Update of the SR
M. Sullivan
Apr 27, 2017
MDI meeting
Outline
• Current beam pipe layout
– How Lumi-monitor fits in
• Improved SR calculations
– Binning for critical energy histograms was found to be too
coarse. This has been resolved.
•
•
•
•
New tt SR background estimate
HH running SR background estimate
WW running SR background estimate
Summary
2/24
10
End view at +/- 1 m
5
cm
Here is
where the
beam pipe
needs to be
enlarged
LumiCal
HOM
absorbers
0
-5
-10
-10
3
-5
0
cm
5
10
10
Central detector
beam pipe +/12.5 cm in Z
radius=15 mm
NEG pump
BPMS
5
NEG pump
BPMS
HOM Abs
Cu
cm
HOM Abs
Be
Be
Cu
0
-5
Central detector
SA inside +/-150
mrad
-10
-2
-1
0
m
1
2
4
3
2
1
m
0
-1
-2
-3
-8
-4
0
m
4
8
5
Features
• The natural chamber wall geometry is OK
• All LumiCal tracks now have a 20 mrad or
higher angle of incidence to the beam pipe
walls
• There looks to be enough room on the other
side of the beam pipe for a NEG vacuum
pump
• Now we come to the next question…..
6/24
Shielding
• The question now arises about shielding the central
detector from SR from the last bend magnet
• The LumiCal needs a window in the beam pipe where
we can no longer put shielding
• For the Z running this is probably not an issue
– The photon energies are very low (Ave scattered=1.8 keV)
• But for the Top running this is more important
– Ave scattered is 200 keV
– Effectively the central part of the beam pipe increases
from +/-12.5 cm to +/-50 cm due to the LumiCal window
– This will increase the number of photons going into the
central chamber (factor of 10? More?)
– GEANT simulation comparison will tell us the answer
7/24
tt scattered photon energy spectrum in Jan.
The photons that
cause trouble are
coming from the
high energy tail of
the bend radiation
8/24
Scattered energy spectrum for tt in Mar.
522458 out of 100 million
incident scatter through the tip
I found an inaccuracy in
my code where the
binning for the critical
energy histograms was
calculated too coarsely.
Came about because
there are very strong FF
quads and a very soft last
bend magnet
9/24
Energy scattered/incident ratio
10/24
Scattered energy spectrum from HH
433219 out of 1billion incident
scatter through the tip
Number incident > 10
keV is 187 million/xing
so 81,000 scatter from
the tip
11/24
Scattered energy spectrum for WW
389692 out of 10 billion
incident scatter through the tip
Number incident > 10
keV is 28 million/xing so
109 scatter from the tip
12/24
WW scat. ener. with expanded scale
13/24
10
Central detector
beam pipe +/12.5 cm in Z
radius=15 mm
NEG pump
BPMS
5
NEG pump
BPMS
HOM Abs
Cu
cm
HOM Abs
Be
Be
Cu
0
-5
Central detector
SA inside +/-150
mrad
-10
-2
-1
0
m
1
2
14
For the Top running
• 2.1109 photons are incident on the mask tip
from every beam bunch (9.9108 > 10 keV)
• 0.52% scatter through the mask tip (5.15 million)
• Of these, 1.4% go through 1 cm of Ta (72,000)
• Or 0.16% go through 2 cm of Ta (8200)
• This is looking like it might be OK
• We will probably need 2 cm of shielding (Ta, W
or Pb) near the mask tip
• Once the photons are going through the shield
at a 45 deg or smaller angle of incidence 1 cm of
shielding should be enough
• A detailed GEANT simulation should verify this
15/24
What about the other running points?
• SR photon critical energies are listed here
–
–
–
–
–
The critical energy of the last soft bend magnet
For the Top (175 GeV) –
100 keV
For the Higgs (125 GeV) – 40 keV
For the WW (80 GeV) –
9.5 keV
For the Z (46 GeV) –
1.8 keV (3.6 keV?)
• More simulation runs with the GEANT4 model of
the beam pipe
• Do we want/need the LumiCal for the Higgs?
• Stay tuned……
16/24
Summary
• The LumiCal looks OK at the Z running
– Even with smaller beta* optics (needs to be checked)
• We need a Be beam pipe for the LumiCal
window in order to minimize the RL to the
LumiCal and to minimize the HOM power in this
region
• The LumiCal window will cause central detector
SR backgrounds to increase at the Top running
because of the higher energy of the scattered
photons and some reduced shielding but in
general SR backgrounds look like they can be
controlled
17/24
FF quads
• Magnet designs are converging and the next
big step is to get initial dimensions for the
cryostats
• Can we have warm bores as asked?
• How much actual space is needed for the
magnets and correction coils and
compensation coils
18/24
Conclusions
• A great deal of progress has been made in
deciding on baseline parameters and general
layout of the IR
• SR at the Z does not appear to be an issue
due to the very low photon energies
• SR backgrounds at the Higgs and Top will be
more of an issue. The photon energies are
significantly higher, but at first blush it looks
like they can be controlled
19/24