2017/11/13
MolFlow simulation setup
General information
Gas sheet system Geometries in MolFlow are obtained and estimated by the these 2 figures.
Simulation focus So far, the simulation only consider nozzle chamber, outer chamber, differential pumping chamber, and interaction chamber. 3 skimmers are included. Supersonic free expansion is not considered. Electrodes and MCP are not included in the interaction chamber yet.
Geometries
Simulation geometries
Skimmers 45 o rotated 2 nd skimmer (z = 2.5 cm): 2 sided, opaque y 1 st skimmer (z = 0 cm): 3 rd skimmer (z = 36.5 cm): 1 sided, opaque 2 sided, opaque z x
Nozzle chamber Nozzle chamber: 2 sided, opaque In current setup, particles are travelling outside the nozzle chamber. No particle is existed inside the chamber.
Outer chamber Outer chamber: 1 sided, opaque
Differential pumping chamber Differential pumping chamber: 1 sided, opaque
Short pipe connection 1 1 mm Short pipe between outer and differential pumping chambers: 1 sided, opaque This short pipe section is used to prevent particle travels from outer chamber to differential pumping chamber directly without going through the 2 nd skimmer.
Interaction chamber Interaction chamber: 1 sided, opaque
Short pipe connection 2 1 mm Short pipe between differential pumping chambers and interaction chamber: 1 sided, opaque This short pipe section is used to prevent particle travels from differential pumping chamber to interaction chamber directly without going through the 3 rd skimmer.
Boundary conditions
Outgassing arbitrary Outgassing boundary @ 1 st skimmer
Pumping speed 270 L/s 67 L/s 690 L/s
Gas dumping surface Sticking factor = 1 All particles reach this surface will be absorbed, which is used as gas beam dump.
Results
Number of outgassing particles Des: 7033688 for outgassing boundary More particles can be released by increasing the simulation time for reducing statistical noise.
General result
Gas beam density profile Transparent facets for visualization 2 cm e d c a b c d e b z = z = z = z = z = 38.6 cm 45.16 cm 58.3 cm 71.44 cm 77.8 cm a Hits: Hits: Hits: Hits: Hits: 13125 13082 13066 13059 13067 (beam interact location)
2017/11/28
General information
Gas sheet system Geometries in MolFlow are obtained and estimated by the these 2 figures.
Simulation focus So far, the simulation only consider nozzle chamber, outer chamber, differential pumping chamber, interaction chamber, and dumping chambers. 3 skimmers are included. Supersonic free expansion is not considered. Electrodes and MCP are not included in the interaction chamber yet. Moveable pressure gauge is not included in the dumping chamber.
Geometries
Simulation geometries
Gas dumping chambers Gas dumping chambers: 1 sided, opaque The gas dumping surface assumption from previous slide is no longer used.
Boundary conditions
Pumping speed 67 L/s 270 L/s
Results
Number of outgassing particles Des: 7242666 for outgassing boundary More particles can be released by increasing the simulation time for reducing statistical noise.
General result
Gas beam density profile 2 cm Transparent facets for visualization f e d c a b c d e f z = z = z = z = z = z = 38.6 cm 45.16 cm 58.3 cm 71.44 cm 77.8 cm 142 cm b Hits: Hits: Hits: Hits: Hits: Hits: +13738 +13747 +13721 +13734 +13722 +14603 -31 -75 -81 -103 -142 -1279 (beam interact Forward a Backward location)
2017/12/06
Design for gas sheet beam requirement
Gas jet and proton beam parameters jet thickness 0.2 mm Current concern jet width 10 mm jet number density 4e11 /cm^3 (10% effect) background vacuum 1e-10 torr beta function 1.5 m sig_x,y 0.7 mm KE 2.5 MeV proton number 9.00E+10 bunch length 0.37 us (bunched) 1.8 us (injected) jet gas nitrogen and helium inclination angle 45 degrees detedtor distance 20 cm electric field 1e4 V/m So far, we only concern about the gas sheet beam dimension at the interaction location
Gas sheet beam dimension calculation Assume the gas particle paths are straight lines Gas source Gas source center projection area projection Interaction location 2 nd /3 rd skimmer z Particle flow direction 1 st skimmer skimmer 1 skimmer 2 skimmer 3 gas sheet (interaction location) Skimmers’ diameter 180 µm 400 µm dimensions & width 57.91 µm length 6.193 mm Locations: z 0 mm 25 mm 365 mm 583 mm Obtain from calculation
Projection from 3 rd skimmer (at interaction location) Gas source area projection Top left corner -4 -5 x 10 x 10 1.5 10 1 8 0.5 0.2 6 y [m] y [m] 0 mm 4 -0.5 2 -1 0 -1.5 -5 -4 -3 -2 -1 0 1 2 3 4 5 -5 -4.98 -4.96 -4.94 -4.92 -4.9 -4.88 -4.86 -4.84 x [m] x [m] -3 -3 x 10 x 10 10 mm Gas source center projection
Projection from 2 nd skimmer (at interaction location) Gas source area projection -3 x 10 6 4 Gas source center projection 2 y [m] 0 -2 -4 -6 -8 -6 -4 -2 0 2 4 6 8 x [m] -3 x 10 3 rd skimmer projection Gas beam that pass through the 2 nd skimmer covers the entire 3 rd skimmer
Result gas beam profile (at interaction location) Des: 12,519,166 from outgassing boundary Hits (forward/backward): 4622/0 Each cell is (0.05 mmm) 2 , by pixel counting, the gas beam dimensions are 10 mm *0.2 mm *Simulation should be ran longer to get better statistical result
Change of particle density along propagation
In the case of free propagation z = 5 cm 16 x 10 Gas source: Virtual surface: 12 Diameter = 180e-6 m z = 5 cm 10 particle density [1/m 3 ] Particle density = 6.37e20 1/m 3 Area = (1 cm) 2 8 z = 0 cm Distribution: [cos( θ )] 100 6 Result particle density 4 2 5 5 0 -3 x 10 0 -3 x 10 -5 -5 y [m] x [m]
Analytical approximation Source particle density Source area 101 f 100 Distribution function: , cos 2 With respect to gas source 2 2 f , sin d d 1 n A f , s s Particle density: n , , R 0 0 2 (solid angle for entire hemisphere) R Distance from gas source Basically overlap with MolFlow result 16 x 10 11 16 x 10 10 11 9 10 particle density [1/m 3 ] 9 8 particle density [1/m 3 ] 8 7 7 6 6 5 5 4 4 5 3 0 -5 3 -3 0 5 x 10 -5 5 0 5 y [m] 0 -3 -5 x 10 -5 -3 x [m] x 10 -3 y [m] x 10 x [m] In this simple case of free propagation, without the interference of skimmers, downstream particle density can be analytically approximated if the simple gas source properties is known.
2017/12/13
Simulation result after long running time
MolFlow simulation 1 st skimmer Virtual transparent surfaces (6 in total): Outgassing profile: (cos θ) 1000 For visualizing gas sheet beam profile In simulation: Desorbed particle #: 4.06e9 Run time: 3~4 days on desktop
Particle density profile Hits Virtual Width Length Surface # z [mm] backward forward - [mm] [mm] forward backward 6 1420 7.46E-01 24.4 1.527E+06 41490 1.485E+06 5 778 3.11E-01 13.3 1.496E+06 1208 1.495E+06 length 4 714.4 2.86E-01 12.2 1.496E+06 621 1.495E+06 3 583 2.00E-01 9.93 1.496E+06 312 1.495E+06 width 2 451 1.14E-01 7.68 1.496E+06 133 1.496E+06 1 386 7.16E-02 6.55 1.496E+06 63 1.496E+06 Interaction location 8.00E-01 30 7.00E-01 Width [mm] 25 6.00E-01 Length [mm] 20 Length [mm] Width [mm] 5.00E-01 4.00E-01 15 3.00E-01 10 2.00E-01 5 1.00E-01 0.00E+00 0 0 200 400 600 800 1000 1200 1400 1600 z [mm]
Particle density profile
Particle density profile 16 16 16 z = 386 mm z = 451.6 mm z = 583 mm x 10 x 10 x 10 18 10 5 9 4.5 16 8 4 14 7 3.5 number density [1/m 3 ] number density [1/m 3 ] number density [1/m 3 ] 12 6 3 10 5 2.5 8 4 2 6 3 1.5 4 2 1 2 1 0.5 0 0 0 -1.5 -1 -0.5 0 0.5 1 1.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -3 -2 -1 0 1 2 3 4 along width [m] -4 along width [m] -4 along width [m] -4 x 10 x 10 x 10 16 16 15 z = 714.4 mm z = 778 mm z = 1420 mm x 10 x 10 x 10 3 2.5 6 2.5 5 2 number density [1/m 3 ] number density [1/m 3 ] number density [1/m 3 ] 2 4 1.5 1.5 3 1 1 2 0.5 0.5 1 0 0 0 -5 0 5 -5 0 5 -1.5 -1 -0.5 0 0.5 1 1.5 along width [m] along width [m] along width [m] -4 -4 -3 x 10 x 10 x 10
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