The c4 in the user name is by accident only there seems to be 3 other brianc's on the net and they must all have similar interests to my own! Plain ole brianc is always taken times 3 about every web site I visit!

   As for the temperatures that can be achieved check out Edmund Scientifics web site they offer a 2 foot diameter perfect mirrored parabola that will hold a quarter of an inch focal point & achieve 2,500 deg. F temperature!

   That is a good thought on using the pipe as the pivot point. Very elegant and simple and well worth incorporating into my final design.

   I have my first tracking system designed using some very small but powerfull pv cells driving relays hooked up to dc gearmotors that has proven to work out very well in the prototype stage.

   The first working model should be done next week and will be installed on a dual axis parabolic dish solar cooker.

   I will post pictures of unit in the coming week.

   The great thing about the design is that the relays will handle 7 amps of current at 30vdc so you can drive some big torque dc gearmotors if necessary. From the input side the relays only require 1.2 milliamp current at 12v dc. The small PV cells I am using to drive the relays are epoxy encapsulated and produce 8v at 44 milliamps in full sunlight. They have been very reliable at tripping the relays.

You mentioned that  your using a deep trough design.  Such a design uses its material inefficiently.  if the edges of the trough are twice the height from the bottom of the trough as the focal point, the edges are at 60 degrees.  at the edge for an added inch of materials, you only add 1/2 an inch of sunlight.

for the opposite situation, the focal point is twice the height from the bottom of the trough as the edge of the trough, the edges are at 30 degrees. at the edge for an added inch of material, you add .8 inch of sunlight.  With the focal point so high it is hard to put on a lid.  So, in this case, you'll probably use a "glass" evacuated collector.

If you going to put a lid over your trough, to make the best use of your materials, put the focal point at the same height as the edges of the trough.

here is a link to more pics on the mit lesothos project: http://www.solarturbinegroup.org/media/

here is a pic of the pipe they used.  From the picture, it seems like their pipe is only about 1 1/2 inch at the most.  And, their trough is HUGE compared to yours.  I would think you could get away with a pipe of only 1".

Not sure what they are  using to mount the "glass" tube.  what is that grey stuff and the red stuff.  And why are they using a clamp?