to net mass loss. But shredding of PM W by ion exposure over 1600 pulses (‘Baklava’ effect) looks like definite problem, not seen in W25Re exposed the same way. Exposure of W-La rod (vertical grains) produces different topology from Plansee horizontal grains. Smoother but with deeper-looking ‘ruts’. More exposures are planned Plasma-sprayed W (O’dell) appears to suffer mass loss during light exposure (1.4 J/cm 2 ) Latest Knowles velvet shows good survivability, some tip melting. Need to re-expose at below melting threshold. Near-term plans: more WRod, velvet exposure at lower dose. W-on ferritic steel, CVD? Pulsed Power Sciences, Sandia National Laboratories TJR 04/16/2004