- Email: [email protected]
Operational experience with the 450 kV injector for the superconducting cyclotron
a
Nuclear
Instruments
and Methods
in Physics
Research
A 382 (1996)
192-196
/. __ __
B!!Z
NUCLEAN INSTNUMENTS & METNODS IN PNYSlcs; RUsZ%?n
EUEWIER
Operational experience with the 450 kV injector for the superconducting cyclotron G. Ciavola*,
M. Castro, L. Celona, F. Chines, S. Gammino,
S. Marletta
INFN-LNS, Via S. Sofia 44, 95123 Catania, Italy
Abstract In order to get a correct bunching of the tandem beams to be injected into the K-800 superconducting cyclotron at LNS and to improve further the transmission inside the tandem, the construction of a new injector providing 450 keV negative ions became necessary. The project, funded in 1990, is now complete. The commissioning of the 450 kV injector has been carried out paying particular attention to some technical problems: I ) the presence of two different sources, which permits to switch easily from one source to the other, has required to double all the hardware, except for the analyzing magnet and for the gas box, in order to be effective in reducing downtimes for maintenance: 2) the reduction of the electrical noise. which disturbs the computer control system; 3) the management of 79 analogic parameters and I IO digital parameters, which has been performed in an environment where the classical control system via insulated bars fails because of the high potential gradient (10 kV/in), one of the highest ever obtained in conditioned air environment for injectors. The main features of the 450 kV injector will be summarized. The main details of the commissioning with the platform performances will be presented and some details of ion optics will be given.
1. The design of the 450 kV injector At the Laboratorio Nazionale del Sud of Catania a new injector working at a potential of 450 kV has been designed and built [l-3]. This injector is essential to optimize the coupling between the I5 MV tandem (working since 1984 with a 150 kV injector) and the superconducting cyclotron (Fig. I), either in the transversal and in the longitudinal phase space. The 450 kV injector (Figs. 2 and 3) allows both to increase the beam transmission inside the first tube of the tandem (because the injected beam divergence decreases) and to increase the bunching efficiency, which increases with the injection energy. Therefore, the total beam current which can be injected into the superconducting cyclotron with the required phase, will increase significantly with the new injector. The design maximum voltage has been achieved without significant problems, in spite of the relevant field gradients, among the highest ever achieved in conditioned air boxes. This result has been obtained by means of a careful design study of the electromagnetic problems and of a very precise machining of each part of the platform and of the box. The study of the equipotential lines, which puts in
* Corresponding author. Tel. +39 95 542262. 542302. e-mail [email protected]. 0168~9002/96/$15.00
Copyright
P/I SO168-9002(96)00501-3
fax
+39
95
evidence the critical points where the electric field gradient is higher, has been carried out with the code POISSON. A typical graphical output is shown in Fig. 4. The maximum gradients arising in the comers towards the ground are of the order of 9 kV/cm for the design voltage of 450 kV. An important operational feature of this injector is that two different sources may be ready at the same time, thanks to the two ports of the magnet. We provided power supplies and electrical connections for each source, so that we can switch by console from the source located on the 90” port to the one located on the 63” port. This allows us to get a long operation time without stops for maintenance. Moreover a short time is required for changing an exhausted source. We will always have available a clean source, ready to be mounted. The run up time to reach a good vacuum for operation is about 3 h when replacing the source. It takes about half an hour to have a stable beam, ready for the injection into the tandem, when we change the target in the Kingston model 200 source. We are also developing a multi-target loader for a model 200 ion source to increase the operation time without maintenance to some months. The gas box is able to supply four different gases regulated by a thermomechanical gas dosing valve UDV135, making it possible to change gas by console. The vacuum plant is totally automatized by a PLC (programmable logic controller) Hitachi E-64 HR (40 input124 output).
0 1996 Elsevier Science B.V. All rights reserved
193
G. Ciavola et al. I Nucl. Instr. and Meth. in Phys. Res. A 382 (1996) 192-196
Fig. I. Layout of the Laboratorio
Three different pumping units are controlled by the PLC (90” unit, 63” unit, out magnet unit) and allow to pump the chamber and the source separately. The start/stop of each unit is independent and we can operate locally or by console; most of the important status and vacuum measurements are readable by console. The operating vacuum is in the order of 2 X lo-’ mbar, obtained by means of two 600 I Is pumps located before and after the analyzing
Nazionale
del Sud.
magnet, upside constraints.
2. Hardware
down
mounted
because
of mechanical
and software of the control system
The control procedure has been fully automatized the operator’s attendance has been simplified.
so that
Fig. 2. The design of the 450 kV platform.
IV. RADIOACTIVE
ION BEAMS
G. Ciavola et al. I Nucl. Instr. and Meth. in Phys. Res. A 382 (1996) 192-196
Fig. 3. A photo of the 450 kV injector
The injector hardware has to solve a number of probIems (41, coming from the fact that the injector has a very high voltage, particularly: - the electrical plant at 450 kV potential; _ the need to have a precise ground reference, so that the circuits, which are insulated with respect to each other,
have no potential fluctuations which may originate an electric discharge: _ the shield of electronics from electromagnetic ir tterference caused by electrical discharge, which may oc:cur inside the injector because of the different potentials of the sources;
G. Ciavola et al. I Nucl. Instr. and Meth. in Phys. Res. A 382 (1996) 192-196
Fig. 4. A POISSON graphical output for the calculations of gradients.
_ the readout and the transmission
of the signal from the console to the platform. The above problems are often enhanced by the use of sophisticated technologies. that are able to detect very low signals and are easily affected by any noise. Different technical solutions have been tried to get finally a stable and reproduceable ion beam. An Intel 8051 microcontroller has been used as a basis for the computer control. It uses the master-slave technique to communicate on a BITBUS network. The master is a Personal Computer located in the console room which communicates with the slaves located on the injector by optical fibres (the PC is the man-machine interface, the slaves are the interfaces towards the field). Two different modules are used as slaves: one set of iRCB 4410 digital I/O modules is used to control the actuators, the on/off states readout of valves, power supplies, flowmeters and the readout of vacuum; another set of iRCB 4420 analog I/O modules is used to set and read the analogic signals (currents and voltages of power supplies, temperatures, dosing valves troughputs, etc.). Two other modules have been designed and realized to match the different requirements of the BITBUS network, one for the analysis magnet control and the other for the network master. The structure of the control may be divided into three different parts: I ) source control, directly by BITBUS; 2) vacuum system control, done by a PLC connected to BITBUS via digital I/O; 3) 90” magnet control, performed by a Gaussmeter, connected to BITBUS via RS-232. The system software has an architecture consisting of two parts which communicate with each other. One of these is implemented on the BITBUS network, the other one works on the dedicated PC which controls the entire process. By using the real time operating system iDCXSI,
19.5
implemented on board of BITBUS modules, we have designed the different processes. The first process takes care only of the data communication to and from the BITBUS (typical network transfer rates are in the order of 375 kbps). The second process controls the hardware linked to the injector parameters. Some routines have been implemented into the processes to rise the security level of the controt system and to permit an accurate control on the data transmission of the BITBUS link. This gives a reasonable confidence on the network activity and commands the operative procedures for the security stop of the injector in case of failures. The software implemented on the PC consists of routines related to the management of the man-machine interface and of the transmission to the BITBUS network. The routines related to BITBUS filters the informations to be passed to and from the man-machine interface process. The man-machine interface uses the GUI (graphics user interface) of the Windows package, which is easy to use and allows the user to see on the screen the input-output commands, permitting complete control of the system. The typical parameters for the data acquisition are of the order of 300 ms, which is well inside our requirements.
3. The ion optics The design of the ion optics for the two sources have been calculated assuming the source emittance to be 457~ mm mrad (at 20 keV) for both the sources and the beam lines have been designed with a large acceptance so that 100% of the beam extracted by the source can be injected into the tandem. The beams produced by this source have intensities in the order of few PA, therefore space charge forces do not affect them as long as the size is not lower than a few mm. The beam lines of the two sources follow the same philosophy and share most of the elements. The analysis section is somewhat different but the transport section from the image point of the analysis magnet to the matching point with the tandem (namely the low energy aperture) is equal, except for the element setting. The analysis section for the 63.43” port consists of a bidimensional einzel lens, followed by an unidimensional electrostatic lens, whose function is to limit the vertical size of the beam inside the magnet gap (50 mm). The magnet has a B,,, = 1 T and p = 900 mm. Another einzel lens gives the double waist at the image point of the magnet. For the 90” port the analysis section consists of an einzel lens, followed by an unidimensional electrostatic lens and by the magnet, which in this case works as a double focusing dipole with p = 600 mm. By shaping the angle of the exit and entrance faces of this magnet it is possible to
IV. RADIOACTIVE ION BEAMS
G. Ciavola
196
et al. I Nucl. Instr. and Meth.
in Phys. Res. A 382 (1996)
450 KV INJECTOR
100
60 50
192-196
18 .“‘,,,,‘,“““,,‘,,,“,‘,“,,,,’ 150 200 250 300 350 Iqjection energy (kev)
100
400
450
Fig. 5. The measured heam transmission from the 834 Hiconex sputtering source mounted on the 450 kV injector to the tandem.
perform not only focusing in the horizontal direction but also in the vertical direction. This allows the second einzel lens to be switched off for the 90” port beam line. The transport section consists of two electrostatic quadrupole triplets which limit the dimensions of the beam to less than 35 mm total, so that a beam pipe of 100 mm diameter allows an easy beam transport. The final goal of a beam diameter at the tandem stripper lower than 5 mm for both the horizontal and vertical direction has been achieved with a measured efficiency of 83 to 86% (Fig. 5), in spite of the asymmetry of the electric field and of the beam aberrations which usually reduce the transport efficiency. Taking into account the presence of the grid lens at the entrance of the tandem, which transmission is about 868, it can be said that a measured transmission higher than 97% has been achieved. This number may be compared with the ones measured on the 150 kV injector; until 1992 the transmission was about 45%. after the installation of the new optics [3] the transmission reached 75%.
4. Platform performance
and operational
experience
The accelerator tube consists of 60 gaps with a total resistance of 1.66 X lo9 R. The drain current from the high voltage power supply has been measured up to 450 kV (Fig. 6). The maximum power which can be. dissipated by the water flow is 10 kW. The measured water conductivity is 0.15 p.S and its flux is 0.6 m3/h. The freon circuit is able to dissipate more than 5 kW by means of a flow of 0.9 m3/h. A noticeable
Oymo VOLTAGE [KVI
Fig. 6. The measured current vs. voltage.
technological effort was spent on the climatized box which maintains a temperature of 20°C and a maximum relative humidity of 30%. The refrigerating power is about 15 kW for a total flow of 6500 m’/h. Since spring 1995 the 450 kV injector has been able to inject the beams inside the tandem and the major technological problems have been solved, so we can conclude that commissioning of the 450 kV injector has been satisfactory.
References [l] G. Ciavola et al., Nucl. Instr. and Meth. A 244 (1986) 162. [2] G. Ciavola et al., Proc. 2nd Eur. Part. Act. Conf., Nice (1990) p. 491. [3] G. Ciavola et al., Nucl. Instr. and Meth. A 328 (1993) 64. [4] G. Ciavola et al., LNS internal report, 251111995.
Nuclear
Instruments
and Methods
in Physics
Research
A 382 (1996)
192-196
/. __ __
B!!Z
NUCLEAN INSTNUMENTS & METNODS IN PNYSlcs; RUsZ%?n
EUEWIER
Operational experience with the 450 kV injector for the superconducting cyclotron G. Ciavola*,
M. Castro, L. Celona, F. Chines, S. Gammino,
S. Marletta
INFN-LNS, Via S. Sofia 44, 95123 Catania, Italy
Abstract In order to get a correct bunching of the tandem beams to be injected into the K-800 superconducting cyclotron at LNS and to improve further the transmission inside the tandem, the construction of a new injector providing 450 keV negative ions became necessary. The project, funded in 1990, is now complete. The commissioning of the 450 kV injector has been carried out paying particular attention to some technical problems: I ) the presence of two different sources, which permits to switch easily from one source to the other, has required to double all the hardware, except for the analyzing magnet and for the gas box, in order to be effective in reducing downtimes for maintenance: 2) the reduction of the electrical noise. which disturbs the computer control system; 3) the management of 79 analogic parameters and I IO digital parameters, which has been performed in an environment where the classical control system via insulated bars fails because of the high potential gradient (10 kV/in), one of the highest ever obtained in conditioned air environment for injectors. The main features of the 450 kV injector will be summarized. The main details of the commissioning with the platform performances will be presented and some details of ion optics will be given.
1. The design of the 450 kV injector At the Laboratorio Nazionale del Sud of Catania a new injector working at a potential of 450 kV has been designed and built [l-3]. This injector is essential to optimize the coupling between the I5 MV tandem (working since 1984 with a 150 kV injector) and the superconducting cyclotron (Fig. I), either in the transversal and in the longitudinal phase space. The 450 kV injector (Figs. 2 and 3) allows both to increase the beam transmission inside the first tube of the tandem (because the injected beam divergence decreases) and to increase the bunching efficiency, which increases with the injection energy. Therefore, the total beam current which can be injected into the superconducting cyclotron with the required phase, will increase significantly with the new injector. The design maximum voltage has been achieved without significant problems, in spite of the relevant field gradients, among the highest ever achieved in conditioned air boxes. This result has been obtained by means of a careful design study of the electromagnetic problems and of a very precise machining of each part of the platform and of the box. The study of the equipotential lines, which puts in
* Corresponding author. Tel. +39 95 542262. 542302. e-mail [email protected]. 0168~9002/96/$15.00
Copyright
P/I SO168-9002(96)00501-3
fax
+39
95
evidence the critical points where the electric field gradient is higher, has been carried out with the code POISSON. A typical graphical output is shown in Fig. 4. The maximum gradients arising in the comers towards the ground are of the order of 9 kV/cm for the design voltage of 450 kV. An important operational feature of this injector is that two different sources may be ready at the same time, thanks to the two ports of the magnet. We provided power supplies and electrical connections for each source, so that we can switch by console from the source located on the 90” port to the one located on the 63” port. This allows us to get a long operation time without stops for maintenance. Moreover a short time is required for changing an exhausted source. We will always have available a clean source, ready to be mounted. The run up time to reach a good vacuum for operation is about 3 h when replacing the source. It takes about half an hour to have a stable beam, ready for the injection into the tandem, when we change the target in the Kingston model 200 source. We are also developing a multi-target loader for a model 200 ion source to increase the operation time without maintenance to some months. The gas box is able to supply four different gases regulated by a thermomechanical gas dosing valve UDV135, making it possible to change gas by console. The vacuum plant is totally automatized by a PLC (programmable logic controller) Hitachi E-64 HR (40 input124 output).
0 1996 Elsevier Science B.V. All rights reserved
193
G. Ciavola et al. I Nucl. Instr. and Meth. in Phys. Res. A 382 (1996) 192-196
Fig. I. Layout of the Laboratorio
Three different pumping units are controlled by the PLC (90” unit, 63” unit, out magnet unit) and allow to pump the chamber and the source separately. The start/stop of each unit is independent and we can operate locally or by console; most of the important status and vacuum measurements are readable by console. The operating vacuum is in the order of 2 X lo-’ mbar, obtained by means of two 600 I Is pumps located before and after the analyzing
Nazionale
del Sud.
magnet, upside constraints.
2. Hardware
down
mounted
because
of mechanical
and software of the control system
The control procedure has been fully automatized the operator’s attendance has been simplified.
so that
Fig. 2. The design of the 450 kV platform.
IV. RADIOACTIVE
ION BEAMS
G. Ciavola et al. I Nucl. Instr. and Meth. in Phys. Res. A 382 (1996) 192-196
Fig. 3. A photo of the 450 kV injector
The injector hardware has to solve a number of probIems (41, coming from the fact that the injector has a very high voltage, particularly: - the electrical plant at 450 kV potential; _ the need to have a precise ground reference, so that the circuits, which are insulated with respect to each other,
have no potential fluctuations which may originate an electric discharge: _ the shield of electronics from electromagnetic ir tterference caused by electrical discharge, which may oc:cur inside the injector because of the different potentials of the sources;
G. Ciavola et al. I Nucl. Instr. and Meth. in Phys. Res. A 382 (1996) 192-196
Fig. 4. A POISSON graphical output for the calculations of gradients.
_ the readout and the transmission
of the signal from the console to the platform. The above problems are often enhanced by the use of sophisticated technologies. that are able to detect very low signals and are easily affected by any noise. Different technical solutions have been tried to get finally a stable and reproduceable ion beam. An Intel 8051 microcontroller has been used as a basis for the computer control. It uses the master-slave technique to communicate on a BITBUS network. The master is a Personal Computer located in the console room which communicates with the slaves located on the injector by optical fibres (the PC is the man-machine interface, the slaves are the interfaces towards the field). Two different modules are used as slaves: one set of iRCB 4410 digital I/O modules is used to control the actuators, the on/off states readout of valves, power supplies, flowmeters and the readout of vacuum; another set of iRCB 4420 analog I/O modules is used to set and read the analogic signals (currents and voltages of power supplies, temperatures, dosing valves troughputs, etc.). Two other modules have been designed and realized to match the different requirements of the BITBUS network, one for the analysis magnet control and the other for the network master. The structure of the control may be divided into three different parts: I ) source control, directly by BITBUS; 2) vacuum system control, done by a PLC connected to BITBUS via digital I/O; 3) 90” magnet control, performed by a Gaussmeter, connected to BITBUS via RS-232. The system software has an architecture consisting of two parts which communicate with each other. One of these is implemented on the BITBUS network, the other one works on the dedicated PC which controls the entire process. By using the real time operating system iDCXSI,
19.5
implemented on board of BITBUS modules, we have designed the different processes. The first process takes care only of the data communication to and from the BITBUS (typical network transfer rates are in the order of 375 kbps). The second process controls the hardware linked to the injector parameters. Some routines have been implemented into the processes to rise the security level of the controt system and to permit an accurate control on the data transmission of the BITBUS link. This gives a reasonable confidence on the network activity and commands the operative procedures for the security stop of the injector in case of failures. The software implemented on the PC consists of routines related to the management of the man-machine interface and of the transmission to the BITBUS network. The routines related to BITBUS filters the informations to be passed to and from the man-machine interface process. The man-machine interface uses the GUI (graphics user interface) of the Windows package, which is easy to use and allows the user to see on the screen the input-output commands, permitting complete control of the system. The typical parameters for the data acquisition are of the order of 300 ms, which is well inside our requirements.
3. The ion optics The design of the ion optics for the two sources have been calculated assuming the source emittance to be 457~ mm mrad (at 20 keV) for both the sources and the beam lines have been designed with a large acceptance so that 100% of the beam extracted by the source can be injected into the tandem. The beams produced by this source have intensities in the order of few PA, therefore space charge forces do not affect them as long as the size is not lower than a few mm. The beam lines of the two sources follow the same philosophy and share most of the elements. The analysis section is somewhat different but the transport section from the image point of the analysis magnet to the matching point with the tandem (namely the low energy aperture) is equal, except for the element setting. The analysis section for the 63.43” port consists of a bidimensional einzel lens, followed by an unidimensional electrostatic lens, whose function is to limit the vertical size of the beam inside the magnet gap (50 mm). The magnet has a B,,, = 1 T and p = 900 mm. Another einzel lens gives the double waist at the image point of the magnet. For the 90” port the analysis section consists of an einzel lens, followed by an unidimensional electrostatic lens and by the magnet, which in this case works as a double focusing dipole with p = 600 mm. By shaping the angle of the exit and entrance faces of this magnet it is possible to
IV. RADIOACTIVE ION BEAMS
G. Ciavola
196
et al. I Nucl. Instr. and Meth.
in Phys. Res. A 382 (1996)
450 KV INJECTOR
100
60 50
192-196
18 .“‘,,,,‘,“““,,‘,,,“,‘,“,,,,’ 150 200 250 300 350 Iqjection energy (kev)
100
400
450
Fig. 5. The measured heam transmission from the 834 Hiconex sputtering source mounted on the 450 kV injector to the tandem.
perform not only focusing in the horizontal direction but also in the vertical direction. This allows the second einzel lens to be switched off for the 90” port beam line. The transport section consists of two electrostatic quadrupole triplets which limit the dimensions of the beam to less than 35 mm total, so that a beam pipe of 100 mm diameter allows an easy beam transport. The final goal of a beam diameter at the tandem stripper lower than 5 mm for both the horizontal and vertical direction has been achieved with a measured efficiency of 83 to 86% (Fig. 5), in spite of the asymmetry of the electric field and of the beam aberrations which usually reduce the transport efficiency. Taking into account the presence of the grid lens at the entrance of the tandem, which transmission is about 868, it can be said that a measured transmission higher than 97% has been achieved. This number may be compared with the ones measured on the 150 kV injector; until 1992 the transmission was about 45%. after the installation of the new optics [3] the transmission reached 75%.
4. Platform performance
and operational
experience
The accelerator tube consists of 60 gaps with a total resistance of 1.66 X lo9 R. The drain current from the high voltage power supply has been measured up to 450 kV (Fig. 6). The maximum power which can be. dissipated by the water flow is 10 kW. The measured water conductivity is 0.15 p.S and its flux is 0.6 m3/h. The freon circuit is able to dissipate more than 5 kW by means of a flow of 0.9 m3/h. A noticeable
Oymo VOLTAGE [KVI
Fig. 6. The measured current vs. voltage.
technological effort was spent on the climatized box which maintains a temperature of 20°C and a maximum relative humidity of 30%. The refrigerating power is about 15 kW for a total flow of 6500 m’/h. Since spring 1995 the 450 kV injector has been able to inject the beams inside the tandem and the major technological problems have been solved, so we can conclude that commissioning of the 450 kV injector has been satisfactory.
References [l] G. Ciavola et al., Nucl. Instr. and Meth. A 244 (1986) 162. [2] G. Ciavola et al., Proc. 2nd Eur. Part. Act. Conf., Nice (1990) p. 491. [3] G. Ciavola et al., Nucl. Instr. and Meth. A 328 (1993) 64. [4] G. Ciavola et al., LNS internal report, 251111995.