massimo caccia, p.i. universita’ dell’insubria [uins] como (italy) & infn- sezione di...
DESCRIPTION
The MIMOTERA: a monolithic pixel detector for real-time beam imaging and profilometry [ U.S. patent no. 7,582,875 ]. Featuring: Designers: G. Deptuch [ FERMIlab] W. Dulinski [IRES-Strasbourg] DAQ: A. Czermak [INP-KraKow] I. Defilippis [SUPSI-Lugano]. Exploitation team: - PowerPoint PPT PresentationTRANSCRIPT
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Massimo Caccia, P.I.
Universita’ dell’Insubria [UINS]
Como (Italy)
&
INFN- Sezione di Milano
GSI, Darmstadt, July 22nd, 2011
The MIMOTERA: a monolithic pixel detector for real-time
beam imaging and profilometry[U.S. patent no. 7,582,875 ]
Featuring: Designers:
G. Deptuch [FERMIlab]W. Dulinski [IRES-Strasbourg]
DAQ: A. Czermak [INP-KraKow] I. Defilippis [SUPSI-Lugano]
Exploitation team:A. Bulgheroni [UINS/JRC Ispra] C. Cappellini [UINS] L. Negrini [UINS] M. Maspero[UINS] F. Toglia [UINS] F. Risigo [UINS] M. Jastrzab[AGH-Krakow] S. Martemyianov [ITEP/UINS]
Staff at HIT & CERN-AD M. Holzscheiter [MPI-Heidelberg & UNM Albuquerque, US] R. Boll [Heidelberg University]
Staff at LARN-Namur:A. C. Heuskin [LARN] A.C. Wera [LARN] S. Lucas [LARN]
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17.136 × 17.136 mm2
digital
28 columns (30 clocks)
112 rows (114 clocks)
MimoTera
chip size: 17350×19607µm2
array 112×112 square pixels,
four sub-arrays of 28×112 pixels read out in parallel tread/integr<100µs (i.e. 10 000 frames/second)
Backthinned to the epi-layer (~ 15 µm ), back illuminated through an ~80 nm entrance window
AMS CUA 0.6 µm CMOS 15 µm epi,
no dead time
Essentials on the MIMOTERA (1/2):
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Essentials on the MIMOTERA (2/2):
Charge To Voltage Factor = ~250nV/e- @ 500fF well capacity of ~ 36 MeV Noise ~1000 e- 280 e- kTC (ENC) @ 500fF
pixel 153×153 µm2 square pixels,
two 9×9 interdigited arrays (A and B) of n-well/p-epi collecting diodes (5×5 µm2) + two independent electronics – avoiding dead area,
In-pixel storage capacitors – choice ~0.5 pF or ~5 pF to cope with signal range (poly1 over tox capacitors),
153 m
Layout
of
one p
ixel
A B
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Original push for the MIMOTERA development:minimally invasive real-time profilometry of hadrontherapy beams by secondary electron imaging[IEEE Trans.Nucl.Sci. 51, 133 (2004) and 52, 830 (2005))]
vacuum chamber
HV
secondary emission foil
electron detector
PROFILE/CURRENT MEASUREMENT
beam
Basic principle: collection and imaging of secondary 20 keV electrons emitted by sub- m thin Aluminum foils
The SLIM installed on an extraction line at the Ispra JRC-Cyclotron(p, 2H, 4H at energies 8-38 MeV, 100 nA- 100uA)
Secondary electrons emitted by a proton beam through a multi-pin hole collimator (Ø = 1mm, pitch = 1.5-6.5 mm)
Step 1 Step 2 Step 3
Today: results on beam imaging by DIRECT IMPACT on the sensor
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Introductory slides on different imaging modalities
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The analysis matrix
Imaging modality
Frame by frameDifferential Imaging
(pair of frames)
Analog pulse
a11 a12
Counting a21 a22meth
od
s
• is any of the matrix elements more robust and reliable?• any irreducible problem preventing to use any of them?
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Imaging modalities: Advantages and disadvantages
Single matrix+ single polarity signal+ spot the detail of the
matrix (e.g. hot pixels)- strongly dependent on a
good pedestal calculation
- And even more on a reliable pedestal variation tracking (due to thermal effects, Charge Collection efficiency variations, else)
Differential imaging- both positive and
negative signals- If pile-up occurs, the
signal averages out to ZERO
- Matrix details can be masked off
+ NO NEED of pedestals+ self-tracking of the
pedestal variations
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Methods: Advantages and Disadvantages
Analog Info- provides and effective
measurement of the intensity, requiring a [possibly time dependent] calibration
- Possibly affected by Pixel-to-pixel gain variations (requires a normalization, implemented by measuring the signal in sigma units)
+ it works also when pile-up occurs
IDEAL for real-time,
qualitative, imaging More difficult to get a
quantitative measurement
Counting+ provides a direct measurement
of the flux [provided you can spot in an unbiased way the hit pixels…]
+ in principle, no calibration required
+ not expected to depend on local gain variations
- HARD to use it as pile-up approaches [look at the non-fired pixels..]
RELIABLE & ROBUST for a quantitative approach
as the pile-up probability increases, play with the integration time…
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Assisting the AD-4 [ACE] collaboration [ACE, http://www.phys.au.dk/~hknudsen/introduction.html]
Michael Holzscheiter, ACE spokesperson (left), retrieves an experimental sample after irradiation with antiprotons, while Niels Bassler (centre) and Helge Knudsen from the University of Aarhus look on [courtesy of ACE]
[courtesy of ACE]
“Cancer therapy is about collateral damage” compared to a proton beam, an antiproton beam causes four times less cell death in the healthy tissue for the same amount of cell deactivation in the cancer.
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Shot-by-shot beam recording at the CERN anti-proton decelerator tests
beam characteristics:-120 MeV energy- 3x107 particles/spill- 1 spill every 90”- FWHM ~ 8 mm
acquisition modality: - triggered imaging modality: - differential radiation damage: - irrelevant so far
[max no. of spills on a detector: 1436]
data taking runs: - September 2009 - June 2010 - October 2010
Single shot picture
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Generally speaking, the beam is stable… unless it moves!
Antiproton.wmv
Quantitative information:• profiling, compared to a GafChromic film • Intensity, compared to a calibrated ionization chamber (UNIDOS, by PTW)
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Profiling the beam[PRELIMINARY RESULTS:• FWHM calculation checked, • errors on the GAF still being evaluated]
With a GafChromic Film, integrating the spills over a full
run…and PROJECTING
With the MIMO, overlaying the 120 events in run #37 events to mimic the Gaf
FWHM = 7.64 ± 0.05 mm FWHM = 7.11 ± 0.05 mm
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More on the analysis..Step 1: Preparation of the reference beam image.
Find a proper observable, possibly independent from quarter-to-quarter gain variation:
A plot of the mean values of every pixel, averaged over all of the spills in the run
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Step 2: check the x & y projections
2 remarks:
projections look pretty smooth, implying the normalized quantity is not so bad
deviations from the gaussian are significant…(qualitative and quantitative analysis)
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Step 3: move from projections to slices:
X slicesY slices
FWHMx = f(y) [and the other way round)
i.e.
being F & G the marginal distributions
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Step 4: estimate the “width” as the mean FWHM over the central 9 slices
Vs.
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Monitoring the intensity fluctuations
MIMO Vs
UNIDOS*
*The PTW UNIDOS is a high performance secondary standard and reference class dosemeter / electrometer
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HIT [Heidelberg Ion-Beam Therapy Center]: Quality control of pencil Carbon Ions & proton beamshttp://www.klinikum.uni-heidelberg.de/index.php?id=113005&L=en
The f
aci
lity b
uild
ing
The accelerator complex[patients treated since 2008]
The b
eam
para
mete
rs
Interested in high granularity (in time & space) because they do feature “intensity-controlled raster-scan technique”
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beam time characteristics:- duty cycle 50%- spill duration 5 s- FWHM ~f(particle, intensity, energy)
acquisition modality: - free run imaging modality:
radiation damage: - relevant but not dramatic
[Total exposure time so far ~ 3h; about 1’-2’ per run at a specified nrj,
intensity]
data taking runs: - May 2010 - October 2010
Data taking conditions & qualitative information
€
Signal − Pedestal[ ]i
∑i
, i∈ROI
I = 7x107 particles/s, C ionsTime development of the beam
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Quantitative information (C ions)
Intensity Scan
Energy Scan
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Playing back the data
Carbon5.wmv
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Imaging the LARN Tandem beams at Namur (B)
Main interests:
- The MIMO as a real-time, high granularity “digital” alumina screen, to optimize the set-up
- QC of the beam in terms of homogeneity
- quick measurement of the absolute intensity (particle counting!)
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beam time characteristics:- continuous beams!- any ion (!) with an energy in MeV/amu range- intensities [103;108] p/cm2/s range
acquisition modality: - free run; MIMOin vacuum
radiation damage: - may really be dramatic![Total exposure time so far ~ 60h; p, , C ion beams]
imaging modality:- standard: signal - pede- differential: (i,j,n) = signal (i,j,n) - signal(i,j,n-1)- based on < 2(i,j,N) >- digital with a pixel dependent threshold
data taking runs: - July 2008, April 2009 + series of short runs since April 2010 performed by the people at LARN - next extensive run planned for end of May 2011
Data taking conditions & qualitative information
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Beam profile with different imaging modalities[protons, E = 1.2 MeV, I = 6 x 105 p/cm2/s]
Signal - pede: + easy & classic - critical wrt pedestal variations
Delta: + robust against pedestal variations - failing as pile-up is approaching
Delta2 : + applicable also for high intensities - emphasizes local differences
Counting with pixel dependent thresholds:+ quite robust against detector degradation- failing as pile-up approaches
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Real-time profiling
Image of a tilted beam
Flat beam
2 frames
10 frames
20 frames
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Preliminary measurements on the intensity
Proton beam, 5 Gy/m = 2 x 106 p/cm2/s
Still working on the absolute particle counting, since it is a tough business…
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Intensity by counting, with a pixel dependent threshold based on a common pre-set spurious hit level
DATA SETA page from my logbook
-Scan runs 1,2,4,5• #3 excluded because of a significant beam instability• #6 & 7 excluded here because they require an overlap of several events to achieve the required sensitivity+ ion source flickering
- rely on the unfired pixels to reduce the pile-up effects
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Linearity, up to 8.8 x 106 particles/cm2/s
• protons, 1.2 MeV energy; • MIMO clocked at 2.5 MHz• differential mode• pixel dependent threshold at 5% spurious hit level
-p0 ≠ 0, we are still cutting off a few pixels which were actually hit- as usual, a trade off between sensitivity and purity has to be searched for..- clocking at 25 MHz, we can use the MIMO in counting mode till ~ 108 particles/cm2/s
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Conclusions
The MIMOTERA appears to be an interesting device for RT beam profilometry at high granularity in space & time
radiation hardness is a certainly a concern, especially at Tandem beams [but so far we did not manage to kill a single detector…]
more tests are on the way, to quantify its lifetime in beam hours
other facilities showed some interests (Krakow, ITEP Moscow) and tests are planned