To-Ka-Mak
to(roidal'naya) kam(era s) ak(sial'nym magnitnym polem ) ‘toroidal chamber with axial magnetic field.’
- Soft X-ray Diagnostics -
Overview Measuring soft x-ray emission is a useful and non-invasive diagnostic for studying internal plasma properties and MHD mode structure and dynamics. The HBT-EP tokamak is equipped with two multi-chord soft x-ray systems to study interna profile and fluctuation behavior. A 32-channel soft x-ray tomography (SXRT) system composed of discrete diodes with a thin film filter of Titanium, Zirconium, an dCarbon coated directly on to the diode face is used to reconstruct 2-D plasma emissivity profiles at a single toroidal location. Resolution of the system is sufficient to measure the structure and evolution of edge (m,n) =<2,1) tearing modes. The SXRT system is in the proces of being reinstated after being out of use for ten years.
in addition, a 16-channel "fan-array" assembly based upon a linear diode array and a 400nm Beryllium filter measure emission predominantly from teh plasma core. A planned upgrade to the fan-array form measuring temperature profiles using a multiple set of filters and additional diode arrays is being designed in cooperation with the Princeton Plasma Physics lab.
Soft X-ray Emission
- Soft x-rays of interest in HBT-EP are generated through Bremsstrahlung and recombination radiation.
- Emission sprectrum gives internal information about the plasma.
- Emission depends on temperature, density, and ion charge.
Tomography Algorithm
- Measure chord-integrated emission with SXRT diodes.
- Weight function Wi(r,θ) accounts for the diode sight lines.
- Extract equilibrium emission by smoothing raw data.
- Extract fluctuations in SXR emissivity by subtraction off the smoothed equilibrium background.
- Fit the equilibrium and fluctuation data separately using a least-squares method with Fourier-Bessel basis functions.
- -Use Fourier bases for poloidal variation, Bessel functions for radial variation.
- Use magnetic data to determine the major radius and origin of the coordinate system.
- Fit m = 0 - 3 and l = 0 - 7 for the Bessel functions.
- -Solve linear system Ax=d using SVD psuedoinverse
- x contains coefficients of the basis functions.
- d contains the measured diode responses.
Ongoing Development: Further upgrades to the soft-xray diagnostics.
- Multiple Fan Arrays There are plans to install multiple fan arrays with aluminum filters which will replace the multiport tomography system.
Projects
| Magnetic | Optical | Feedback | Other |
|---|---|---|---|
| Ferritic Wall | Soft X-Ray | Data Acquisition | Hall Probe |
| Poloidal Sensors | Thomson Scattering | Power Amplifiers | Bias Probe |
| Toroidal Sensors | Fast Camera | CPCI | Mach/Float Probe |
| Rogowski Coils | D-Alpha | Signal Amps | Rotation |