25 lines
846 B
Markdown
25 lines
846 B
Markdown
# Implementation
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## `index_rt` {#sec:index_rt}
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The `index_rt` is a unique index assigned to each combination of beam
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propagation mode and number of passes into the plasma.
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Initially `index_rt` is 1 for the ordinary mode or 2 for the extraordinary
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mode. Due to the mode mixing, on subsequent passes each beam splits into two
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modes and the `index_rt` is updated as:
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```fortran
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index_rt = 2*index_rt + 1 ! for the O mode
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index_rt = 2*index_rt + 2 ! for the X mode
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```
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It follows that ordinary(extraordinary) modes respectively have odd(even)
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indices and the number of passes is given by $\lfloor \log₂(1 + \tt index\_rt)
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\rfloor$. For example, an `index_rt`=19 denotes the following chain:
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$$
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\begin{aligned}
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\text{mode:} && O &→ X → O → O \\
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\text{\tt index\_rt:} && 1 &→ 4 → 9 → 19
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\end{aligned}
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$$
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