Kaschuck Yu.A., Krasilnikov A.V., Prosvirin D.V., Tsutskikh A.Yu. SRC RF TRINITI, Troitsk, Russia Status of the divertor neutron flux monitor design and integration ITPA-10 Moscow, Russia

Requirements : Total neutron strength  n/s Accuracy 10% Temporal resolution 1 ms Neutron Flux Monitoring System as a tool for ITER fusion power measurement Proposed NFM System consists of: External NFM – set of 235 U fission chambers Internal NFM – 235 U micro fission chambers Divertor NFM – 235 U and 238 U FC Key FC properties: - high radiation resistance - wide dynamic range of measurements - low sensitivity to gamma radiation - high temperature operation - technology availability - long-time experience of application in fission reactor

NFM Systems Integration Integration : Micro fission chambers – behind blanket modules inside tokamak External NFM - set of FC in moderator at the radial port plug (limiter) Divertor NFM – set of FC inside divertor cassette Issue of the integration:  meet ITER requirements  provide absolute calibration

 Analysis of present NFM system operation and integration shows the necessity of high sensitive neutron flux monitor at the divertor level to provide diagnostic requirements and possibility of absolute calibration  Arrangement of high sensitive 235 U (~1.5g) and high purity 238 U (~1.5g) fission chambers will meet required accuracy and temporal resolution for neutron flux dynamic range over 7 orders of magnitude  In both case the proposed fission chamber is a combination of low and high efficient chamber with sensitivity difference 1:10 3 Divertor Neutron Flux Monitor Conception:

Design features:  238 U FC has a B 4 C (~1g/cm 2 of 10 B) thermal neutron shield to reduce transmutation changes of efficiency  235 U FC will be surrounded by water moderator (thickness 5-7 cm) to increase sensitivity. Water can be used from cassette cooling system  Additional blank chamber will be used for background contribution measurements (EM noise, gammas, etc)  Divertor NFM system includes three similar modules located toroidal around the VV to increase sensitivity and guarantee a cross calibration

Specification of DNFM Fission Chambers Fission chamber 1234 Radiator type 235 U (90%) 238 U (99.998%) Electrode area, cm Mass of radiator, g   Sensitivity, cps/(n/cm 2 s)   Dimensions* (   l ), mm  250  500 Temperature, C  350 * - including water moderator

Divertor NFM Integration

DNFM response analyzed using MCNP 4C code:  the simplest model includes full torus vacuum vessel and shielding blanket modules (SS+H 2 O) with elliptic cross- section  monoenergetic (14 MeV) toroidal symmetric neutron source with poloidal distribution and peaking factor 1  3 MCNP Analysis of DNFM Operation  Neutron flux (1  14MeV) at the divertor level has been calculated  Detection efficiency variations were analyzed for vertical and horizontal plasma core shift  Fast neutron fluxes for calibration point source moving toroidally along the VV axis were calculated  Detection efficiency variation versus neutron source peaking factor is under analysis now (in progress)

MCNP analysis results: neutron group fluxes at the divertor level

MCNP analysis results: DNFM efficiency variations for vertical and horizontal plasma core shift

DNFM integration in the new divertor cassette

Conclusions We are planning to continue DNFM activity: Improve the MCNP model including a divertor cassette with T dome support Improve the MCNP model including a divertor cassette with T dome support Development of DNFM fission chamber prototypes for ITER relevant tests (high temperature operation, wide neutron flux range measurement etc.) Development of DNFM fission chamber prototypes for ITER relevant tests (high temperature operation, wide neutron flux range measurement etc.) Integration in the novel divertor cassette Integration in the novel divertor cassette Advance calibration scenario including DNFM Advance calibration scenario including DNFM DNFM official status needs to update (at the moment - RF voluntary task as not credit diagnostic) DNFM official status needs to update (at the moment - RF voluntary task as not credit diagnostic)