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Experiments on generation of He++ ions in ECR ion source with pumping by 75 GHz gyrotron

Experiments on generation of He++ ions in ECR ion source with pumping by 75 GHz gyrotron. Vladimir Zorin Institute of Applied Physics Nizhny Novgorod, Russia . The experiments were stimulated by November WP4 meeting in Grenoble . Work package title: Beta Beam.

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Experiments on generation of He++ ions in ECR ion source with pumping by 75 GHz gyrotron

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  1. Experiments on generation of He++ ions in ECR ion source with pumping by 75 GHz gyrotron Vladimir Zorin Institute of Applied Physics Nizhny Novgorod, Russia

  2. The experiments were stimulated by November WP4 meeting in Grenoble

  3. Work package title: Beta Beam ECR task: continuation of work with a 60 GHz ECR ion source for bunching studies of 6He and 18Ne started within EURISOL DS with the objective of reaching the high efficienciesneeded for the beta-beam.

  4. Gas Ion beam Magnetic field lines J MW Ion extractor ECR ion source There are many parameters which determine plasma composition. But, key one is plasma confinement time (plasma life time).

  5. Requirements for ECR ion source High gas efficiency – it is: Shot pulse duration High ionization degree (He++>>He+) - plasma life time 60 GHz microwaves

  6. Plasma life time Classical (collisionless) Long plasma life time High ionization degree Intermediate area Quasi- gasdynamic (collisional) Short plasma life time Lower ionization degree

  7. Schematic & parameters of SMIS 75 Gyrotron: Frequency 75 GHz (λ = 4 mm)Power 150 kWPulse duration 800 µs Faraday cup or Langmuir probe on manipulator Vacuum system:residual pressure 3·10-6Torr Filled with HeP = 3·10-5 - 10-2Torr Microwave window Time-of-flight ion analyzer: drift tube 1m, gap 90 ns, resolution 10 – 20. Simple mirror magnetic trap: length L = 23 cm,mirror ratio κ = 4Bmax = 5T Microwave lens: F = 30 cmmaximum power density200 kW/cm2 Two grid extractor: gap 22 mm,Umax = 20 kV, = 150 mm

  8. 1. Experiments in former times

  9. Quasi-gasdynamic confinement Quasi- gasdynamic (collisional) Short plasma life time Lower ionization degree Total beam current: 300 emA Rising slope 14 µs Operating conditions: P = 4·10-4 Torr , He PMW = 150 kW Bplug= 4 T

  10. 2. Experiments made in December 2009

  11. Preionization. Stimulated ECR discharge. Classical (collisionless) Long plasma life time High ionization degree Penning discharge electrode MW Due to Penning discharge, ECR gas breakdown was reached with lower gas pressure.

  12. Classical confinement

  13. What is between? Classical (collisionless) High ratio He++/He+ But long pulse duration What is between? Quasi- gasdynamic (collisional) Short pulse duration But low ratio He++/He+

  14. Further experiments and modeling Experimental data contains some contradictions, results are really very preliminary. Additional experiments have to be done. Ion beam should be formed and analyzed (temporal evolution, charge composition). Intermediate area of parameters have to be studied (between classical and qusi-gasdyanamic confinement) 4. Computer optimization of gas efficiency: looking for balance between pulse duration and ratio He++/He+

  15. MHD instability

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