New Concept - RESOURCE
Justification of New Concept to Increase the Resource of the PS+WLS System in the Installations for High Energy Physics
Tech Area / Field
- INF-SIG/Sensors and Signal Processing/Information and Communications
3 Approved without Funding
Joint Institute of Nuclear Research, Russia, Moscow reg., Dubna
- Research Institute of Optical and Physical Measurements, Russia, Moscow
- CERN, Switzerland, Geneva\nFermilab (Fermi National Accelerator Laboratory), USA, IL, Batavia
Project summaryPlanned experiments, e.g. CDF and D0 at the Tevatron (USA) and ATLAS, CMS, ALICE at the LHC (CERN), require a design figure of 10 years for the period of failure-free operation (i.e. resource). With the energy of 2 to 10 TeV and luminosity of 1032 - 1034cm-2 s-1, the irradiation loads D to scintillators (PS) and light guides (WLS) overcome the maximum permissible dose D and the resource tr decreases sharply.
Earlier one expressed the resource as a ratio of independent values:
tr/kn [hour] = Dlim [Gy] / D [Gyhour-1],
and did not consider the factor of assurance kn (safety coefficient). The maximum permissible dose Dlim was determined according to the variation of optical properties of the PS or WLS under the high-rate irradiation D » 102... 103 Gy ґ hour-1 of small samples with the low energy sources 60Co, 90Sr, etc. The obtained values Dlim » 50... 70 kGy seemed acceptable for future installations.
Nevertheless, conditions of the PS+WLS operation in real calorimeters and "trackers" differ in several aspects from those ones typical for tests:
- field of irradiation is mixed and the LET is »20 keV ґ mm-1 comparing to the gammas of 60Co when LET is » 0.2 ke V ґ mm-1;
- radiation-induced oxidizing takes place, as long as the dose rate D is by 4 orders of magnitude lower than in the tests;
- dimensions of scintillators and length of lightguides are large;
- light flux, » 1015 cm-2 ґ s-1, is much higher than that one in small samples.
That difference was noted as long ago as 1985: see, e.g. CERN 85-08 and Nucl. Inst. & Meth. A240 (1985).
Recently we performed WA-98 experiment at CERN (ZDC calorimeter, irradiation with Pb nuclei, energy 157.7 GeV per nucleon) and obtained Dlim = 5... 7 kGy, i.e. the value was lower by an order of magnitude than the value for the same scintillator samples irradiated by 60Co, see JINR Rapid Comm. 3(77) 1996. We estimated the resource of the PS+WLS systems for installations under design: Tile, ATLAS - 5 years; D 0 - 2 years; CDF -1 year; Tracker, ATLAS, CMS - 3 months; Endcap, CMS -1.5 months.
Inasmuch as it is impossible to achieve 10... 100-times improvement of the PS and WLS radiation stability by means of traditional methods of chemical and technological nature, the dilemma appears: either to change periodically the PS+WLS system (this is complicated from the technical side and inexpedient from the economical one) or to use our new concept for the detailed planning of irradiation sessions and rest periods when the system recovers its properties. If the relaxation time (rest period) were short, this would not affect the results of fundamental investigations carried out by physicist-experimentalists.
The concept essence is to shorten significantly the relaxation time of the optical properties after irradiation and to prove that the irreversible processes do not reach the "emergency level" in result of the long-term photo-radiation degradation of polymers.
The project aim is to integrate the expert knowledge in the field of radiation material sciences, to generalize the existing techniques for the long-term forecast of Dlim (t) and to substantiate the new concept to increase the system tr.
The problem complexity arises from the multiple-parameter dependence of Dlim on: D (radio oxidizing), time, temperature, light intensity, radiation field (LET), dimensions of the PS, environment, etc.
The scientific novelty is the use of the relaxation time instead of the maximum permissible dose. Therefore the new chemical, agents are necessary: photo-stabilizers, anti-oxidizers, modifiers of polymer structure, etc. The novelty is also the investigation of the second term, D, entering the resource formula by means of detailed simulations of the dose distributions with Monte-Carlo method.
The methodology is directed to the achievement of the demanded resource:
- development of a technology and trying out the efficiency of the new chemical dopants using the small test samples irradiated with the moderate D values under varying temperature and light inten-sity;
- experimental modeling of the photo-radiation aging at the full-scale PS+WLS model including the РЕМ under conditions of cycling irradiation with the different isotopes simultaneously and the accompanying optical-physical measurements;
- computer simulation of the various dynamic irradiation regimes typical for the real operation con-ditions of installations for high energy physics;
- irradiation of the model at the particle beam of 100 GeV energy at least, in order to find out the influence of the radiation field on the Dlim as well as to correct the input data for "RESOURCE" code.
The project feasibility is proved by the analysis of the long-term radiation stability of the polymer-isolated electrical cables at the US nuclear power plants and by the agreement of the forecast and the results obtained after the 12-year operation under radiation of low dose rate. Calculations were made with the use of superposition principle "time - temperature - dose rate" that made the physical justification for the transition from the tests at high D to the real operation at low D. Moreover, the project authors have already approved the superposition principle by the full-scale experiments in 1985 at different accelerators, nuclear reactor and sources, see Appendix to JINR Comm. P14-95-104, Dubna, 1995.
The expected results: experimental verification of the new concept; development of instruc-tions and methodical matters allowing one to solve a broad range of scientific and engineering tasks for optimization of operation regimes of installations, in order to achieve the necessary resource of the PS+WLS system and other numerous assembles and units subjected to the radiation loads. The database of input parameters will include the new experimental results both of physical-chemical and technological nature obtained while carrying out the project. The new technology will not complicate the construction but, instead, simplify it and reduce the cost of the PS+WLS system.
Project leader - Prof. Lev N. Zaitsev, Doct.Tech.Sci., Principal Scientist, JINR.
Executive manager - Mr. Alexander A. Astapov
Address: Laboratory of High Energies, JINR, Dubria 141980, Moscow region, Russia.
Phone:+  (095) 926-22-22, +  (096-21) 62-991, +  (096-21) 64-569
Fax:+  (096-21) 66-666
International institution Joint Institute for Nuclear Research,
Russian state institution Research Institute for Optical-Physical Measurements
Prof. R.Kamermans (experiments)
Address: Dept. of Subatomic Physics, University of Utrecht, Princetonplein 5, P.O.Box 80000, NL-
3508 ТА UTRECHT, Netherlands
Phone: +  (30) 532-517
Fax: +  (30) 518-686
Address: Fermilab, P.O.Box 500, MS 345, Batavia IL 60510, USA
Phone: + (630) 840-44-09
Fax: + (630) 840-44-52
Project duration - 36 months (900-man ґ month).