X7 - CHANGES FROM SECONDARY TO TERTIARTY MODE AND BACK

The X7 beam can be operated in secondary or tertiary mode. For tertiary beams the intensity incident on the X7 target should be between 1.0 and 1.5E7 particles per SPS cycle, whereas in secondary mode this intensity may never exceed 1E6 particles per SPS cycle. This intensity is measured with TRIG-1 of the X7 beam.
The beam is in secondary mode, as soon as the X7 momentum matches the one of the H3 parent beam. If the X7 momentum is significantly (>10 percent) different from the H3 momentum, a tertiary beam is selected.

In tertiary mode, the H3 collimators are open:

To go from tertiary to secondary mode

Please execute the following steps in the indicated order:

  1. Reduce the intensity on TRIG-1 by closing selected collimators in the H3 beam. A special program exists for this in the X7 tree: 
                   TUNE / SPECIAL / INTENSITY
    First put the upper jaw of COLL-1 to approximately 0 mm. Fine-tune this position until the TRIG-1 rate decreases to about 1E6 without reducing significantly the TRIG-1 rate of the other beam!

    If necessary, the upper jaw of COLL-5 (same function as COLL-1) can be used to refine this task:

    Once this has been achieved, close COLL-8 (and COLL-9 if necessary) to reduce the TRIG-1 rate further to the wanted flux:

  2. Load the secondary beam file (e.g. X7.8) -> MAGNETS only: 
                   FILES / LOAD / X7.8 / YES / MAGNETS
    and check the magnet status afterward.
  3. Remove the target head in X7: 
                   TUNE / SPECIAL / MODES / TARGET / EMPTY
  4. There is no need to have an absorber in the beam: 
                   TUNE / SPECIAL / MODES / ABSORBER / 0
  5. If necessary, the flux in X7 can be adjusted with COLL-1 and COLL-2 in the X7 beam itself: 
                   TUNE / SET / COLL / 1 (or 2) / JAWS / -x / y

To go from secondary mode to tertiary beams

Essentially the same modifications have to be made in roughly reversed order:

  1. Put in the required target head (e.g. Beryllium or Copper)
  2. Load the tertiary beam file (e.g. X7.7) : 
                   FILES / LOAD / X5.7 / YES / ALL
    Check the magnet status afterward.
  3. Make sure that COLL-s 3 and 4 of X7 (equivalent to COLLs 8 and 9 of H3) are sufficiently open (± 40 mm). If necessary, open them with 
                   TUNE / SET / COLL / 3 / JAWS / -40/ 40
    and similarly for COLL 4.
  4. If required, put in an absorber
  5. Only at the end, increase the TRIG-1 intensity with 
                   TUNE / SPECIAL / INTENSITY
    Set COLL-1 to obtain a TRIG-1 flux between 1.0 and 1.5E7. A good setting was > +5 mm. Leave COLL-8 and COLL-9 at ± 40 mm.
Last updated by Lau Gatignon on 6 November 1997