Transcript Beam line optics questions Many thanks to Kevin Tilley, Marco Apollonio, Mark Rayner and others who have taken us where we are. --

Beam line optics questions
Many thanks to Kevin Tilley, Marco Apollonio, Mark Rayner and others
who have taken us where we are.
-- Remaining issues and questions on matching the beam line
-- additional future requests and ideas
MICE CM32 Goals of the Meeting Alain Blondel
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Beam line matching
-- The beam coming out of the decay solenoid is prepared in
14m long Downstream Beam Line section
-- dipole D2, which ensures momentum selection,
-- two quadrupole triplets
beam line tuning  optically matched beam of
-- emittance N at the entrance of the cooling channel,
-- central momentum pz in the middle absorber of the step VI configuration.
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Matching can only be approximate
conditions to be fulfilled simultaneously:
1. beam matched in SS1 downstream of the diffuser, with
=x,y= 2pz[GeV/c]/0.3 Bz[T]
=x,y = 0.
2. beam size at entrance of diffuser = beam size at exit of the (thin) diffuser,
2x,y= (1/) N  , with =E/m
3. The beam angular divergence at entrance vs exit of the diffuser,
2x’,y’ (in) + 2,MS = 2x’,y’ (exit)= (1/) N /
4. P(D2) = (pz (nom) @ middle of step VI central absorber) + Sum(dP/dx)
The available knobs are:
i) Thickness of a high Z diffuser
ii) the quadrupole currents to tune inx,y and inx,y
iii) D2 magnet excitation
Because the emittance of the incoming beam is x y the matching cannot be
exactly performed. In addition the horizontal dispersion is large.
This seems to be manageable for N = 6 and 10 mm, but not for N = 3mm
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Possible cures:
1. Exact matching was not even attempted, only an average solution was proposed
based on 4D ‘beta-functions’ which take an average value without attention to x-y
difference.
Suggest analysis to understand the problem,
see if matching recipe itself could be improved?
2. It
----
is possible that culling the input beam would improve the situation
modify trigger to force symmetric beam at TOF1?
insert collimators at level of D2?
select at analysis level
(easiest, can be studied on real beam now,
…but careful that this effectively reduces available statistics)
3. Understand what momentum dispersion does to us?
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Other needs
-1- we need an optics (« pion » beam presumably with P~350 MeV/c)
that sends the beam through B=0 MICE channel with largest efficiency
-- EMR run to reach EMR
-- tracker TOF2 and EMR alignement/calibration runs for Step IV
Presumably by creating a focus around the middle of MICE
STEP IV.Alignment
BMICE=0
EMR run
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Chosing the D2 momentum right at the backward decays leads to
introducing a kinematic boundary in the middle of the muon momentum
spectrum. This leads to a very asymmetric momentum distribution.
We should try raising D2/D1 to catch a more symmetric situation
Will this give more pions? Would like to study this on G4beamline before
doing it in the real beam.
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Muons or pions?
Would like to ask a question:
In ‘pion beam’ mode we have a very nice sample of muons with narrower
momentum spread… What is the rate and what is the emittance of that beam?
Can it be useful to something?
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