ARIES: Fusion Power Core and Power Cycle Engineering

1
Modeling Analysis of Carbon Fiber Velvet Tested
in RHEPP Ion Beam Facility

• A. R. Raffray, J. Pulsifer, M. S. Tillack, X.
  Wang
• University of California, San Diego
• With input from T. Knowles (ESLI) and T. Renk
  (SNL)
• HAPL Review
• GA, San Diego
• April 4-5, 2002

2
Energy Deposition as a Function of Penetration
Depth in Carbon Flat Wall Under RHEPP Ion Spectra

• Ion Beam data obtained from T. Renk in
  terms of time, voltage and current density for
  each ion
• - 5.11x104 J/m2
• - Energy Split
• - 16 H
• - 26 C
• - 57 C
• Energy deposition computed as a function of
  penetration depth for given ion spectra
• based on SRIM stopping power data

3
How Does the RHEPP Energy Deposition Compares
with the 154 MJ DD Target Spectra Case for R6.5
m?

• Energy Deposition fromRHEPP dominated by C
  ions
• Energy deposition from DD target spectra
  dominated by deuterium and tritium ions
• C and H ions have different penetration depths
  and energy deposition profiles
• RHEPP reproduces the debris ion energy
  deposition level and penetration depth within a
  factor of 2

4
Volumetric Heat Generation as a Function of Space
and Time in Carbon Flat Wall Under RHEPP Ion
Spectra
5
Temperature History for Carbon Flat Wall Under
RHEPP Ion Spectra

• Updated sublimation model for C from Philipps
  recommendation
• IFE reactor-like CFC thermal conductivity as a
  f(T) (235 W/m-K for T gt1800 C)
• - Max. Temp. 4370C
• - Corresponding sublimated thickness
  calculated as 0.032 mm per shot for 5.1x104
  J/m2)
• Measurement from T. Renk on POCO Graphite 20
  mm after 75 shots, 0.27 mm per shot for 5.5x104
  J/m2
• Not clear what grade of POCO graphite was used
  but k would be much lower

6
Maximum C Temperature and Sublimation Loss per
Shot as a Function of Energy Density and kcarbon
for Same RHEPP Ion Energy Level

• Sublimation model from Philipps data derived
  for Tlt4000K
• As expected, thermal conductivity plays a key
  role and it is possible to sublimate 1 mm per
  shot at energy density of 4 x104 J/m2 if k lt 100
  W/m-K
• POCO graphite seems to have low k and would be
  a poor material to validate CFC grade armor
• It is very important to conduct experiments on
  well characterized material and with good
  diagnostics (surface T and mass loss)

7
Carbon Fiber Geometry Model
Fiber characteristics Fiber length 2500mm
Fiber diameter 6.5mm Fiber k 100-200
W/m-K 1.5 fiber volume fraction 98.5 void
fraction Fiber separation, y
47mm yeff 215mm
8
Carbon Fiber Energy Deposition Model

• Penetration depth set as a function of location
  in fiber based on angle of incidence and
  including shadowing effect from upstream fibers
• Energy deposition calculated as a function of
  penetration depth and including angle effect
  which effectively increase the area seeing the
  ion flux

9
Results for Carbon Fiber Under RHEPP Ion Spectrum
Angle Max. Temp.(C) Avg. Fract. Subl.
Loss Left Right Fiber Tip Overall. 0
4390 4390 1 0.015 5.2 4092 4352 0.
43 0.0065 10 4170 4292 0.31 0.0046 20
4213 4041 0.15 0.0023 Fractional
sublimation loss of 1 is equivalent to
0.032mm per shot Sublimation loss for
fiber based on temperature distribution at
tip Major difference with flat plate is very
low density of fiber (0.015) In agreement
with post-experimental examination of fiber
showing no visible ablation or loss of material
Temperature Contour at Time Corresponding to
Tmax for 10 Case
10
Concluding Remarks from Fiber Analysis

• Difficult to model flat POCO graphite case in
  the absence of fully characterized property data
  and temperature surface temperature measurement
• - Need to use actual material or material
  closely-ressembling (in properties) reactor
  grade armor
• - Need to fully characterized material
  properties
• - Need to conduct experiments with adequate
  diagnostics
• Based on the fiber model (and consistent with
  experimental observation), much less material is
  ablated from the fiber
• - Incidence angle effect on local sublimation
• - More importantly, fiber density effect on
  total sublimation