Page 4 - ntegrated diagnostic and data analysis system of the C-2W advanced beam-driven field-reversed configuration plasma experiment

10K114-3 Thompson et al.
Rev. Sci. Instrum. 89, 10K114 (2018)
that typically delivers 30 pulses at 1 kHz and 2 J per pulse plus a burst of 6 pulses at 13 kHz or 4 pulses at 20 kHz, optics that collect scattered light at 16 points along a line through the center of the plasma between −9 cm < r < 64 cm, and a set of polychromators in which each has five wavelength channels.
A Vision Research Miro Lab 310 camera (typically oper-
ated at 384 × 384 pixels and 19 550 fps) takes images of
the C-2W plasma inside the CV. As on C-2U,20 the camera
is coupled to a custom re-entrant optical system to optimize
the side-on, radial, wide-angle view of the plasma and a fil-
ter wheel to select specific bandpass filters between shots. An
end-on, axial view camera is also planned to facilitate ongo-
ing work on the tomographic reconstruction of the plasma
21
eters with ranges spanning λ = 200 nm–1100 nm provide
survey spectroscopy of the FRC core and SOL with a min-
imum integration time of ∼1 ms. A vacuum ultraviolet (VUV)
spectrometer22 is also ready for installation on the CV. In addi-
tion, a multi-chord bremsstrahlung system measures unbound
electron radiation in two narrow bands (one near 523 nm and
the other near 1000 nm) generally free of atomic and molecular
emission in order to calculate the effective ionic charge Zeff .
Preliminary C-2W measurements agree with the value Zeff ∼
5,23
Charge exchange recombination spectroscopy (CHERS)
measurements of both impurities and main deuterium and
hydrogen plasma ions will expand significantly on C-2W. Lim-
ited measurements of the main ion temperature and rotational
velocity were accomplished by modulating one of the heat-
ing NBs on C-2U since that experiment lacked a dedicated
24
the total radiated power, plasma position, and 3D radiation profile. The total radiated power from the plasma within the CV was typically on the order of 100 kW in C-2U but is expected to raise as temperatures increase on C-2W.
NB shine through is monitored by secondary electron emission (SEE) detectors built into the four beam dumps that
emissivity.
Four Avantes AvaSpec model ULS2048-EVO spectrom-
range.
FRC plasmas on C-2W are formed with deuterium and
3,5
1.3 observed on C-2/U within the uncertainty.
arrays of filtered detectors monitoring deuterium Balmer-alpha line emission are also planned to assist reconstruction of the neutral density profile within the CV.
diagnostic neutral beam (DNB).
is impractical on C-2W and a new DNB is under construction to support CHERS on the experiment. Spectroscopic measure- ments of the SOL electron temperature Te and density ne by performing dual wavelength imaging of helium gas puffed into the SOL25 are planned.
32
plasma pressure according to other measurements and anal-
3
studies the Doppler-shifted Balmer-alpha line emission from
re-neutralized confined fast-ions that charge exchange with NB
atoms or halo neutral atoms. Tests of FIDA on C-2U demon-
strated the feasibility of the technique for characterizing the
27
12 −3 cm
yses from C-2U. FIDA is a special class of CHERS that
sistent with earlier C-2U results showing ne ∼ 5 × 10
32
ne in the other mirror region at z = −3.06 m. Light scattered
from a 2 J/pulse, 100 Hz repetition rate, Nd:YAG laser operat-
ing at 1064 nm is collected at 5 spatial points across the radius
17
super-thermal ion population of a beam-driven FRC.
Various bolometers are being deployed on C-2W to mea- sure the total flux of electromagnetic and neutral particle energy emitted by the plasma. The bolometer array includes multiple 100 channel bolometers based on 20 channel absolute extreme ultraviolet (AXUV) photodiodes, two AXUV total radiation bolometers that view the whole plasma, a series of single chord AXUV bolometers along the length of the CV, and pyro-electric crystal bolometers. Together, these units measure
of the plasma jet.
operate at 1064 nm and are collocated in the same enclosure, which allows swapping of the beam destinations to measure jet Te with higher temporal resolution if needed. Langmuir probes measured T e ∼ 40 eV in the C-2U jet. Similar jet T e is expected in C-2W when operated with a C-2U-like field con- figuration, but it should rise substantially when field expansion in the inner divertors is implemented, Fig. 1(b). Consequently,
Heating beam modulation
study effort builds on the C-2U program similar elements.
and contains many
Improved fast-ion deuterium-alpha (FIDA) spectroscopy
capability will be deployed on C-2W26 to study the substan-
tial fast-ion population that provides up to 50% of the total phase.
Multi-chord
service C-2W’s eight heating beams.
28
Neutralized plasma
ions and fast ions escaping the CV are analyzed with two
neutral particle analyzers (NPAs). One NPA is based on elec-
trostatic separation.
29
The other NPA operates in an E||B
configuration, permitting simultaneous energy and mass dis-
crimination of particles with high energy resolution and
30
sustained with hydrogen NB injection.
an average thermal ion temperature Ti ∼ 0.5 keV which
produces a small number of DD nuclear reactions sufficient
for diagnostic purposes. Additionally, the NBs can be doped
with a minority fraction of deuterium so that fusion prod-
ucts can be used to diagnose beam-injected fast ions. The
2.5 MeV neutrons produced in these reactions are detected
with fast scintillation detectors mounted just outside the vac-
31
B. Plasma jet diagnostics
The FRC SOL collapses into axial jets beyond the
X-points of the FRC, as illustrated in Fig. 1. These jets extend
through the ends of the CV into the inner divertors, forma-
tion sections, and outer divertors. The transition between the
relatively dense jet plasma and the diffuse expanding plasma
in the divertors changes depending on the selected magnetic
configuration, e.g., Fig. 1(a) verses Fig. 1(b). The C-2W jet
uum chamber.
the spatial distribution of 3 MeV protons generated by DD fusion.
A set of in-vacuum proton detectors observe
Multi-chord, multi-wavelength interferometry provides
plasma jet density profile information in the mirror region at
z = 3.06 m from the CV mid-plane. Three chords operating
at λ = 10.6 μm are optimized for high density periods, e.g.,
translation of the FRCs, and two chords at λ = 1 mm provide
sensitivity to the lower ne expected during the sustainment
33
ations under C-2U-like conditions, Fig. 1(a), are broadly con-
Preliminary data from the 1 mm system during oper-
in the plasma jet.
The jet TS system will provide measurements of Te and
Both the jet and FRC core Thomson lasers
C-2W currently has