alignment for 2010 run and n_tof 2009 beam profile

Alignment for 2010 run and n_TOF 2009 beam profile

M. Calviani (CERN), S. Andriamonje (CERN), E. Berthoumieux (CEA), C. Guerrero (CIEMAT),

M. Calviani - n_TOF Analysis Meeting CERN

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Outline

23 September 2010

• Alignment campaign review for 2009 and 2010, summary of activities• Activities in 2010• Update on the experimental beam profile

RESULTS AS OF APRIL 2010 (n_TOF Collaboration Board 04/2010)

Complete set of analysis routine now freely available /afs/cern.ch/exp/ntof/XYMGAnalysis now responsibility of CEA


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Introduction – summary of 2009 observations

23 September 2010

• Measured neutron fluence during the 2009 run was ~20% less than expected (comparison with simulations and old official fluence)

• n_TOF experimental beam profile misalignment of the 2nd collimator• 11% of fluence recovered in November 2009 tilt of ~2 mm of 2nd collimator (-8 mm upstr., -6 mm downstr.)!

-9, -4 = -5 mm

0, -4 = +4 mm

-4, -4 = 0 mm

-8, -4 = -4 mm

-7, -4 = -3 mm

-6, -4 = -2 mm

In 2010 the alignment has been performed by looking at the

spallation target• 5 cm left radially (looking at target) to intercept the maximum of the fluence

NB: the theoretical beam line (with which the 2nd collimator is aligned) has been defined by looking at the 1st collimator center


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Alignment campaign 2010

23 September 2010

Surveyor’s theoretical beam line defined with the following steps:

1. A theodolite is placed in the Escape Lane (FIC2 place), where fixed (2001) reference points are placed in the floor

2. Theodolite view is set to 0.67° proper inclination of the TOF line. For the radial direction, uses a reference in the EL

3. Observation: The center of the theodolite is very close to the mechanical center of the neutron window 1. Vertical ok2. Horizontal is shifted by ~1 cm


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Alignment campaign 2010

23 September 2010

The 1st collimator is shifted up by 1.9 cm, left by 0.75 cm, looking to the target

• No information on the possible tilt• Explains the 2009 movements on the 2nd collimator• ~9% decrease in fluence from the simulations• Movement possible but not easy (not foreseen for now)• NB: this shift was always in place, since the construction of the facility!2010 Alignment will be performed by looking:

• Vertically mechanical center of the window• Radially 5 cm to the left of the mechanical center

• New reference points will be established in the EAR-WS


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2010 plans on alignment

23 September 2010

1. First measurements included the movement of the 2nd collimator to try maximizing the fluence

• vertical movement only• horizontal movement available but too

risky for the moment (possible if beam profile show a significant horizontal skew)

2. SiMon + XYMG with 10B or 235U sample

• simultaneous profile and fluence variation evaluation

• borated water (*) CEA data• 235U will allow to have a

reasonable statistics in the HE part

• XYMG current routine (v. 2.8/2.9) limited by a significant dead-time (signal is ~200 ms long)

X-Y MicroMegas

Silicon Monitor

Monitoring MGAS


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X-Y MicroMegas for n_TOF (1/2)

Detector based on the “bulk” technique Active region is separated in two active regions:

• conversion (drift) 480 V• amplification (mesh) gap 330 V

Anode segmented into 106 strips for each X and Y pad (tilted 90 deg.)

Application for monitoring of the n_TOF neutron beam• Neutron beam profile from thermal up to ~1 MeV• Detector used for helping in the alignment of the experimental area

• experimental (almost real-time) position of the neutron beam

23 September 2010

n_TOF Collaboration Meeting 2009


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X-Y MicroMegas for n_TOF (2/2)

Neutron converter, enriched 10B4C, deposited by sputtering on a 3 cm radius on a coppered (1mm) kapton (12.5 mm) substrate.

• thin ~ 24 nm thickness (no dead-time)• thick ~ 2 mm thickness (for the high energy

part)

60 mm x 60 mm with 106 strips per pad 566 mm pitch 212 channels too much for fADC two multiplexer card based on Gassiplex concept have been used 2 output directly to the n_TOF fADC Trigger signal is available through the mesh signal n_TOF available Gassiplex is able to read only 96 strips (reduced active area) DAQ and analysis routine have been specially developedOperation principle:

• Read consecutively all the X and Y strips• 2 ms per strip total of ~192 ms• dead-time issues if the count rate is too

high (but non-paralyzable)

23 September 2010



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X-Y MicroMegas Analysis procedure (1/2)• Digitized Gassiplex signals are the input of the analysis• Each mesh signal trigger the aperture of a gate of 192 ms wide (T/H)• In order to record MeV neutrons, the prompt flash is remove “by hardware” in the Gassiplex trigger stage

192 ms

Pedestal runs are needed to evaluate mean value of the signal is each of the strips• + level shift

Amplitude distribution of signals after pedestal subtraction and level shift correction (+/- 2 channels baseline) 23 September 2010



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X-Y MicroMegas Analysis procedure (2/2)• Cluster analysis used to search for strips that have fired above the mean value of baseline (> 10 ch above baseline with >= 1 fired strip)• “Center-of -charge” applied to define the interaction point

Coincidence method to reconstruct a 2D image of neutron beam

• # fired strips >1• rotation of 225 deg. to obtain

image as of neutron beam• energy selection based on

TOF 23 September 2010



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X-Y MicroMegas 2009 results up to 1 keV

Assumed tilt is in agreement to what has been found during the 2nd collimator alignment tests

Fit on data performed on the

base of a gaussian + step function

th. - 1 eV1

eV –

1 ke

V

• Simulation assuming perfect alignment• Simulations assuming -2 mm tilt upstream 2nd collimator

th. - 1 eV 1 eV

– 1

keV

23 September 2010


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Updates on the experimental beam profile 2009 with XYMG 100 keV – 1 MeV

23 September 2010

Horizontal Vertical


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X-Y MicroMegas 2010 results

23 September 2010

Beam profile run 10099-10101:Main observations:• beam profile seems to be symmetric effectiveness of 2nd collimator alignment• data at higher energy mainly limited by statistics (with analysis routine v2.9 (the latest by MC)) improved by updates by CEA


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Analysis routines

23 September 2010

1. Freely available (source included) at /afs/cern.ch/exp/ntof/XYMG

2. Detailed description of the routines can be found on http://cdsweb.cern.ch/collection/n_TOF%20Internal%20Notes?ln=en as a private Internal Note (accessible to members of the [email protected] e-group

• X-Y MicroMegas analysis: how to run the programs, n_TOF-INT-2010-002, July 2010

• New 2D MicroMegas detector for n_TOF beam profile: description and preliminary results, n_TOF-INT-2010-001, July 2009

3. Now CEA has taken over the work and implemented the suggested improvements

• namely the integration of the mesh signal in the analysis, which will lead to an improved statistics

• better calibration especially at higher energies

http://cdsweb.cern.ch/collection/n_TOF%20Internal%20Notes?ln=en

http://cdsweb.cern.ch/collection/n_TOF%20Internal%20Notes?ln=en

mailto:[email protected]


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For the future if needed: proposal for 1st collimator

23 September 2010

Needs for the 1st collimator:1. Understand if tilting is

present (it may affect significantly the fluence)

2. Consider the possibility to shift it down into the proper location

2. ShiftingAction complex by the fact that it requires lifting an heavy piece• The downstream part is fixed into the wall• The upstream part can be moved down

• removal of the filter station• adjustment of the TOF line

We can measure it with the help of a planar laser, similarly to what we did for the 2nd collimator• it requires some work and still an uncertainty of 1-2 mm is to be taken into account

1. TiltingFilter station

1st collimatorupstream

downstream

NB: geometer’s independent action


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Conclusions

23 September 2010

1. n_TOF beam line up to the Experimental Area is aligned by looking at the spallation target neutron window• 2nd collimator is aligned accordingly• 1st collimator is shifted/tilted, no easy way to move it

back to proper position its effect on the flux reduction account to few %

2. Review of the XYMG analysis as performed in 2009 and beginning of 2010

3. Status of the analysis routines

4. Good agreement with simulated beam profile

1. Indications on the misalignment of the 2nd collimator

2. Predictions have been verified experimentally could be used for alignment purposes


17 23 September 2010

End



Evident misalignment of the 2nd collimator upstream bellow~ 1 cm (?)

Upstream bellow

Dowstream bellow

Upstream bellow

Results after the optimizations

April 2009

November 2009 also April 2010



Only 96 strips are read over a total of 106 (effect on beam position)

alignment for 2010 run and n_tof 2009 beam profile

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