CONTROL SYSTEM DESIGN FOR ACCELERATOR BASED IRRADIATION EXPERIMENT N.K. Das # , S. Sahoo, N. Gayathri, S. Pal, Variable Energy Cyclotron Centre, Kolkata S. Ray, B. Chatterjee, Dept. Of ECE, Calcutta Institute of Engineering and Management, Kolkata Abstract A real time control system has been designed for accelerator based irradiation experiments on miniature specimen of reactor grade materials. High power beam deposits large amount of heat on the small sample specimen resulting in the possibility of melting or evaporation of the sample, which can lead to accidental situations. Therefore, a fast and time critical heat removal system has been designed and modeled using Matlab Simulink. In this paper we present the modeling and simulation of the control system considering the safety features incorporated in the design. This simulation study will help the feasibility study of the control system design for accelerator based irradiation experiment and present a guideline for safe operation of the experimental setup. INTRODUCTION In the DAE Medical Cyclotron project one of the beam lines will be used for material science experiments. 15MeV proton gives a bulk damage upto 0.5 mm with a flat damage profile upto 0.3 mm (excluding peak damage region and ion stopping range) whereas 30MeV proton gives a damage up to 1.7 mm with a flat profile upto 0.7mm. In this unique facility actual samples of clad tubes and reactor components can be irradiated. The damage rate achievable with the 200 μA beam is about 10 -5 displacement per second (dpa/sec). During the irradiation experiments the sample gets heated because of the high energy deposition (15-30MeV beam energy, 50 micro ampere beam current) on the sample. It is necessary to dissipate the heat of the sample to prevent uncontrollable rise in temperature of the specimen (typically 600 to 1000 degree Centigrade in 1 Sec), which may lead to melting or vaporization and contaminate the chamber. Ultimately this unwanted situation may lead to radiation hazards and it may also affect the cyclotron sub- systems. A real time control system is required to take care of the abnormal rise of temperature of the sample. In addition to the abnormal rise of sample temperature there are possibilities of other accidental conditions viz., chamber pressure increase, coolant failure in the Havar foil arrangement and failure of heat exchanger. There are other possible causes also that can increase the sample temperature such as: sudden stopping of coolant, insufficient coolant flow, sudden Beam current increase, X-Y scanner failure. Abnormal rise of the sample temperature above a certain limit, the situation may lead to accidental condition. So a heat removal system is essential to overcome these hazards. In this paper, we have observed the dynamic response of the Heat Removal Control System using Simulink. HEAT REMOVAL SYSTEM A beam current having beam power of 15 KW is the heat source to the sample. A closed helium cooling system is provided to meet the cooling requirements of the irradiation target. Helium is selected in view of its good heat transfer properties and its inertness against proton environment. Helium gas is injected in the form of high velocity jets impinging over the target. Because of the large amount of heat generated over thin targets, the loss of helium cooling during irradiation would lead to instantaneous melting of the targets. In order to prevent this, helium supply to the target is provided from a pressurized tank at 10 bars with adequate storage capacity to ensure continuous supply of coolant for ~ 5 min even after the loss of pumping power. This time is sufficient for the operator to trip the beam and avoid melting of the target. A schematic of the helium cooling circuit arrangement is shown in Fig. 1. Fig 1: Schematic of the helium cooling circuit arrangement Helium cooling circuit consists of helium compressor, pressurized buffer tank, heat exchanger, oil-filter, flow meters (F1, F2), etc. The Compressor is used to inject helium over the target surface through buffer tank. Flow _____________________________ # niludas@vecc.gov.in