User Guide for the P0 proton Beam to NA50/NA60


The P0 complex was designed and built to serve the experiments in the high-internsity underground cavern ECN3 with primary proton and heavy ion beams. The proton beams can be derived from the T4 or T6 primary targets and serve either the K12 (beam mode P42+K12) or the H10 branch. From the T4 target there is also the option to provide a clean electron beam.
In this user guide we describe only the operational aspects of the operation of the P0 complex for NA50 and NA60 during the fixed target proton period. The beam mode is either P41 (user index <227>) or P61 (user index <245>). The first three chapters describe the primary proton beams. The specific features for the P41 electron mode are discussed separately in chapter 4.

1. Preparations at the start of a proton run

At the start of a proton run, a number of operations have to be performed (by SL-EA) to allow a correct and safe operation of the P41/P61 beam in attenuated primary beam mode:

Normally the analog chamber MWPC 1+2 is left in place for the proton period.

As soon as the beam from the SPS onto T4, T6 is stable and correct (check the profiles and divergence at the target with EA/BEAM/TARGET/SCAN, respectively EA/BEAM/TARGET/ANGLE), you are ready to tune the beam.
The complete tuning procedure is described separately for the P41, respectively P61 and the H10 sections of the beam. Please note that the H10 part of the beam offers the choice of 3 different versions of the optics:

  1. The so-called Convergent Optics (as for NA10 and NA38) with magnification 0.25 in the horizontal plane, 0.8 in the vertical plane,
  2. The so-called Parallel Optics (a wrong and confusing name!) with magnification 0.8 in both planes,
  3. The Intermediate Optics with magnification 0.5 in both planes, i.e. nicely in between the two extremes mentioned above. The standard optics for proton beams is the Parallel optics. It tends to provide good performance for physics, together with maximal steering possibilities at the NA50 target. Horizontal steering is done with Bend-12 (6 Amps/mm at 400 GeV/c), vertical steering with Trim-13 (12 Amps/mm). The horizontal and vertical angle can be adjusted with Trim-12, resp. Trim-11. Fine steering of the end of the beam in the other optical modes is described in the H10 User Guide.

    2. Observation of the performance of the beam

    3. How to find back good conditions?

    After a change of beam conditions (re-steering, spill optimisation, wobble changes, gradual drifts, etcetera), it may be necessary to re-optimise the beam somewhat. Normally this can be achieved in three successive steps:

    1. Find back the beam flux through the first 4 collimators.

      Normally Collimators 1 to 4 should have rather small apertures, centred around zero (typically of the order of ±3 mm). Leave these apertures unchanged and do the following four scans (resp. double scans):

      P41:

      • Center at COLL-1 with a single scan of BEND-5 on EXPT-1, 10 steps of 4 Amps at 400 GeV/c.
      • Center at COLL3, leaving the steering at COLL-1 unchanged, with a double scan of BEND-2 + 0.225 TRIM3 via 
             TUNE/DBL-SCAN/EXPT/1/2/BEND/5/TRIM/3/5/5/0.225
      • Center at COLL-2 with a single scan of TRIM1 on EXPT-1, 10 steps of 2 Amps at 400 GeV/c.
      • Center at COLL4, leaving the steering at COLL-2 unchanged, with a double scan of TRIM1 - 5.0 TRIM4 via 
             TUNE/DBL-SCAN/EXPT/1/2/TRIM/1/TRIM/4/5/2/-5.0

      P61:

      • Center at COLL-1 with a single scan of TRIM2 on EXPT-1, 10 steps of 2 Amps at 400 GeV/c.
      • Center at COLL3, leaving the steering at COLL-1 unchanged, with a double scan of TRIM2 - 3.18 TRIM3 via 
             TUNE/DBL-SCAN/EXPT/1/2/TRIM/2/TRIM/3/5/2/-3.18
      • Center at COLL-2 with a single scan of TRIM1 on EXPT-1, 10 steps of 2 Amps at 400 GeV/c.
      • Center at COLL4, leaving the steering at COLL-2 unchanged, with a double scan of TRIM1 - 5.0 TRIM4 via 
             TUNE/DBL-SCAN/EXPT/1/2/TRIM/1/TRIM/4/5/2/-5.0
      If necessary adjust the flux by opening or closing COLL-1 and COLL-3.
      In the 2000 run, COLL-2 has some difficulties to set around position 0. Try to avoid using this collimator!
      Never use the SLIT option. Always use the JAWS option.

      For small adjustments the program TUNE/SPECIAL/ADJUST-COLL allows to slightly increase or decrease the gap without making big steps in between (to correct for mechanical play). Note, however, that this program does not update BIM.0 and that it has no error trapping. If it does not give the expected result, please use TUNE/SET/COLL instead!

    2. Center the beam at T8.

      At the old T8 location, just downstream of Fiscs 5 and 6, the NA60 collaboration sometimes installs their 'beamscope' detector, size 1x1 mm2. It is of course important to hit this detector with the beam which is even smaller than the detector (RMS about 0.35 mm in each plane!). This is achieved by the following "Finger scans":

      TUNE/SCAN/FINGER/Fisc #/Position/2/magnet/ etcetera):

      		Fisc
      Position      		 Reference
      position      		 Steering
      element

      		Fisc-6 (H)0.8TRIM-10

      		Fisc-5 (V)-1.4BEND-10
      Then check with the users that the beam is indeed centred on their detector. If necessary, fine adjustments should be made.
      To correct for the resulting change of horizontal angle at T8, scan BEND-11 through COLL-11 = ±1 mm onto EXPT-1 and set the best value. The vertical angle can be corrected with a TRIM-7 scan onto EXPT-1

    3. Steering to the main experiment


      The steering at the experiment is best achieved by Finger scans onto Fiscs 9 and 10:

      		Fisc
      Position      		 Reference
      position      		 Steering
      element

      		Fisc-10 (H)-0.2BEND-12

      		Fisc-9 (V)1.3TRIM-13
      Please verify and document the beam shape with Fisc profiles of Fiscs 9 and 10 (with 0.2 mm steps).
      If necessary, a more precise scan be made onto the halo counter, which has a 3 mm diameter hole. Normally it is plugged into EXPT-10. Before the scans, the experiment should remove their target, otherwise the halo rate would be dominated by backsplash from the target.

      Sometimes the experiment wants to scan the trigger rate (EXPT-4) versus X and Y position over a wider range. The trigger rate increases dramatically when the beam hits the edges of the Beryllium Oxyde absorber (diameter 7 mm). The interpretation of these scans depends strongly on the configuration of the experiment and should therefore be analysed together with the experimenters.

    4. Special instructions for electron beams in P41

    Electrons may be produced via conversion of photons resulting from po decays. This option exists only from T4. The setting up involves most of the steps for proton beams (see section 1), but there are a few differences:

    The electron files usually need some tuning at the beginning of each new electron period. The suggested procedure consists of four scans: Bend-2H, Trim-2V, Bend-12H and Trim-13V onto the EXPT scaler sampling the electron counter rate.

    Last updated : 17 October 2001 by Lau Gatignon