Set the Physics Controls

This section lets you set physics control parameters. It does not read any diagnostic data.

<0=MO> Option for SHOT 58505 @ 3.400 s? <Ph>: ,

\* Options are:

 1) Major radius of the vacuum vessel (<=0 --> R0) ........... <2.650>
 2) HW half-width of the vacuum vessel (<=0 --> 1.1a) ........ <1.000>
 3) HH half-height of the vacuum vessel (<=0 --> 1.1a) ....... <1.000>

 4) Ion convection multiplier for heat transport ............. <1.5>
 5) Electron convection multiplier for heat transport ........ <1.50>
 6) Charge-exchange fraction reabsorbed into the plasma ...... <0.500>

 7) BB Include beam-beam neutron calculations ................ <YES>
 8) BT Include beam-target neutron calculations .............. <YES>
 9) BA Include beam-beam atomic physics ...................... <YES>
10) ED Include energy diffusion in Fokker-Plank equation ..... <YES>

11) BEam-driven current ...................................... <YES>
12) BOotstrap current ........................................ <YES>
13) CUrrent profile .......................................... <Neoclassical>
14) SHafronov shift nonlinear ................................ <YES>

15) RO Include rotation effects .............................. <NO>

16) Alpha heating............................................. <ON>

17) SPecials:  Shifts, Sawtooth model, j(r), MHD numbers ..... <STANDARD>
18) ITeration controls ....................................... <STANDARD>
19) IDentify this as a nonstandard run ....................... <NO>

<1=PC;> Physics control option? <1>:   SP

• Major radius of vacuum vessel: 2.650 meters.
• Half-width & half-height of vacuum vessel: 1.03 meters.
• Ion convection multiplier: 1.5.
• Electron convection multiplier: 1.5. The total heat flux carried by the ions and electrons across a given flux surface is divided into a convection term due to particle flows (, where is the convected heat flux, is the particle flux, T_j is the local temperature, and C_j is the user-assigned convective multiplier) and conducted flows, .

  See Mike Zarnstorff's talk on heat transport analysis from the Santander workshop for a discussion of the appropriate values of C_j under various circumstances. The value of 1.5 is suggested only for consistency with a large collection of SNAP analyses of TFTR supershots, for which the convective multipliers are typically set to 1.5 to avoid nonphysical negative values of .

• Charge-exchange fraction reabsorbed in the plasma: standard recommended values are 0.5 for supershots, and 0.75 for L-mode plasmas.

  Reionization of fast neutrals generated via charge-exchange of the fast ions is treated very crudely in SNAP. In principle, the linear neutral trajectories should be followed, allowing the appropriate fraction of neutrals to be ionized at each step according to the local cross-sections. Some of the beam power which is initially calculated to be charge-exchanged would then be recovered elsewhere in the plasma. Such a calculation is well beyond SNAP's capabilities at present. SNAP simply assumes that a fixed fraction of the charge-exchange power is reabsorbed, and that it is absorbed locally, i.e., at the same radius where the initial charge-exchange event occurred.

  The suggested values are derived from a handful of comparisons with TRANSP calculations, which do follow the neutral trajectories in a Monte-Carlo fashion to determine what fraction is reabsorbed, and where. Somewhat different values are obtained if one tries to match the recaptured number versus the recaptured power of the charge-exchange neutrals.

• Beam-beam and beam-target neutrons calculations: ON. The beam-target and beam-beam neutron calculation require considerable CPU time, so switches have been added to skip them. Having them on is a useful check against experimental data.
• Beam-beam atomic physics: ON. This allows the incident beam neutral population to be ionized by charge-exchange on the existing beam-ion population.
• Beam energy diffusion in the Fokker-Planck equation: ON.
• Beam-driven and bootstrap currents: ON. Presumably the details of the j(r) profile don't have a significant effect on most of SNAP's calculations (beam deposition and thermalization, local transport, fusion reactivity, stored energy). The assumption by SNAP that the plasma has reached an equilibrium j(r) profile is often not satisfied in beam discharges, so SNAP's calculation of it from Spitzer or neoclassical resistivity is suspect with or without the beam-driven and bootstrap corrections. A meaningful estimate of the j(r) profile would require a time-dependent TRANSP analysis.
• Current profile: NEOCLASSICAL (again, unimportant for beam analyses). Since Mike Zarnstorff's analysis of the loop voltage with TRANSP indicates that neoclassical theory adequately describes the data, NEOCLASSICAL is the suggested profile switch. This will have a more significant effect in ohmic discharges, where the only power source is ohmic heating, and especially if the plasma is determined from the resistivity.
• Shafranov shift: NONLINEAR. The nonlinear calculation is thought to be more accurate. By examining a large collection of SNAP analyses, Cris Barnes has come to the conclusion that turning on the switches for the nonlinear Shafranov shift and the beam-driven and bootstrap currents yields the best mapping of measured profiles to flux surfaces.
• Rotation effects: ON (if a rotation profile is provided). If this switch is activated, SNAP will include several rotation effects in its calculations, including:
  • The effect of rotation on the deposition profile (all cross-sections will be computed in the rotating plasma frame).
  • The investment of beam power in pushing the plasma.
  • The return of this power as viscous heating.
  • The rotational stored energy.
  • The rotational energy balance, to deduce \ from the measured .
• Identify this as a nonstandard run: NO. Turn this switch ON if you have reason, in advance, to suspect (or know) that the SNAP\ run is bogus. For example, if you've manually increased to determine the sensitivity of the SNAP results to uncertainties in , please set this switch to ON. You might also want to turn it ON for your first few SNAP analyses. SNAPIN will turn this warning flag ON if you move profile points--see section 3.7.2.
• SPECIALS: STANDARD. Specify profile shifts, sawtooth models, j(r), and MHD numbers.
• ITERATION CONTROLS: STANDARD. Controls tolerances for convergence and the maximum number of iterations for computing various quantities.

Physics has two special submenus, Special and Iterations, which keep track of standard settings of their parameters and warn you if you've got any nonstandard values by highlighting them in the submenus and in the physics menu. The standard values are those remembered from the SNAP.INI file. Note that there are two columns of values in the menus--the first column shows the current settings and the second column shows the standard values.

The Special submenu controls profile shifts, sawtooth model, j(r), and MHD numbers.

<1=PC;> Physics control option? <1>:   SP

\* Options are:

 1) SH Shafranov shift ...................................  YES       YES
 2) BF B-field shift .....................................  YES       YES

 3) SS Shafranov shift source..........................Kinetics  Kinetics
 4) DC Include diamagnetic current in j(r) analysis ......   NO        NO
 5) PS Include Pfirsch-Schluter current in j(r) analysis .   NO        NO

 6) SM Sawtooth model for ions ...........................   NO        NO
 7) SC Chi-i inside q=1 if sawtooth ion model selected ... 1.00E+02  1.00E+06

 8) SF Sawtooth Flattening ...............................   NO        NO
 9) R1 r(q=1) ............................................ 1.20      1.20
10) R2 r(mix) ............................................ 1.68      1.68

11) RAtional surfaces ....................................   25        25

12) REset all special physics values to standard values.

<2=SP;> Special physics option? ....................... Current  Standard <1>:

The Iterations submenu controls tolerances for convergence and the maximum number of iterations for computing various quantities. Don't change these unless you understand what the various controls do.