Ionizing Interstellar gases

[Brian Mansur <bmansur@oc.edu>]

Here we go again (sound of two my bits clinking on the table)

I was up late a few nights ago, pondering as I sometimes do, just how in the 
world we are going to get a ram scoop/brake/mag-sail to work without 
spending unbelievable amounts of energy (which is another problem I was 
thinking about but don't have time to elaborate much on before I need to go 
to class.

I mentioned before how I read about in 29a the following

Begin Excerpt

**************************************************
Design Project Newsletter - Week 29a
**************************************************
From: segerge@msrc.wpafb.af.mil (GAYLORD E. SEGER)
Date: Mon, 6 Feb 1995 08:35:56 +0500


From: "jim" <jim@bogie2.bio.purdue.edu>

>Jason Cooper writes:
>
>>Every time I hear of the ramscoop, people keep referring to the scoop as 

>>a physical thing.  How much consideration has been given here to an
>>electromagnetic scoop, and a simple ionizing laser to take care of the
>>incoming hydrogen?
>
>Your operative word is "simple."  Such a laser would need to have a beam
>divergance of nearly one radian in order to ionize even some of the 
incoming
>dust and gas.

With some form of magnetic scoop out front of the physical intake, a
smaller beam divergence will be neccessary to avoid damaging the scoop.
You want ionization to take place in advance of the magnetic scoop, anyway,
so there's another reason for a tighter beam.


>  As the beam diameter reaches that of the intake scoop, the
>energy densities would need to be on the order of 10^4 joules per square
>centimeter.  Assuming an intake scoop diameter of a conservative 100 
meters,
>the laser would need to be able to output power on the order of 1 terawatt 

>(10^12) watts.  Also bear in mind that most laser processes are only about 
10
>percene efficient.  This would require that the laser consume 10 terawatts 
of
>electrical power to produce its one terawatt of optical power.  Though the 

>numbers are quick and dirty, they ought be good to an order of magnitude.

End Excerpt

Ten Terrawatts is way too much power for such a small effect.  So I figured, 
why not fire the beams perpendicular to the direction of the ship?  This 
would act like a laser shield that the particles hit and are ionized by.  It 
saves a lot of power that would otherwise be wasted hitting only 1 atom per 
cubic centimeter.  Of course, I don't know how powerful the beam needs to be 
to be effective to a distance of 1000 km in any direction.  Some know some 
numbers.  If they are too big, we may just have to go without a magnetic 
scoop/sail.