1 / 32

Preconceptual Design of DNB Collimating Apertures

Preconceptual Design of DNB Collimating Apertures. Steve Scott April 28, 2003. Can Achieve 2.9 cm DNB Footprint with Two 3.0 cm Apertures. Advertised DNB spot size = 6.0 cm (1/e). Beam Divergence 0.86 o Aperture widths Aperture 1 3.0

mostyn
Download Presentation

Preconceptual Design of DNB Collimating Apertures

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Preconceptual Design of DNB Collimating Apertures Steve Scott April 28, 2003

  2. Can Achieve 2.9 cm DNB Footprint with Two 3.0 cm Apertures Advertised DNB spot size = 6.0 cm (1/e) Beam Divergence 0.86o Aperture widths Aperture 1 3.0 Aperture 2 3.0 Aperture heights Aperture 1 20.0 Aperture 2 20.0 Aperture positions Aperture 1 220 Aperture 2 340 DNB footprint (FWHM) 2.96 MSE signal strength 81.9 Power to Aperture 2 15.0% Max Ap 2 power dens 4.6

  3. Footprint Size Increases Less than 1mm Assuming More Conservative Divergence Conservative DNB spot size = 7.0 cm (1/e) Beam Divergence 1.00o Aperture widths Aperture 1 3.0 Aperture 2 3.0 Aperture heights Aperture 1 20.0 Aperture 2 20.0 Aperture positions Aperture 1 220 Aperture 2 340 DNB footprint (FWHM) 3.03 MSE signal strength 65.1 Power to Aperture 2 16.6% Max Ap 2 power dens 3.9

  4. Motivation • DNB: full-width, half-max = 8-9 cm. • At plasma center, DNB is approximately at 45o with respect to Rmajor. • Dr = 8-9/sqrt(2) = 5.6 – 6.4 cm (at r=0) • Dr / a = 0.26 – 0.29 • Would like to get say FWHM = 4 cm, corresponding to Dr / a = 0.13

  5. Projection of MSE Fiber Sightlines in Horizontal Midplane DNB cutoff DNB 1/e DNB centerline DNB 1/e DNB cutoff Assumed Beam Size: 9 cm (1/e) with cutoff at 12 cm

  6. DNB cutoff DNB 1/e DNB centerline DNB 1/e DNB cutoff Projection of MSE Fiber Sightlines in RZ Plane Assumed Beam Size: 9 cm (1/e) with cutoff at 12 cm • 1. Very little radial resolution is lost by the vertical extent of the fiber bundle. • 2. Vertical extent of fiber bundle is only ~ +/- 2 cm, smaller than size of DNB

  7. There is Significant Channel Overlap with Present Beam Size (9 cm 1/e, 12 cm cutoff) 10 9 8 7 Emission from Full-Energy DNB 6 5 4 3 2 1 Note: Channel 4 has significant overlap with channels 2,3,5 and a little overlap with channels 1 and 6!

  8. Imposing an 8-cm cutoff Provides Reasonable Radial Resolution at the Plasma Edge, but still Poor at the Center

  9. 6-cm cutoff

  10. 4-cm cutoff: Moderate Radial Resolution in Plasma Core

  11. 2-cm cutoff (original assumption): Little Channel Overlap

  12. Slotted Aperture of width 4, 3, 2 cm causes signal reduction of factor 1.9, 2.5, 3.6

  13. TFTR DNB Scraper Schematic bellows liner scraper grid • Oval copper lining • Not adjustable • Takes only small fraction of power • No active cooling… • Radiation + conduction to vacuum vessel • Scraper • 1-2 cm thick copper plate • Located at end of DNB beamline, about ½ distance from grid to plasma (like CMOD) • Opening adjustable. When closed, forms calorimeter • Small overlap to ensure closure in spite of possible warping • Cooling at back … inertially cooled during 0.5 sec beam pulse Thanks to Gerd Schilling

  14. Focal Distance Grid Aperture #1 Aperture #2 Target Procedure to Compute Effect of Apertures on Beam Size • Launch vectors from grid, through focal point, onto target. • Establish circular grid on target with diameter = beamlet size corresponding to beam divergence. • For each point on target grid, decide whether ray from grid to target hits aperture or Target. • Increment computed power to Aperture #1, Aperture #2 or target as appropriate.

  15. Aperture Distance 220 Aperture width 10 (WIDE) FWHM 6.3 MSE Signal 176

  16. Aperture Distance 220 Aperture width 2.0 FWHM 4.6 MSE Signal 71

  17. Moving Aperture Closer to Plasma Makes it More Effective (duh …) Aperture Distance 320 Aperture width 2.0 FWHM 2.2 MSE Signal 62

  18. Summary of Single-Aperture Performance for Locations at 2.2 and 3.2 meters from the DNB Grid -------- Aperture ----------- ----- DNB Size ---- MSE Signal Location Width FWHM 1/e 95% 220 10.0 6.3 7.6 13.0 176 3.0 4.6 5.5 9.4 101 2.5 4.6 5.5 9.4 86 2.0 4.6 5.5 9.0 71 1.5 4.6 5.5 9.0 54 320 10.0 6.2 7.5 11.8 172 4.0 3.8 4.6 6.6 112 3.0 3.0 3.6 5.8 88 2.5 2.6 3.1 5.0 75 2.0 2.2 2.7 4.6 62 1.5 1.9 2.3 3.8 47 Not great Pretty good, but signal is compromised Assumptions: 10 cm diameter grid, focal length = 400 cm, target at 400 cm, (1/e) beamlet divergence = 1.1o… beamlet diameter = 7.7 cm

  19. Calculations Using Two Apertures

  20. Summary of Two-Aperture Performance for Locations at 2.2 and 3.2 meters from the DNB Grid -------- Aperture ----------- Power MSE DNB Ap-1 Ap-2 SIGNAL Width-2 Width-2 FWHM 2.25 2.70 2.98 55% 15% 53 2.50 3.00 3.18 51% 14% 62 3.00 3.00 3.08 43% 17% 70 3.20 3.23 43% 16% 73 3.30 3.31 43% 15% 74 3.50 3.45 43% 15% 77 3.75 3.62 43% 11% 80 4.00 3.77 43% 10% 83 Assumptions: 10 cm diameter grid, focal length = 400 cm, target at 400 cm, (1/e) beamlet divergence = 1.1o… beamlet diameter = 7.7 cm

  21. Gas evolution from aperture surface leading to reionization loss Possible local melting of surface Model: canonical semi-infinite slab of uniform material, uniform heat flux q applied starting at t=0, neglecting radiative losses: DT = (2q/k)(kt/p)0.5 Copper: k = k / rC = 1.16 10-4 m2/sec k = 400 watts / meter / kelvin r = 8900 kg/m3 C = 386 Joules / kg / Kelvin DNB: qavg = (5.0 Amps) (50,000) / p (0.09/2)2 = 3.9 107 watts/m2 q = qavg exp(-r2/s2) where s = 0.6*FWHM = 0.054 meters Surface Heating of Aperture by DNB

  22. Assume 50 ms beam pulse: DT = 265 exp( - (r/0.054)2 ) kelvin Maximum surface temperature rise beam pulse for Copper: Horizontal Aperture DTmax dimension (cm) 50 ms 1000 ms 4 231 oC 1033 5 214 957 6 195 872 7 174 778 8 154 689 Melting temperature of Copper = 1083 oC. Conclusion: gas evolution may be an issue for a 50 ms beam, and melting may be a problem for a long-pulse beam. For the short-pulse beam, we could eliminate gas evolution by continuously heating the aperture to maintain its temperature > 150 oC . Surface Heating of Aperture by DNB, cont’d

  23. For the long-pulse beam, we could: Tilt the aperture to spread the incident heat flux over a larger area – limited by available space. Actively cool the aperture – more expensive. Could use 2 apertures – 1st one closer to grid takes most of the heat, 2nd one closer to plasma is inertially cooled. Surface Heating of Aperture by DNB, cont’d

  24. Tungsten and moly provide the best protection against melting ~ Tmelt/DTheat

  25. MSE can’t provide radially-resolved q-profile measurements with the DNB in its present configuration. A two-aperture system looks technically feasible: 1st aperture @end of DNB beamline - takes most of the heat; actively cooled. 2nd aperture, closer to plasma, uncooled, provides final collimation. We lose about a factor 2-3 in signal strength to get ~ 3 cm spatial resolution. Conclusions

More Related