RFNC-VNIIEF’s contribution to theconstruction of the PHOS Spectrometer:mechanical design, cooling system andtemperature control
D. Budnikov
S. Filchagin

General information
PHOS spectrometer
Technical data:
lead-tungstate crystals (PbWO4) 17920
modularity
5
area of a crystals sensitive
surface8.67 m2
total crystal weight
12.927 t
operating temperature

-25ºC

2

PHOS spectrometer overall dimensions

0

1

2490

8069

2366

4
2

3

His height is 1.70 m

The total weight is around of 24.5 tons
3

The main mechanical partsof the PHOS spectrometer
PHOS: 5 modules (plan)
3584 crystals per module

Crystal: PbWO4
PbWO4 volume: 0.94 м3
Total crystal weight: 7.75 t
Strip unit 8×2
Working temperature: minus 25°C

4

PHOS module installation

There are 4 modules in the PHOS spectrometer .
One of the modules (#1) has half of the crystals matrix (3584/2 = 1792).
The total crystal quantity is12544 in the PHOS spectrometer5

PHOS module
ModuleThe PHOS spectrometer module consists of 3584
single detection channels forming a matrix of
64×56 crystals, so that 64 crystals are placedalong the axis OX with a step of 22.6 mm, and 56
crystals – along the axis OY with a step of 22.7mm.
Its overall dimensions are 1734×1594×757 mm

X
Y

Z
O

6

Single registration channel
Preamplifier board

APD-preamplifier

The module consists ofthe set of crystals
PbWO4, the 22×22 mm
crystal front facing thedirection of photons
emitted from the LHC
beam interaction point.
The density of crystals
material is =8.28 g/cm3.
The weight of one
crystal is 0.721 kg.
The crystal manufacturer
was the stock-company“Severnyje Kristally”,
Apatity, RUSSIA.

PbWO4 crystals

7Crystal matrix

Front view of crystal matrix as seen fromthe interaction point

The detection channels with installed
APD-photodiodes and preamplifier boards

The thickness of glue seal between the crystal end and the surface of photodiode is 0.05…
0.25 mm. The presence of the air inclusions inside the seal is not allowed.
The optically transparent glue “Melt-Mount Quick-Stick”, Cargille Laboratories, USA is used.

8

Process of assembling the Strip unit

The weight of the each Strip unit is approx. 12 kg

Crystals are packed mechanically into
groups of 2x8, referred to as Strip units

9Calculation of the main module frame
0,4 mm

Displacements

σmax =137 kg/cm2

Stresses

Results of the mechanics-and-strength calculation of the glass-cloth-baselaminate body and cooling panels with T-section at their horizontal position
under crystals’ loading during 0.5g starting acceleration

10

PHOS mechanical design: summary

1. The mechanical design of the detector is very stable
over more then 10 years of operation.
2. The mechanical design of the module provides allconditions to reach a temperature of minus 25C for the
crystal matrix.
3. In future we plan to divide the module into two parts,
named “cold” part with crystals and “warm” one withelectronics to have a possibility to service the electronics
at any time (when there is no a beam)11Temperature & cooling: requirements
Physical factors:
1. PWO light yield strongly depends on temperature
2. APD gain strongly depends on temperature
3. We have to avoid water in FEE zone (warm volume)
4. We have to remove heat from electronics( ≈ 2% per 1ºC )( ≈ 5% per 1ºC )( dew point ≈ 12ºC )Therefore to achieve 1% energy resolution:
1.
2.
3.
4.

High precision temperature measurements in PWO matrix requiredHigh cooling stability required
Warm volume Temp. control & cooling
FEE water cooling required

PHOS requirements:
T operation -25 ºC,
T stability± 0.1 ºC,
T precision ± 0.05 ºC
12

Cooling system - scheme
Magnet L3
Ni-100 sensors, ELMB
Humidity sensors

PHOS
PWO-matrix(cold volume)
FEE(warm volume)

Magnet L3

Cooling system
Controller
RS-485

Ethernet, DIM> 50 mDetector
Control
System,PVSS

CAN

Control
Unit
Power
Unit

Cooling Unit
Freon R404A
Heat exchanger

T-sensors,
P-sensors
Main Line> 20 mPumping Unit
C6F14

Back Line13

Temperature & humidity measurement
Ni-100 temperature sensors (made in RFNCVNIIEF) are mounted between the crystals
and have a thickness less than 100 m to notenlarge gaps between them.
There are 128 temperature sensors and 20
humidity sensors:
Technical parameters

Precision of measurement
Thickness
Working temperature range± 0.05°C;
0.1 mm;–30…+30°C

Temperature monitoring in PWO matrix for each
module - 24 sensors;monitoring in warm volume (FEE
Temperaturezone) for each module - 8 sensors;
Humidity monitoring in warm volume (FEE zone)
for each module - 5 sensors14Cooling system software — AliPhosCool
in Run 1, Run 2

There was not any failure of cooling system due to softwarefor 8 years of operation
15

Results: PHOS-RUN2 PbWO4 matrix
temperature

More than 900
working days

2015

2016

2017

Results: PHOS-2017 temperature PbWO4

242 days of cooling in 201730.03.2017

27.11.201717

PHOS-2017: temperature distribution in PWO2

PWO2
T= -23.97 ± 0.05°C

18

PHOS-2017: temperature distribution in PWO1

28.06.2017

PWO1: there are two
peaks
T1= -25.35 ± 0.1°C
T2=-26.61 ± 0.02°C
19PHOS-2017: temperature distribution in PWO1
(peak 1)Гора ЮраPWO1
Женевское
озеро ± 0.1°C
T= -25.35
LHC

SPS
PS
CERN

Alexei.Kuryakin@cern.ch

20

PHOS-2017: temperature distribution in PWO1
(peak2)Гора Юра

PWO1(2)
Женевское
озеро
T= -26.61± 0.02°C
LHC

SPS
PS
CERN

Alexei.Kuryakin@cern.ch

21

PHOS RUN2: Conclusions
1.The uninterrupted operation of thecooling system is provided in RUN 2.
2. The temperatures of
PWO2=-23.97±0.05°C - satisfy
PWO3=-23.02±0.10°C
PHOS
PWO4=-23.60±0.04°C
requirements
2.PWO1 temperature has got two peaks
T1=-25.35±0.1°C, T2=-26.61±0.02°C
This was hapened due to the part of FEE disabling ≈28.06.2017

3.The cooling power is ≈45% of max.

22

PHOS spectrometerThanks!

23

PHOS spectrometer location from IP
IP
R4600
Crystals’ surface
5299
20°

20°
20°

20°

There are 5 modules in
the PHOS spectrometer
cradle. The weight ofeach is approx. 4.0 t.

The distance is 4600 mm from the IP up to the crystals’ surface
24Calculation of the cell cristal structure
0,0065 mm

Displacements

σmax =82 kg/cm2

Stresses

The maximum working loading onto the cellular structure is a weight ofcrystals at the horizontal position in the cells while calibration.

25

Calculation of the main module frame in
the vertical position
0,2 mm

Displacements

σmax =246 kg/cm2

Stresses

Results of the mechanics-and-strength calculation of the glass-cloth-baselaminate body and cooling panels with T-section at their vertical position undercrystals’ loading26

PHOS-2017: temperature distribution in PWO3

PWO3
T= -23.02 ± 0.1°C

27

PHOS-2017: temperature distribution in PWO4

PWO4
T= -23.6 ± 0.04°C

28