The NEXT 100 geometry

General considerations

The geometry of NEXT-100 is complex and this page has the aim of explaining the assumptions and the simplifications that have been made w.r.t. the technical drawings, to be able to run simulations efficiently.

The 0 of the z axis (axis of the TPC) in the global reference frame is placed at the beginning of the drift volume and is usually referred to as gate. There are three fundamental dimensions that are used in more than one class in the code to place the different volumes correctly relatively to each other, i.e.:

• The distance between the gate and the surface of the tracking plane (TP).
• The distance between the gate and the surface of the sapphire windows.
• The length of the step that is cut out in the bars of the inner copper shielding, in the energy plane (EP) side.

Additionally, there is a fourth fundamental dimension, which does not appear in the code, but is used to adjust volume positions in several places, i.e., the distance between the surface of the EP copper plate and the teflon reflectors (24.8 mm).

In the current version of the code, the meshes are simulated as dielectric of arbitrary thickness; this thickness is also propagated throughout the code to place all the inner volumes correctly.

Vessel

The vessel is a union of several volumes, as explained in this document. The flanges are simulated simply as external volumes; however, the EP flange has a part that goes inside the vessel, which holds the EP plate. To simulate this we do the following:

1. We build a solid cylinder made of stainless steel.
2. We build a smaller cylinder made of xenon.
3. We cut out two thin cylinders from the xenon volume, in the place where the inner part of the EP flange goes.
4. We place the xenon volume inside the stainless steel one.

Energy plane

The following simplifications have been done:

• The flanges of the copper huts behind the PMTs haven't been simulated, therefore their mass must be added to the activity of the huts.
• Only the central hole for the gas flow has been simulated. The other three ones (close to the borders) are not straight, but they bend at roughly the middle of the copper thickness, and we have decided not to simulate them.
• The PMT bases are made of two different pieces: only the internal part is being simulated, which contains pins and resistors. The external part (dirtier, which contains the capacitors) is supposed to be placed on top of the huts, which are also cut diagonally. However, in the simulation the huts are not cut, and the external part of the bases is not simulated. A generator behind the copper huts is used to simulate their rejection factor.
• The screws of the sapphire windows are not being simulated. Their activity must be added either to the windows (worst case) or to the copper (best case).