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The first five years' experience with the HI-13 tandem accelerator at CIAE
Nuclear Instruments and Methods in Physics Research A328 (1993) 34-38 North-Holland
NUCLEAR INSTRUMENTS &METHODS IN PHYSICS RESEARCH Se(;hor~A
The first five years' experience with the HI-13 tandem accelerator at CIAE Guan Xialing, Qin Jiuchang, Yang Bingfan, Zhang Canzhe, Yu Yunfeng, Du Xueren and Ge Jiyun Department of Nuclear Physics of CIAE, P.O. Box 27,5, Beijing 102413, China
Five years have passed since the HI-13 tandem accelerator at CIAE was accepted from HVEC in 1986. In this period, one year consisted of testing operations and four years of full operation. The highest terminal voltage reached with the ion beam was t2.6 MV using the original 72 in. inclined field tubes. The laddertron chain has accumulated about 16000 h of running time up tn now. Experimental beam time is about 14600 h. More than 20 ion species have been accelerated through the machine, in this paper, the operation, maintenance and improvement of the HI-13 tandem are described.
1. Introduction T h e last large H V E C t a n d e m accelerator, the HI-13 t a n d e m at the C h i n a Institute of A t o m i c Energy (CIAE), was a c c e p t e d from H V E C in O c t o b e r 1986 [1]. A f t e r one year of testing operations, in A u g u s t 1987, the whole laboratory, including the accelerator and various e x p e r i m e n t facilities such as the fast n e u t r o n time of flight s p e c t r o m e t e r , scattering c h a m b e r s , Q D D D m a g n e t i c s p e c t r o m e t e r , in b e a m ~,-ray spcctroscope system and ~,-ray s p e c t r o m e t e r , was declared c o m p l e t e d and passed the g o v e r n m e n t a l a c c e p t a n c e check. T h e HI-13 t a n d e m a c c e l e r a t o r came into full operation at thc b e g i n n i n g of 1988. A f t e r one ycar of full operation, in o r d e r to p r o m o t e f u n d a m e n t a l rcscarch work in China, the e s t a b l i s h m e n t of the Beijing National T a n d e m A c c e l e r a t o r Laboratory ( B E N T A L ) was a n n o u n c e d . Since then, the B E N T A L has served not only C I A E , but also outside users, b o t h domestic and foreign. D u r i n g this period, a second stripper consisting of 240 foils was installed in the first dead section on the high energy side, and was b r o u g h t into o p e r a t i o n immediately. Four new b e a m lines were built for more a n d more physical e x p e r i m e n t s in target room III. O n e set of h o m e m a d e l a d d e r t r o n chain has b e e n r u n n i n g as well as the H V E C chain. A new technology for ladd e r t r o n chain assembly has b e e n developed by ourselves. A negative ion source test b e n c h has b e e n designed, m a n u f a c t u r e d and tested in our laboratory. A polarized ion source with a 200 n A polarized p r o t o n b e a m has b e e n c o n n e c t e d to the t a n d e m injector table.
T h u s far, the l a d d e r t r o n chain system of this m a c h i n e has a c c u m u l a t e d a b o u t 16000 h.
2. Operation T h e m a c h i n e is used in multidisciplinary studics; the main research fields are nuclear reactions, nuclear structures, n e u t r o n physics, nuclcar data m e a s u r e m e n t a n d some nuclear technology application studies, such as accelerator mass spectrometry and heavy ions irradiation d a m a g c studies. T h e r e is a program c o m m i t t c c which evaluates all the s u b m i t t e d proposals for cxpcrim e n t s at the t a n d e m . A b o u t 2 0 - 3 0 % of b e a m time is supplied to outside users. M o r e t h a n 100 research programs, p r o p o s e d by 18 different units, have b c c n c o m p l e t e d or are underway. T h e o p e r a t i o n a l status of the HI-13 t a n d e m over the past five years is s u m m a r i z e d in table 1. In this period, the highest terminal voltage for exp e r i m e n t s was 12.6 MV, which is 97% of the maximum rated terminal voltage of 13 MV. T h e lowest terminal voltage with sufficient b e a m transmission was 2.08 MV. The distributions of b e a m time with ion species for 1990 and 1991 are shown in fig. 1. T h e distributions of b e a m time with terminal voltage, for 1990 a n d 1991, arc shown in fig. 2. U p to now, more than 20 ion species, such as H, D, He, B, Be, C, O, F, AI, Si, P, S, CI, Ni, Cu, Br a n d I, havc b c c n accelerated t h r o u g h the machine. T h r e e kinds of ion sources, a model 725 d u o p l a s m a t r o n source, a model 710 charge cxchangc source and a model 834 s p u t t e r source, are used in the
0168-9002/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
Guan Xialing et al. / Initial testing and operation of a HI-13 tandem accelerator
35
4~ ~e
[gill] 119
IIIIIIIN,
8 H
O
lie
Be
C
0
F
Sl
P
S
Nt
C.
0
]'o~
78o
-
°
.
°
288
: ~ "lllllll
H
O
He
8
C
0
F
I'~
Sl
0
S
2/9
~
l~z ~-
T
H
0
H
0
]on
Fig. 1. Beam time distribution according to ion species for the past two years: (A) 1990, (B) 1991. As can be seen from table 1, t h e r e were eight a n d nine t a n k o p e n i n g s in the first two years of full o p e r a tion due to a deficiency of spare parts a n d lack of o p e r a t i o n a l experience.
HI-13 t a n d e m . A new source, a model 200 cesium s p u t t e r intensive ion source, is u n d e r installation a n d adjustment; it is m a d e by Kingston Scientific Corporation, U S A , a n d was designed by A l t o n [2].
(^) 1 9 9 6
688
4~ 488
IM !
36
I
a2
,,,,,,,,,,]llllllHInlllll!! .......111[1111110111111111 3
2
5
4
haur 6ee
6
(B)
5m
I
7
19Sl
8
ll'[llllli
1|
11
12
13
645 m ~
I]Eo
451
24 8
4S4
421
50
09
lllrrllll
l 2 3 4 5 8 7 $ 9 1| II 12 13 ~t Fig. 2. Experimental time distribution according to terminal voltage for two years: (A) 1990, (B) 1991.
I. ELECTROSTATIC ACCELERATORS
36
Guan Xialing et al. / Initial testing and operation of a HI-13 tandem accelerator
Since the overhaul at the end of 1989, the machine has been operating very well. Everything, including the injecting system, the laddertron system, the control system and the vacuum system, are running smoothly. There were only five tank openings in 1990 and the following two years. The limitation of the highest terminal voltage for the HI-13 tandem was due to sparking between the terminal and the tank wall; tube or column sparks were very rare. More than 80% of sparks occurred at both ends of the terminal high voltage equipotential region, particularly on the lower half of the equipotential rings on the high energy side. The transmission efficiency of the machine is from 65% or greater for a proton beam to less than 30% for a heavy ion beam, depending on the ion species, the beam intensity, the vacuum status, the terminal voltage, the stripper quality and the optical matching performance. The HI-13 tandem accelerator has a single drift buncher system. For normal bunching mode, the injecting energy of the ion beam should strictly be required to match the length of the drift tube. For our machine, due to the available injecting energies of the initial beam, we are restricted within the limit of 70-150 keV, and 1' the lengths of the drift tube of the buncher are 16, 42.5 and 58.5 cm only. In this case, it seriously restricts the bunchable ion species. Only proton, deuteron and carbon beams can be compressed into a narrow pulse. In order to extend the region of the pulsed beam, in general two methods can be selected; one is to increase the injecting energy to, for example, 300 keV, and the other is to have a variable-length drift tube. That is not very easy. One method, the nonstandard bunching model, has been developed in our laboratory, by which much more heavy ion species can be bunched with the same geometry as that of a single drift buncher and the same rf power supply. With the same injecting energy, say 120 or 130 keV, and the same drift length but different initial phases, various heavy ion beams can be bunched into good pulsed beams. With this nonstandard mode, not only are the bunchable ion species
Table 1 Operational status of the HI-13 tandem machine over the past five years Year
Status
Beam time for experiments [h]
Tank openings
1987 1988 1989 1990 1991
half operation full operation full operation full operation full operation
1700 2500 2800 2800 3300
4 9 8 5 5
Table 2 The bunching parameter for some ion species Ion Injecting Modulating Length of Initial Pulse species energy, Wo voltage, E m drift tube phase FWHM [keV] [kV] [cm] [deg] [ns] H D 7Li 9Be 12C
14N 160 I~F 32S
120 120 130 130 13{) 120 130 130 130 130
7.36 5.34 5.18 3.78 3.19 2.35 2.44 2.30 2.16 2.22
58.5 42.5 42.5 16 16 16 16 16 16 16
- 7 - 6.7 -34.5 24.5 18 4.5 1.5 -4.2 11 -40.5
0.6 0.8 1.04 1.28 1.40 1.92 1.88 1.96 2.12 2.72
increased, but also the injecting energy is located in the middle region of the available energy instead at a very high or very low energy. According to this method, some pulsed beams, such as helium, carbon, oxygen and fluorine, are available with sufficiently good F W H M values at the experimental target. For the HI-13 tandem pulse system, the nonstandard bunching mode's theoretical parameters for some ion species are listed in table 2.
3. Maintenance and improvement 3.1. The laddertron system
At the beginning of the installation and adjustment of the laddertron, particular attention was paid to minimizing the transverse runout in the direction parallel to the pulley axes. As is well known, the adjustment for reducing the runout is very vexatious and time-consuming. Almost one month was spent reducing the runout of the complete chain to about 1.6 mm peak to valley measured midway with the chain moved slowly by hand. After 5000 h running, severe damage to the bearing and shaft on the ground pulley was found and many pits were also found in several idler groove tyres. After carefully repairing the pulley and the idler wheel, the laddertron chain was re-installed. More than two weeks were again spent reducing the runout to 2 ram. In the middle of N o v e m b e r 1989, when the laddertron had operated for 8800 h, the chain broke down on one side. (This is the only time that the laddertron chain has broken down thus far.) At that time, most of the nylon links were damaged with one or both sides worn down by more than 1 mm, therefore the laddertron chain was running in a parallelogram instead of a rectangle. Almost all of the journals and bushings were also torn
Guan Xialing et aL / Initial testing and operation of a HI-13 tandem accelerator
37
R70 °, fast neutron time of flight spectrometer - R60 °, a scattering chamber for charged particle fission and heavy ion fusion studies R50 °, high energy -/-ray goniometer - R20 °, a G120L Q D D D magnetic spectrometer L40 °, high spin spectroscopy set-up; a good goniometer with four arms can be used to arrange Ge(Li) detectors or anti-Compton B G O - H p G e detectors L10 °, hyper-fine interactions. After three years' operation, as research work developed, more b e a m lines were needed. In the second stage, four new beam lines have been designed, installed and tested, located on L20, L30, L50 and L60 in experiment room III: L20 °, ultra-sensitive mass-spectrometer L30 °, a general purpose target chamber L50 °, a secondary radioactive beam line L60 °, target chamber for application studies. -
-
-
-
Fig. 3. The negative ion source test bench. (l) Ion source, (2) einzel lens, (3) E x B filter, (4) steerers, (5) and (8) slits, (6) and (9) Faraday cups, (7) magnetic analyzer, (10) and (11) turbo-molecular pumps.
-
-
and worn down. The machine had to be shut down immediately and the chain reassembled. During the process of chain reassembling, a new laddertron assembling technology was developed in our laboratory. The technology is based on that of the H V E C , but the process is quite different. This reassembly procedure was so successful that only two days were spent reducing the runout to 1.4 mm. By the end of 1990, a h o m e m a d e laddertron chain had been assembled using the same procedure. It was again demonstrated that the new assembly technology is satisfactory. Only 10 h were required to adjust the runout to less than 1.5 mm. Later, both chains performed very well, with the machine running smoothly with the beam at a terminal voltage of 11.5-12.6 MeV. U p to now, two sets of complete laddertron chains have been utilized alternatively in this machine; one is a H V E C chain and the other is made in China.
-
-
3.3. The ion source test bench
In order to maintain and adjust our four kinds of negative ion sources, an ion source test bench was designed, manufactured, installed and tested in our laboratory from September 1989 to October 1991. The test bench consists of an ion source, an einzel lens, an electron eliminator, a pair of electrostatic steerers, two slits, a magnetic analyser and two Faraday cups. This test bench is very easy to match to the four kinds of negative ion sources. As shown in fig. 3 it is equipped with two sets of molecular pumps. An isolating high voltage transformer is used to supply the power. Step motors and optical fiber controllers are used to control the components of the source.
3.2. The new beam lines 3.4. A polarized ion source
The switching magnet of the HI-13 tandem accelerator can accommodate up to 14 beam lines. However, in the initial stage, only six beam lines, purchased from H V E C , were installed in three experimental rooms:
1
2
3
A Lamb-shift polarized ion source is being developed at C I A E . This source produces a polarized negative hydrogen or deuterium ion beam. A schematic
4
~
7
8
9
p2 p3 pI Fig. 4. The polarized ion source configuration: pl-p5 pumps, F = Faraday cup, x = valves, (1) duoplasmatron, (2) accel-decel electrodes, (3) Cs cell, (4) spin filter, (5) Ar exchanger, (6) focussing lenses, (7,9) E S quadrupoles, (8) Wien filter. I. ELECTROSTATIC ACCELERATORS
38
Guan Xialing et al. / Initial testing and operation of a HI-13 tandem accelerator
diagram of this polarized ion source is shown in fig. 4. A spin filter is used to polarize the metastable hydrogen or deuterium atomic beam. The cavity of the spin filter mounted in a uniform axial magnetic field consists of a quadrant where the static and rf field are applied. The spin filter consists of a silver-plated copper cylinder 7 cm long and 15 cm in diameter, In order to obtain a uniform axial magnetic field, the solenoid coil is composed of a main coil, two end coils and a modulation coil. A rf power-leveling system using PIN diode modulators has been set up. The system can feed the rf power into the cavity at two levels: a lower level (8-200 mW) for ordinary operation, and a higher power level (0.2-2 W) for full quenching of metastable atoms. An automatic amplitude control circuit is employed to improve the stability of the rf field amplitude in an active cavity. The spin-quantization axis of the polarized ion beam from the argon canal is along the beam direction; an external spin-precession system was designed to provide full spin orientation requirement. As shown in fig. 4, the beam is brought into focus at the middle of the spin processor by means of an electrostatic quadrupole doublet. The beam is brought into focus at the entrance of a 150 kV preaccelerator tube by another quadrupole doublet located downstream from the processor. Thus far, about 200 nA of a polarized negative hydrogen beam has been detected by a Faraday cup at the entrance of the tank. The polarization of the beam was about 75%. 3.5. Tubes and resistors
No important modification has been made to the HVEC 72 in. inclined field tubes and the blue epoxy resistors of our machine, even though almost all large HVEC machines have exchanged their tubes for longer ones and extended the tubes into the dead sections. Fortunately, in five years' operation, the accelerator tubes show no severe damage and no gap exhibits shortening. On careful inspection of all insulating glasses of tubes nos. 1-8 it was found that the colour of some insulators, in tube no. 1, was changed from the original light colour to a dark tea colour. These insulators are located at the straight field between two opposite inclined field sections. The resistors are usually replaced when their value deviates 20% or more from the nominal value. In the past five years, more than 120 resistors have been
replaced. It is well known that the blue resistors of HVEC are too expensive to hold sufficient spares. It is necessary to modify the resistor system, such as the new ones designcd by Strasbourg Laboratory. On one hand, we need time to develop our homemade resistor system, and on the other hand, because 72 in. tubes are used, the gradient is lower than for the tandem machines of other laboratories, therefore the old blue resistors are still available. In such a case, Legnaro Nazionari Laboratory gave us great help at the right time. They sent our laboratory all their blue resistors free of charge. We now have sufficient blue resistors to use in our operation until the new homemade resistors are completed.
4. Conclusion The HI-13 tandem accelerator at the China Institute of Atomic Energy, Beijing, has operated satisfactorily during its first five years. In order to improve the operation conditions, some important parts of the accelerator have been replaced, or are going to be replaced by homemade parts, such as the laddertron chain, the idler rims, the nylon insulator links, the dividing resistors, some parts of the vacuum system and even the accelerator tubes. Thus far, no important modification has been made to the HI-13 tandem accelerator, for instance extending the accelerator tube to 88 in. and installing a portico-type intershield structure. Our great interest has been concentrated on the post superconducting linac accelerator. A further development plan for the HI-13 tandem is under consideration.
Acknowledgments We acknowledge the contributions of all operation crews in our laboratory. We wish to thank the carbon foil preparation group and the polarized ion source group for their efforts during the last five years.
References [1] Qin Jiuchang et al., Nucl. Instr. and Meth. A268 (1988) 31. [2] G.D. Alton, Nucl. Instr. and Meth. A287 (1990) 140.
NUCLEAR INSTRUMENTS &METHODS IN PHYSICS RESEARCH Se(;hor~A
The first five years' experience with the HI-13 tandem accelerator at CIAE Guan Xialing, Qin Jiuchang, Yang Bingfan, Zhang Canzhe, Yu Yunfeng, Du Xueren and Ge Jiyun Department of Nuclear Physics of CIAE, P.O. Box 27,5, Beijing 102413, China
Five years have passed since the HI-13 tandem accelerator at CIAE was accepted from HVEC in 1986. In this period, one year consisted of testing operations and four years of full operation. The highest terminal voltage reached with the ion beam was t2.6 MV using the original 72 in. inclined field tubes. The laddertron chain has accumulated about 16000 h of running time up tn now. Experimental beam time is about 14600 h. More than 20 ion species have been accelerated through the machine, in this paper, the operation, maintenance and improvement of the HI-13 tandem are described.
1. Introduction T h e last large H V E C t a n d e m accelerator, the HI-13 t a n d e m at the C h i n a Institute of A t o m i c Energy (CIAE), was a c c e p t e d from H V E C in O c t o b e r 1986 [1]. A f t e r one year of testing operations, in A u g u s t 1987, the whole laboratory, including the accelerator and various e x p e r i m e n t facilities such as the fast n e u t r o n time of flight s p e c t r o m e t e r , scattering c h a m b e r s , Q D D D m a g n e t i c s p e c t r o m e t e r , in b e a m ~,-ray spcctroscope system and ~,-ray s p e c t r o m e t e r , was declared c o m p l e t e d and passed the g o v e r n m e n t a l a c c e p t a n c e check. T h e HI-13 t a n d e m a c c e l e r a t o r came into full operation at thc b e g i n n i n g of 1988. A f t e r one ycar of full operation, in o r d e r to p r o m o t e f u n d a m e n t a l rcscarch work in China, the e s t a b l i s h m e n t of the Beijing National T a n d e m A c c e l e r a t o r Laboratory ( B E N T A L ) was a n n o u n c e d . Since then, the B E N T A L has served not only C I A E , but also outside users, b o t h domestic and foreign. D u r i n g this period, a second stripper consisting of 240 foils was installed in the first dead section on the high energy side, and was b r o u g h t into o p e r a t i o n immediately. Four new b e a m lines were built for more a n d more physical e x p e r i m e n t s in target room III. O n e set of h o m e m a d e l a d d e r t r o n chain has b e e n r u n n i n g as well as the H V E C chain. A new technology for ladd e r t r o n chain assembly has b e e n developed by ourselves. A negative ion source test b e n c h has b e e n designed, m a n u f a c t u r e d and tested in our laboratory. A polarized ion source with a 200 n A polarized p r o t o n b e a m has b e e n c o n n e c t e d to the t a n d e m injector table.
T h u s far, the l a d d e r t r o n chain system of this m a c h i n e has a c c u m u l a t e d a b o u t 16000 h.
2. Operation T h e m a c h i n e is used in multidisciplinary studics; the main research fields are nuclear reactions, nuclear structures, n e u t r o n physics, nuclcar data m e a s u r e m e n t a n d some nuclear technology application studies, such as accelerator mass spectrometry and heavy ions irradiation d a m a g c studies. T h e r e is a program c o m m i t t c c which evaluates all the s u b m i t t e d proposals for cxpcrim e n t s at the t a n d e m . A b o u t 2 0 - 3 0 % of b e a m time is supplied to outside users. M o r e t h a n 100 research programs, p r o p o s e d by 18 different units, have b c c n c o m p l e t e d or are underway. T h e o p e r a t i o n a l status of the HI-13 t a n d e m over the past five years is s u m m a r i z e d in table 1. In this period, the highest terminal voltage for exp e r i m e n t s was 12.6 MV, which is 97% of the maximum rated terminal voltage of 13 MV. T h e lowest terminal voltage with sufficient b e a m transmission was 2.08 MV. The distributions of b e a m time with ion species for 1990 and 1991 are shown in fig. 1. T h e distributions of b e a m time with terminal voltage, for 1990 a n d 1991, arc shown in fig. 2. U p to now, more than 20 ion species, such as H, D, He, B, Be, C, O, F, AI, Si, P, S, CI, Ni, Cu, Br a n d I, havc b c c n accelerated t h r o u g h the machine. T h r e e kinds of ion sources, a model 725 d u o p l a s m a t r o n source, a model 710 charge cxchangc source and a model 834 s p u t t e r source, are used in the
0168-9002/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
Guan Xialing et al. / Initial testing and operation of a HI-13 tandem accelerator
35
4~ ~e
[gill] 119
IIIIIIIN,
8 H
O
lie
Be
C
0
F
Sl
P
S
Nt
C.
0
]'o~
78o
-
°
.
°
288
: ~ "lllllll
H
O
He
8
C
0
F
I'~
Sl
0
S
2/9
~
l~z ~-
T
H
0
H
0
]on
Fig. 1. Beam time distribution according to ion species for the past two years: (A) 1990, (B) 1991. As can be seen from table 1, t h e r e were eight a n d nine t a n k o p e n i n g s in the first two years of full o p e r a tion due to a deficiency of spare parts a n d lack of o p e r a t i o n a l experience.
HI-13 t a n d e m . A new source, a model 200 cesium s p u t t e r intensive ion source, is u n d e r installation a n d adjustment; it is m a d e by Kingston Scientific Corporation, U S A , a n d was designed by A l t o n [2].
(^) 1 9 9 6
688
4~ 488
IM !
36
I
a2
,,,,,,,,,,]llllllHInlllll!! .......111[1111110111111111 3
2
5
4
haur 6ee
6
(B)
5m
I
7
19Sl
8
ll'[llllli
1|
11
12
13
645 m ~
I]Eo
451
24 8
4S4
421
50
09
lllrrllll
l 2 3 4 5 8 7 $ 9 1| II 12 13 ~t Fig. 2. Experimental time distribution according to terminal voltage for two years: (A) 1990, (B) 1991.
I. ELECTROSTATIC ACCELERATORS
36
Guan Xialing et al. / Initial testing and operation of a HI-13 tandem accelerator
Since the overhaul at the end of 1989, the machine has been operating very well. Everything, including the injecting system, the laddertron system, the control system and the vacuum system, are running smoothly. There were only five tank openings in 1990 and the following two years. The limitation of the highest terminal voltage for the HI-13 tandem was due to sparking between the terminal and the tank wall; tube or column sparks were very rare. More than 80% of sparks occurred at both ends of the terminal high voltage equipotential region, particularly on the lower half of the equipotential rings on the high energy side. The transmission efficiency of the machine is from 65% or greater for a proton beam to less than 30% for a heavy ion beam, depending on the ion species, the beam intensity, the vacuum status, the terminal voltage, the stripper quality and the optical matching performance. The HI-13 tandem accelerator has a single drift buncher system. For normal bunching mode, the injecting energy of the ion beam should strictly be required to match the length of the drift tube. For our machine, due to the available injecting energies of the initial beam, we are restricted within the limit of 70-150 keV, and 1' the lengths of the drift tube of the buncher are 16, 42.5 and 58.5 cm only. In this case, it seriously restricts the bunchable ion species. Only proton, deuteron and carbon beams can be compressed into a narrow pulse. In order to extend the region of the pulsed beam, in general two methods can be selected; one is to increase the injecting energy to, for example, 300 keV, and the other is to have a variable-length drift tube. That is not very easy. One method, the nonstandard bunching model, has been developed in our laboratory, by which much more heavy ion species can be bunched with the same geometry as that of a single drift buncher and the same rf power supply. With the same injecting energy, say 120 or 130 keV, and the same drift length but different initial phases, various heavy ion beams can be bunched into good pulsed beams. With this nonstandard mode, not only are the bunchable ion species
Table 1 Operational status of the HI-13 tandem machine over the past five years Year
Status
Beam time for experiments [h]
Tank openings
1987 1988 1989 1990 1991
half operation full operation full operation full operation full operation
1700 2500 2800 2800 3300
4 9 8 5 5
Table 2 The bunching parameter for some ion species Ion Injecting Modulating Length of Initial Pulse species energy, Wo voltage, E m drift tube phase FWHM [keV] [kV] [cm] [deg] [ns] H D 7Li 9Be 12C
14N 160 I~F 32S
120 120 130 130 13{) 120 130 130 130 130
7.36 5.34 5.18 3.78 3.19 2.35 2.44 2.30 2.16 2.22
58.5 42.5 42.5 16 16 16 16 16 16 16
- 7 - 6.7 -34.5 24.5 18 4.5 1.5 -4.2 11 -40.5
0.6 0.8 1.04 1.28 1.40 1.92 1.88 1.96 2.12 2.72
increased, but also the injecting energy is located in the middle region of the available energy instead at a very high or very low energy. According to this method, some pulsed beams, such as helium, carbon, oxygen and fluorine, are available with sufficiently good F W H M values at the experimental target. For the HI-13 tandem pulse system, the nonstandard bunching mode's theoretical parameters for some ion species are listed in table 2.
3. Maintenance and improvement 3.1. The laddertron system
At the beginning of the installation and adjustment of the laddertron, particular attention was paid to minimizing the transverse runout in the direction parallel to the pulley axes. As is well known, the adjustment for reducing the runout is very vexatious and time-consuming. Almost one month was spent reducing the runout of the complete chain to about 1.6 mm peak to valley measured midway with the chain moved slowly by hand. After 5000 h running, severe damage to the bearing and shaft on the ground pulley was found and many pits were also found in several idler groove tyres. After carefully repairing the pulley and the idler wheel, the laddertron chain was re-installed. More than two weeks were again spent reducing the runout to 2 ram. In the middle of N o v e m b e r 1989, when the laddertron had operated for 8800 h, the chain broke down on one side. (This is the only time that the laddertron chain has broken down thus far.) At that time, most of the nylon links were damaged with one or both sides worn down by more than 1 mm, therefore the laddertron chain was running in a parallelogram instead of a rectangle. Almost all of the journals and bushings were also torn
Guan Xialing et aL / Initial testing and operation of a HI-13 tandem accelerator
37
R70 °, fast neutron time of flight spectrometer - R60 °, a scattering chamber for charged particle fission and heavy ion fusion studies R50 °, high energy -/-ray goniometer - R20 °, a G120L Q D D D magnetic spectrometer L40 °, high spin spectroscopy set-up; a good goniometer with four arms can be used to arrange Ge(Li) detectors or anti-Compton B G O - H p G e detectors L10 °, hyper-fine interactions. After three years' operation, as research work developed, more b e a m lines were needed. In the second stage, four new beam lines have been designed, installed and tested, located on L20, L30, L50 and L60 in experiment room III: L20 °, ultra-sensitive mass-spectrometer L30 °, a general purpose target chamber L50 °, a secondary radioactive beam line L60 °, target chamber for application studies. -
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Fig. 3. The negative ion source test bench. (l) Ion source, (2) einzel lens, (3) E x B filter, (4) steerers, (5) and (8) slits, (6) and (9) Faraday cups, (7) magnetic analyzer, (10) and (11) turbo-molecular pumps.
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and worn down. The machine had to be shut down immediately and the chain reassembled. During the process of chain reassembling, a new laddertron assembling technology was developed in our laboratory. The technology is based on that of the H V E C , but the process is quite different. This reassembly procedure was so successful that only two days were spent reducing the runout to 1.4 mm. By the end of 1990, a h o m e m a d e laddertron chain had been assembled using the same procedure. It was again demonstrated that the new assembly technology is satisfactory. Only 10 h were required to adjust the runout to less than 1.5 mm. Later, both chains performed very well, with the machine running smoothly with the beam at a terminal voltage of 11.5-12.6 MeV. U p to now, two sets of complete laddertron chains have been utilized alternatively in this machine; one is a H V E C chain and the other is made in China.
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3.3. The ion source test bench
In order to maintain and adjust our four kinds of negative ion sources, an ion source test bench was designed, manufactured, installed and tested in our laboratory from September 1989 to October 1991. The test bench consists of an ion source, an einzel lens, an electron eliminator, a pair of electrostatic steerers, two slits, a magnetic analyser and two Faraday cups. This test bench is very easy to match to the four kinds of negative ion sources. As shown in fig. 3 it is equipped with two sets of molecular pumps. An isolating high voltage transformer is used to supply the power. Step motors and optical fiber controllers are used to control the components of the source.
3.2. The new beam lines 3.4. A polarized ion source
The switching magnet of the HI-13 tandem accelerator can accommodate up to 14 beam lines. However, in the initial stage, only six beam lines, purchased from H V E C , were installed in three experimental rooms:
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A Lamb-shift polarized ion source is being developed at C I A E . This source produces a polarized negative hydrogen or deuterium ion beam. A schematic
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p2 p3 pI Fig. 4. The polarized ion source configuration: pl-p5 pumps, F = Faraday cup, x = valves, (1) duoplasmatron, (2) accel-decel electrodes, (3) Cs cell, (4) spin filter, (5) Ar exchanger, (6) focussing lenses, (7,9) E S quadrupoles, (8) Wien filter. I. ELECTROSTATIC ACCELERATORS
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Guan Xialing et al. / Initial testing and operation of a HI-13 tandem accelerator
diagram of this polarized ion source is shown in fig. 4. A spin filter is used to polarize the metastable hydrogen or deuterium atomic beam. The cavity of the spin filter mounted in a uniform axial magnetic field consists of a quadrant where the static and rf field are applied. The spin filter consists of a silver-plated copper cylinder 7 cm long and 15 cm in diameter, In order to obtain a uniform axial magnetic field, the solenoid coil is composed of a main coil, two end coils and a modulation coil. A rf power-leveling system using PIN diode modulators has been set up. The system can feed the rf power into the cavity at two levels: a lower level (8-200 mW) for ordinary operation, and a higher power level (0.2-2 W) for full quenching of metastable atoms. An automatic amplitude control circuit is employed to improve the stability of the rf field amplitude in an active cavity. The spin-quantization axis of the polarized ion beam from the argon canal is along the beam direction; an external spin-precession system was designed to provide full spin orientation requirement. As shown in fig. 4, the beam is brought into focus at the middle of the spin processor by means of an electrostatic quadrupole doublet. The beam is brought into focus at the entrance of a 150 kV preaccelerator tube by another quadrupole doublet located downstream from the processor. Thus far, about 200 nA of a polarized negative hydrogen beam has been detected by a Faraday cup at the entrance of the tank. The polarization of the beam was about 75%. 3.5. Tubes and resistors
No important modification has been made to the HVEC 72 in. inclined field tubes and the blue epoxy resistors of our machine, even though almost all large HVEC machines have exchanged their tubes for longer ones and extended the tubes into the dead sections. Fortunately, in five years' operation, the accelerator tubes show no severe damage and no gap exhibits shortening. On careful inspection of all insulating glasses of tubes nos. 1-8 it was found that the colour of some insulators, in tube no. 1, was changed from the original light colour to a dark tea colour. These insulators are located at the straight field between two opposite inclined field sections. The resistors are usually replaced when their value deviates 20% or more from the nominal value. In the past five years, more than 120 resistors have been
replaced. It is well known that the blue resistors of HVEC are too expensive to hold sufficient spares. It is necessary to modify the resistor system, such as the new ones designcd by Strasbourg Laboratory. On one hand, we need time to develop our homemade resistor system, and on the other hand, because 72 in. tubes are used, the gradient is lower than for the tandem machines of other laboratories, therefore the old blue resistors are still available. In such a case, Legnaro Nazionari Laboratory gave us great help at the right time. They sent our laboratory all their blue resistors free of charge. We now have sufficient blue resistors to use in our operation until the new homemade resistors are completed.
4. Conclusion The HI-13 tandem accelerator at the China Institute of Atomic Energy, Beijing, has operated satisfactorily during its first five years. In order to improve the operation conditions, some important parts of the accelerator have been replaced, or are going to be replaced by homemade parts, such as the laddertron chain, the idler rims, the nylon insulator links, the dividing resistors, some parts of the vacuum system and even the accelerator tubes. Thus far, no important modification has been made to the HI-13 tandem accelerator, for instance extending the accelerator tube to 88 in. and installing a portico-type intershield structure. Our great interest has been concentrated on the post superconducting linac accelerator. A further development plan for the HI-13 tandem is under consideration.
Acknowledgments We acknowledge the contributions of all operation crews in our laboratory. We wish to thank the carbon foil preparation group and the polarized ion source group for their efforts during the last five years.
References [1] Qin Jiuchang et al., Nucl. Instr. and Meth. A268 (1988) 31. [2] G.D. Alton, Nucl. Instr. and Meth. A287 (1990) 140.