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Geneva, CERN, 13.8.2014
Contents
- What is VADIS?
- The problem
- Explanation
- CPO model
- Original approach
- Our model
- Results and conclusions
- Future work
Optimalization of beam width and geometry parameters of VADIS cavity - - PowerPoint PPT Presentation
Optimalization of beam width and geometry parameters of VADIS cavity - - PowerPoint PPT Presentation
Optimalization of beam width and geometry parameters of VADIS cavity Miroslav Macko Comenius University, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovakia Supervisor: Thierry Stora CERN, ISOLDE Geneva, Switzerland
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What is VADIS?
Geneva, CERN, 13.8.2014
- Versatile Arc Discharge Ion Source
- Cavity
- Cylindrical symmetry
- Difference in aperture
Source: [1] Liviu Constantin Penescu
MK7 VADIS MK7 VADIS
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How it works?
- Anode at 150 V
- e- accelerated to 150 eV by grid
- Ions created in collisions with neutral atoms
- Positive ions extracted in aperture
Geneva, CERN, 13.8.2014
Source: [1] Liviu Constantin Penescu
MK7 VADIS
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The problem
Geneva, CERN, 13.8.2014
Source: [1] Liviu Constantin Penescu
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Explanation
Geneva, CERN, 13.8.2014
- Ions extracted at temperature ~ 2000°C
- Kinetic energy: 2000°C ~ 0,2 eV
- Borders of active volume – 149,8 V potential line
because 150V-0,2V=149,8V
Source: [1] Liviu Constantin Penescu
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CPO model
Geneva, CERN, 13.8.2014
- Potential line penetration (MK7)
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CPO model
Geneva, CERN, 13.8.2014
- Potential line penetration (VADIS)
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CPO model
Geneva, CERN, 13.8.2014
MK7 VADIS
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Original approach
- Ions and electrons -> space charge in cavity
- Two calculations
- a) Electrons (ions negligible)
- b) Ions (electrons negligible)
- Result = superposition of two fields
Geneva, CERN, 13.8.2014
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Original approach (example)
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Electrons Ions
Source: [1] Liviu Constantin Penescu
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Original approach (results)
Geneva, CERN, 13.8.2014
Source: [1] Liviu Constantin Penescu
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Our idea
- Is previous approach the best possible?
- What about interaction between electrons and ions?
Geneva, CERN, 13.8.2014
- Electrons „set“ potential for ions
- Before including ions it may be useful to study
how electrons act under different conditions
- After that sending ions into „specificaly tailored“
potential of electrons (future work)
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Our model
- How to calculate potential assuming space charge
- f electrons?
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Our model
- What is typical shape of such
potential?
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Our model
- What is typical shape of such
potential?
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Our model
- How can we influence
these parameters?
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Our model
- How can we influence these parameters?
- Possible tools
- a) „Better aiming“
- b) Change of current density
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- a) Better aiming by change of beam radius
- b) Current density by change of cathode temperature
Richardson´s law: J=AT2exp(-W/kT)
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- Definition of beam radius „r“
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Our model
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Simulated data (MK7)
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Simulated data (VADIS)
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Potential minimum
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MK7 VADIS
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MK7 VADIS Neck value
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Potential minimum
MK7 vs. VADIS
Neck value
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Infinite charged cylinder?
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Quo vadis VADIS?
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- Can we reproduce potential shape on axis by
summation of potentials of infinitezimaly thin discs?
Q(z) z dq1 dq2 dq3 dq4 dq5
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Quo vadis VADIS?
Geneva, CERN, 13.8.2014
- Is shape in radial direction really charged cylinder
potential?
- Poisson equation in cylindrical coordinates
- How much ions „ruin“ these models?
- What measurable variables we can obtain?
- Are these consistent with experiment?
- What is the influence of changed geometry?
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Geneva, CERN, 13.8.2014
References:
- [1] Liviu Constantin Penescu, Techniques to
produce and accelerate radioactive ion beams, Bucharest, 2009
- [2] FH Read and NJ Bowring, The CPO programs
and the BEM for charged particle optics, Nucl. Instr.
- Meth. A645, 273-277 (2011)
Aknowledgments:
- I would like to thank Thierry Stora for his advices and