TJ-II:Pellet injector

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Diagram of the TJ-II pellet injector

A compact multi-barrel pellet injector system is being developed for the TJ-II stellarator (location: sector B2). Its design is based on the system currently installed at the MST facility (Univ. Winconsin) and will provide maximum flexibility at minimal cost, while also allowing for future upgrades. It is a four-barrel system destined for use both as an active plasma diagnostic and as a plasma fueling source. In order to achieve both objectives it will be sufficiently flexible to allow frozen hydrogen pellets with diameters from 0.4 to 1 mm to be formed and accelerated to velocities between 100 and 1000 m s-1. However, floor space restrictions and nearest-neighbor considerations limits the overall length to <1.7 m (mechanical punch end to final guide tube interfaces). This will be done by redesigns of the MST gun barrel, vacuum coupling, gas dump and guide tube sectors. Finally, the system is completed by stand-alone instrumentation and controls, as well as LabView controlled gas manifolds. [1] [2] [3] [4] [5] Recently, the system was used to inject tracer-encapsulated solid pellets. [6]

Pellet injector testing setup, February 2012
Image of 1 mm pellet
Tomographic reconstruction of emission from Bolometry after pellet enters TJ-II plasma


  1. K.J. McCarthy et al, A compact flexible pellet injector for the TJ-II stellarator, Proc. 21st IEEE/NPSS Symposium on Fusion Engineering 2005 (SOFE05)
  2. K.J. McCarthy et al, A compact flexible pellet injector for the TJ-II stellarator, Rev. Sci. Instrum. 79 (2008) 10F321
  3. S.K. Combs, C.R. Foust, J.M. McGill, L.R. Baylor, J.B.O. Caughman, D.T. Fehling, J.H. Harris, S.J. Meitner, D.A. Rasmussen, K.J. McCarthy, M. Chamorro, R. Garcia, C. Hidalgo, M. Medrano, E. Mirones, J. Olivares, and R. Unamuno, A New Four-Barrel Pellet Injection System for the TJ-II Stellarator, Proceedings 2011 IEEE/NPSS 24th Symposium on Fusion Engineering, June 26–30, 2011, Chicago, Illinois
  4. S. K. Combs et al., Results from Laboratory Testing of a New Four-Barrel Pellet Injector for the TJ-II Stellarator, Fusion Science and Technology, 64, 3 (2013) 513
  5. N. Panadero, K. J. McCarthy, E. de la Cal, J. Hernández Sánchez, R. García, M. Navarro and TJ-II team, Observation of Cryogenic Hydrogen Pellet Ablation with a Fast-frame Camera System in the TJ II Stellarator, 43rd EPS Conference on Plasma Physics, Leuven, Belgium (2016) P1.008
  6. N. Tamura, K.J. McCarthy, H. Hayashi, et al., Tracer-Encapsulated Solid Pellet (TESPEL) injection system for the TJ-II stellarator, Rev. Sci. Instrum. 87 (2016) 11D619