Page 8 - CHARACTERIZATION OF THE C-2W PLASMA GUNS

Nucl. Fusion 57 (2017) 116021
open- eld-line/SOL plasma, for which a new set of inner divertors (located between con nement and formation sec- tions) will be deployed in C-2W.
4. Summary
The C-2U experimental program commenced with various key system upgrades from C-2, which include increased total NB input power to ~10+ MW (15 keV hydrogen, higher current at reduced beam energy), tilted injection angle and enhanced edge-biasing capability for boundary/stability control. The upgraded NBI system enabled signi cant plasma performance advances and had a profound impact on C-2U performance: e.g. reduction of peripheral fast-ion losses; increased core heating; rapidly established dominant fast-ion pressure; better NB-to-FRC coupling with reduced shine-through losses; and current drive. Under optimum C-2U operating conditions, plasma sustainment for ~5+ ms was successfully achieved, in which the performance was limited by hardware and stored energy constraints such as the NBs’ pulse duration and the current sourcing capability of the end-on plasma guns. The C-2U plasma performance, including the sustainment fea- ture, has a strong correlation with NB pulse duration, with the diamagnetism persisting even several milliseconds after NB termination due to the accumulated fast-ion population. For the well-con ned FRC regime global power-balance analysis showed a strong positive correlation between electron temper- ature and energy con nement time; i.e. the electron energy con nement time in C-2U scales strongly with a positive power of Te.
Acknowledgments
The authors wish to thank the entire TAE Team for their dedi- cated work and effort on the C-2U project, our Budker Insti- tute colleagues for many key contributions to our experiment and beam development, and our shareholders who made this exciting research effort possible.
ORCID iDs
H. Gota et al
H. Gota T. Asai
https://orcid.org/0000-0001-6475-2912 https://orcid.org/0000-0001-9440-0117
[4] Binderbauer M.W. et al 2015 A high performance eld- reversed con guration Phys. Plasmas 22 056110
[5] Tuszewski M. et al 2012 Field reversed con guration con nement enhancement through edge biasing and neutral beam injection Phys. Rev. Lett. 108 255008
[6] Gota H. et al 2015 Improved con nement of c-2 eld-reversed con guration plasmas Fusion Sci. Technol. 68 44
[7] Guo H.Y. et al 2015 Achieving a long-lived high-beta plasma state by energetic beam injection Nat. Commun. 6 6897
[8] Binderbauer M.W. et al 2016 Recent breakthroughs on C-2U: Norman’s legacy AIP Conf. Proc. 1721 030003
[9] Schmitz L. et al 2016 Suppressed ion-scale turbulence in a hot high-β plasma Nat. Commun. 7 13860
[10] Hoffman A.L. and Slough J.T. 1993 Field reversed con guration lifetime scaling based on measurements from the Large’s Experiment Nucl. Fusion 33 27
[11] Galeotti L. et al 2011 Plasma equilibria with multiple ion species: Equations and algorithm Phys. Plasmas 18 082509
[12] Roche T. et al 2016 Enhanced magnetic eld probe array for improved excluded ux calculations on the C-2U advanced beam-driven eld-reversed con guration plasma experiment Rev. Sci. Instrum. 87 11D409
[13] Thompson M.C. et al 2016 Diagnostic suite of the C-2U advanced beam-driven eld-reversed con guration plasma experiment Rev. Sci. Instrum. 87 11D435
[14] Gota H. et al 2014 Overview of C-2 eld-reversed con guration experiment plasma diagnostics Rev. Sci. Instrum. 85 11D836
[15] Gota H. et al 2012 Internal magnetic eld measurement on C-2 eld-reversed con guration plasmas Rev. Sci. Instrum. 83 10D706
[16] Onofri M. et al 2015 Simulations of the C-2/C-2U eld reversed con gurations with the Q2D code Bull. Am. Phys. Soc. 60 BP12.00032
[17] Onofri M. et al 2016 Transport simulations of the C-2 and C-2U eld reversed con gurations with the Q2D code Bull. Am. Phys. Soc. 61 CP10.00088
[18] Deng B.H. et al 2012 Electron density and temperature pro le diagnostics for C-2 eld reversed con guration plasmas Rev. Sci. Instrum. 83 10E339
[19] Beall M. et al 2016 Improved density pro le measurements in the C-2U advanced beam-driven eld-reversed con guration (FRC) plasmas Rev. Sci. Instrum.
87 11E128
[20] Zhai K. et al 2016 The upgrade of the Thomson scattering system for measurement on the C-2/C-2U devices Rev. Sci. Instrum. 87 11D602
[21] Schmitz L. et al 2014 Multi-channel Doppler backscattering measurements in the C-2 eld reversed con guration Rev. Sci. Instrum. 85 11D840
[22] Gupta S. et al 2016 Transport studies in high-performance eld reversed con guration plasmas Phys. Plasmas
23 052307
[23] Rej D.J. and Tuszewski M. 1984 A zero-dimensional transport model for eld-reversed con gurations Phys. Fluids
27 1514
[24] Trask E. et al 2014 C-2 lithium campaign power balance Bull. Am. Phys. Soc. 59 UP8.00018
[25] Trask E. et al 2016 C-2U Experimental Transport Analysis Bull. Am. Phys. Soc. 61 CP10.00064
[26] Kaye S.M. et al 2007 Con nement and local transport in the National Spherical Torus Experiment (NSTX) Nucl. Fusion 47 499
[27] Kaye S.M. et al 2013 The dependence of H-mode energy con nement and transport on collisionality in NSTX Nucl. Fusion 53 063005
References
[1] Tuszewski M. 1988 Field reversed con gurations Nucl. Fusion 28 2033
[2] Steinhauer L.C. 2011 Review of eld-reversed con gurations
Phys. Plasmas 18 070501
[3] Binderbauer M.W. et al 2010 Dynamic formation of a hot
eld reversed con guration with improved con nement by supersonic merging of two colliding high-β compact toroids Phys. Rev. Lett. 105 045003
8