| Paper | Title | Page |
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| MOPCP009 | Development of Power Supplies for 3-Ф, 240 kW RF System with Crowbar Protection for Superconducting Cyclotron at VECC | 60 |
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| RF system of K-500 super conducting cyclotron at VECC is a complex three phase system operating in the frequency range of 9 MHz to 27 MHz with maximum acceleration potential of around 100 kV feeding to each of three Dee cavities placed in median plane of cyclotron 120° apart through coupling capacitors. Each phase consists of chain of amplifiers and resonator operating in synchronization and at final stage of each phase, a high power water cooled Tetrode Tube (Eimac 4CW 150,000 E) as an RF high power amplifier each capable of delivering 80 kW of RF power. Individual power supplies for biasing Anode (20 kV, 22 Amp), Filament (16 V, 225 Amp), Screen (1600 V, 1 Amp) and grid (-500 V, 0.1 Amp) each for all three high power Tetrode Tubes are designed, developed and commissioned indigenously in VECC Cyclotron building and have been in operation from last few months successfully. Anode supply is common to all three tubes, rated at 20 kV, 22 Amp, 450 kW along with fast acting crowbar protection using Ignitron. This paper describes about the technical challenges in the development of the power supplies and special features of protection systems. | ||
| MOPCP058 | Commissioning Experience of the RF System of K500 Superconducting Cyclotron at VECC | 162 |
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Funding: Department of Atomic Energy, Govt. of India. Radio frequency system of Superconducting cyclotron at VECC, has been developed to achieve accelerating voltage of 100 kV max. with frequency, amplitude and phase stability of 0.1 ppm, 100 ppm and ±0.5 degree respectively within 9~27 MHz frequency. Each of the three half-wave coaxial cavity is fed with rf power (80kW max.) from a high power final rf amplifier based on Eimac 4CW150,000E tetrodes. Initially, the whole three-phase RF system has been tuned for operation with RF power to the cavities at 19.1994 MHz and thereafter commissioned the cyclotron with neon 3+ beam at external radius at 14.0 MHz. In this paper, we present brief description of the rf system and behaviour observed during initial conditioning of the cavities with rf power and the way to get out of multipacting zone together with discussion on our operational experience. We have so far achieved dee voltage up to 52 kV at 14 MHz with 20 kW of RF power fed at each of the three dees and achieved vacuum level of 4.5 x 10-7 mbar inside the beam chamber. We also present discussion on the problems and failures of some RF components during commissioning stage and rectifications done to solve the same. |
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| MOPCP065 | Closed Loop RF Tuning for Superconducitng Cyclotron at VECC | 180 |
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| The RF system of Superconducting cyclotron has been operational within 9 - 27 MHz frequency. It has three tunable half-wave coaxial cavities as main resonators and three tunable RF amplifier cavities. A PC-based system takes care of stepper motor driven coarse tuning of cavities with positional accuracy ~20 μm and hydraulically driven three couplers and three trimmers. The couplers, in open loop, match the cavity impedance to 50 Ω in order to feed power from RF amplifier. Trimmers operate in closed loop for fine tuning the cavity, if detuned thermally at high RF power. The control logic has been simulated and finally implemented with Programmable Logic Controller (PLC). Precision control of trimmer (~20 μm) is essential to achieve the accelerating (Dee) voltage stability better than 100 ppm and also minimizing the RF power to maintain it. Phase difference between Dee-in and Dee-pick-off signals and the reflected power signals (from cavity) together act in closed loop for fine tuning of the cavity. The close loop PID control determines the final positioning of the trimmer in each power level and achieved the required voltage stability. | ||
| MOPCP059 | Theoritical Analysis and Fabrication of Coupling Capacitor for K500 Superconducting Cyclotron at Kolkata | 165 |
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| K500 SC cyclotron has already been constructed and commissioned after spiraling Ne3+ internal beam with 70 nA upto extraction radius(670 mm) at Variable Energy Cyclotron Centre at Kolkata, India. Several problems have been experienced related to the coupling capacitor of the radio frequency system including it's sever burning during commissioning of the cyclotron. Making of the dissimilar joints between alumina ceramic and copper of the coupling capacitor demands the usage of vacuum furnace to avoid the cracking of the ceramic. Therefore exhaustive analysis has been carried out to facilitate the in-house fabrication of the coupling capacitor without using the vacuum furnace in case of emergency. The maximum allowable rate of temperature rise for the ceramic and the optimum thickness ration of the copper to ceramic has been estimated. Finally fabrication of the coupling capacitor has been carried out in-house without employing vacuum furnace. At present the coupling capacitor is performing well as maximum 57 kV DEE voltages were been achieved the till date. This paper presents the details of the analysis and experiences gain during the fabrication of the coupling capacitor. | ||
| MOPCP076 | Operational Experience of Superconducting Cyclotron Magnet at VECC, Kolkata | 203 |
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| The Kolkata Superconducting cyclotron magnet has been operational in the center since last few years and enabled us to extensively map magnetic fields over a year covering the operating range of the machine and successful commissioning of internal beam. The magnet cryostat coupled with the liquid helium refrigerator performs satisfactorily with moderate currents (<550A) in both the coils. The superconducting coil did not undergo any training and over the years has not suffered from any quench. Author would share the experience and difficulties of enhanced overall heat load to the liquid helium refrigerator at higher excitations of coils. This creates instability in the operation of liquid helium refrigerator and finally leads to slow dump. Rigorous study has been carried out in this regard to understand the problems and operational logic of liquid helium refrigerator has been modified accordingly to alleviate from. Some other measures have also been taken from cryostat and cryogenic distribution point of view in order to reduce the heat load at higher excitations. | ||
| MOPCP095 | Experiment and Analysis: Partial Loss of Insulation Vacuum in K-500 Superconducting Cyclotron During Energization | 248 |
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| At higher currents in superconducting coil of K-500 Superconducting cyclotron, it was found that the insulation vacuum surrounding the LHe vessel gets worsen with increased current in the coil,finally leading to slow dump of power of the coil. This is a limitation for further increasing current value in the superconducting magnet coil. But once the current value returned to zero, vacuum reading reaches its initial value. Experiment & analysis have been done to quantify the contribution of molecular gas conduction on heat load because of this partial loss of insulation vacuum. Experiment was done to quantify how much betterment in terms of heat load is possible by incorporating additional vacuum pump. The cryostat safety analysis because of loss of insulation vacuum has become very important at this new scenario. Analysis has been done to know what could be the maximum pressure rise with time in case of loss of vacuum. This data has been used to know what should be the relieving mass flow rate to avoid any pressure burst accident. Finally this data has been compared with the existing relief valve. It is found that the existing safety system can take care of such incident. | ||
| MOPCP095 | Experiment and Analysis: Partial Loss of Insulation Vacuum in K-500 Superconducting Cyclotron During Energization | 248 |
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| At higher currents in superconducting coil of K-500 Superconducting cyclotron, it was found that the insulation vacuum surrounding the LHe vessel gets worsen with increased current in the coil,finally leading to slow dump of power of the coil. This is a limitation for further increasing current value in the superconducting magnet coil. But once the current value returned to zero, vacuum reading reaches its initial value. Experiment & analysis have been done to quantify the contribution of molecular gas conduction on heat load because of this partial loss of insulation vacuum. Experiment was done to quantify how much betterment in terms of heat load is possible by incorporating additional vacuum pump. The cryostat safety analysis because of loss of insulation vacuum has become very important at this new scenario. Analysis has been done to know what could be the maximum pressure rise with time in case of loss of vacuum. This data has been used to know what should be the relieving mass flow rate to avoid any pressure burst accident. Finally this data has been compared with the existing relief valve. It is found that the existing safety system can take care of such incident. | ||