03.06.2015IHEP,Protvino,Russia 1 Current status of a gas luminosity monitor Sergei Erin † † For the LCAL group V.Bezzubov,S.Erin, A.Ferapontov, Yu.Gilitsky,V.Korablev,

21.04.23 IHEP,Protvino,Russia1

Current status of a gas luminosity monitor

Sergei Erin†

† For the LCAL group V.Bezzubov,S.Erin, A.Ferapontov, Yu.Gilitsky,V.Korablev, M.Lobanov, A.Rybin,V.

Suzdalev, K.Suzdalev

21.04.23IHEP,Protvino,Russia2

Requirements to luminosity monitor

Dynamic luminosity range 1030?-1034cm-2s-1 with reasonable integration time.

Bandwidth ~ 10 MHz to resolve luminosity of individual bunches.

Improve energy flow measurement in forward/backward direction.

High radiation hardness ~ 10 MGy/year

and etc. [1]


Choice of detector

One of number options is a gas ionization calorimeter filled with C3F8. Extensive studies of gas ionization calorimeters have been performed in the last decade[2]. It has been experimentally proved that hadrons/electromagnetic gas calorimeters posses a number of attractive features like good energy resolution, high uniformity and stability, simple calibration and high intrinsic radiation hardness at low cost. Using gas C3F8 one can achieve a good energy resolution and rather low equivalent noise energy even at atmospheric pressure [3].


Properties of C3F8

Density =0.0075 g/cm3 Molecular weight

188 Drift velocity

V=0.07mm/ns at

~800V/atm.


Properties of C3F8

C3F8 is a gas with electronegative properties

-attachment coefficient -Townsend coefficient

and coefficients as a function of electric field


Properties of C3F8


Previous tests and results

Systematic studies of a gas EM calorimeter with 3 and 1.5 mm thick lead absorbers have been performed using electron beams of the 70 GeV IHEP accelerator. Heavy freon C3F8 at pressure up to 1.8 atm. was used as a working gas.

The equivalent noise energies for the calorimeter tower are equal to 150 and 180 MeV for the fine and course calorimeter structures at 1 atm. gas pressure.

The energy resolution for two types of calorimeter are presented on this fig. It depends weakly on the gas pressure above 0.9 atm. and HV above 600 V.

The constant terms are compatible with zero. These are the best characteristics achieved so far for gas ionization

calorimeters. [4]







So the prototype looks. The thickness of Pb- absorbers is of 3 mm and the thickness of gas bigap is 10mm.

On the back side of the gas vessel one can see the readout connectors.



On this photo one can see PCB and absorber for one module of the calorimeter



On this photo are presented one module of gas calorimeter





On this two photos one can see a procedure of assembling for gas calorimeter


Luminosity monitor design

The monitor consist of W- absorber plates and the volume between the absorber plates is filled a gas C3F8 with overpressure 0.5 atm.

The sensor volume between the two absorber plates contains a PCB layers with a pad structure. The absorber plates are grounded and PCB with pads structure on both sides is on high voltage.


Luminosity monitor design


MC simulations of luminosity monitor

The MC results were received with Geant 3.21 and BRAMS.

The energy resolution of gas monitor for different angles of projectiles one can see on the next figures. This results were obtained with Geant.






Relative measurement of luminosity

The measurement of the current of the gas ionization will be used for this purpose. This measurement is available for beam steering.

The precision expected is about 1%


Relative measurement of luminosity

The total current from a calorimeter for electron with E=26 GeV and beam intensity 103 . This current was measured for the calorimeter with 3mm thick absorbers.


The control of gas purity

These measurements were carried out with proportional counter working in ionization mode. The current was measured with Kethley 619.


Radiation damage

We yet did not spend own measurements of radiation damage. Therefore I shall bring the data received in [8].

Small (<10cm2) static liquid C6F14 was irradiated up to 3*1013 fast neutrons.cm2. Studies showed the long-lived radioisotope F18(106 min.,511 KeV -emitter). For instantaneous rate of neutron about 106 neutrons cm-2s-

1 the expected level of activity is in the range 104-105 Bq.g-1.


Radiation damage

Small (<10cm2) static liquid C6F14 was exposed to Co60 gamma irradiation. After an absorbed dose of 6 Mrad surfaces of aluminum and stainless steel samples immersed in liquid C6F14 were covered with a polymeric layer of 0.4 m. The reasons are the impurities containing C-H groups.


Radiation damage

Conclusions:

Density of a gas is less than a density of liquid in 103 times .

Therefore we can expect that up to 5- 6 Grad we shall not observe the signal degradation from radiation damage.


Future plans

December 2003 – test beam run Continue MC simulations of luminosity monitor Study of gas properties like drift velocity,

attachment coefficient. MC simulation of gas properties with Magboltz ( S.Biagi kindly modified his program for C3F8).

Mechanical design of luminosity monitor


References

1. TESLA-Detector:Instrumentation of the very forward region2. S.Denisov, et al., Nucl.Instr. And Meth. A 335(1993)1063. S.R.Hunter, et al., Phys.Rev. A38(1988)584. S.Denisov, et al., Nucl.Instr. And Meth. A 419(1998)5905. S.Denisov, et al., Nucl.Instr. And Meth. A 494(2002)3696. S.Denisov, et al., presented at the IMAGING 2003, INTERNATIONAL CONFERENCE

ON IMAGING TECHNIQUES IN SUBATOMIC PHYSICS, ASTROPHYSICS, MEDICINE, BIOLOGY AND INDUSTRY, Stockholm, Sweden 24 – 27 June 2003

7. S. Denisov, S. Erin, N. Fedyakin preprint IHEP 99-35, 19998. E.Anderssen et al, CERN 99-09 CERN/LHCC/99-03, pp421-426

Documents

03.06.2015IHEP,Protvino,Russia 1 Current status of a gas luminosity monitor Sergei Erin † † For the LCAL group V.Bezzubov,S.Erin, A.Ferapontov, Yu.Gilitsky,V.Korablev,