Vacuum vessel
Vacuum Vessel Port Layout
| Section |
Location/Port |
Diagnostic(s) |
Gate Valve / View |
| PA |
Midplane 6" CF |
GV / Plasma | |
| 4x Upper/Lower 2.75" CF |
Poloidal visible spectroscopy |
GV / Plasma | |
| Upper Left 2.75" CF |
Vessel Filament |
GV / Plasma | |
| Lower Left 2.75" CF |
Empty |
GV / Plasma | |
| Upper/Lower angled 3.38" CF |
Empty |
GV / Plasma | |
| Upper/Lower Center 1.5" CF |
Bare / Plasma | ||
| Top Rectangular |
Bare / Plasma | ||
| Bottom Rectangular |
Bare / Plasma | ||
| AB |
Midplane |
Neutral Beam / Thomson scattering laser exit |
GV / Plasma |
| Bottom 2.75" CF |
Center Stack RTDs (1-4) |
Bare? / Plasma | |
| Top 2.75" CF |
Center Stack RTDs (5-8) |
Bare? / Plasma | |
| BC |
Upper 6" CF |
GV / Shell | |
| Midplane 6" CF |
GV / Plasma | ||
| Lower 6" CF |
Blank -> ?Getter Thermocouples? |
Bare / Shell | |
| Bottom 4.62" CF |
Shell Penetration |
Bare? / Plasma | |
| Top 4.62" CF |
Shell Penetration |
GV / Plasma | |
| Left Mini CF |
Beam-scraper RTDs |
GV / Plasma | |
| CD |
Upper 6" CF |
Upper shell flux loops |
Bare / Shell |
| Midplane 8" CF |
ChERS hydra port |
GV / Plasma | |
| Lower 6" CF, Left 2.75" |
Lower shell flux loops |
Bare / Shell | |
| Lower 6" CF, Right 2.75", End |
Lower shell flux loops |
Bare / Shell | |
| Lower 6" CF, Right 2.75", Tee |
Toroidal array north-side sensors (#s 1-5) |
Bare / Shell | |
| DE |
Upper 6" CF |
Upper re-entrant shell thermocouple |
Bare / Shell |
| Midplane 8" CF |
Li filler / mirror |
GV / Plasma | |
| Lower 6" CF |
Lower re-entrant shell thermocouple |
Bare / Shell | |
| Top Rectangular |
Lower South Shell Heater Feedthroughs |
Bare / Shell | |
| Bottom Rectangular |
Upper South Shell Heater Feedthroughs |
Bare / Shell | |
| EF |
Upper 6" CF |
Overpressure burst disk |
Bare / Shell |
| Midplane 8" CF |
GV / Plasma | ||
| Lower 6" CF |
Empty |
Bare / Shell | |
| FG |
Upper 6" CF |
Empty |
Bare / Shell |
| Midplane 8" CF |
Resitive Bolometer |
GV / Plasma | |
| Lower 6" CF |
South RGA |
GV / Shell | |
| Bottom 4.62" CF |
Shell Penetration |
Bare? / Plasma | |
| Top 4.62" CF |
South E-beam / Li Granule Dropper? |
GV / Plasma | |
| GH |
Upper 6" CF |
Vessel Ion Gauge / Fast Ion Gauge |
GV / Shell |
| Midplane Tangential 6" CF |
Phantom Camera / Midplane Li Evaporator |
GV / Plasma | |
| Lower 6" CF |
Rogowski coil |
Bare / Shell | |
| HI |
Upper downward CF |
Edge Thomson scattering views |
GV / Plasma |
| Midplane 4.62" CF |
Thomson scattering laser entrance |
GV / Plasma | |
| Lower angled 6" CF |
ECH horn |
GV / Plasma | |
| Lower downward CF |
Filterscope? Lyman-alpha diode? |
GV / Plasma | |
| Top Rectangular |
HFS puffer valve/feedthrough,Thomson views |
GV / Plasma | |
| Bottom Rectangular |
Thomson viewing dump |
Bare / Plasma | |
| IJ |
Upper 6" CF |
Upper shell flux loop sheath grounds |
Bare / Shell |
| Midplane 6" CF |
AXUV Bolometer/Lyman-alpha arrays |
GV / Plasma | |
| Lower 6" CF |
Lower shell flux loop sheath grounds |
Bare / Shell | |
| JK |
Rectangular |
Pump duct / Beam Dump |
Bare / Plasma |
| Bottom 4.62" CF |
Shell Penetration |
Bare? / Plasma | |
| Top 4.62" CF |
Shell Penetration |
GV / Plasma | |
| KL |
Midplane, Left 2.75" CF |
Beam Dump |
Bare? / Plasma |
| Midplane, Center 2.75" CF |
LFS puffer valve/feedthrough? |
Bare / Plasma | |
| Midplane, Right 2.75" CF |
LOWEUS? |
GV / Plasma | |
| Upper, Top 3.38" CF |
Empty |
Bare / Shell | |
| Upper, Middle 3.38" CF |
Empty? Bdot feedthrough? |
Bare / Shell | |
| Upper, Bottom 3.38" CF |
Empty |
Bare / Shell | |
| Lower, Top 3.38" CF |
Empty? Bdot feedthrough? |
Bare / Shell | |
| Lower, Middle 3.38" CF |
Empty |
Bare / Shell | |
| Lower, Bottom 3.38" CF |
Empty |
Bare / Shell | |
| LM |
Upper/Lower 8" CF |
Top+bottom internal vertical field coils |
Bare / Shell |
| Midplane 6" CF |
Li filler / mirror |
GV / Plasma | |
| Top Rectangular |
Lower North Shell Heater Feedthroughs |
Bare / Shell | |
| Bottom Rectangular |
Upper North Shell Heater Feedthroughs |
Bare / Shell | |
| MN |
Midplane, Left 2.75" CF |
Blocked by diamagnetic loop North RGA? |
GV / Plasma* |
| Midplane, Center 2.75" CF |
Filterscope? |
GV / Plasma | |
| Midplane, Right 2.75" CF |
Langmuir probe? |
GV / Plasma | |
| Upper, Top 3.38" CF (2.75" reducer) |
Bare / Shell | ||
| Upper, Middle 3.38" CF |
Empty |
Bare / Shell | |
| Upper, Bottom 3.38" CF |
Diamagnetic loop feedthroughs, empty feedthroughs? |
Bare / Shell | |
| Lower, Top 3.38" CF |
Empty |
Bare / Shell | |
| Lower, Middle 3.38" CF |
Empty |
Bare / Shell | |
| Lower, Bottom 3.38" CF |
Empty |
Bare / Shell | |
| NO |
Upper Downward CF |
Filterscope? |
GV / Plasma |
| Midplane 6" CF |
Sample exposure probe? |
GV / Plasma | |
| Bottom 4.62" CF |
Shell Penetration |
Bare? / Plasma | |
| Top 4.62" CF |
North E-beam |
GV / Plasma | |
| OP |
Upper 6" CF (2.75" reducer) |
Upper saddle coils |
Bare / Shell |
| Midplane Tangential 6" CF |
Midplane Li evaporator |
GV / Plasma | |
| Lower 6" CF, Right 2.75" |
Lower saddle coils |
Bare / Shell | |
| Lower 6" CF, Left 2.75" |
Toroidal array north-side sensors (#s 6-10) |
Bare / Shell |
Unassigned feedthroughs:
- Beam-dump RTDs
- HFS Langmuir Probes
Vacuum Vessel Construction
The LTX vacuum vessel, legacy hardware from CDX-U, is a 70 cm 304-stainless steel cylindrical shell with end caps on the top and bottom and a sealed center-stack. Each top and bottom plate has four rectangular ports (two at the east and west shell breaks, and two and the center of the north and south shell pairs), as well as four circular ports aligned with the circular shell penetrations.
"The vacuum chamber wall was formed by rolling a 3/8" thick sheet into a 56" outer-diameter cylinder and welding the sheet together at the vertical joint where the two ends of the sheet meet each other. Large diameter rings to mate between the cylindrical chamber wall and the top and bottom vacuum chamber plates (from the previous version of CDX-U ) were cut from 1.5" thick 304 stainless-steel sheet with a plasma torch. One side of each ring was faced-off with a large milling machine and the newly flattened side of one of the rings was welded to the top of the rolled cylinder. The opposite side of the newly attached ring was then faced off. and the process was repeated for the other ring. The final inner and outer-diameter cuts were then made on the rings. With the rings firmly welded onto the main vessel cylinder, the vessel structure had enough rigidity to begin cut ting port holes and welding the rectangular and circular ports onto the main cylindrical chamber." Menard, J. E. (1998). High-harmonic fast wave coupling and heating experiments in the CDX-U spherical tokamak. Princeton University. Princeton University. Retrieved from [2]
Vacuum Vessel The LTX vacuum vessel was originally designed for and installed on CDX-U in 1996 [94]. The vessel consists of a cylindrical outer wall (the “tub”), top and bottom flanges, and inboard flanges that seal the vacuum vessel to the centerstack. The outer vessel wall was constructed from rolled, 3/8” thick stainless steel with an inner radius of 0.702 m. This “tub” is organized into 16 segments and contains numerous ports for diagnostic access and electrical feedthroughs for in-vessel diagnostics (Figures 3.4 and 3.5. The top and bottom flanges are also constructed from stainless steel and are sealed to the “tub” with O-ring seals. The centerstack itself is housed in an Inconel 625 tube (6.875” outer diameter, 42” height, 1/16” wall thickness) and contains the Ohmic winding and return legs for the toroidal field coils [95]. For LTX, the outboard upper and lower rings on the vacuum vessel “tub”, which contain the O-ring sealing surfaces for the top and bottom flanges, were machined thinner to permit installation of the shell inside the vacuum vessel. Gussets were added to the top and bottom flanges for mechanical support to prevent flexing during vessel pump down. The outer centerstack surface (which is inside the vacuum vessel) is protected by a heat shield constructed from a layer of 0.03” thick pre-baked mica mat and 1/16” thick stainless steel shim. The heat shield was fabricated in three curved segments that are single point attached to the centerstack mounting gussets; single point attachment prevents the formation of a toroidal current path in the heat shield. To further protect the vessel against high- temperatures, the O-rings inside the Wilson seals used for re-entrant LTX hardware were replaced with Kalrez O-rings which are chemically resistant and suitable for use in high temperature (up to 327 ◦C) environments. Berzak, L. F. (2010). Plasma Start-up in a Spherical Tokamak with Close-fitting Conducting Walls. Princeton University. Princeton University. Retrieved from [3]
| Vessel cylinder outer radius |
71.1 cm |
| Vessel cylinder inner radius |
70.2 cm |
| Vessel cylinder height |
89.9 cm |
| Vessel volume |
1.37 m3 |
| Center column outer radius |
9.4 cm |
| Center column limiter outer radius |
11. cm |
