SEETFDAQ spectra

SEETFDAQ spectra

The following spectra have been defined for the SEETFDAQ version of SpecTcl:

see.ppac.{u,d,l,r} These one dimensional spectra histogram the raw signals from the four sides of the PPAC detector. They are mostly used by NSCL staff for debugging purposes.

see.ppac.a This one dimensional spectrum histograms the PPAC anode signal.

see.ppac.{x,y} These one dimensional spectra histogram the computed x and y positions of particles passing through the PPAC.

see.ppac.y_vs_x A two dimensional histogram that plots the computed x position against the computed y position from the PPAC.

see.ppac.{x,y}_profile X and Y profile spectra for the PPAC. profile spectra are essentially compressed position spectra with a settable compression factor.

see.sci.{u,d,l,r} One dimensional energy spectra from the four segments of the segmented scintillator.

see.sci.counts A one dimensional four channel spectrum that histograms the total counts in each of the four segments of the segmented scintillator.

see.trend{u,d,l,r} Trendlines for the four scintillator spectra. A trendline is a spectrum that shows a history of counts vs. time, like a strip chart.

Some of the spectra described above are controlled by parameters. These parameter are read from Tcl variables. The values of the parameters can be set via the Tcl set command. The paragraphs below describe:

• How to manipulate TCL Variables.
• How the PPAC position spectra are computed and the parameters that influence this computation
• How the PPAC profile spectra are computed and the parameters that influence this computation.
• How the Scaler trendline spectra are computed and the parameters that influence this computation.

Manipulating TCL Variables

[htb]
	 set name 
$value$
	 %  set ppac.x.scale1 .8993
	  .8993
	 %  set ppac.x.scale1
	  .8993 
	 %

Several TCL Variables control the way spectra are incremented. You will naturally want to save the value of these variables so that they can be re-used in later runs of SpecTcl. Several command procedures have been implemented to support this:

SaveParams Saves these parameters to the file named file.

SaveStartupParams Saves these parameters to the file named  /config/opparams.tcl. This file is read by SpecTcl on startup.

SaveTempParams Saves these parameters to the file named  /config/tempparams.tcl

The save files are simple Tcl scripts. The variables saved can be restored via the tcl source command. For example in the SpecTcl command window:

[htb]
	 %  source opparams.tcl

reloads the default settings for these parameters.

The sample shows two forms of the set command. The first form sets the value of the variable ppac.x.scale1 to .8993. The second form displays the value of the variable without mofidying its value.

PPAC Position Spectra

The PPAC position spectra require a calculation of the position. For a given pair of signals (e.g. l and r for left and right), The position calculation is done as follows. First calibrated left and right positions are computed as follows: lc = (l+pl)*ml + cl

l_c = (l + p_l)*m_l + c_l

r_c = (r + p_r)*m_r + c_r

Where pl, prp_l, p_r] are random values uniformly distributed between 0 and 1. And the m's and c's are calibration slopes and offsets respectively. Next:

slr = lc + rc

s_lr = l_c + r_c

If this value is too small, smaller than slrmins_lrmin] the computed position is considered invalid. If the position is valid, the final value x is computed via: x = ((rc-lc)/slc)*xm + xo

x = m_x ((r_c - l_c))/(s_lc) + o_x

where xm, xom_x, o_x] are additional linear calibrations for the final position.

The SpecTcl variables are as follows:

PPAC Profile Spectra

The PPAC profile spectrum is essentially a compressed PPAC position spectrum. For each position axis, the position value (e.g. xx]) is multiplied by a constant pscalep_scale] and then histogrammed. The two scale variables are called: ppac.x.profilechans and ppac.y.profilechans respectively.

Scaler Trendline Spectrum

Scaler trendline spectra show the time evolution of the count rates in the scintillator scalers. The periodic scaler increments are summed into a channel for a fixed dwell time that can be set. When time of the sum exceeds the dwell time, either the next channel is selected or, if the previous channel was the last channel, the spectrum is shifted left one channel and the last channel is used again.

Note that the scaler trendline spectra are destroyed and created at the beginning of each run, in order to allow you to change the number of channels of trend information maintained. All four trend spectra are controlled, therefore, by a channel count and a dwell time. The channel count is the TCL Variable see.trend.Channels. The dwell time (in seconds) is see.trend.SecondsPerChannel.

SEETFDAQ spectra