I would say no to that transister- its only rated to 500mA MAX.
yea some of them are max 600 (depending on maker) either way a 2222 pushing an amp even with non constant current is a recipe for smoke
It has a gain of least 20, so at full current (my previous 660mA calculation) you will need 33mA or less going into the base to turn it full on. That 33 mA will be coming thru Ra, and to turn off the transistor the 555 will turn on its output and sink the current to ground (see a 555 datasheet, such as http://www.national.com/ds/LM/LM555.pdf)
agreed a 555 will do it no problem, without looking at a datasheet I want to say one can handle a couple hundred ma keeping voltage in consideration (200ma at 5v is a different wattage dissipation than 200ma at 15 volt, though its a very stout little chip, with 9 volts it should be ok, again without looking at the datasheet or running the numbers …)
lol anyway yes PWM is the most practical answer to your problem, it will give you the effect you want without having to get a big fat nasty expensive wire-wound pot
( I actually have a Korean war era big fat nasty wire-wound potentiometer in my collection, bought it in a thrift store with 3 other coffee jars of stuff obviously from a old, probably recently upgraded to the sky ham for 25 cents for all 3 jars, and its gold to me, military grade construction and precision even for this era, its like geek money and feels like s*x while turning it ;D … its nice. 1.5 inches wide, 2 inches tall, 1 inch thick, and potted in “sculpted” rubber)