RoentDek DLD120, Руководство пользователя

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MCP Delay Line (Version 6.2.90.5) Page 9 of 80
Figure 2.1: Operation principle of the delay-line-anode
The Hexanode has an additional layer. It is possible to calculate the two-dimensional particle position from the signals of
any two layers. The signals from a third layer serve as a redundant source of information for cases where signals are “lost”
due to electronic dead-time (multiple hit events), non-continuous winding schemes (anode with central holes) or non-perfect
electronic threshold conditions/damping on special very large delay-line anodes.
If you mount the anode to your MCP set with the wires of the innermost layer aligned with respect to the desired up/down
direction in your digital screen image (i.e. Y-direction) and if you follow the connection scheme in the next section, the
position calculation can be done with following codes:
The position in a hexagonal coordinate frame is coded by the arriving time differences from signals in opposite corners of the
anode.
u = (x1 – x2) * d1
v = (y1 – y2) * d2
w = (z1 – z2) * d3 + o
Equation 2.2
If 1/v
i
is the single path signal propagation speed for a delay line layer I (v
i
is slightly different for each layer) then d
i
is given
by
1/d
i
= 2 v
i
* Δ t Equation 2.3
Δ t is the TDC channel width. d
i
must be precisely known to make the images obtained via different layer combination
coherent. o is an offset value that shall unify the “time difference zero” of all three layers, i.e. it must be chosen so that
geometrically the position lines for calculated u, v, w have a common crossing point, e.g w must be zero when u and v are
zero.
For the HEX80 approximate values for v
i
are 0.737, 0.706 and 0.684mm/ns, from inner to outer layer (u, v, w). o differs
from anode to anode and is close to zero unless the connection cables have varying length.
To achieve optimal results v
1
, v
2
, v
3
and o must be calibrated for each delay-line by using acquired data (off-line).
The hexagonal frame can be transformed into a Cartesian coordinate system by the following equations using only two of the
hexagonal coordinates respectively:
Xuv = Ox u
+
( )
Oy v u
+ −
2
3
1
Yuv =
Xuw = Xuv
Equation 2.4
( )
Oy u w
+ −
2
3
1
Yuw
=
Xvw =
( )
Ox
+ +
w v
( )
Oy v w
+ −
3
1
Yvw =
Ox and Oy are offsets.
For detectors with central hole, the gaps in the wiring have to be taken into account. Please contact
RoentDek
for the
program codes appropriate for your detector.