ALEPH in 1999 Alain Blondel, Ecole Polytechnique

1
Changing the absorbers how does it fit in the
MICE experimental programme?
Besides the requirement that the amount of
multiple scattering material be minimum, the
physics request from MICE on the absorbers is
also that of variability
Which materials? Which variability? in which
context and how often?
let us first have a look at the running scenario
2
Consider the baseline MICE measurement Optics
nominal optics with 3 flips (spectrometer
coupling coupling and spectrometer with - -
polarities) beta function 42 cm, nominal
momentum 200 MeV/c DE-10.5MeV in all three
absorbers and 10.5 MeV in the RF cavities on
crest. to do an emittance in/out curve one needs
diffuser thickness all the way from the minimum
to 4 X0, probably 5 points and to cover the
momentum range one needs to set the beam at steps
of about one rms. (such as 150, 175, 200, 225,
250 MeV/c) This gives 25 points to measure, in
principle each taking 20 minutes, (for 10-3
precision) plus time for changeovers ... a good
24 hours of very busy data taking. (how long
does it take to change diffuser thickness? how
long does it take to change beam
momentum?) (this will come after several months
of debugging which can be done with plastic or
whatever is most practical)
3
Coupling Coils 12
Spectrometer solenoid 1
Matching coils 1.11.2
Focus coils 1
Spectrometer solenoid 2
Focus coils 3
Matching coils 2.12.2
Focus coils 2
m
Beam PID TOF 0 Cherenkov TOF 1
RF cavities 1
RF cavities 2
Downstream particle ID TOF 2 Cherenkov Calorimet
er
Diffusers 12
Liquid Hydrogen absorbers 1,2,3
Incoming muon beam
Trackers 1 2 measurement of emittance in and
out
4
4 X0
possible design for absorber II
remote control
Beam
5
a series of measurements to determine equil.
emitance
A determination of equil. emittance is essential
in view of a muon cooling ring
6
A series of measurements
7
Now if one wants to redo this for the 6 optical
configurations of the proposal (various betas and
nominal momentum), this will take 6 days.
Repeat for the different polarities (solenoid
mode) and one has an intense 3 weeks of data
taking period with a given set of absorbers and
RF volts... if all goes well.
Then time has come to change the absorbers (2
weeks intervention?) and to take data again for
three weeks etc. It soon becomes evident that a
full summer will be very usefully spent if all
goes well and if we have the beam solenoid.
8
The last parameter to investigate is RF volts.
This can be done in several ways. -- connect the
8 MW RF power all to one 4-cavity module. This
increases the local volts by sqrt(2), (and
decreases the overall voltage by sqrt(2)) --
operate at L N2 temperature this allows increase
of gradient and volts by 1.5 to 1.7. -- combine
the two allows to reach a gradient of over 16
MV/m in one 4-cavity module obviously this is a
major operation that requires lots of RF work.
at the same time this will be the ONLY moment
where one would need to change the thickness of
the LH2 abosrbers to protect the detectors.
9
The absorber plays a role beyond provideing
dE/dx protects trackers against RF
electrons! This is helped by the magnetic
field. But only in the flip situation.
e-
g
e-
10
Preliminary conclusion At least for the first
year of operation the thickness of LH2 absorber
will not need to be changed. It will be
required to change the absorber to other
materials to investigate their qualities MICE
aims at observing cooling precisely and measure
the equilibrium emittance precisely (relevant for
cooling ring and Muon collider) Changing the
thickness of absorber will come when
investigating operation with higher gradients and
will come along with other major hardware
modifications (to the RF)