1. Development of the muon monitor for the T2K experiment
H. Kubo, K. Matsuoka,
M. Yokoyama, T. Nakaya
for T2K collaboration
DPF/JPS 2006, Hawaii
contents
introduction to the T2K
muon monitor
2. beam test results
ionization chambers
diamond detectors
3. future plans

2. Introduction off axis beam provides “narrow band” neutrinos ～0.7GeV
requires a precise control of the beam direction
beam axis
off axis angle
neutrino energy spectrum
at various off axis angles

3. Introduction We determine the beam axis by measuringν
We determine the beam axis by measuring
the profile center of muons.
→　muon monitor (MUMON)
decay volume
beam
dump p π
target
& horn
μ(>5GeV)
110m
diagram of the
T2K neutrino beamline
muon monitor

4. Requirement determine the direction of neutrino beam within 1mrad
→ 3cm precision of the muon profile center
high intensity measurement
～10^8 muons/cm2/spill (at maximum)
bunch by bunch monitoring　(～700ns interval)
survive in a high radiation environment
700 ns
58 ns
1spill = 8 bunches
3.5 s
6 μs
×10^7
muons/cm2/bunch
at full intensity
T2K beam structure

5. Basic design
We use two independent systems, the arrays of ionization chambers and semiconductor detectors (Si PIN PDs or diamond detectors)
To obtain 3cm precision of the profile center, we require less than 5% systematic errors for each chamber in this 7×7 configuration.
160cm
beam
7×7 tubes of
ionization chambers
160cm
semiconductor detectors

6. Detectors (1) parallel plate ionization chambers
simple ― robust & maintenance free
A tube contains 7 pairs of plates.
similar to NuMI design
7.5cm×7.5cm signal electrodes
10cm×10cm bias electrodes
made by radiation tolerant parts
We use 2 gases to cover a wide dynamic range.
Ar gas (for commissioning beam, from 1% of the T2K beam)
He gas (up to full intensity of the T2K beam)
operated in 1 atm
10cm
prototype
ceramic spacer

7. Detectors (2) Si PIN photodiodes CVD (chemical vapor deposition)
（HAMAMATSU S ）
Si PIN photodiodes
low cost
well known properties
radiation damage
for commissioning beam
CVD (chemical vapor deposition)
diamond detectors
developed by CERN RD42
radiation hard
fast response
unknown properties
expensive
for full intensity beam
10mm
10mm
thickness 300μm
9.5mm
9.5mm
thickness 500μm

8. Beam test

9. Motivation & measured items
To fix the IC design
gap size, chamber gases, ...
bias voltage scan
linearity
(with 2 gap sizes, He and Ar gas)
To check the basic performance of CVD diamonds
warm-up time
stability

10. Beam status of Uji electron LINAC
100 MeV
electron
beam radius ～0.8 cm
pulse width ～50 ns (T2K 1bunch-like)
interval ～60 ms
10^6 - 10^9
electrons/pulse
covers T2K
1% to 100%
50 ns
test beam
60 ms

11. Test of ionization chambers

12. IC prototype prototype A tube contains 3 pairs of plates.
10mm
3mm
3mm
50cm
prototype
A tube contains 3 pairs of plates.
G10 plate (not radiation tolerant)
7.5cm×7.5cm signal electrodes (same as actual type)
gap 3mm(left, center) and 10mm
gap precision ～100μm
Chamber tube slides horizontally. → tested one by one

13. Setup for ionization chambers
Si profile monitor IC
CT0
CT1
CT2
3mm
3mm
10mm
beam line
oscilloscope
AMP
AMP
attenuator
ADC 3ch
ADC
ADC
ADC 9ch
Beam intensity is monitored by three CTs.
Beam profile is monitored by the Si PD array.
Electron beam is well contained in a detector area.
beam radius ～0.8cm << signal electrode size = 7.5cm

14. Raw signal triangle-shape pulse size ― same as expected charge (～1nC)
200 mV
bias 1000V (1kV/cm)
intensity ～9×10^8 e-/pulse
(corr. T2K full intensity)
He gas 10mm-gap
600 ns
triangle-shape
pulse size ― same as expected charge (～1nC)
response ≒ electron drift time
Drift velocity is faster than expected, because of existence of impurity gases.
10 mm-gap may be too slow to separate bunches (700ns).
3 mm-gap is about 3 times faster than it.

15. He gas, bias voltage scan
3mm
10mm
0.05% / V
operation
voltage
operation
voltage
scan 0 → 400 (1200) V, and some points again
Bias fluctuations will not cause problem in high voltages.
10 mm-gap chamber losses more charge. ← attachment (by O2)
We expect that it will be improved by increasing gas flow.
reproducibility : within 2%　→ OK!
Difference between two 3mm-gap chambers is within 3%
as expected from gap precision 0.1mm/3mm. → OK!

16. He gas, linearity 3mm-gap chamber responses almost linear up to
T2K
10%
T2K
10%
T2K
full
T2K
full
3mm-gap
10mm-gap
beam intensity
beam intensity
3mm-gap chamber responses almost linear up to
9×10^8 particles/pulse/plate ≒ T2K full intensity.
about 3% difference from the extrapolated line →OK!
10mm-gap chamber slightly saturates.
about 10% difference from the extrapolated line
→ because of recombination
3mm is OK, but 10mm may needs a correction to use.

17. Ar gas, bias voltage scan
gap size normalized
T2K commissioning beam intensity (～1%)
scan 0 → 400 (1200) V, and some points again
operation
voltages
Both 3mm and 10mm has plateau around 300 V/cm.
After that, gain decreases (dissociative electron attachment ).
reproducibility : within 1%　→ OK!
Difference between two 3mm-gap chambers is within 3% (gap precision) → OK!

18. Ar gas, linearity Enough size of signals are obtained
T2K 1%
T2K
10%
T2K
50%
3mm-gap
3mm-gap
beam intensity
beam intensity
Enough size of signals are obtained
down to T2K 1% intensity.
3mm-gap chambers response almost linear up to around T2K 5% intensity.

19. IC conclusion We can use ICs for T2K MUMON. good reproducibility ～ 2%
difference between two 3mm-gaps ～ 3%
→ within the requirement for 7×7 ch
Response of 3mm-gap chamber is so linear with both gases that we can use it without correction.
→ We choose 3mm-gap than 10mm-gap.
→ We can operate ICs with 2 gases

20. Test of diamond detectors

21. Setup for diamond detectors
Si profile monitor
CT0
CT1
CT2
4 diamonds
between 2 Sis
beam line
attenuator
oscilloscope
AMP
AMP
attenuator
ADC 6ch
ADC
ADC
ADC 9ch
put four diamond detectors between Si PDs (reference)
about 20% of the electron beam hits the diamonds

22. Raw signal Diamond responses very quickly. need some attenuation
bias 400 V
6×10^7 e-/cm^2/pulse (T2K full ×4)
signal size ～ 50V
100mV, 1/500 ATT.
Diamond responses very quickly.
Si have a long tail in such a high intensity.
need some attenuation

23. Diamond, bias voltage scan
30%
beam
dia3
Si1
dia1
Si2
dia4
dia2
intensity ～ 9×10^6e-/cm^2/pulse
(corr. T2K full intensity)
scanned up to 600V
no plateau
bias voltage dependence is less than 500V
30% variation among samples

24. Diamond, linearity linear within 2% among T2K intensities → OK ±2%
beam intensity
from the change of the beam condition

25. Warm-up time & stability
Diamonds need some irradiation before reaching stable gains.
Warm-up times are much different among samples.
after the warm-up time, the gain is stable within 2%

26. CVD diamond conclusion
Basic performance is not bad.
acceptable bias dependence ～
good linearity ～ 2% among T2K intensities
stability ～2% →OK
But there are unknown properties,
we need more study .
large variation among 4 samples ～30%
warm-up time is quite unknown.
reproducibility is not good
(maybe from the references or the beam condition)

27. Future plans
Now We are producing the next prototype of IC
( 7ch a tube, using ceramic plates, ...)
and testing actual readout electronics.
next beam
～JFY2006 finalize MUMON design
JFY2007 start production of MUMON
MUMON installation start !
beam on

28. backup slides

29. T2K neutrino beam line
２８０ｍ
１１０ｍ
Pions are made at the target from the proton beam.
Then only π＋s are focused by the sequence of horns. Some of them decay into neutrinos and muons in the 110m-long decay volume.
Muons over 5GeV penetrates the beam dump.
Neutrinos goes through the near detectors toward the far detector, SK.

30. Error estimate of the beam center
in 7×7 configuration
5% systematic errors make 3cm uncertainty of the beam center

31. Non-linearity (He gas)
T2K
full
T2K
full
T2K
10%
T2K
10%
difference from the extrapolated lines
about -3% for 3mm-gaps, -10% for 10mm-gap
@T2K full intensity
fluctuations is about ±2% around T2K 10% intensity
(but it also contains CT fluctuations)
from 10% to 100% of T2K intensity, 3mm-gap is OK !
10-mm gap may needs correction

32. Linearity (Ar gas) T2K T2K 1% 1% 3 mm 100V T2K T2K 1% 1% 10 mm 300V
difference from extrapolated lines

33. Linearity (Ar gas) @ higher intensity
T2K
10%
T2K
50%
T2K
10%
3mm-gap
100V
T2K
50%
10mm-gap
300V
T2K
10%
T2K
10%
difference from extrapolated lines

34. Recombination correction
T2K
10%
T2K
10%
difference from the fit curve
we can correct the effect of recombination
with this fitting method
but for 3mm chambers, it is found that we don’t have to do this within T2K intensities

35. Linearity (diamond) linear within 2% among T2K intensities
Because of the small active area and the beam radius,
yields are much affected by the beam condition.
(second points from the left)
from the change of beam condition

36. Warm up time diamonds need some time to warm up
2 types of the responses
dia1,2 fast response
dia3,4 slow response
HV on/off & beam on/off test
both show similar responses
case1 ― keep beam on & HV off, then HV on(500V)
it takes about 10sec to supply
case2 ― keep HV on(500V) & beam off, then beam on
it takes 1sec to open the shutter

37. Warm up time beam on/off continually at first dia1,2 ～5sec to warm up
dia3,4 ～3min to warm up
after the 5min interval
dia1,2　～5sec to warm up
dia3,4 ～20sec to warm up
we have to check at 3.5sec
interval (actual spill)

38. Stability stable within 2% after 3minutes
no point regions are ADC overflow