LHCb 2000-064 RICH
27 June 2000
A SUPPORT NOTE FOR THE USE OF
PIXEL HYBRID PHOTON DETECTORS
IN THE RICH COUNTERS OF LHCB

T. Gys
On behalf of the LHCb-RICH group
CERN, Geneva, Switzerland
Abstract
This document is a support note for the use of a hybrid photon detector with integrated silicon
pixel readout in the ring imaging Cherenkov detectors of the LHCb experiment. The photon
detector is based on a cross-focussed image intensifier tube geometry where the image is demagnified by a factor of 5. The anode consists of a silicon pixel array, bump-bonded to a
binary readout chip with matching pixel electronics. The document starts with the general
specification of the baseline option, followed by a summary of the main results achieved so
far during the R&D phase. A future R&D programme and its related time table is also
presented. The document concludes with the description of a photon detector production
scheme and time schedule.
–––––––––––––––––––––––––

Corresponding author. Address: EP Division, CERN, CH-1211 Geneva 23, Switzerland.
Phone: ++41 22 767 83 07. Fax: ++41 22 767 32 00. Email: Thierry.Gys@cern.ch
1
1.1
GENERAL SPECIFICATION
Introduction
The baseline photon detector of the LHCb RICH system [1] is the hybrid photon
detector (HPD) which uses a silicon detector anode inside a vacuum envelope. A photocathode is deposited on an optical input window in the envelope, and the photoelectron
released by an incident photon is accelerated onto the silicon detector by an applied high
voltage of ~20 kV (corresponding to ~5000 e- released in the silicon). Commercially
available examples of HPDs exist, but do not meet fully the specific LHCb requirements, in
particular the large area coverage (~2.9 m2) with high active-to-total area ratio (~70 %), small
granularity (2.52.5 mm2 at the photo-cathode level) and high speed (25 ns timing
resolution).
The present HPD development [2] is being carried out in close collaboration with the
company Delft Electronic Products (DEP) [3]. It is based on a cross-focussing tube design,
de-magnifying by a factor of ~5 the photo-cathode image onto a small detector array with
O(500 m) pixels, bump-bonded to a binary readout chip with matching pixel electronics
integrated inside the vacuum envelope of the tube. The feasibility of this approach was
demonstrated in 1994 by the successful realization of the “Imaging Silicon Pixel Array
(ISPA) tube” [4]. The first ISPA-tubes, based on magnetically focussed electron optics, had a
one-to-one mapping geometry resulting in a total active surface of 4.88.0 mm2. They were
initially developed to read out small diameter scintillating fibres for particle tracking [5] and
have also been shown to be an excellent detection tool for biomedical applications [6].
The performance of cross-focussed, or first generation, image intensifiers is well
known [7]. In particular, these devices can reach a limiting spatial resolution of up to 100 line
pairs per mm (lp/mm) (or equivalently, the full width at half maximum of the point spread
function (PSF) is 10 m). Their image distortion, caused by variations of the linear demagnification along the radial distance, does not generally exceed 10 % at the edge, and can
be corrected off-line. This tube geometry is robust to external electric field perturbations and
allows for the shielding of low magnetic fields [8]. Additionally, small pixels with bumpbond connections present little load capacitance to the front-end electronics (giving low noise
and high speed) and a compact anode structure with a limited number of feed-throughs.
Binary electronics have low power consumption (~50 W per channel) and are consequently
well adapted to implementation in a vacuum tube. In addition, they have been shown to be
compatible with the demanding bake-out cycles (typically 350 ºC for 5 hours) needed for
high-quality photo-cathodes.
1.2
Pixel-HPD description
The baseline pixel-HPD for the LHCb RICH counters is shown in Figure 1. It is based
on an electrostatically-focussed tube design, with a tetrode structure, de-magnifying by a
factor of ~5 the photo-cathode image onto a small silicon detector array with 1024 pixels
each 500 m × 500 m in size and arranged as a matrix of 32 rows and 32 columns. The
nominal operating voltage is 20 kV corresponding to ~5000 electron-hole pairs released in
the silicon. The voltage difference between photo-cathode and first electrode is adjustable and
1
defines the precise value of the de-magnification factor. The silicon pixel detector array is
bump-bonded to a binary readout chip (described in section 1.4). This assembly is mounted
and wire-bonded onto a Pin Grid Array (PGA) ceramic carrier.
Cherenkov photons can be detected over an active diameter of 75 mm. Since the overall
tube diameter is 83 mm, the tube active area fraction is (75/83)2=0.817. The photo-cathode is
of the “thin-S20” multi-alkali type. Quantum efficiency (QE) values measured from a
prototype tube are listed in table 1 (see also section 2.2). They include light reflection losses
(~4 %) at the entrance face of the 7 mm-thick quartz window and its transmission (~35 % at
200 nm), and correspond to a QE(E)dE integral value of 0.77 eV.
The tube window is made of quartz. It has a spherical shape, with 7 mm thickness and
55 mm inner radius of curvature. Light refraction at the window results in a radial coordinate
correction factor of ~1.047. The baseline de-magnification law of the electron optics is:
rp = 0.200rc - (0.4 10-3 mm-1)rc2
rc and rp are the radial coordinates on the photo-cathode and the pixel array,
respectively, and are expressed in mm. This de-magnification is achieved by polarizing the
photo-cathode at -20kV, the first electrode at -19.7kV and the second electrode at -15.8kV
(see bottom part of Figure 1). Consequently, the photo-cathode image (a portion of a sphere
of 36 mm active radius) is de-magnified as a disk ~6.7 mm in radius on the pixel array. This
value is smaller than the half size of the pixel array (8 mm) and allows some overhead in
coverage, given the estimated image distortions due to stray magnetic fields (see section 2.2
for details). Taking into account the window lens effect, the pixel size at the window input is:
0.5 mm(1.047/0.200)=2.62 mm on the tube axis and
0.5 mm(1.047/(0.200-(0.4 10-3 mm-136 mm)))=2.82 mm at the edge.
The values for the PSF standard deviations (at the window input) are approximately
constant over the tube radius and equal to 400 m. All the above figures are valid in absence
of magnetic field.
1.3
Integration
The hexagonal close-packing factor is 0.907, so theoretically, the active area fraction is
(75/83)20.907=0.741. With a 0.9 mm-thick mu-metal shield, and considering the mechanical
tolerance, a gap of at least 4 mm between tubes is needed, resulting in a packing factor of
(75/86)20.907=0.674. Improvement of this factor by the use of a thinner shield with higher
saturation induction and a thicker window, ie an increased lens effect, is envisaged. With a
tube pitch of 87 mm, a total of 430 tubes are needed to cover the RICH photon detection
surface (see Table 2). In this number estimate, a pointing geometry is assumed for the
RICH 1 counter, ie the tube axes are parallel to the average angle of incidence of the
Cherenkov photons. For the RICH 2 counter, the tubes lie in a plane corresponding to the
2
photon detection surface, the tube axes being normal to this plane. Detailed mechanical
studies for the mounting of the tubes are being carried out, and take into account the specific
environmental and space constraints of the two RICH counters (see the two RICH mechanics
support notes for details [9,10]).
1.4
Binary front-end electronics
A front-end binary pixel chip optimized for photo-electron detection in the LHCb RICH
must meet the following requirements. Firstly, the chip must correctly discriminate hits and
time-tag them with a specific bunch crossing. This requires that the front-end amplifier has a
shaping time of  25 ns, and that the discriminator applies a threshold of < 2000 e– with a
pixel-to-pixel RMS spread of < 200 e– to uniformly identify the low signals ( 5000 e–) due
to single photoelectrons. Secondly, the nature of the LHCb experiment places strong demands
on the digital circuitry that stores the discriminated hits [11]. High occupancy (maximum 510 %), high level-0 trigger rate (mean 1 MHz) and a long level-0 latency (4.0 s) require that
the chip be capable of storing a large number of hits for a long period and be able to transfer
data at a high rate to minimise dead-time.
The pixel-HPD chip is segmented into “super-pixels” of 500 m × 500 m, arranged as
a matrix of 32 rows and 32 columns. Each super-pixel is in turn sub-divided into 10 smaller
pixel cells, each of size 50 m × 500 m. The silicon sensor also consists of elements of
50 m × 500 m. Each sensor pixel is connected via a solder bump-bond to a read-out chain
(Figure 2) including differential preamplifier (250 e– RMS noise) and shaper (25 ns shaping
time) followed by a discriminator (2000 e– average threshold, 30 e– RMS spread with 3-bit
adjust). With this electronics performance, the effect of charge sharing between sub-pixels is
minimized, and the photoelectron detection efficiency is dominated by the photoelectron
backscattering (18 %) at the silicon detector surface. This efficiency is expected to reach
90 %.
The discriminators of the 10 pixels in a super-pixel will be OR-ed together, thus
combining the hit information from the 10 front-ends. The dimensions of a super-pixel
correspond to the required LHCb granularity, whilst its segmentation reduces the hit
occupancy seen by the front-ends and decreases the risk of any corresponding pulse pile-up.
The result of the OR will enable one of the 20 delay units within these 10 pixels. Each delay
unit can delay a single hit for a period of time which can be set to match the trigger latency.
Thus a maximum of 20 hits can be stored at any one time in a channel. Following the trigger
coincidence, data is stored in a de-randomizing buffer implemented as a FIFO memory with
the capacity for 16 events. This reduces losses caused by statistical fluctuations in the trigger
rate. The number of columns (32) is common to the global LHCb architecture [12]. It allows
the data from a chip to be read out in ~900 ns ((32 equivalent rows  25 ns) + data headers)
through 32 parallel lines at a rate of 40 MHz. Simulations show that a 16-deep FIFO read out
every 900 ns will reduce the dead time below 1 %. Further details on the L0 chip
specifications are given in the L0 electronics support note [13].
3
The pixel-HPD tubes will be grouped as pairs, in order to form a “unit”. One unit has
thus 21024=2048 channels (25641130 active1). The total number of units is 215. Due to
the multiplexing factor of 32 in the chip readout, the number of readout channels per unit is
232=64 and the total number 64215=13760. Two options to transfer the L0 data off the
detector are currently under evaluation: twisted-pair copper links using Low Voltage
Differential Signalling, or optical fibres using a parallel or serial approach (see off-detector
electronics support document [14] for details).
2
2.1
SUMMARY OF MAIN RESULTS FROM R&D
Half scale pixel-HPD prototype
A half-scale pixel-HPD prototype tube has been manufactured by DEP at the end of
1997. Its input window is made of quartz and is 40 mm in active diameter. The photo-cathode
(multi-alkali S20 type) is deposited on a spherical surface. The photoelectron image is
focussed onto the flat surface of a silicon detector chip mounted in the die cavity of a
standard ceramic carrier. The silicon detector is a pixelated structure bump-bonded to the
LHC1 chip developed by the RD19 Collaboration [15]. This comprises an array of 12816
pixels of 50500 m2 giving a total silicon active surface of 6.48.0 mm2. Taking into
account the de-magnification ratio of ~4, the input granularity is ~0.22.0 mm2. The nominal
operating voltage of the tube is 20 kV. The LHC1 chip is being used for charged particle
tracking detectors in heavy ion experiments. Each detector pixel is individually connected to
a readout chain containing amplifier (100 ns peaking time, ~160 e- RMS noise), discriminator
with globally adjustable threshold (minimum ~3000 e- with a pixel-to-pixel RMS spread of
~500 e-), globally adjustable delay line with local fine-tuning, coincidence logic and memory.
Every cell can be individually addressed for electrical tests and masking. The analogue power
consumption is below 50 W per channel. Figure 3 is a photograph of the tube attached to its
electronics support board. The cable protruding from the tube is for the high voltage.
The absolute efficiency at detecting single photoelectrons has been measured in detail
in the laboratory [16], using a low-intensity light-emitting diode (LED) operated in pulsed
mode. This efficiency is governed by the comparator threshold distribution within the pixel
electronics readout chip (Figure 4). The measurement made at 90 V silicon detector bias and
20 kV tube voltage indicates that 71 % of the pixels in the matrix are firing. 12 % of the
pixels have too low a threshold and, since they fire on their own electronics noise, they were
electrically masked prior to the measurements. The remaining 17 % have too high a threshold
and are insensitive to single photoelectrons. The number of sensitive pixels is confirmed by
measurements with an electrical test pulse input across calibration capacitors connected to the
pixel pre-amps. For those pixels which are sensitive at 20 kV, the single photoelectron
detection efficiency is 81 %. The residual inefficiency is attributed to the combined effects of
the comparator threshold distribution, charge sharing at the pixel boundaries and
photoelectron backscattering at the silicon detector surface. A photoelectron detection model,
1
The photo-cathode image in each tube is de-magnified as a disk ~6.7 mm in radius on the pixel array. The
number of active pixels per tube is thus (6.7mm)2/0.25mm2=564. Due to magnetic field effects, this number
as well as the pixels involved are expected to vary from tube to tube.
4
including these effects, is in good agreement with the data. The electron optics behave as
expected and confirm the principle of de-magnifying a photoelectron image onto a small
silicon area. The measured de-magnification is 0.225 on-axis and 0.250 at the periphery. The
PSF standard deviation is ~40 m.
This half-scale pixel-HPD prototype has successfully detected Cherenkov air rings
produced by high-energy pions in prototypes of the LHCb RICH system (Figure 5). Light
yield and Cherenkov angle resolution (Figure 6) are in good agreement with expectations.
These beam test results, reported in [17,18], confirm the laboratory measurements. The
detected number of photons is less than that detected by a commercial HPD tube. This can be
largely explained by the non-optimal quantum efficiency of this first prototype (~15% at
200 nm and ~12 % at 400 nm, including the window transmission), and the high comparator
thresholds of the LHC1 electronic readout chip. This quantum efficiency has since been
improved by ~50 % after the manufacturing of a similar prototype used for biomedical
applications [19].
2.2
Full-scale pixel-HPD prototype
The 40:11 mm prototype has been manufactured with existing parts and its active area
(<50 %) is rather poor. Full-scale prototype tubes have been developed. They exhibit good
quantum efficiency and a higher active-to-total area ratio. Detailed design studies of the
electron optics indicated that a ratio of ~80 % could be achieved using electron optics based
on a tetrode structure. The electrodes are also shaped in such a way that the tube performance
is unaffected by the proximity of other tubes or magnetic shielding. The baseline dimensions
of the tube are 72 mm active input diameter and 18 mm output diameter and it is nominally
operated at 20 kV. The optical input window is spherical and made of quartz, and the photocathode is a multi-alkali S20 type.
A first prototype has been produced in September 1998. It is equipped with a phosphor
screen anode coupled to a CCD camera [20] (Figure 7). From electron optics measurements,
the tube active area is 81.7 %. The de-magnification is 0.207 on-axis and 0.237 at the edge.
The corresponding standard deviations of the PSF at the anode plane are ~33 m and ~54 m
respectively. Three HPD versions of the 72:18 mm tube have also been manufactured (the
first one in October 1998) [21] (Figure 8). The quantum efficiencies (which include light
reflection losses at the entrance face of the quartz window and its transmission) of these
prototypes range from 22 to 26 % at 270 nm and from 16 to 20 % at 400 nm (Figure 9). The
corresponding QE(E)dE integral values range from 0.69 to 0.77 eV. Each anode is currently
equipped with a 61-pixel silicon detector read out externally with the analogue VA2 chip
(1.2 s peaking time) [22]. The pixels are hexagonal with dimension of 2 mm flat-to-flat.
These tubes were first evaluated in the laboratory using a procedure similar to the one used
for the half-scale prototype. A typical photoelectron response is shown in Figure 10. The
average signal-to-noise ratio is ~11 at nominal tube operation (20 kV tube high voltage, 60 V
silicon detector bias voltage).
5
A cluster of three such tubes has been installed in the LHCb RICH 1 prototype
(Figures 11, 12) for beam tests purposes [23]. Cherenkov rings produced by charged particles
traversing a C4F10 gas radiator have been successfully detected (Figure 13). Measured light
yields agree to within 10 % with the values expected from the quantum efficiency curves. The
observed photoelectron number Npe corresponds to a figure of merit per tube
N0Npe/(L × sin2c) between ~225 and ~250 cm–1, after corrections to take into account light
reflection losses on the mirror and the 25 mm-thick quartz plate, and geometrical coverage.
The Cherenkov angle resolution per C4F10 gas ring is around 0.3 mrad, and is dominated by
the size of the pixels used for these tests (~10 mm at the tube window level). Effects of
charged particles traversing the window at various angles of incidence have also been
measured. A detailed analysis of the data is reported in another support note [23].
Magnetic field tests have been carried out in the laboratory, using the full-scale tube
equipped with a phosphor screen, and both a small solenoid and a Helmholtz coil providing
magnetic fields of up to 30 Gauss. The performance of the electron optics has been studied in
detail and the complete results will be reported in a technical note [24]. They can be
summarized as follows. A 200 mm long, 0.9 mm thick, cylindrical mu-metal shield has been
used. In order to minimize light shadowing effects, the shield was protruding by only 20 mm
with respect to the window centre. The shield attenuation as well as the image distortions of
the shielded tube have been measured in longitudinal and transverse fields of 10, 20 and
30 Gauss. In case of a transverse field, a non-uniform image shift occurs. It is maximal on the
tube axis and is equal to 0.3 mm at 30 Gauss. In case of a longitudinal field, image rotation
and distortion occurs. The periphery of the image remains confined within a circle of 7 mm in
diameter at 30 Gauss. In all cases, the PSF is barely affected. Image distortions can be
corrected for off-line.
A PGA ceramic carrier with large die cavity, high number of wire-bonding connections,
and compatible with the full-scale pixel-HPD tube and manufacturing process has been
manufactured by the company Kyocera in Japan. It will be used to encapsulate in a full-scale
tube the ALICE-LHCb chip (see next section) in replacement of the present 61-pixel detector
with external readout (Figures 14,15).
2.3
LHCb pixel electronics developments
The LHC1 electronics and the silicon detector chip used in the half-scale prototype
were not optimal for photoelectron detection. The feasibility of pixel electronics suited for
HPD applications in LHCb has been demonstrated in recent pixel developments. A threshold
of 1400 e– with an RMS of 80 e–, using a 3-bit adjustment per pixel, has been achieved on a
chip designed for X-ray photon imaging [25]. An additional test chip, fabricated in a
commercial 0.5 m CMOS process, has a peaking time of 25 ns and exhibits a timewalk of
< 25 ns for signals 100 e– above threshold. Its time resolution therefore meets the LHCb
requirement. The analogue power consumption is below 50 W per channel. In addition, the
chip has been demonstrated to be radiation tolerant up to 600 kRad, which is beyond the
integrated dose of 30 kRad predicted for the RICH detectors [1]. This radiation tolerance is
due to the intrinsic features of the technology and the use of special layout techniques
6
described in [26]. Finally, a test chip fabricated in a 0.25 m commercial CMOS process [27]
exhibits a minimum threshold of 1500 e– with an RMS spread of 160 e– without adjustments
to individual pixels. A 3-bit adjustment per pixel reduces this spread to 25 e–. Operation of a
chip with such a low and uniform threshold will improve the efficiency of detecting single
photoelectrons by minimizing the effects described in section 2.1. This chip has also been
irradiated and is still fully operational after a 30 MRad dose of X-rays. As well as radiation
tolerance, this technology offers a high component density which is essential for pixel design.
A set of such 0.25 m CMOS chips has been sent to DEP for bake-out tests and subsequent
electronic tests show that the chip performance is not affected.
A full pixel chip has been designed as a collaborative effort between the ALICE pixel
tracker project [28] and the LHCb RICH. The basic pixel size is 50 m × 425 m and there
will be 8192 such channels arranged in 256 rows and 32 columns. A schematic of the
circuitry within each pixel cell is shown in Figure 16. The front-end has been designed
specifically to handle the high occupancy in some areas of the RICH detectors. The chip
architecture has been designed in such a way as to allow the chip to be operated in one of two
modes. The first mode is for ALICE and each pixel front-end will enable one of two delay
units per channel. The results of the trigger coincidence will then be stored in a 4-event FIFO
buffer within each pixel. In the second mode, envisaged for LHCb, the discriminators of 8
pixels will be OR-ed together. This effectively creates a 3232 matrix of super-pixels each of
400 m × 425 m, which is close to the LHCb requirement, and has the advantages described
in section 1.4. A maximum of 16 hits can be stored at any one time in a super-pixel. Finally, a
16-event buffer is created by configuring together four of the 4-event buffers. The 32
columns are read out in ~800 ns through 32 parallel lines at a rate of 40 MHz. This chip has
been submitted end of April 2000, and its testing is expected to begin in July 2000. Pixel
sensors will be available at the same time, in order to start the bump-bonding process.
3
SUMMARY OF FUTURE R&D PROGRAMME AND TIME TABLE
3.1 Full-scale pixel-HPD prototypes with ALICE-LHCb electronics
The full-scale prototype tubes tested so far meet the LHCb requirements, with the
exception of the silicon detector and electronics chip. Consequently, no further development
is needed for what concerns the tube design. The manufacturing of full-scale prototype tubes
including the new ceramic carrier mentioned in section 2.2, and the new chip and sensor
assembly mentioned in section 2.3, will start in autumn 2000. These tubes will be tested in
the laboratory and in the beam.
3.2 Final LHCb pixel electronics
As described in section 2.3, the chip currently under design comes close to meeting the
LHCb requirements. To match the full specification described in section 1.4 will require a
further iteration. The only design changes will be the increase from 8 to 10 in the grouping of
pixels in a super-pixel and the corresponding addition of more rows of pixels. This final
design would begin in summer 2000, following the characterization of the current chip and be
completed by Christmas 2000.
7
3.3 Full-scale pixel-HPD prototypes with final LHCb electronics
The design of the final ceramic carrier will be carried out in the second half of 2000, in
parallel with the final chip design. Delivery of the final ceramic carrier and electronics is
expected by spring 2001. The manufacturing of full-scale prototypes will start in spring 2001.
4
SUMMARY OF PRODUCTION TIME TABLE
The tube manufacturer DEP has proposed in its offer a tube production rate of 20 per
month. Counting backwards from the time of the RICH commissioning (mid 2004), this
means that the production has to start at the beginning of 2002. Since the first batches of final
anodes will have to be ready by the same time, mounting and wire-bonding of sensor-chip
assemblies onto ceramic carriers will have to start in summer 2001. The time schedule for
future R&D and production is reproduced in Table 3.
Possibilities to increase the tube production rate have been discussed with DEP. This
rate can be increased from 20 to 30 tubes per month. In this case, an extra investment is
required.
8
References
[1] The LHCb Collaboration, LHCb Technical Proposal, CERN/LHCC 98-4, LHCC/P4,
20 February 1998.
[2] M. Campbell et al., “Development of pixel hybrid photon detectors for the RICH
counters of LHCb”, LHCb/98-035, 30 January 1998.
[3] Delft Electronic Products (DEP) B.V., P.O. Box 60, Dwazziewegen 2, NL-9300 AB
Roden, The Netherlands.
[4] T. Gys et al., Nucl. Instr. and Meth. A 355 (1995) 386.
[5] C. D’Ambrosio et al., IEEE Trans. Nucl. Sc. vol. 43 no. 3 (1996) 2127, and references
therein.
[6] D. Puertolas et al., IEEE Trans. Nucl. Sc. vol. 44 no. 5 (1997) 1747, and references
therein.
[7] I.P. Csorba, “Image Tubes”, Howard W. Sams & Co., 1985.
[8] T. Gys and D. Piedigrossi, “Performance of electrostatically-focussed image
intensifier tubes in low magnetic fields”, LHC-B/97-026, 14 November 1997.
[9] G. Barber et al., “The mechanical design of LHCb RICH 1”, LHCb 2000-077 RICH .
[10] O. Ullaland et al., “LHCb RICH 2 mechanics” LHCb 2000-079 RICH..
[11] J. Christiansen, “Requirements to the L0 front-end electronics”, LHCb Technical Note
LHCb FE 99-29, 30 July 1999.
[12] J. Christiansen, “An overview of the LHCb experiment and its electronics”,
Proceedings of the Third Workshop on Electronics for LHC Experiments,
CERN/LHCC/97-60, 21 October 1997.
[13] K. Wyllie, “Level-0 Electronics for the LHCb RICH”, LHCb 2000-075 RICH.
[14] J. Bibby and S. Wotton, “ODE Electronics for the LHCb RICH”, LHCb 2000-074
RICH .
[15] E. Heijne et al., Nucl. Instr. and Meth. A 383 (1996) 55.
[16] M. Alemi et al., “First operation of a hybrid photon detector prototype with
electrostatic cross-focussing and integrated silicon pixel readout”, preprint CERNEP/99-110, 12 July 1999, in press with Nucl. Instr. and Meth. A.
[17] M. Alemi et al., Nucl. Phys. B. (Proc. Suppl.) 78 (1999) 360.
[18] E. Albrecht et al., Nucl. Instr. and Meth. A 433 (1999) 159.
[19] C. D’Ambrosio et al, Nucl. Phys. B. (Proc. Suppl.) 78 (1999) 598.
[20] M. Alemi et al, IEEE Trans. Nucl. Sc. vol. 46 no. 6 (1999) 1901.
[21] E. Albrecht et al, Nucl. Instr. and Meth. A 442 (2000) 164.
[22] E. Albrecht et al., Nucl. Instr. and Meth. A 411 (1998) 249.
[23] S. Easo et al., “Analysis of pixel-HPD beam tests” , LHCb 2000-070 RICH.
[24] T. Gys and D. Piedigrossi, “Performance of full-scale pixel-HPD tubes in low
magnetic fields”, LHCb 2000-069 RICH, in preparation.
[25] M. Campbell et al, IEEE Trans. Nucl. Sc. vol. 45 no. 3 (1998) 751.
[26] W. Snoeys et al., Nucl. Instr. and Meth. A 439 (2000) 349
[27] M. Campbell et al., IEEE Trans. Nucl. Sc. vol. 46 no. 3 (1999) 156.
[28] The ALICE Collaboration, Inner Tracking System Technical Design Report,
CERN/LHCC 99-12, ALICE TDR 4, 18 June 1999.
9
 [nm]
200
240
270
400
600
QE [%]
10.2
22.0
25.7
19.3
4.3
Table 1
Measured quantum efficiency values QE at given light wavelengths  for a thin-S20
multi-alkali photo-cathode deposited on a 7 mm-thick quartz window.
10
RICH 1
RICH 2
Total
Surface [mm2]
21000600
21200640
Number of tubes
476
2((515)+(414))
Total
168
262
430
Table 2
Number of pixel-HPD tubes needed to cover the RICH photon detection surface,
assuming a hexagonal packing of the tubes and a tube pitch of 86 mm.
11
ID Task Name
1 Full-scale
2000 2000
2001 2001
2002 2002
2003 2003
2004 2004
Qtr 41 Qtr 1
2 Qtr 23 Qtr 34 Qtr 4
1 Qtr 1
2 Qtr 23 Qtr 34 Qtr 4
1 Qtr 1
2 Qtr 23 Qtr 34 Qtr 4
1 Qtr 1
2 Qtr 23 Qtr 34 Qtr 4
1 Qtr 12 Qtr 2
3
tubes with ALICE-LHCb chip
2
Chip submission
3
Chip manufacturing
4
Chip testing
5
Tube assembly and testing
6
Prototyping completed
3/11/11
29/12 29/12
7
8
Final front-end electronics
9
Design
10
Submission
11
Manufacturing
12
Testing
1/1
1/1
1/1
1/1
13
14
Final tube prototypes
15
Carrier design
16
Carrier submission
17
Carrier manufacturing
18
Tube assembly and testing
19
Prototyping completed
31/12 31/12
20
21
Photodetectors
22
Prepare specs/invite tender
23
Place anode assembly orders
24
Anode production and testing
25
Place tube order
26
Tube production and testing
27
Assemble and test units
2/4
2/4
30/9
30/9
Table 3
Time schedule for future R&D and tube production.
12
Figure captions
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10
Fig. 11
Fig. 12
Fig. 13
Fig. 14
Fig. 15
Schematic design (top) of a pixel- HPD prototype tube. The electron optics are
based on a tetrode structure with cross-focussing. On the anode is mounted a
silicon detector chip comprising 1024 pixels, bump-bonded to their associated
binary front-end electronics chip. Engineering drawing (bottom) of the actual
tube. The mu-metal magnetic shield protrudes by 20 mm. The ceramic carrier is a
19×19 PGA type plugged into a Zero Insertion Force (ZIF) socket.
Pixel architecture in the binary front-end electronics chip.
Photograph of the 40:11 mm pixel-HPD prototype tube connected to a printed
circuit board via a standard, zero insertion force, pin grid array socket.
Differential number of firing pixels as a function of tube high voltage, reflecting
the comparator threshold distribution within the LHC1 electronics chip. The
silicon detector bias is 90 V.
Accumulated data set of Cherenkov air rings produced by 120 GeV/c – in a
quarter-scale prototype of the LHCb RICH 1 system. The Cherenkov photons are
detected by a half-scale pixel-HPD prototype.
Reconstructed Cherenkov angle distribution corresponding to the rings of
figure 5. The average Cherenkov angle is ~24.0 mrad, and the RMS resolution is
~1.7 mrad.
Photograph of the 72:18 mm prototype tube equipped with a phosphor anode and
read out with a CCD camera.
Photograph of the 72:18 mm HPD prototype tube equipped with a 61-pixel anode
and read out externally with the VA2 analogue chip.
Quantum efficiency curves (top) and quartz window transmission (bottom) of the
72:18 mm prototype tubes.
Typical photoelectron spectrum recorded from a 72:18 mm HPD prototype tube
operated at 20 kV and read out with external analogue electronics (1.2 s peaking
time). A fit to the data is indicated by the solid line and yields a photoelectron
average of 1.42.
Full-scale prototype of the LHCb-RICH 1 detector used for the pixel-HPD cluster
tests.
Photograph of the 72:18 mm HPD cluster. The tube axes were distant by 85 mm.
Accumulated data set of Cherenkov rings produced by 120 GeV/c negative pions
traversing a C4F10 gas radiator. The circle is the result of a fit to the data.
Present (top) and final (bottom) anode configuration of the full-scale pixel-HPD
tube. The present configuration uses a 61-pixel detector with external analogue
readout. The final configuration will have a 1024-pixel detector bump-bonded to
its binary readout chip. The circles indicate the size of the photo-cathode image
de-magnified on the pixel array.
Photograph (top) of the PGA ceramic carrier used to encapsulated the ALICELHCb chip in a pixel-HPD tube and drawing (bottom) representing the chip wirebonded to the carrier.
13
Fig. 16
Super-pixel circuitry in the LHCb mode of the ALICE-LHCb binary front-end
electronics chip.
14
Figure 1
15
Figure 2
16
Figure 3
17
Figure 4
18
Figure 5
19
Figure 6
20
Figure 7
21
Figure 8
22
Figure 9
23
Figure 10
24
Figure 11
25
Figure 12
26
Figure 13
27
Figure 14
28
Figure 15
29
Figure 16
30