Reflectometer on Fusion Experiment

1
Reflectometer on Fusion Experiment

• Expensive, custom-made diagnostic instrument on
  fusion experiments.
• Limited opportunities for acquiring data from
  tokamaks.
• Emit radio frequency waves, measure reflected
  wave.
• Locate turbulence in plasma by correlating
  reflections from frequencies.

2
Goals for Software Simulation of Reflectometer
Challenges Solutions
Develop new Java GUI for portability.
Graphical input for visual verification. Web
service -
Java applet GUI in web browser.
Java servlet on server side inside firewall.
Simulation runs on compute servers. Grid
certificates, MyProxy server. Scale to 8-bit
data on server. Client color-codes
to original range. Transform only visible pixels
for efficient image blending. Develop reusable
modules for graphs, plasma cross sections,
monitoring, run history, credential management.
Visualize input output with minimal changes to
existing Fortran simulation code.
Different computer platforms. Increase
accessibility of simulation to physicists at
different locations, different institutions.
Distribution,
installation Security Blend reflected
waves with input plasma. Data size exceeds
memory limits Transfer technology to other
fusion codes.
3
Multi Tier Architecture
http Web Server
Compute Cluster
Firewall
Experiment Data Server Acquired data Standardized
Form
Internal Server
Users PC, Mac, Linux
Java Servlet
Java Client GUI
Input Plasma
Parametric Model
Data compression netCDF files
Simulated Device
Full Wave Solution
Wave Propagation Simulation
CorrelationGraphs
4
Distribute Processing to Optimize Resources
2. Web server is accessible from anywhere on
Internet. Forwards requests to Java servlet
running in Tomcat container behind firewall.
4. Compute servers retrieve or model input
plasma and run simulation code. Compute cut-off
visualization.
http Web Server
Compute Cluster
1. Java UI runs on users computer for
interactive graphics display. Sends requests to
web server.
Firewall
Experiment Data Server Acquired data Standardized
Form
3.Servlet can access files on portal and
run programs.
Internal Server
Users PC, Mac, Linux
Java Servlet
Java Client GUI
Input Plasma
Parametric Model
Data compression netCDF files
Simulated Device
6. Extract compress data needed by applet for
display.
Full Wave Solution
CorrelationGraphs
Wave Propagation Simulation
7. Compute graphs on server, send graph objects
to applet.
5. Large output files saved in users working
directory on portal storage area.
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Benefits of Java Client Applet
Always run latest version, compatible with
compute service maintained on server side.

• Portable.
• No software installation.
• Accessible by Internet.
• Read URL files over the net.
• GUI classes.
• Porter, Duff image blending methods.

Elfresco The Full Wave Reflectometer Simulation
Code w3.pppl.gov/fwr
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Server Functions

• Input plasma
• Run program to generate parametric model of
  plasma.
• Run program to retrieve standardized form of
  plasma from database of experiments.
• Import netCDF file of electron density,
  temperature, magnetic field.
• Compress input plasma to new file. Link to a
  URL. Send URL to client.
• Save input plasma file in working directory.
• Run wave propagation simulation code
• Read new lines in progress file, return to client
  for monitoring.
• Compress output to new file. Link to a URL.
  Send URL to client.
• Create correlation graph and send to client.
• Run management
• Create working directory for each new simulation
  run.
• Assemble list of run history and send to client.
• Send prior run parameters to client.
• Schedule a run directory to be archived.
• Delete a run directory.
• Retrieve users X.509 credentials from MyProxy
  server.

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Visualize Input Plasma Cross Sections

• Electron Density Temperature
  Magnetic Field

3. x 1019
1 keV
1 T
Coils surround the vacuum vessel so magnetic
field extends beyond the plasma.
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Input Plasma Experimental Shot
MDS Database Acquired data Shot 108730
Shot 108731 Shot ... Standard Form Run
108730-A83 Run 108731-A83 Run ...
Process into Standardized Form
Acquired data from each shot
Retrieve 2-D Profile Electron Density
Temperature Magnetic Field netCDF file -
Input to wave simulation
National Spherical Torus Experiment Produces
shots of plasma within the vacuum vessel
surrounded by magnetic field coils.
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Input Plasma Parametric Model
Calculate profiles when measured data from
experiment is not available.
Parameters Major Radius Minor
Radius Maximum Electron Density Maximum
Temperature Maximum Magnetic Field Ellipticity
Shift
Ellipticity .8
Electron density temperature are highest at
center of plasma and decrease toward edges.
Ellipticity 1.3 Shift 30
Ellipticity 1.3
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Input Plasma Simulate New Design

• Programatically create density, temperature,
  magnetic field profiles.
• Cross section of ITER, the international fusion
  project to be constructed, is shown with 1
  transmitter and 4 receivers.
• Transmitter sends waves toward plasma.
• Receivers measure reflected amplitude of
  reflected waves.

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Wave Reflection Layer (Cut-off Location)

• O-mode LX-mode
  RX-mode

Visualizing location in plasma where a radio
frequency wave will be reflected. Helps the
user select frequency for investigating a
specific location in the plasma. Color bands
preferred to grayscale for perceiving frequency
range even though information is only 1
dimensional. Transmitter is outside the plasma,
on the left or right side. Emits waves toward
plasma. Color code indicates frequency of wave
reflected at a location.
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Wave Reflection Calculation

• Reflectometers emit radio frequency waves,
  typically up to 140 Ghz.
• Waves penetrate plasma proportional to frequency.
• O-mode (ordinary emitted waves) reflection
  location
• X-mode (circularly polarized emitted waves)
  reflection location

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Interactive Graphical Input
Visually verify input before running simulation

• User positions transmitter and receivers.
  Specify frequencies.
• Full Wave (high density) Paraxial (lower
  density) compute regions.
• Regions text drawn with white shadow to
  increase visibility.
• Interactive crosshair on graph for finding
  reflection location (R 1.92) of 53 Ghz wave.

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Multi-Tier Simulation Graphical Output

• Simulation computes amplitude of reflected waves.
• Visualized relative to O-mode reflection
  locations. Graphed at upper right.

User interface assembles all input. Sends as
HTTP request to servlet Run simulation. Polls
for incremental updates to monitor progress of
simulation. Server compresses output for display.
Creates output in a URL file. Applet downloads
from URL and displays results.
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Visualize Solution from Simulation
53 Ghz wave reflection is displayed.
Blending shows wave reaching reflection layer (R
1.92) predicted by color-coded cut-off
visualization.
45 Ghz wave can not propagate as far as 53 Ghz so
it reflects at R 2.1
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Efficient Image Blending
Input Plasma 600 x 900
Transform to blend buffer only the visible pixels
corresponding to Display Area.
r2 , z2
r2 , z2
r1 , z1
r2 , z2
Full Wave
Paraxial
r1 , z1
Blend Buffer (500 x 500 pixels) Allocated to size
of Display Area. Input arrays are clipped before
transforming.
Display Area in Java applet (500 x 500 pixels)
Computed Simulation of reflected waves - 1000 x
400.
Pixels per meter is greater than input
plasma. Horizontal
resolution ? vertical resolution Full wave gt
paraxial resolution.
r1 , z1
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Correlation Graphs Created on Server

• Correlation graphs of 4 frequencies between 2
  receivers.
• Decreasing correlation indicates fluctuation and
  turbulence areas in the plasma.
• Graphs created on server where all data is
  accessible.
• Graphing software, written in Java, integrates
  data exploration and display.
• Graph objects containing actual data are
  created in Java servlet.
• Serialized graphs sent to Java applet as HTTP
  response.
• Graph class running in applet has methods for
  display and exploration.
• Graphs are not static images. Graphs have
  interactive display features.

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Security Model

• User applies for X.509 certificate.
• Requires approval by human.
• Create users work directory within portal.
• Sub-directory for each run created automatically.
• Globus runs jobs in protected directory on
  compute server.

Credential stored on MyProxy server. Retrieved by
servlet via user password. No certificate files
for user to misplace.
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Reusable Software Components

• Develop object-oriented Java classes for applet
  and servlet.
• Scientific Graphics
• Gryph.java base class for objects, graphical
  glyphs, drawn in R-Z coordinate system. Extended
  for rectangular regions, antenna icons, wave
  paths.
• f(x) graphs, indexed f(x, i ) graphs with
  time-step animation.
• Color-coded f(x,y) graphs legends of plasma
  cross sections.
• Simulations
• Sign on to portal. Retrieve manage security
  credentials.
• Submit jobs.
• Monitor a run.
• Applet polls from a new thread so GUI can
  continue running.
• Maintain run history.

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Conclusion

• Successful approach for adding graphical input
  and output to simulation with minimal changes to
  original Fortran code.
• Web service makes simulations more accessible to
  user community.
• System architecture optimizes resources of
  various computers.
• Credential server is convenient for users and
  compatible with security.
• Browser memory limits overcome by scaling data on
  server.
• Efficient blending of zoomed images by
  transforming only visible pixels.
• Visualization guides choosing frequencies.
• Reusable modules enable web services for other
  fusion simulation codes.

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Multi-Tier Graphical Web Service for Simulating
Reflectometry in Plasma

• Eliot Feibush, Gerrit Kramer, Ernest Valeo,
• Raffi Nazikian, Douglas McCune
• Princeton Plasma Physics Laboratory