Massimo Caccia, P.I. Universita’ dell’Insubria [UINS] Como (Italy) & INFN- Sezione di Milano

1. 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

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

3. 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

4. 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

5. Introductory slides on different imaging modalities

6. The analysis matrix methods • is any of the matrix elements more robust and reliable? • any irreducible problem preventing to use any of them?

7. 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

8. 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

9. 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]

10. 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

11. 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)

12. 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

13. 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

14. 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)

15. 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

16. Step 4: estimate the “width” as the mean FWHM over the central 9 slices Vs.

17. Monitoring the intensity fluctuations MIMO Vs UNIDOS* *The PTW UNIDOS is a high performance secondary standard and reference class dosemeter / electrometer

18. 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”

19. 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

20. Quantitative information (C ions) Intensity Scan Energy Scan

21. Playing back the data Carbon5.wmv

22. 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!)

23. 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

24. 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

25. Flat beam Real-time profiling Image of a tilted beam 2 frames 10 frames 20 frames

26. 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…

27. 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

28. 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

29. 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