2019_APS_Titus_Calorimeter_v4

Direct Measurement of Injected Neutral Beam Power in C-2W
J.B. Titus, S. Korepanov, K. Pirogov, K. Knapp, and the TAE TEAM
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
Abstract
C-2W Neutral Beams
Tunable Beams
In TAE Technologies’ current experimental device, C-2W (also called “Norman”),1 record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (15 – 40 keV, total power up to 20 MW), advanced divertors, end bias electrodes, and an active plasma control system. Heating, current drive, and refueling from neutral beam injection are essential to
2 FRCsustainment.Previously,evaluatinginjectedneutralpowerreliedonthemodelingofneutralizationandductlosses. Anewtungstenwire
calorimeter has been designed, built, calibrated on a test stand, and implemented in the confinement vessel to make the first direct measurements of the injected beam power into C-2W. An array of 8 wires are arranged along the beam injection port so that the beam power deposition profile can be reconstructed to find the total injected power. We will report on the calorimeter design, calibration methods, and early experimental results from C-2W, including the optimization effort to increase the input power by improving beam aiming and neutralization.
The C-2W neutral beams are based on C-2U injectors with modifications to the ion sources and power supplies for 30 ms pulses
Five Static Beams (15keV)
• 30% more power
• Four arc-discharge plasma sources
• 3-electrode ion-optical system with multi-aperture slit optics for beam formation
Three Tunable Beams (15 – 40 keV)
• They switch between 3-electrode to 4-electrode system when high voltage is ramped
• 4-electrode system leads to smaller divergence
• Voltage waveforms are used Active Control
• Tunable beams can be linked to active feedback control to balance pressure while ramping magnetic fields3
Example of a ramp of beam energy, compared to a static beam
Motivations
The switching of IOS from 3-grids to 4-grids.
Note: the divergence of the beam decreases after the switch
Ion Source
Neutralization Tank
Bending Magnets
C-2W
Ion beam
Neutral beam Injected Neutral Beam
Neutralization losses Beam duct
~20%
losses ~10%
Beam Duct
Wire Calorimeter
• This diagnostic is inspired by similar diagnostics on GDT, TMX, ITER
• Individual diagnostics are installed at the end of each beam duct
• Each wire experiences a change in temperature (!T) due to beam power deposition (Pdep)
• A current is applied to each wire and the wire’s resistance (R) is measured:
'( , 12 "#$%=) Δ+ ,−10 =Δ+
#$% -
m ~ mass, C ~ specific heat, 3 ~ temperature coefficient, )#$%~ beam pulse
• Eight measurements are made for a profile of power deposition
• The diagnostic was designed using two models:
• Beam propagation model to get power deposition from beam
• 2D heat transfer model with thermal radiation for expected wire resistance and temperature
0.4mm wire diameter
• As the beam travels from the ion source to the main confinement vessel, there are two loss mechanisms:
• Neutralization
• Travel through beam duct
• Injected power from beams is estimated from test stand measurements of beam size and a beam propagation model2
• A direct measurement of injected neutral beam power is needed to
increase our understanding of fast ion efficiencies and source terms in power balance calculations
• Measurements are used to optimization beam injection and power balance calculations
Gettering shielding
Modeling of a Wire Calorimeter
Installation and Calibration
• [Left] A geometric beam propagation model2 is used to find the power density incident on each wire
• [Right] Each power density is applied to a 2D heat transfer model (10 x 1000 points) at x=0
• Energy leaves the system via emissivity at x=10
Geometric Model of Neutral Beam
Wires
Two-Dimensional Heat Transfer with Thermal Radiation
Power density of beam
Beam deposition
Conduction
Thickness of wire
Resistance
Evolution of 2D temperature inside wire
Thermal emission
Evolution of total resistance in a wire
• [Above] The beam (via power density) is injected into the wire for 30 ms
• Throughout the beam pulse, heat is transferred mostly in the x-direction
• [Right] The resistance increases during the beam pulse
• These models have helped us determine the size of the wires, and the
applied current and voltage to use
• Each calorimeter has a unique measuring efficiency
• C-2W has multiple loss channels, so it is not adequate
to calibrate in situ
• Calibrations conducted on Neutral Beam Test Stand:
Wire Calorimeter installed in C-2W
Beam Dump
Wire calorimeters in beam line
Pre-Optimization
• • •
Identical beam line as C-2W
Neutral beam parameters are well known no magnets or neutralization, minimizing measurement uncertainty
Calibration of Electrical Power to Measured Power
40
35
30
25
20
15
10
5
y = 0.66x - 2.9
0
0 10 20 30 40 50 60
Energy [kJ]
• Total average injected power: 7.6 MW
• 58% of the maximum designed injection power (13
MW)
• These measurements help to improve calculations of neutral beam coupling efficiency
• With help from the new calorimeters, the neutral beams can be optimize
Average Injected Power
1.6 1.2 0.8 0.4
0
12345678
Neutral Beam
Beam Optimization
Alignment
Beam Duct
Neutralization
• As pressure increases, an equilibrium pressure is reached
• Too much pressure leads to negative effects on the plasma generators
Beam Currents
• The beam propagation model2 bound by experimental data points is used to estimate the power lost in the beam duct
• A balance between meniscus and perveance focusing forces minimizes divergence
• As beam current increases, power is gained from:
• Increasing currents
• Losing less power to the beam duct
After First Iteration of Beam Optimization
•
•
•
•
•
•
Using the new calorimeters, a subset of beams were determined to be misaligned
Ion sources are on a gimble, capable of moving in four directions
Within ~10 shots, each beam was better aligned
Neutralization is regulated by puff valve pressure
A scan of puff valve pressure reveals optimum settings
Example:
Neutralization Scan
21
20
19
18
17
16
Optimum Regime
0 10 20 30 40 50 Puff Valve Pressure [PSI]
1.6 1.2 0.8 0.4
• Current injected neutral beam power: 10.5 MW • 80% of the designed injected power
• This percentage is near what Long-pulsed NB’s (> 1 s) typically account for ( ~90% of inject beam power )
• Further optimization is underway by:
• Aligning ion sources
• Optimization of neutralization
• Increasing beam currents
Optimum Current
Initial Ave. Injected Power
Curre nt Ave. Injected Power
0
12345678
Neutral Beam
• Five static beams (15keV) and three tunable beams (15-40keV) are currently in operational on C-2W; a fourth is being installed
• Active feedback control with neutral beams will be implemented presently
• Eight wire calorimeters were installed and are currently in operation on every shot
• Pre-optimized study with calorimeters revealed lower than expected injected power into CV
• After some beam optimization via alignment, neutralization, and increased beam current, inject power increased 35%
• Beam optimization using the calorimeters continues on C-2W
References
Acknowledgements
We thank our shareholders for their support and trust, and all fellow TAE staff for their dedication, excellent work, and extra efforts.
1H. Gota et al, Nucl. Fusion 59, 112009 (2019).
2J. B. Titus et al, Rev. Sci. Instrum. 89, 101123 (2018).
3 see J. Romero, Abstract: UP10.00127 : The C-2W plasma control system : Overview and experimental results
Summary
Length of wire
Temperature [K]
Temperature [K]
Temperature [K]
Temperature [K]
Temperature [K]
Power [MW]
Measured Energy [kJ]
Power [MW]
Signal [arb.]