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Design Considerations for Beam Port Insulator Rings

Design Considerations for Beam Port Insulator Rings. Simon Yu Lawrence Berkeley National Laboratory ARIES Meeting October 24, 2001. What is the Propagation Window for Channel Assisted Pinch?. Beam Dynamics (LSP) (10 ns timescale) Channel Formation (10 s timescale)

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Design Considerations for Beam Port Insulator Rings

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  1. Design Considerations for Beam Port Insulator Rings Simon Yu Lawrence Berkeley National Laboratory ARIES Meeting October 24, 2001

  2. What is the Propagation Window for Channel Assisted Pinch? • Beam Dynamics (LSP) • (10 ns timescale) • Channel Formation • (10 s timescale) • Breakdown Management is a key component of channel formation: • - breakdown in the channel when voltage is applied • - no breakdown to the chamber walls • Beam port insulator rings are designed to inhibit breakdown to chamber walls 1

  3. Channel transport could ease chamber focus requirements and reduce driver costs Laser Z-Pinch Stable? ~ 5 Torr Xe ~50 kA Return path/ channel interaction ? 2 Breakdown to Walls?

  4. Z-Pinch Formation is a 3-step process 3

  5. Gas Breakdown Management The key parameter for gas breakdown is E/p - (E=electric field, p=gas density) For Xenon, breakdown occurs at Design goal: (1) create reduced density hole (nch) in channel such that (E/p)ch > (E/p)Xe (2) Maintain low E/p everywhere else in chamber (where gas density is n0) (E/p)0 < (E/p)Xe Necessary condition: where Rchamber ≈ length of channel ≈ chamber radius and Rport ≈ radius of port insulator (E/p)Xe = 60 V/cm/torr nchRchamber < n0Rport 4

  6. From breakdown requirement, port size given by ≈ Rport > Rchamber. We have done some hydrodynamics calculations to determine (nch/no) < 0.1. (Black body radiation model) We need a port design that is acceptable electrically and structurally Two port designs were constructed which were compatible with thick liquid walls. We have constructed another port design which MAY be more compatible with dry wall and wet wall concepts. PORT DESIGN 5

  7. PREPULSE phase - HYDRODYNAMIC EXPANSION Gas Density Gas Temperature t=0 T=60s 6

  8. nch/n0 7

  9. nch/n0 (Initial temperature /300º K) 8

  10. Beam Energy Loss Places Constraint on Maximum Density in Channel Example: 4GeV Pb ions going through 4 m of 0.5 Torr Xe gas will lose 9 % of its energy. In general Where Zg - atomic number of gas Zi - effective charge state of stripped ion  - speed of ion / speed of light 9

  11. Fusion Chamber for Channel Assisted Pinch Current-carrying Channel Target Return current channel 10

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  14. New Insulator Geometry Insulator Chamber wall (ground potential) Xe filled chamber Metal wall (high potential) Channel axis 13

  15. Electric Field Profile (Poisson Calculations) 14

  16. Near Term Objectives • Continued studies of channel hydrodynamics to determine nch/n0 • Continued electrical optimization of insulator (Poisson) • Structural integrity and protection of insulator (Raffray et al) 15

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