There are several options to calculate the bootstrap current in TRANSP, which are described below.

- NLBOOT=.T.
- Set this flag to
`NLBOOT=.T.`

to enable the bootstrap current calculations based on an aspect ratio approximation. This option is compatible with an anomaly factor`XBSTRAP`

(default value is XBSTRAP=1.0) that may be specified in the namelist. - The following options, in addition to NLBOOT=.T. select more advanced models, which are mutually exclusive.
- NLBOOTW=.T.
- Use this option to select the boostrap current computed in the fully general geometry NCLASS neoclassical code. This is compatible with the parameter XBSTRAP described above.
- The parameter
`XL1NCJBS`

can be used to specify a value of the normalized radius (r/a) inside which the NCLASS bootstrap current is not to be believed, but replaced by a smooth extrapolation to zero on axis. The default, XL1NCJBS=0.1, is the minimum, recommended value. - NLBOOT_SAU=.T.
- Use this option for full generalized geometry and arbitrary collisionality bootstrap current as in O. Sauter, C. Angioni and Y. R. Lin-Liu, Phys of Plas 6(7), 2834 (1999)
- This option is compatible with XBSTRAP described above and with XL1NCJBS. However, the latter correction might not be needed for this model, thus XL1NCJBS=0.0 may be advisable.
- Set
`SAUTER_NC_ADJUST(2)`

to a value other than 1 to scale the electron collisionality used in the Sauter bootstrap model. - Set
`SAUTER_NC_ADJUST(3)`

to a value other than 1 to scale the ion collisionality used in the Sauter bootstrap model. - For these controls the default value is 1.0 and the allowed range is 0.0 to 10.0.
- NLBOOTHAGER=.T.
- Use this option to select the parametrization by R. Hager [Phys. Plasmas 23, 042503 (2016)], which is a correction to the Sauter model to include higher collisionality regimes, based on calculations run with XGCA.
- This option is compatible with XBSTRAP and with XL1NCJBS. However, like for the Sauter model, it might not be needed to use this parameter and XL1NCJBS=0.0 might be advisable.
- The additional outputs PLJBSHAGER (SAUTER HAGER bootstrap current
**J•B**), and CURBSHAGER (SAUTER HAGER bootstrap current density A/cm^{2}) are avialable in the TRANSP output. - NLBOOTNEO=.T.
- USe this option to select the bootstrap current computed in the gyrokinetic neoclassical model NEO.
- This option is compatible with XBSTRAP and with XL1NCJBS, although XL1NCJBS=0.0 may be advisable.
- Set
`NEO_SMOOTH_BOOT=.T.`

to smooth the bootstrap current calculated by NEO, if needed. - Please cite the following papers if using this option in TRANSP:
- E. Belli and J. Candy, Plasma Physics and Controlled Fusion, vol. 50, 095010 (2008).
- E. Belli and J. Candy, Plasma Physics and Controlled Fusion, vol. 51, 075018 (2009).
- E. Belli and J. Candy, Plasma Physics and Controlled Fusion, vol. 54, 015015 (2012).

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