Introduction

SNAP is a steady-state, one-dimensional kinetic transport analysis code that has been used extensively at PPPL over the last decade to analyze confinement and transport in TFTR plasmas. It provides a ``snapshot'' of local plasma conditions, local heating rates, and local transport coefficients at a single time in the plasma discharge. SNAP also computes several diagnostic simulations, for example the total neutron emission, the poloidal , the surface voltage consistent with neoclassical resistivity, and the ion temperature that would be observed by a chordally-integrating x-ray crystal spectrometer, for comparison with actual diagnostic measurements. SNAP's major calculations include:

1. Mapping of diagnostic data, .
2. Solution of the Grad-Shafranov equation to obtain the magnetic equilibrium (Shafranov-shifted circular flux surfaces).
3. Calculation of the current density profile (Spitzer or neoclassical resistivity) and ohmic heating power density, optionally including beam-driven and bootstrap currents.
4. Neutral beam heating:
   • Deposition of beam neutrals as fast ions.
   • Calculation of first-orbit losses and other first-orbit effects.
   • Numerical Fokker-Planck calculation of the fast-ion distribution function and fast ion density.
   • Calculation of power torque densities delivered to thermal plasma ions and electrons.
5. RF heating: modification of the SHOOT code to calculate the distribution function of the minority-ion energetic tail, plus the collisional coupling of power from the tail population to the thermal plasma.
6. Analysis of a single chordal-integrated visible Bremsstrahlung intensity measurement or loop voltage to determine plasma . The IZIFLAT post processor (see Section 3.10.1) treats non-flat profiles.
7. Calculation of the local ion densities n_h(r), n_d(r), , (hydrogen, deuterium, and light and heavy impurities) using the measured n_e(r), the measured or guessed (r), the contribution from heavy elements Z_effm(r) (typically from pulse-height analysis of soft x-ray emission), the calculated beam density, and a user-specified ratio.
8. Integration of the measured or inferred kinetic profiles (T_e(r), T_i(r), n_e(r), n_d(r), ...) and fast ion density (from Fokker-Planck equation) to obtain pressure profiles and stored energy.
9. Calculation of the neutral density profile n₀(r) using the measured edge source from H emission, gas puff, and beam neutral sources.
10. Calculation of local transport coefficients (, , , D_e(r)) from the calculated power deposition profile and measured temperature, density, and velocity gradients.
11. Calculation of the expected neutron emission from thermonuclear, beam-thermal, and beam-beam fusion reactions.
12. (optional) Calculation of the T_i(r) profile using the ion power balance with a model for ion heat transport (neoclassical or ).

The data inputs to SNAP are the measured profiles ( n_e(r), T_e(r), T_i(r),, Z_eff(r), P_rad(r)) and scalar measurements such as total plasma current, , beam power, gas puff rate, etc. The SNAPIN program reads in the necessary TFTR data, allows editing of that data and the selection of physics models, and writes a SNAP input file, SNAP.DAT. Virtually all of the work involved in running a SNAP analysis is centered on preparing this input file with SNAPIN.

The results of SNAP's analysis are presented in a set of plots. All of SNAP's results are saved in the SNAP archives. A number of utilities exist to extract and plot data from these archives for any snap-try ever performed. CUPLOT [], the standard TFTR data presentation and manipulation package, can plot SNAP data. Selected SNAP output can also be extracted and written into LOCUS-style [] databases using the MINGL [] program.

This guide describes:

• How to prepare SNAP input files with SNAPIN.
• How to run SNAP itself in interactive and batch mode.
• How to examine the SNAP output.
• Various SNAP utilities.
• Some of the physics models incorporated into SNAP.

  
Figure 1: Overview of SNAP Utilities and Files