Fitting transport models to 14MeV neutron camera data D C McDonald, K D Zastrow and I Voitsekhovitch

Time [s] KN3 D-T neutron flux (vert.) KN3 data for T puff Inner channels see puff later than outer ones puff seen by KS3 Puff diffuses to core

TRANSP models the expected 14MeV neutrons from given diffusion and pinch profiles –Time consuming to optimise the profiles –not clear how to discuss errors Methods for fitting transport models choose a D(r) and v(r) run TRANSP to produce n T (r,t) and R KN3 i (t) run SANCO to produce n T (r,t) then calculate R KN3 i (t) choose initial D(r) and v(r) calculate  2 and choose new D(r) and v(r) Automatically finds an optimised parameterised solution with correlated errors Initial version only treats neutron reactivity in 1d UTC TRANSP

stronger inboard emissivity in core similar inboard/outboard emissivity at r/a  0.6 TRANSP fast ion density r and  dependencies artificially plotted on concentric ellipses Beam-plasma neutron emissivities are not constant on a flux surface For JET beam trajectories fast ion birth orbits can be divided into radial 3 zones: –passing orbits in the plasma core –trapped orbits at  mid-radius with inboard banana tips –trapped orbits in the plasma periphery with outboard banana tips This results in a poloidal dependence of the parallel velocity and hence fast particle density / fusion emissivity (also volume and field line angle) C. Challis Poloidal asymmetry in 14MeV emission

The result of the asymmetry is that UTC cannot match the This is a clear sign that the 1d model really is inadequate Some method is required to include the poloidal asymmetry in UTC

Linearised neutron emission For trace tritium DT neutron emission is the sum of the emission from individual elements of the T profile If we could take the TRANSP predicted signals from each element, we would completely describe the 2d neutron profile PPPL has a long term (~6 months) plan to output this data We can do it with 1 TRANSP run for each element

TRDT PPF (61097 UID=dmcd) DTrr: rr=01,..., 19 The simulated KN3 signal for each unit density profile element (channel, t) (cts m/s) RHOT: radial position of each element in root normalised toroidal flux (r) RTOT: total 14MeV count rate for each unit density profile element (r,t) (cts m 3 /s) SVrr: simulated volume fuelling SWrr: simulated wall fuelling The TRDT DDA and how to use it Using the PPF Form DT(channel,r,t) and RTOT(r,t) Put your T density profile onto the RHOT grid n T (r,t) Sum over channels to get predicted 14 MeV signals R tot (t) =  r RTOT(r,t)  n T (r,t) KN3(channel,t) =  r DT(channel,r,t)  n T (r,t)

t = 23.35s Consistency of method First cross-check is against a TRANSP run with a full n T (r,t) profile The plots show that the matrix method agrees with the full run for both –total 14 MeV neutrons –individual cameras Small disparity in the central cameras is largely due to noise from TRANSP Monte- Carlo simulation TRANSP matrix

Poor match on outer channelsMuch better match on outer channels UTC with 1d reactivity modelUTC with 2d TRANSP reactivity The initial UTC runs, with 1d reactivity, could not match the inner and outer vertical KN3 cameras together With the matrix method we get much better agreement on the KN3 vertical cameras The  2 ’s are still too big on some channels, which is believed to be due to effects from... –sawteeth –ELMs –neutral particles Effect of method on UTC Fit to vertical 14 MeV cameras

Plan of action Method requires a TRANSP runs for all tritium puff shots, so these need to be requested We propose that these runs are started now and that they are carried through to a UTC analysis Timing: Initial TRANSP run and validation~ 3 days 20 basis function runs and TRDT ~ 1 day Basic UTC analysis ~ 1/2 day All done ~half done 20 shots selected for EPS

Summary TRANSP fitting of D(r) and v(r) to neutron data is slow, tedious and does not result in a measure of significance for the results UTC resolves these problems, but its original 1d reactivity model couldn’t reproduce the asymmetric neutron emission Solution is to use UTC with a 2d description of the neutron model passed from TRANSP as a matrix Greatly reduces asymmetry of UTC fit to neutron data Do require TRANSP runs for all tritium puff shots Further problems: saw teeth/ELMs transport, the effect of CX with neutral particles