Difference between revisions of "Coulomb Focusing"

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[[Radiative Processes in Astrophysics|Course Home]]
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===Short Topical Videos===
 
===Short Topical Videos===
 
* [http://youtu.be/LXGBGNR5JxI Coulomb Focusing (Aaron Parsons)]
 
* [http://youtu.be/LXGBGNR5JxI Coulomb Focusing (Aaron Parsons)]
  
 
===Reference Material===
 
===Reference Material===
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===Need to Review?===
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* [[Collisional Excitations]]
  
 
===Related Topics===
 
===Related Topics===
* Collisional Excitations
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* [[Detailed Balance]]
  
 
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Latest revision as of 17:38, 5 December 2017

Course Home

Short Topical Videos[edit]

Reference Material[edit]

Need to Review?[edit]

Related Topics[edit]

Coulomb Focusing

Imagine an incident electron has kinetic energy .

Coulomb focusing gives cross-section.

We want to know how far away an electron with can be aimed and still hit the radius cloud around the ion. This is , the impact parameter. Our collision cross-section . Our angular momentum is conserved, so

We know that , where is the velocity to the original electron velocity. This is a result of it falling toward the ion. Then:

Generally, the Coulomb focusing factor because we want to excite, not ionize. , so:

is the “collisional strength”, and generally is 0 below the threshold, goes to 1 at the threshold, and decreases for increasing , with some occasional spikes. Generally, it is of order 1, with some slight temperature dependency.

2000 K gas. , so . Then