An Interesting Poster to look at from the Tri Alpha Energy Team in California

Jet Outflow Measurements on the C-2U Beam Driven Field-Reversed Configuration Experiment
D. Sheftman1, D. Gupta1, T. Roche1, M. Thompson1, H. Zhang1, F. Giammanco2, F. Conti2, P. Marsili2, C. Moreno2 and the TAE team 1TRI ALPHA ENERGY, INC., P.O. Box 7010, Rancho Santa Margarita, CA 92688-7010 2 Department of Physics, University of Pisa, Italy
 Abstract
Knowledge and control of the axial outflow of plasma particles and energy along open field lines are of crucial importance to the stability and longevity of advanced beam-driven FRC plasma. An overview of the diagnostic used to perform measurements on the open field line plasma on C-2U is presented, including impurity Doppler spectroscopy, microwave interferometry, triple probe measurements and radial impurity emission profile scanning. Results of these measurements provide the jet ion temperature and axial velocity, electron density and fast fluctuations. In addition, comparison between measured and estimated jet outflow measurement will be presented.
 Microwave interferometry reveals fast fluctuations in jet
 Clear correlation with “staircase” magnetic flux loss
 Clear correlation with mid-plane microbursts, measured through FIR
interferometer at confinement center
 Time delay between z=0 and z=2.25m microbursts shows
that propagation velocity of magnetic flux and fast ion energy losses fits well with ion acoustic waves
 Doppler spectroscopy- typical results  Good fit with Maxwellian distribution
𝑓 λ ∝ exp − λ − λ0 2
𝜎2 − 𝜎2
λ 𝑖𝑛𝑠𝑡
 Ion temperature and velocity obtained from fitting
𝜎2−𝜎2 ∆λ
𝑇[keV]=4.7∙105 λ 𝑖𝑛𝑠𝑡 𝑣 =− 𝑐 𝑖 λ2𝑖λ
 Spectrometer calibration uncertainty results in ±10 km/s absolute velocity error
 Typical relative velocity and temperature errors: ±2 km/s and ±25eV respectively
 Radial measurements-Impurity emission profile
 Emission of O4+ line at different radial chord views of jet measured
To PMTs
278.1nm O4+, z=2.25
 Emissivity e(r) calculated through Abel inversion
𝜀 𝑟 = 𝜎 𝑇 𝑛 𝑛 𝑒𝑒𝑂
r
nO- Oxygen concentration
 Triple probe results show that 𝛆 ∝ 𝐧𝐞
(assuming uniform Oxygen distribution)
𝑛𝑒∝𝑒𝑥𝑝−𝑟2 [1] 𝑎 - jet radius𝑎2
 Microwave interferometry- ultra sensitive jet diagnostic
 2mm wavelength
 80mm beam diameter
 Two Gunn oscillators
heterodyned at 100MHz
 Sinj and Cosj measured,
integrated density calculated from phase (see bottom Fig.)
 Successful multiple fringe counting, despite loss of signal due to beam refraction
Spectrometer chords
 Doppler spectroscopy- jet ion velocity and temperature diagnostic
 Chromex 250-IS spectrometer, f=250mm, 3600 gr/mm
 Exit spectra magnified x30 onto 3x32 channel PMT arrays
 PMT channel resolution 0.045nm, total range 1.44nm
 Instrumental broadening 0.06-0.1nm (@20-100 mm slit width)
 Collects light from formation section, at different locations
 Measured and calculated outflow velocity  Jet velocity estimated from:
 Particle losses
 Integrated electron density  Measured radius
𝑓 𝑛𝑒𝑑𝑙∙2 𝜋𝑎
𝑣=
f- D+ FRC particle loss flux
 Radial measurements-Triple Probe  Limited insertion- up to r=20cm
 Constant Voltage applied V+-V->Te/e
 Electron temperature and density calculated (see Fig on right):
𝑒𝑉−𝑉 + 𝑓𝑙
z=2.25m
𝑇=
𝑒 𝑙𝑛2
𝑛𝑒 =
𝐼 , 𝐴-probe surface 𝑒𝑐𝑠𝐴
on z-axis (see bottom left fig.)
To digitizers
M=30
M=1
3 Fiber optic chords
PMT 106 V/A arrays Amplifiers
𝑒
λ𝑒
2 2
4π𝑐 m𝜀 4𝜋𝑐 𝑚𝜖0∆𝜑
𝒏𝒅𝒍= 𝑛𝒆𝑑𝑙 =
2 l𝑒 2
0 ∆φ
Triple Probe,
impurity emission view
Collimator+mount
Radiation
Enlarged view
Z=4.65m
Z=2.65m Z=3.9m
C-2U device
Interferometer view on z=2.25m
Open field line (jet) plasma
FRC core, z=0
 Summary
 Microwave interferometry provides measurement of jet integrated
electron density and fast fluctuations
 Impurity Doppler spectroscopy provides ion temperature and outflow velocity of jet
 Triple probe and impurity emission profile provide electron density and effective jet radius measurements
 Latter measurements coupled with flux loss of main plasma D+ ions provide calculation of jet outflow velocity. It is shown that impurity ions, despite larger mass, follow jet at velocity not less than main ions
 References
[1] M. Tuszewski, Plasma Phys. Control. Fusion 26, No. 8 (1984)