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Power Neutral Beam on RFX-mod: Design and Mission

Power Neutral Beam on RFX-mod: Design and Mission. M Valisa, M Gobbin, L Grando, L Marrelli, S Martini, R Piovan, A Rizzolo, P. Zaccaria and the RFX team Consorzio RFX Y. Hirano, S. Kiyama, H. Sakakita AIST Tsukuba. Outline.

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Power Neutral Beam on RFX-mod: Design and Mission

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  1. Power Neutral Beam on RFX-mod:Design and Mission M Valisa, M Gobbin, L Grando, L Marrelli, S Martini, R Piovan, A Rizzolo, P. Zaccaria and the RFX team Consorzio RFX Y. Hirano, S. Kiyama, H. Sakakita AIST Tsukuba

  2. Outline • - Mission : to study physics of energetic particles on RFX • - Design status : • Issues to be solved to connect the AIST beam on to RFX-mod • Diagnostics to be implemented for the beam exploitment OUTLINE

  3. Motivation • Advanced scenarios have been reached in Tokamaks • by controlling the current profile. Methods include use of • neutral beams and radio frequency injection • As in Tokamkas, auxiliary power can be used in RFP’s to optimize plasma control and performance and widen the physics studies. • MST ( Madison, Wisconsin) is testing • - Lower Hybrid & Berstein waves & Neutral Beam Injection for current drive and heating (25keVx40A) • TPE-RX (Japan) has developed a 1.2 MW neutral beam injector.

  4. The TPE-RX beam is available TPE-RX (*) has been dismantled (Jan 2008) . Unique opportunity to loan their Neutral Beam. Beam characteristics Positive Ion source (filament type) Energy : 25 keV Ion Current : 50 A Pulse Duration : 30 ms (*) AIST – Tsukuba Japan

  5. The TPE-RX beam Strong focussing: 4 cm of minimum waist Suitable to fit the existing RFX-mod ports( 100 - 150 mm)

  6. The TPE RX Neutral Beam Injector Source Expansion chamber

  7. The TPE RX Neutral Beam Injector

  8. The power supply

  9. Scientific objectives • • Plasma heating • • Momentum injection • • Current drive • Control of MHD dynamo and tearing • activity. • • Fast particle confinement, beta and instabilities. ( Alfven mode • excitation by fast ions. In particular, mediation of energy • transfer to thermal ions) • Core particle source

  10. On RFX only radial injection possible

  11. Consequences of the radial injection • The initial pitch of the particle is zero (but for the beam divergence): the initial velocity is mainly perpendicular to the field ( apart from the large divergence term). • Particles ionized on the Low Field side are deeply trapped. • Particles ionized beyond the axis are passing. • Current and momentum drive is low Detailed simulation of the experiment to be done shortly • evaluate best position for diagnostics Z, cm R, cm (ORBIT simulation by M. Gobbin)

  12. Beam attenuation Because of the 25 keV, shine-through issues are not severe for the RFX densities (ADAS data / flat density profile) In RFX a(minor radius) = 0.459 m

  13. Heating • 1 MW of injected power in standard discharges is marginal to be sizeable on top of the typical RFX input power > 10 MW. • Slowing down time is 40-60 ms, against a confinement time of approx 3 ms, so that heat release is diluted in time. Heating efficiency will be low • Perhaps some effect during enhanced confinement regimes (QSH, PPCD, OPCD..) with reuced input power . From P. Innocente et al RFP workshop 2008, Stockholm 2 MA

  14. Fast Ion Physics Relevance: Sufficient confinement of fast ions (MeV) is a mandatory requisite of burning plasmas. Collective modes excited by fast ions can enhance energy and momentum losses and cause wall damage Long time-scale non linear processes are expected from interaction of collective modes and fast ion dynamics as well as between drift waves and turbulent transport Fast Ion Physics

  15. Fast Ion Physics • - In MST 25 keV particles have • exp. confinement times ( 30 ms)! • Fiksel G. et al 2005 Phys. Rev. Lett. 95 125001 MST >Neutron emission in MST after beam short pulse

  16. Fast Ion Physics • Estimated Slowing down time • in RFX-mod ~ 40-60 ms (Simulations in progress including main losses mechanisms, • i.e. mg perturbations, ripple, CX etc.) • Gobbin et al Nucl. Fusion 48 (2008) 075002

  17. Installation on RFX not trivial • Design and construction of a new mechanical interface (expansion chamber and stand). • Is a Residual Ion Dump necessary? • Design of a new magnetic shield for the source and the neutralizer (higher stray fields on RFX than on TPE) • Design of the power supply layout and connection to the beam • Procurement and installation of ancillary equipment (cooling, gas valve PS etc) • Integration in the RFX timing sequence • Personnel training (Collaboration from TPE RX expected ) • Development of kinetic models for simulation and interpretation (Colalboration with MST would be helpful) • Development of diagnostics

  18. Screening mg fields Max filed tolerated in • ion source ~ 0.5mT • neutralizer ~ 1mT Source neutralizer ongoing work Filaments are ON 30 sec before pulse Therefore must stand the field generated by the magnetizing windings (60 mT) during charging time( few sec.s) before the RFX-mod discharge Screen must not perturbe the RFX field .

  19. Diagnostics • An NPA diagnostic presently being procured for general Ti measurements on RFX-mod will also be used to study fast ions produced by the power NBI • Development/ procurement of a Fast Ion Losses Diagnostic (FILD) to directly study the losses due to instabilities. • Neutron diagnostic only if D operation will be permitted • CERS will be expanded to the power beam. NBI diagnostics

  20. NPA • Currently discussing about the use of the old NPA of RFX ( originally built for JET in the early 80’s) and the loan of a ACORD model (IOFFE Institute) from Greiswald (IPP COLLABORATION) in view of (possibly) the procurement of a Compact NPA ( IOFFE) IOFFE INSTITUTE http://www.ioffe.rssi.ru/ACPL/npd/npahtml/00/00.htm Old JET NPA efficiency vs neutr. pressure ( high –top – and low – bottom energies)

  21. Fast Ion Losses Diagnostic • FILD allows to directly study the losses due to instabilities. • Scheme as in JET and ADEX-U: magnetic spectrometer disperses fast ions onto a scintillator, the strike point depending on gyroradius and pitch angle. • Detector head: 3-dimensional ion collimator, stainless steel plate coated with scintillator powder and a graphite cap. • Collimator geometry to be optimized by simulating typical particle trajectories of interest.

  22. Alternatively FILD realized with Faraday foil collectors: • Charged particles penetrate a stack of conducting foils, separated by insulating foils. • Number of foils passed before being stopped and generating a current signal depends on their energy . Alternatively: Faraday cup collector

  23. Timeline (Temptative • Delivery Autumn 2008 • Installation Winter 2008 /Spring 2009 ( various steps during RFX ordinary maintainance periods) • Commissioning/connection to RFX Summer/Autumn 2009 • Installation of related diagnostics Autumn/Winter 2009 • Operation Winter 2009 / early 2010 Timeline

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