In most fields "breakdown" is negative, something you don't want, and it might well also be the case once, having "created" plasma (for the purposes of nuclear fusion), that plasma degenerates. Maybe. Maybe if there is not continued heat input it reverts to its initial gaseous state, I don't know. At any rate, ideally this won't happen, and the aim is to heat plasma to a temperature that is totally, or nearly, self-sustaining.

The term "plasma breakdown" is indeed used in nuclear fission for the "creation" of plasma. It something of a misnomer, however, since the plasma does not break down (not at this point, anyway), but rather the gas does, forming the plasma. I guess, at the risk of appearing grammaticastic, nuclear physicists make lousy grammarians.

On fait alors circuler un courant électrique dont l'action déclenche un « CLAQUAGE » puis une ionisation du gaz, et enfin sa transformation en plasma.
http://www.iter.org/fr/mach/fuelcycle

As a first step to starting the fusion reaction, all air and ANY IMPURITIES MUST BE EVACUATED from the Vacuum Vessel. The powerful Magnets that will help to confine and control the plasma are then turned on and the low-density gaseous fuel is introduced into the Vacuum Vessel by a gas injection system. Once the fuel has been introduced into the vacuum chamber, an electrical current is applied to the system which causes the gas to BREAK DOWN electrically, become ionized, and FORM A PLASMA.
http://www.iter.org/mach/fuelcycle

 Give a small puff of gas into the vessel (this neutral gas fills the whole vessel)
 Ramp up the flux in the transformer to obtain a high Electric field (this leads to PLASMA BREAKDOWN
[ ... ]
PLASMA BREAKDOWN
 Gas mostly neutral. But always one of the electrons is free
 The electric field accelerates this electron which gains in energy
 When the fast electron hits one of the atoms it can ionize it and generate an additional electron
 The avalanche leads to the BREAK DOWN
 Works well for low density (long mean free path) and high electric field
 Conditions mostly empirically determined
[ ... ]
Short time after the PLASMA BREAKDOWN one starts the feed back control of the plasma current
It is slowly ramped to a stationary value required by the discharge
www2.warwick.ac.uk/fac/sci/physics/research/cfsa/people/.../lecture10.ppt

www.springerlink.com/index/mv271w05j7223x60.pdf
In the initial stage, PLASMA BREAKDOWN and heating will be produced by an ECRH ... candidates for magnetically Confined Nuclear Fusion experiments. For the ...


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Note added at 7 hrs (2011-09-17 21:35:40 GMT)
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iopscience.iop.org/0741-3335/39/1/012/pdf/0741-3335_39_1_012.pdf
– (ii) the loop voltage required to obtain the stable plasma-current ramp-up must be greater than that to ACHIEVE PLASMA BREAKDOWN only;

iopscience.iop.org/0963-0252/18/2/.../pdf/0963-0252_18_2_025013.pdf
Microwave power required to ACHIEVE PLASMA BREAKDOWN, to sustain the plasma ...

meetings.aps.org/Meeting/DPP11/Event/151742
... to ACHIEVE PLASMA BREAKDOWN in the applied electric field. This constraint could be overcome by puffing pre-ionized plasma into the chamber instead of neutral ...

nstx.pppl.gov/DragNDrop/Publications_Presentations/.../Gates_FED.pdf
– which should be enough to ACHIEVE PLASMA BREAKDOWN and ramp up (in black).

digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1471&context=etd
required to ACHIEVE PLASMA BREAKDOWN. A difference of 10 to 20% in any of the above may result in no plasma. The banks displayed in fig. ...