Table of Contents

S800 Tuning (XDT)

This page gives the steps that are followed when tuning the S800. The two possible tuning modes are included, namely, the Focus mode and the Dispersion-matching mode.

Before proceeding, it is mandatory to complete all the steps of the to-do list necessary to prepare the S800 for tuning. The preparation of the S800 for tuning is covered by the A1900 prior to every experiment.

Focus Mode

For most of the experiments in the S800, the analysis line is run in focus mode. In this optics, the analysis line is achromatic, i.e. the dispersive position of the beam focused in the target area (pivot point) does not depend on the momentum. Thus, this mode provides the biggest momentum acceptance (4%). On the other hand, since the spectrograph focal plane is chromatic, the resolution is limited to about 1 part in 1000 in energy.

Unreacted beam

In the first part of the XDT, the rigidity of the S800 is typically set to match the value of the fragment beam (selected in the A1900) after passing through the S800 target. This is where the term “unreacted beam” comes from.

Send beam to FP

Object scintillator setup

FP scintillator setup

S800 spectra E1 down vs. E1 up.

Ionization Chamber setup

IC.raw spectrum.

CRDCs setup SpecTcl window SpecTcl window

Timing setup

At present, there are three electronic “sources” with time information for ToF calculation: ORTEC TACs, Phillips TDC, and Mesytec MTDC. Some background information can be found here. page

Checking Particle ID and rate at S800 FP page

Analysis line classic PPAC setup (Focus optics only)


Setting Optimization

Dispersion Matching Mode

In the dispersion-matching optics, the S800 focal point is achromatic, i.e. the position of the beam in the dispersive direction does not depend on the momentum. As a consequence, the beam is momentum-dispersed on the target area (pivot point) with a dispersion of about 10 cm/%. The main goal of the tuning is to ensure that the position and angle dispersion are cancelled at the focal plane, thus maximizing the resolution at that point. We also want a good image in the object position, which will also contribute to increase the resolution at the focal plane.

Charge-exchange experiments require typically this optics. In some cases, the beam used is 3H, which has a rather high rigidity (around 4.8 Tm). This imposes a serious constrain, because the maximum rigidity of the spectrograph is 4 Tm. Thus, in this case, the tuning of the S800 is done with 3He, produced with a CH2 target.

S800_DISPMATCH window.

Dispersive angle. Non-ispersive angle.


Dispersive angle. Non-ispersive angle.

Dispersive angle. Non-ispersive angle.



XG before tuning. XG after tuning.

Reaction Setting

Setting up Reaction Settings


right|Trigger GUI

Time setup schematics

Double peak structure in TDC