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Acceptance & Scraping. Chris Rogers Analysis PC 04-05-06. Overview. Why it isn’t easy to place a constraint on detector apertures General view on the acceptance of the cooling channel A better - but still not perfect - requirement on the measurement of high emittance particles Implications. - PowerPoint PPT Presentation
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Acceptance & Scraping
Chris RogersAnalysis PC04-05-06
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Overview Why it isn’t easy to place a constraint on detector
apertures General view on the acceptance of the cooling channel A better - but still not perfect - requirement on the
measurement of high emittance particles Implications
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Effect of Losing Muons
What is the effect of losing muons? How does it effect emittance measurement
Is the standard criterion (0.999 efficiency) sufficient? Quantify the argument that “losing signal muons
(because the TOF is too small) at larger amplitude will bias the measurement more”
How does a mis-measurement effect the measurement of cooling channel efficiency?
“Surely muons on the edge of the beam will never make it into an accelerating structure anyway”
Consider the “acceptance measurement” (number of muons within a certain acceptance)
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Effect on Emittance Measurement Measured x variance (<x2>meas ) is related to true x
variance, (<x2>true ) from rejected signal by: Nmeas<x2>meas = Ntrue<x2>true - Nrs<x2>rs
Ref: Analysis PC Aug 19 2005 N is number of muons rs is Rejected signal
Assume that the scraping aperture is at > 2x and 2px
Then after some algebra emittance is given by meas >~ true [1 - (22-1) Nrs/Ntrue]
Losing signal at high emittance will bias the measurement more
This means that for a 1e-3 emittance requirement the efficiency requirement is much tougher than 0.999
More like 0.9995-0.9998 The emittance measurement is very sensitive to transmission
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Beam Dependence
But the number of muons at high amplitude is very beam dependent
Different beams will have very different tails It is not satisfactory to place a requirement on
detector size based on such a quantity The beam I use today will give a completely different
requirement than the beam I use tomorrow Really, we want to use these muons to
demonstrate that we understand the acceptance of MICE
Scraping is an important effect in a Neutrino Factory cooling channel
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Scraping in a Neutrino Factory
In a Neutrino Factory cooling channel, scraping is a first order effect on transmission into an accelerator acceptance
Typical input emittances ~ 12 transverse (FS2A) vs scraping aperture ~ 20
We should be aiming to measure it to the same high precision as we aim to measure emittance
FS2
FS2Z (m) Z (m)
n
Em
itta
nce
//
trans
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Scraping
Aperture 1 Transport Aperture
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There is a closed region in phase space that is not scraped I want to measure the size of this region It is independent of the particular beam going through MICE
Aperture 1
Transport Aperture 2
x
px
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Halo
Consider hard edge accelerator Kill muons that touch the walls No RF or liquid Hydrogen
In a realistic accelerator, there will be some region beyond the scraping region
A reasonable constraint is that we should be able to measure all muons that make it through the hard-edged cooling channel
To get a more serious constraint, need to understand the reduction in cooling channel transmission quantitatively
Soft edgedHard edged
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Apertures under investigation
Three “apertures” in MICE that are under investigation TOF II Diffuser Tracker helium window
TOF IIDiffuser Tracker
Window
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Physical Model842 430 30 40
230
15
150 630
No absorbers or windows
Hard edge -Kill muons that scrape
100014941334
150 200
Tracker AFCAFCAFCTracker RFCC RFCC
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Beams
Consider two sets of particles “Phase space filling” beam 10 pi beam
Phase space filling Place muons on a grid in x, px
Muons at x = 0, 10, 20… and px = 0, 10, 20, … Add spread in either Lcan or pz
10 pi gaussian beam, 25 MeV rms energy spread Cuts at 190<E<260 MeV
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Max Radius vs z - Lcan spread
This is a scatter plot of muons travelling down the cooling channel Vertical lines come because I am only sampling the beam occasionally Drawn a line for the maximum radius of the beam
This is using the beam with a spread in Lcan
radiu
s
z
Radius of MICE acceptance vs z
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Max Radius vs z - Pz spread
Repeat the exercise but now use a spread in Pz
Max.
rad
ius
z
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Max Radius vs z - 10 beam
Repeat the exercise but now use a full 10 beam Max r @ diffuser = 0.128 Max r @ window 1 = 0.136 Max r @ window 2 = 0.121 Max r @ TOFII = 0.273
Max.
rad
ius
z
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W Lau,CM 14
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Gaussian 10 pi beam at Diffuser
A significant number of tracks outside of 10 cm radius Note some of these tracks also pass through the diffuser
mechanism itself It may be possible to arrange the beamline to run in a
less focussed mode with higher energy Try to punch muons through the diffuser mechanism to
populate these tails
DiffuserRadius
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Absorber window Thickness as a function of R (M Green)
15014013012011010090807060504030201000
1
2
3
4
5
6
7
8
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Window Radius (mm)
Win
dow
Th
ick
nes
s (m
m)
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R at tracker windows
No tracks pass through the edge of the windows But the window gets increasingly thick towards
the edges What effect does this have on emittance?
UpstreamZ~-4.6 m
DownstreamZ~+4.6m
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R at solenoid end
The downstream solenoid ends at z=6.011 This is the downstream end of the last coil
But the high amplitude tracks are cut in the tracker
Don’t strike the tracker end
r r
Z=6.111 Z=6.211
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x at TOF
The edge of the beam lies beyond the tof half width While this doesn’t look so bad, if I choose to use a different beam it may well get worse Without materials so this is really a minimum
It may be possible to make the TOF larger than the Ckov and sacrifice some PID in these regions To avoid a very large Ckov
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Summary
I would be happier if the TOF could be bigger It may be possible to compromise by leaving the
calorimeter smaller and losing PID on the fringe While tracks miss the tracker window, I am slightly
nervous about the thickness towards the edge I would be happier if the diffuser could be bigger