wheels

Material in the 'readout wheels'

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View of 1/2 of the vtx/fvtx. The readout wheels on either end consist of 5 planes. An exploded view is here. Click for a bigger view Description below.
Simplified cross section bigger view

Here is a rough description of the planes:

'PCB' is the standard 1/16 inch G10 (or equivalent) board. They are populated with parts (unknown density).
The honeycomb panels have carbon-fiber-epoxy skins. 0.438mm thick each, consisting of 60% by volume graphite fiber and 40% resin. Mean density 1633 kg/m3. The interior is 1.214% volume fraction of aluminum. These panels have cooling tubes embedded, so there may also be some thermal insulation on the outside (6mm rohacell? not shown).
The perimeter of each board is packed with connectors, so you might want to place a solid ring (7×8mm?) of plastic there.
The 'thermal planes' are some material to carry heat to the disk perimeter, where a cooling tube carries it away. This could be thermally conducting graphite (or maybe Aluminum).

Plane	Zmin,max	material	R_in	R_out
1	27.42-xxx	4.85mm honycomb + PCB	24	50
2	31.89-xxx	PCB + 3.18mm thermal plane	24	50
3	34.34-xxx	PCB + 3.18mm thermal	24	50
4	36.78-xxx	PCB + 3.18mm tharmal	24	50
5	xxx-40.00	PCB + 4.85mm honeycomb	2.7	50

All dimensions in cm.

I modeled these materials in Pisa. For the wheels, I claimed a volume SIWH extending from the svx cylinder SIEN out to just short of Helium bag #2 HEB2, and in Z from 26.5-40.0 cm. I shortened Helium bag #1 HEB1 from z=+-30 cm to 26 cm. In the figure above, we have:

Files needed (strip the .txt extension after downloading) :

(updated 28 Feb 2007)

PISA volume	description	PISA material	comment
SIWH	container	cold air
SWRB	readout board	carbon-carbon	c-c was the closest material to PC board I found in Pisa
SWSP	honeycomb support/cooling panel	honeycomb
SWCN	connectors on the perimeter	plastic	modeled as a solid 6×10 mm plastic ring
SWCB	cables and fibers	plastic	There is a huge mess of cables there, which I modeled as a solid wedge-shaped ring of plastic. No copper in there (yet).

Sasha made a radiogram:

Hi all,

I've used Hubert's implementation of "big wheels" in pisa to check how much they will affect electron background in central arms. I found that the increase in electron background will be very small, only ~2%.

One problem is that the default pisa does not have these "big wheels" at all, so the answer is not exactly to the question we were asked, namely, how the extension of big wheels will affect the background. But since the wheels as a whole contribute only 2 additional percent, I think the answer is good enough.

I've attached a plot of R_origin vs Z_origin for the electrons with momentum > 0.3 GeV which are in central arms (that is, produce hits in dch, pc1, and pc3). The plot was done with 100 MinBias AuAu Hijing events. If you count electons originating in the big wheels, and compare to the total number of electrons coming from the VTX, you get ~2%.

Sasha.

Note that the most recent control drawing (1 Mar 07) is a little different: 500 instead of 530 (I took another 30mm for cables), 270 instead of 265 (I took another 5mm for thermal insulation), and 250 instead of 187.

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