Simulation Overview of High-Performance Beam-Driven Field Reversed Configurations

Neutral Beam Injection System for the C-2W Field Reversed Configuration Experiment
A. Dunaevsky,1 A. Ivanov,2 V. Davydenko,2 A. Sorokin,2 V. Kolmogorov,2 S.Putvinski,1 A. Smirnov,1 S. Korepanov,1 M. Binderbauer,1 TAE Team, BINP Team 1TRI ALPHA ENERGY, INC., Rancho Santa Margarita, CA 2BUDKER INSTITUTE, Novosibirsk, Russia
Abstract C-2W Neutral Beam Injectors C-2W NBI with switchable energy Improved grids
§ Similar NBIs were used in C-2U experiment
§ Pulse duration is extended to 30ms
§ Same four arc plasma drivers
§ Improved grids to withstand higher thermal load
§ Ti getter pumps with enhanced pumping speed due to LN2 cooling § Additional grid for operation in the switchable/tunable energy mode
Two phases of the C-2W experimental campaign:
• Plasma sustainment and initial plasma ramp-up with flux conservers
• Plasma ramp-up with active plasma control and switchable energy beams
NBI system parameter
C-2U
C-2W phase 1
C-2W phase 2
Number of 15keV non-switchable injectors
6
8
4
Number of 15-40keV switchable injectors
0
0
4
Beam energy, keV
15
15
15/40
Ion current per source, A
130
130
130
Pulse duration, ms
8
30
30
Power in neutrals through the port, per beamline, MW
1.7
1.7
1.7 @15keV
3.5 @ 40kV
Total NB power, MW
~10
~13
~20
Switching time, ms
-
-
1
Beam e-folding size, cm
16 along Z 4.2 along R
Beam divergence, mrad
38 along Z 11 along R
Parameter
8 x 15kV constant energy beams
4 x 15kV and 4 x 15-40kV switchable beams
Total beam energy
13.6 MW
20.8 MW
Charge exchange factor ~(nσvτ)-1 @ Te = 330eV
3.3
0.7
Heating effect on FRC @ Te = 500eV
0.4
0.8
Reasons for switchable/tunable NBIs:
• Higher heating power (double the C-2U power)
• Lower losses due to charge exchange
• Higher heating efficiency (see poster by Erik Trask et al)
• Tunable beam energy can follow the magnetic field ramp-up • Tunable beams can be used for plasma control system
Two configurations are being tested: • Acceleration-deceleration
• Triode-tetrode
• Newionopticssystem
• Arrangementofslits=>higherstiffness
• Centraldielectricstack=>bettergap
stability
• Slitgeometry=>lowerbeamdivergence
• ModifiedTigetterpumps
• Ignitionhead=>reliableignition
• Magneticscreen=>reliablearcmotion
• Newhighvoltagemodulator
• 30mspulseduration
• Additionalpowersupplyforthetetrode
configuration
C-2U Field-Reversed Configuration (FRC) experiment proved substantial reduction in turbulence-driven losses via tangential neutral beam injection (NBI) coupled with electrically biased plasma guns at the plasma ends. Under such conditions, highly reproducible, advanced beam-driven FRCs were produced and sustained for times significantly longer (more than 5 ms) than all characteristic plasma decay times without beams. To further improve FRC sustainment and demonstrate the FRC ramp-up, the C-2U experimental device is being replaced with a brand new installation, C-2W. The new machine will be equipped with a new NBI system producing a record total hydrogen beam power of 20+ MW in a 30ms pulse. The NBI system consists of eight positive-ion based injectors featuring flexible, modular design. Four out of eight NBI injectors will have a capability to switch the beam energy during a shot from the initial 15 keV to 40 keV at a constant beam current. This feature allows to increase the beam energy and thereby optimize the beam-plasma coupling during the magnetic field ramp up. This presentation provides an overview of the C-2W NBI system, including the design of the switchable energy injectors, layout of the power supply system, and results of the prototype testing.
§ Improved thermal stability @30ms
§ New slit alignment for better overall rigidity of the grid
C-2W FRC Experiment
Phase 1 NBI acceptance tests
Inner divertor
Upgraded NB’s
Phase 1: 13 MW, 30 ms; Phase 2: 20 MW, 30 ms
Upgraded formation sections, 15 mWb trapped flux
End divertor
Plasma-guns and biasing electrodes (In both inner and end divertors)
New magnet
System for field ramp & active control
New confinement vessel, skin time <3 ms
§ C-2W experimental goal: demonstration of the plasma ramp-up
§ 30ms pulse duration
§ New confinement vessel and new divertors; additional inner divertors between the confinement and the formation sections
§ Divertors pumping system with ultra high pumping speed: (0.5-2)*106 L/sec
§ New magnetic system for the field ramp-up
§ Edge biasing by a set of concentric biased electrodes in inner and outer divertors
§ System of fast trim and saddle coils for active plasma control
§ Eight new NBIs, four with capability of switching the beam energy from 15 to up to 40 keV
• 30ms ion beam with the total power of 1.8 MW was successfully generated
• Scraping losses are driven by horizontal beam divergence
• Lower power losses with improved grids
Summary
§ An NBI system upgrade with 30ms pulse capability was built and tested, will be installed on the C-2W machine soon
§ A new NBI system capable for switching/tuning the beam energy is being developed for the Phase 2 of the C-2W experimental campaign
§ The new switchable/tunable energy beam technology allows higher plasma heating efficiency with the beam energy following the magnetic field ramp-up