Neutral Beam inputs in TRANSP

This page summarizes how to describe neutral beams in TRANSP: geometry, energy fractions, and total injected power. During the data step, the program nblist writes these values to the namelist and also creates a composite UFILE (PNBI<shot>.NBI_<seq>) containing beam powers, voltages, and energy fractions. Consequently, many beam controls are absent from the template namelist and are populated by nblist automatically.

Composite UFILE contents

  • Injected Power PINJ(t) [W] for beams 1…N
  • Beam Energy EINJ(t) [V] for beams 1…N
  • Full-energy current fraction FFULL(t) for beams 1…N
  • Half-energy current fraction FHALF(t) for beams 1…N

To read this file, set NLBDAT = .TRUE. and specify PRENB2='PNBI', EXTNB2='NBI' in the namelist.

Global controls

These apply to all PINIs used during the run.

NBSHAP
Ion-source shape. For JET use 1 (rectangular source).
BMWIDR
Half-width of rectangular ion source [cm]. JET: 9.
BMWIDZ
Half-height of rectangular ion source [cm]. JET: 22.5.
REDGE
Half-width of rectangular vessel aperture [cm]. JET: 17.0.
XZEDGE
Half-height of rectangular vessel aperture [cm]. JET: 19.0.
FOCLR
Horizontal focal length [cm]. JET: 1e-3.
FOCLZ
Vertical focal length [cm]. JET: 1.4e-3.
DIVR
Horizontal beam divergence (1σ) [rad]. JET: 1.22e-2.
DIVZ
Vertical beam divergence (1σ) [rad]. JET: 1.22e-3.

PINI-specific controls

For each active PINI, nblist appends a set of entries to the namelist. The time-dependent values PINJ(i), EINJ(i), FFULL(i), FHALF(i) are included but set to zero in the namelist—they are read from the UFILE above.

TBONA(i), TBOFFA(i)
Beam turn-on / turn-off times [s]. Note: unless NLNBTFIX=.FALSE. is set, TRANSP derives on/off from the power UFILE (default on at >5% of max power).
RTCENA(i)
Tangency radius (closest approach to tokamak centerline) [cm].
XLBTNA(i)
Distance source → tangency point [cm].
XYBSCA(i)
Elevation of the ion source relative to midplane.
NLCO(i)
.TRUE. for co-injection with plasma current.
ABEAMA(i), XZBEAMA(i)
Atomic weight / charge of injected species (e.g., D: 2.0 / 1.0).
XLBAPA(i), XYBAPA(i)
Source→aperture distance and aperture elevation of beam centerline. Vessel apertures are rectangular by default.
XBZETA(i)
Toroidal angle of the beam source in right-handed (R, ζ, Z) [deg].

NUBEAM particle position & distribution restart data

NUBEAM stores Monte-Carlo particle snapshots to (a) reconstruct fast-ion distributions, (b) restart, and (c) debug. Only the data required to restart or debug NUBEAM are saved.

Primary MC particle properties

  • nbienay(minb,mibs) — energy fraction (1 full, 2 half, 3 third)
  • einjay(minb,mibs) — injection energy (lab)
  • pmechay — mechanical momentum; pphiay — canonical momentum
  • pinjay — injected power at deposition (no shine-through)
  • vay — |v|; xmuay — magnetic moment (v⊥2/B)

Additional stored data

  • njavay — orbit-avg zone; cxpray — CX control; fppray — FP control; goosay — MC control
  • nbndex — storage index; nbscay — source index
  • rmjionay, xzionay — guiding-center R/Z (previous step)
  • tdepay — deposition time; tfluxay — flux coordinate (Wb); thay — poloidal angle
  • wghtay — MC weight; xiay — xi; xistay — deposited XIFLR / prev. orbit-avg xi
  • xksidy — v∥/v; xzbmay — heavy-ion charge state

Minimum variables for phase-space reconstruction

  • rmjionay → R, xzionay → Z, vay → |v|, xksidy → v∥/v, wghtay → weight

If multiple files exist for a time, read all of them.

Beam vs. fusion particles

From <RUNID>_debug_nbi_fld_state.cdf, read nlfprod(:): 0 → beam (NBI); 1 → fusion product.

Species mass/charge and mapping

From <RUNID>_ps_ts1_state.cdf obtain qatom_ALL, m_ALL with Z = qatom_ALL/ps_xe, m/m_p = m_ALL/ps_mp. Use snbi_to_all, sfus_to_all for species mapping.

Getting particle files

FI_OUTTIM = t1, t2, ...
fi_gzn_unpack <RUNID>_FI_TAR.GZ1

Time averaging and timing

If SELAVG='FBM...', AC quantities are averaged over AVGTIM. Particle lists *_nbi_ptcl_state_*.cdf, *_debug_nbi_ptcl_state_*.cdf are not averaged.

  • _debug_nbi_ptcl_state_*.cdf — written at the beginning of a NUBEAM call
  • _nbi_ptcl_state_*.cdf — written at the end of a NUBEAM call

Empty slot indicator: R=0 and Z=0. Weight=0 → particle killed/not tracked.


Information on Reconstructing fast ion distribution functions from NUBEAM is also described in the presentation by Joshua Breslau and Deyong Liu (TRANSP User Meeting, 2017).