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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:

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slide1

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]

Massimo Caccia, P.I.

Universita’ dell’Insubria [UINS]

Como (Italy)

&

INFN- Sezione di Milano

  • 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]

GSI, Darmstadt, July 22nd, 2011

essentials on the mimotera 1 2
Essentials on the MIMOTERA (1/2):
  • AMS CUA 0.6 µm CMOS 15 µm epi,

17.136×17.136 mm2

28 columns (30 clocks)

  • chip size: 17350×19607µm2

MimoTera

  • 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)

  • Backthinnedto the epi-layer (~15 µm ), back illuminated through an ~80 nm entrance window

Subarray 1

Subarray 2

Subarray 3

Subarray 0

112 rows (114 clocks)

  • no dead time

digital

slide3

Essentials on the MIMOTERA (2/2):

  • pixel 153×153µm2 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,

Layout of one pixel

  • In-pixel storage capacitors – choice ~0.5pF or ~5pF to cope with signal range (poly1 over tox capacitors),

B

A

153 mm

  • Charge To Voltage Factor = ~250nV/e- @ 500fF well capacity of ~ 36 MeV
  • Noise ~1000 e-Å 280 e- kTC (ENC) @ 500fF
slide4

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))]

Step 1

Step 2

Step 3

Basic principle:

collection and imaging of secondary 20 keV electrons emitted by sub- mm 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)

Today: results on beam imaging by DIRECT IMPACT on the sensor

slide6

The analysis matrix

methods

  • 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

Imaging modalities: Advantages and disadvantages
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…

Methods: Advantages and Disadvantages
slide9

Assisting the AD-4 [ACE] collaboration

[ACE, http://www.phys.au.dk/~hknudsen/introduction.html]

“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.

[courtesy of ACE]

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]

slide10

Shot-by-shot beam recording at the CERN anti-proton decelerator tests

Single shot picture

  • 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

slide11

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)
slide12

Profiling the beam

  • [PRELIMINARY RESULTS:
  • FWHM calculation checked,
  • errors on the GAF still being evaluated]

With the MIMO, overlaying the 120 events in run #37 events to mimic the Gaf

With a GafChromic Film, integrating the spills over a full run

…and PROJECTING

FWHM = 7.11 ± 0.05 mm

FWHM = 7.64 ± 0.05 mm

slide13

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

slide14

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)
slide15

Step 3: move from projections to slices:

X slices

Y slices

FWHMx = f(y) [and the other way round)

i.e.

being F & G the marginal distributions

slide17

Monitoring the intensity fluctuations

MIMO

Vs

UNIDOS*

*The PTW UNIDOS is a high performance secondary standard and reference class dosemeter / electrometer

slide18

HIT [Heidelberg Ion-Beam Therapy Center]:

Quality control of pencil Carbon Ions & proton beams

http://www.klinikum.uni-heidelberg.de/index.php?id=113005&L=en

The accelerator complex

[patients treated since 2008]

The facility building

The beam parameters

Interested in high granularity (in time & space) because they do feature “intensity-controlled raster-scan technique”

slide19

I = 7x107 particles/s, C ions

Time development of the beam

Data taking conditions & qualitative information

  • 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

slide20

Quantitative information (C ions)

Intensity Scan

Energy Scan

slide22

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!)
slide23

Data taking conditions & qualitative information

  • 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

slide24

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

Counting with pixel dependent thresholds:

+ quite robust against detector degradation

- failing as pile-up approaches

Delta2 : + applicable also for high intensities

- emphasizes local differences

slide25

Flat beam

Real-time profiling

Image of a tilted beam

2 frames

10 frames

20 frames

slide26

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…

slide27

Intensity by counting, with a pixel dependent threshold based on a common pre-set spurious hit level

  • DATA SET
  • A 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
slide28

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
slide29

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