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results in improved FRC performance.
Main C-2 Impurities
VUV Spectrum
⌅ h⌫ comparable to Core Te
⌅ Emitted by highly charged ions (hot
) Indicative of impurities inside separatrix
Impurity Sources
⌅ Employed survey spectrometers (covered VIS to VUV) and Residual Gas Analyz- ers to study impurity sources in C-2
⌅ FRCbringsin: D,C,N,O,F,Na,Fe, Si
⌅ Plasma Guns add: C, N, O, Fe
⌅ Neutral Beams introduce: H2
⌅ Li-coating reduces: O, N, C, H2 , has no e↵ect on D
Visible Spectrum
⌅ h⌫ few eV, Edge low Te
⌅ Radiated by neutrals and low charge ions
(cold plasma)
) Representative of cold edge plasma
) Shell between Core and SOL emits VUV radiation
C-2 Plasma Zeff
⌅ t = 1 ms: C:<1%, N:3%, O:3%, F:0.3%, Na:0.2% in VUV shell
⌅ t = 2 ms: impurity concentrations in- creased by ⇠ 1.5 times
Spectroscopic Study of Impurity Ion Radial Distribution
in C-2 Beam-Driven Field-Reversed Configuration
D. Osin1, K. Zhai1, M. Beall1, N. Bolte1, Y. Ralchenko2, and TAE Team
1TRI ALPHA ENERGY, INC., P.O. Box 7010, Rancho Santa Margarita, CA 92688-7010 2NIST, 100 Bureau Drive, Stop 8422, Gaithersburg, MD 20899 USA
⌅ C-2 is a macroscopically stable, high-performance field-reversed configuration (FRC), where high plasma temperatures with significant fast ion population and record lifetimes were achieved [1, 2].
⌅ ⌧&5ms;Bw =800G,LFRC '3m,RS '0.35m;Ne ⇠2⇥1013 cm 3,Te ⇠100eV, Ti ⇠500eV-Core;Ne .5⇥1012 cm 3,Te .40eV,Ti .300eV-SOL(R>0.35m).
⌅ Tracking impurities is crucial for monitoring wall conditions and for transport studies
⌅ Knowledge of impurity sources helps reducing charge-exchange and radiative losses and
Comparison: Exp vs Model
⌅ NIST C-R code Ref.[3] used worldwide for EBIT, Tokamak, Z-pinches, LPP
⌅ Quantify impurity concentrations from observed spectral line intensities
⌅ Almost all strong lines identified
⌅ Spectra of moderate charge states of Na, F, O, N and C ions modeled quite accu- rately throughout plasma lifetime
Impurity Charge Profile
⌅ Neutrals and Low charge ions in SOL emit UV-VIS photons
⌅ Moderate charge ions in a shell between Core and SOL radiate mainly VUV
⌅ Higher charge impurities in Core plasma emit mostly soft x-rays
VUV Modeling Results
⌅ Faster than observed ionization rate and conflicting line ratios (using Core [R . 30 cm] Ne, Te data)
⌅ Slower ionization rate, failing to re- produce experimental spectra (testing model with Scrape-O↵-Layer parameters [SOL - R & 45 cm])
⌅ C-R model matches observed VUV-
⌅ Observed VUV-spectra (16 nm to 175 nm) during C-2 plasma lifetime
⌅ Major impurity spectra: C, N, O, F, Na modelled using NIST C-R code
⌅ Impurity charge state radial profile determined experimentally (1st time in FRC)
⌅ Independent measurements (Bremsstrahlung and VUV) revealed low Zeff inside (1.2) and outside (1.5) separatrix
[1] M. Tuszewski et al, ”Field Reversed Configuration Confinement Enhancement through Edge Biasing and Neutral Beam Injection”, Phys. Rev. Lett., 108, p.255008, 2012.
[2] M. Binderbauer et al, ”A high performance field-reversed configuration”, Phys. Plasmas 22, p. 056110, 2015.
[3] Y. Ralchenko and Y. Maron, ”Accelerated recombination due to resonant deexcitation of metastable states”, JQSRT 71, p. 609, 2001.
spectra (with Ne, Te Core and SOL)