Massimo Caccia, P.I. Universita’ dell’Insubria [UINS] Como (Italy) & INFN- Sezione di Milano
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Transcript of Massimo Caccia, P.I. Universita’ dell’Insubria [UINS] Como (Italy) & INFN- Sezione di Milano
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):
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
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
Introductory slides on different imaging modalities
The analysis matrix
Imaging modality
Frame by frameDifferential Imaging
(pair of frames)
Analog pulse
a11 a12
Counting a21 a22meth
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• is any of the matrix elements more robust and reliable?• any irreducible problem preventing to use any of them?
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
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…
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.
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
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)
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
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
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)
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
Step 4: estimate the “width” as the mean FWHM over the central 9 slices
Vs.
Monitoring the intensity fluctuations
MIMO Vs
UNIDOS*
*The PTW UNIDOS is a high performance secondary standard and reference class dosemeter / electrometer
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
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uild
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The accelerator complex[patients treated since 2008]
The b
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Interested in high granularity (in time & space) because they do feature “intensity-controlled raster-scan technique”
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
Quantitative information (C ions)
Intensity Scan
Energy Scan
Playing back the data
Carbon5.wmv
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!)
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
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
Real-time profiling
Image of a tilted beam
Flat beam
2 frames
10 frames
20 frames
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…
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
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
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