src/f1f2.md

F1 - Dispersive focal plane and F2 - Achromatic focal plane
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\author HY


CRIB has two dipole magnets (D1 and D2), both of which have the maximum magnetic rigidity of 1.2 Tm.
The first one produces a momentum dispersion at the F1 focal plane, and second one makes the beam achromatic at the F2 focal plane.
The primary beam and secondary beam are separated by D1, as they have different Brho values.
The secondary beam is focused again at F2, where we usually perform particle identification.

The momentum dispersion at F1 is 16mm/% (%...momentum difference in %), and a 16-mm horizontal offset 
correspond to 1% difference in momentum, and 2% in energy.

F1 slit
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"F1 slit" is movable plates which can cut the beam from left and right sides.

F1 slit is used for:
 -Change momentum acceptance. 
  + Narrow...Define beam energy precisely.
  + Wide...Accept more beams (wider than +/-15 mm is not effective for increasing the beam at F3.)

 -Check the PPAC center by narrow setting.  

 -Slit scan 
  By changing the positions of opening window 
 (like 0+/-10 mm, 20+/-10 mm, -20+/-10 mm, ...), we can have the momentum distribution  
  of the beam without changing the magnet setting. 


Standard detectors
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We have 
PPAC (Parallel Plate Avalanche Counters, see Kumagai et al., NIMA 2000) and a silicon detector (usually called "SSD") are installed as the beamline detectors.

 - F1: PPAC, 150-mm wide , charge-division type.

 - F2: PPAC, 100 x 100 mm2 , delay-line type. (Thickness is equivalent to 13.5 micron Mylar.)

   SSD, 50mm x 50mm, 1.5 mm thick 


 The profiles and timing of the beams can be measured by the PPAC, The resolution of the PPAC is (better than) 1 mm in position, and 0.5 ns in timing. The energy resolution of the SSD is usually few %. The timing of rf signal is also recorded in the data, and can be used as the TOF information between the production target and the detector.

We can perform particle identification using the measured energy and time of flight. 



F1 Degrader
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We can put a thin degrader at F1 to make a better separation between the primary beam and secondary beam, making use of their difference in the energy loss. However, the degrader may enhance the dispersion of the beam.

You have to keep the following condition, in order to maintain the beam in a small shape.

 + d/R< 0.1

 + d...thickness of the degrader2.4 Beamline detectors

 + R...range of the ion in the degrader

When you make measurements at F3 and the Wien filter makes a good purification, F1 degrader is not necessary.

Questions:
 - *How much is the Brho value for the direct primary beam, primary beam after the target (at the some possible charge states) and secondary beam? (You can use CRIB optimizer to calculate them.)*
 - *How much is the distance between the secondary beam you want and the primary beam of the nearest charge state? *
 - *How much is the momentum dispersion of the secondary beam at F1?*
 - *How much should we open F1 slit?
 - *How much is the expected rate of the secondary beam at F2?*