PSD upgrade: Ar-present and Xe-future

1. - Status of the PSD upgrade

2. - PSD performance after upgrade

3. - Problems during the Ar-run

4. - Future scenarios for PSD upgrade

F.Guber, M.Golubeva, A.Ivashkin, S.Morozov, O.Petukhov

(INR, Moscow)

1NA61/SHINE upgrade workshop, CERN 21– 23 February, 2015

History of PSD construction at NA61

• PSD is the first calorimeter with new type of photodetectors – SiPMs (MAPDs).

• The concept test in 2007.

•Active phase of construction in 2010-2012.

•Start of data taking in 2011 in truncated mode before the full construction.

•Fully assembled in 2012 a few months before the physical run.

•44 modules with 440 MAPDs

•Little experience with MAPD.

•Very tight time schedule of construction.

•Minimum control functionality. PSD modules in 2011 Be-run 2

Problems with PSD in Be-runs

1.The PSD cooling system is not working properly (air flow from underground).

2.The temperature control system is not working properly

3. HV control system does not readout MAPD voltages (minimum functionality).

4. No monitoring system for the MAPD gains (minimum functionality).

5. The rise time of PSD trigger signal is slow – problem with the time-amplitude walk and signal delay in trigger box.

6. Electronics noises are rather small but comparable with MIPs signal. It makes problem with muon calibration.

Ebeam =30AGeVEnergy in PSD

Temperature

MAPD gain ~4 %/0C

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Strategy of the PSD upgrade in 2013-2014

1.New cooling system.

2.New temperature control system.

3. New HV control (readout of real voltages).

4. Monitoring system for the MAPD gains (LED stabilized source).

5. New fast amplifiers in each section

6. New PSD trigger signal after fast amplifiers.

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PELTIER COOLER

Scheme of MAPDs temperature stabilizationby Peltier element

Heat sink

Copper rod

Copper heat sink

Alplate

External TECcontroller

PSD module electronics

Compressed air

Ts -sink temperature sensorTo -object temperature seensor

To

Ts

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MAPDs gain monitoring system

Light amplitude is controlled by PIN-diode inside with very low temperature dependence.

Control of MAPD gain at <1% level

Based on stabilized LED source.

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LED amplitude spectrum

E/E~2%

Time amplitude stability ~1%

New slow control system.

• Originally developed for COMPASS ECAL

• Can control up to 127 devices (modules).

• Can control the gain monitoring system too.

• Connection with external computer: USB-2.0 or RS-232.

• Internal bus: RS485

• Maximum length of bus cables: 50 mController for SC

New HV distribution system

• Extremely low power consumption.

• HV stability – 0.01%.

• One external power supply ~12 V.

• Permanent check of correct HV values within given HV gate - There is feedback to HV values!

!

Developer - HVSys Co., Dubna.

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New fast trigger signal

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Signal shape after adder. Rise time ~10 ns

No extra delay of trigger signals!

Present scheme: MAPDFastAmp.G=30

Adder

Fully assembled cooling system, FEE, HV and control system for one module

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How does PSD work after upgrade?

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PSD performance after upgrade (calibration with muons and protons)

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Muon spectrum in one section. Pedestal spread is caused by TEC noise.

Proton spectra at different energies.

First problem in Ar-run: shower leakage for Ar-ions.

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Mean = 5260 GeV

Leakage -> 12%

S1=25k

Brass degrader in front of PSD 50x100 mm2 reduces the left tail without the loss of total energy deposition.

Important for the selection of central collisions!

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Second problem : dependence of reconstructed beam energy on beam rate.

The problem is MAPD pixel’s recovery time ~ some 10 s.

Mean = 4796 GeV

S1=110k

Total loss of Ar-energy is (12+1+9)~22%.

MAPD saturation - > 9%

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Third problem: ADC saturation for energy more 10 nucl./module

Energy spectra in 10 sections, where Ar hits the center of module.

One needs to detect nucleons in range 13 GeV-150 GeV – factor 10 x 10 nucleons => Dynamic range =100. Difficult to get more!

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Forth problem: trigger saturation for energy more 25-30 nucl./module (saturation of amplifiers) for Ar-beam at 150 GeV.

Last two problems are solved by directing the beam in the PSD center. The shower is distributed between 4 central modules.

Energy spectra in 10 sections, if Ar-beam hits the center of PSD.

May be the last problem: already 6 dead TEC controllers are replaced. (internal power supply failure in all samples)

The TEC-1091 is a specialized TEC controller / power supply able to precision-drive Peltier elements.

It features a true bipolar current source for cooling / heating, two temperature monitoring inputs (1x high precision, 1x auxiliary) and intelligent PID control with auto tuning.

The TEC-1091 is fully digitally controller.

If Controller TEC -1091 is dead, the temperature readout works, but temperature can be regulated.

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Sum of the problems in Ar-run.

• Shower leakage from heavy fragments in rear side of PSD (~12%)

• MAPD pixel saturation (~9%),

• Dynamic range of ADC (saturation at 1V) ~ 10 nucleons/module,

• Saturation of trigger signal (adder) at 2.5V ~25 nucleons/module,

• Long-term instability of TEC.

The problem of saturation is solved by directing Ar-beam in the PSD center. In this case the shower is distributed over 4 central modules.

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How PSD can run at Xe beam (A=132) and Pb (A=208)

The shower leakage in rear side of calorimeter for heavy fragments can not be avoided.

Saturation of pixels (recovery time) of MAPDs is inherit feature. Shall we replace them by new SiPMs?

The problem of the dynamical ranges of ADCs and trigger signal could be solved somehow.

A few scenarios can be considered:

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First scenario: to leave PSD for Xe-beam as it is for Ar.

What we have in this case:

•Beam hits the PSD center (4 modules),

•For Xe-energy from 13 GeV to 40 GeV the energy deposition would be less than for Ar-beam at 150 GeV.

•For Xe-energy from 70-150 GeV the gain of four central modules is reduced 4 times.

•The trigger signal from other central modules is attenuated 4 times to keep the equivalence of energy in trigger.

•The dynamical range of ADCs in 4 central modules is extended to 40 nucleons/module or 160 nucleons/(4 modules).

•The trigger signal is saturated at 100 nucleons/module or 400 nucleons/(4 modules).

•This approach can be used for Pb-beam too.

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Second scenario: to replace PSD readout electronics by DRS4.

What we have in this case:

•Two ADCs for low/high gain amplifiers in each section.

•Much larger dynamic range for ADCs.

•Muon calibration and detection of heavy fragments would be done in different ADCs.

•Hopefully new readout electronics would be more reliable. • •No TEC pick-up noises because the signal after amplifier is not attenuated and much higher of noise amplitude. •Needs new PSD calibration with muons and protons.

Matching with readout electronics (present and future variants)

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Two amplifiers increase the dynamical range of detected energies. (especially important for heavy ion program). The saturation amplitude of amp. is about 2.5 V. Additional divider can be installed after Low gain Amp. to reduce amplitude to 1 V. Higher dynamic range.

Present variant : MAPDFastAmp.G=30

Signal adapter

Slow amp.-integrator

DAQ

Future variant : MAPDFastAmp.G=30

DRS

FastAmp.G=120

DRS

(for high energy deposition)

(for low energy deposition+ muon calibration)

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How many DRS channels are needed?

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• 440 MAPDs in PSD.

• 440x2=880 DRS readout channels for individual MAPD readout.

• For the pile-up identification adder signal is used in the time window 8 s (6 groups of 8 modules) 6x8=48 DRS channels

• Total: 1028 DRS channels.

How many DRS channels are needed?

• Present MAPDs were developed in 2008 by Zecotek Co.

• These MAPDs were the only SiPMs with high dynamic range (104 pixels/mm2).

• But the recovery time of the pixels is about 10 s. Not suitable for count rate >105 counts/spill.

• In 2013-2014 a few types of SiPMs with high dynamic range are avaialble.

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Third scenario: to replace present MAPDs by new MPPCs from Hamamatsu Co.

• Hamamatsu MPPC’s S12572-010C/P have pixel size 10x10 m2, 104 pixels/mm2 .

• Recovery time ~10 ns. For WLS-fiber decay time (50 ns) the equivalent pixel density is ~5x104 pixels/mm2 .

• Huge dynamic range, no limitation on count rate.

The shape of single electron pulses of MPPC with high pixel density.

Shall we replace MAPDs in central modules?

For future run with heavy beam one can do the following actions:

1.Do nothing, but reduce the gain in 4 central modules. Proton calibration of these 4 modules is desired.

2.Replace current readout electronics by DRS4. New calibration of all modules is required.

3.Replace MAPDs by new MPPC with high dynamic range and fast recovery time.

It seams that this year we can do step No.1 only. (Fortunately!)

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Summary

Thank You

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