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A pulse-operated polarized H− source of Lamb-shift type
NUCLEAR
INSTRUMENTS
AND
A PULSE-OPERATED
METHODS
141
POLARIZED H-
(I977) 383-386;
:(3 N O R T H - H O L L A N D
PUBLISHING
CO.
S O U R C E OF L A M B - S H I F T T Y P E
Y. M O R I L, A. T A K A G I z, M. K O B A Y A S H I z, Y. W A K U T A ~, S. F U K U M O T O z, K. K I K U C H I 2 and M. S O N O D A ~
Department ()["Nuclear Engineering, Faculty o[' Engineering, Kyushu University Hakozaki 6, Higashi-ku, Fukuoka, 812, Japan z National Laboratory/or High Energy Physics, Oho-machi, Tsnkuba-gun, Ibaraki, 300 32, Japan '
Received 21 September 1976 A pulse-operated polarized H - source o f the Lamb-shift type has been developed at the National Laboratory for High Energy Physics in J a p a n ( K E K ) for future acceleration o f polarized protons in the K E K 12 GeV proton synchrotron. A new spin selection principle proposed by Donnally has been adopted, in which only the hyperfine substate o f 2S1/z with zero total angular m o m e n t u m is selected by causing the transitions o f the other three substates o f 281/2 to 2Pt/2 by an rf electric field m a k i n g an angle of a b o u t 50 with the direction o f a weak static magnetic field. In the preliminary experiments, a 350 nA H beam o f about 60% polarization has been obtained.
Since 1975, a pulse-operated polarized H - source of the Lamb-shift type has been developed at the National Laboratory for High Energy Physics in Japan ( K E K ) for future acceleration of polarized protons in the K E K 12GeV synchrotronS). A new spin selection principle proposed by Donnally z' 3) has been adopted, in which transitions from the hyperfine-structure STATE NUMBER
~
F
1
Fz
substates of the 2St/2 state to those of the 2PI/2 state are induced by an rf electric field in a weak magnetic field. This scheme does not require such a long magnetic field of 575 G as used in conventional Lamb-shift type sources. Therefore, the distance between the cesium and argon charge-exchange canals decreases so as to make the overall length of the apparatus as small as 1 m. Fig. 1 shows the hyperfine splittings for the 2 S 1 / 2
0 1
1147 M H z 10 gauss
1.0
-1
2 2Slj 2
<
I
o rn
E T E 2 E~
n
tlJ Zhi
Z 0
11/.71~
T ~b---o
0.5 z
I
n,,"
EL
I
STATE NUMBER
hi >
F
Fz W3
0 2Pv 2
-1 ' ' ' 10 20 30
1=O B
210 ( gauss )
Fig. 1. Hyperfine splitting For the 2S~/z and 2Pz/2 states o f the hydrogen atom.
' ' ' 7'0 40 50 60 B ( DEGREE )
' 00 90
Fig. 2. Probability o f transition o f the substates 1 3 t o 2 P ~ / z a s a function o f an angle (0) between static magnetic field (B) and rf electric field (E). The value o f IBI is chosen as 10 G a n d the frequency o r E is 1147 MHz.
384
Y. MORI et al.
and 2P1/2 states of hydrogen atoms. If the substates 1-3 of 2Sj/2 transit to the substates of 2P1/2 by an rf electric field in a weak magnetic field and if then the remaining metastable hydrogen atoms in the substate 4 are selectively converted to H - ions by charge transfer in argon gas in a strong magnetic field ( ~ 2 0 0 G ) one can obtain an H - beam of 100% polarization. If a weak magnetic field is parallel to the direction of the rf electric field, the transition probability Wi ( i = 1 , 2, 3 or 4) from the ith state of 2S~/2 to 2P~/2 is proportional to
In fig. 3 is shown a schematic set-up of the pulsepolarized H - source of the Lamb-shift type which is under development at KEK. The H - beam was analysed by a 90" bending magnet at the exit of the argon charge-exchange canal and its intensity was measured with a Faraday cup of 32 mm in diameter. A duoplasmatron 4) developed at KEK was used for our polarized source. It was operated by an external trigger pulse. The pulse duration is 50/ts and the repetition rate 20 pulses per second. A high arc current of 20-30 A could be available which resulted in increases in intensity and proton ratio ( > 7 0 % ) in the (1) beam. A 500 eV H + beam was extracted by the accelE 272./[(E~- h~) ~ + (~,~p/2)~], decel system, both having a 20 mm aperture. A potenwhere o9 is the angular velocity of the rf electric field, tial of - 2 0 to - 3 0 kV was applied to the accelerating E its amplitude, El the energy level difference in the electrode. The positions of these electrodes are adjustatransition and Y2p the level width of the 2P1/2 state. ble along the beam axis in steps of 0.05 mm from the When the frequency of the rf electric field is 1147 M Hz outside of the vacuum chamber. and the strength of the magnetic field 10 G, the ratios The cesium charge exchange canal made of copper of W1, W2, W3 and W4 are was connected with the reservoir made of stainless steel through a 0.I mm thick stainless steel pipe. W~: 14/2:W3:W4 = 0.500: 1.000:02.74:0.035. Because of low thermal conductance, the temperature of the canal wall stayed at most around 60°C when the If a magnetic field is applied at an angle 0 with respect to the rf electric field, the transition probability IV,. reservoir was heated up to around 180°C. The cesium vapor jet from the reservoir did not directly escape out (i = 1, 2, 3) varies as a function of 0 as shown in fig. 2, of the canal but condensed on the canal wall. The while the transition probability W4 is kept unchanged consumption of cesium was about 5 gin 40 h. because the total angular momentum of the substate A pair of deflection plates of 13 cm in length and 4 is equal to zero. The transition probabilities of the 10 cm in width was placed at a distance of 1.5 cm from three substates are nearly equal in the neighbourhood the exit of the cesium charge-exchange canal to deflect of 50 °. With this value of 0, the transitions of the three substates 1-3 of 2S~/2 to 2P~/2 take place selectively, away unwanted charged components in the beam. most distinguishably from that of the substate 4, A positive and negative potential of about 40 V was I ~ a p p l i e d to each of the two plates. thereby enhancing the polarization. 3
6
10 1.
duo-plasmatron
6.
cesium charge exchange canal & reservoir
2.
plasma expans%on cup
7.
deflection plate R.F. cavity (1147 MHz) argon charge-exchange canal Ion and trans. Helmholtz coils
3.
accel, electrode
8.
&. S,
~ c e l . electrode focusing magnet
9. I0.
Fig. 3. Schematic set-up o f the pulse-operated polarized H
source of the Lamb-shift type at KEK.
POLARIZED H- SOURCE .
.
.
.
!
.
.
.
.
i
,
,
,
•
I
,
,
i
385
,
>-1.0 I.-
z LI.I I-z
F=I
LLI
>0.5 <[ .J
0
I0
20 RF-POWER ( d B )
30
40
Fig. 4. Relative intensity of the H - ( 2 S ) beam as a function of rf power. Closed circles and the solid lines show the experimental data and calculated values, respectively.
The argon charge-exchange canal of 20 cm in length and 6 cm in inner diameter was placed 34 cm apart from the exit of the cesium charge-exchange canal. Solenoid coils were wound around the canal to produce a homogeneous axial magnetic field of about 200 G. The cesium and argon charge-exchange regions were evacuated by 10" and 6" oil diffusion pumps respectively. The pressure in the cesium charge-exchange region was typically about (1.5-2) x 10- 5 torr and that in the argon charge-exchange region about (8 9)x × 10-5 tort. As described above an rf electric field should make an angle of about 50 ° with the direction of a weak magnetic field to induce effectively the transitions from the substates 1-3 of 2S1/2 to 2P1/2. The rf electric field was taken parallel to the beam axis and was produced by a TMo~o mode rf cavity of 20.0cm inner diameter and 5 cm overall length. The frequency was 1147 MHz corresponding to the energy difference between the relevant substates. The angle 0 of a weak magnetic field with respect to the beam axis was adjustable by superposing longitudinal and transverse magnetic fields with two pairs of Helmholtz coils as shown in fig. 3. The relative intensity of the H (2S) beam is shown in fig. 4 as a function of relative rf power. Closed circles in the figure represent the experimental data measured at an angle (0) of 50 ° and a magnetic field (B) of 10 G. A relative rf power of 0 dB corresponds to 39 pW in the absolute rf power fed into the cavity. The solid lines show the calculated values of the relative transition probability normalized to the experimental data at an rf power of 26 dB. The experimental and calculated values are in good agreement. At an rf
power of 26 dB almost all hydrogen atoms in the states F = 1 of 2S1/z have been quenched to the 2P1/2 state. At an rf power above 40 dB all the metastable hydrogen atoms ( F = I and 0) will be quenched and the H - beam will become unpolarized because the 2 P atoms transit promptly to the ground state. The polarization of the H - beam could, therefore, be evaluated from the following equation: P ~
(I---I~G)/I
(2)
,
where I - and /fig are the H - beam current at an rf power of 26 dB and that at an rf power of larger than 40 dB, respectively. A variation of the relative intensity of the H - (2S) f
i
i
i
~
i
l
RF-POWER
i
20 dB
0.5
Zo.4
~
0.3
w
~0-2 ._J
0.1
e (o)
Fig. 5. A variation o f the relative intensity o f the H-(2S) beam as a function of angle (0) between B and E. Closed circles and the solid lines show the experimental and theoretical values, respectively.
386
Y. MOR| et al.
beam is shown in fig. 5 as a function of the angle between B and E. Closed circles in the figure represent the experimental values measured at a n rf power of 20 dB and the bar indicates the error in measurement. The solid line shows the calculated values. Both are almost in agreement and at a r o u n d 0 = 50 c~, the intensity of the H - (2S) beam has a m i n i m u m . In a preliminary experiment, a 350 nA H - beam of a b o u t 60% polarization has been obtained, To increase the polarization, the argon pressure in the upstream of the a r g o n charge-exchange canal should be decreased. I m p r o v e m e n t of the evacuation system in this region is now in progress. The authors wish to express their appreciation to
Prof. T. Nishikawa for his continued interest and helpful discussions in this work. They are also greatly indebted to Dr. J. A r a f u n e for his valuable discussion a b o u t the theoretical estimation of the spin selection method and to Mr. K. Itoh for his cooperation during the experiments.
References ~) T. Nishikawa, Proc. 9th Intern. Conf. on High energy accelerators, SLAC (1974) p. 23. 2) B. L. Donnally, Bull Am. Phys. Soc. 12 (1967) 509. 3) R.N. Boyd, J.C. Lombardi, A.B. Robbins and D.E. Schechter, Nucl. Instr. and Meth. 81 (1970) 149. "~) M. Kobayashi, T. Nishikawa and A. Takagi, Proc. 2nd Syrup. on Ion sources and.formation of ion beams, Berkeley (1974) p. 11-5.
INSTRUMENTS
AND
A PULSE-OPERATED
METHODS
141
POLARIZED H-
(I977) 383-386;
:(3 N O R T H - H O L L A N D
PUBLISHING
CO.
S O U R C E OF L A M B - S H I F T T Y P E
Y. M O R I L, A. T A K A G I z, M. K O B A Y A S H I z, Y. W A K U T A ~, S. F U K U M O T O z, K. K I K U C H I 2 and M. S O N O D A ~
Department ()["Nuclear Engineering, Faculty o[' Engineering, Kyushu University Hakozaki 6, Higashi-ku, Fukuoka, 812, Japan z National Laboratory/or High Energy Physics, Oho-machi, Tsnkuba-gun, Ibaraki, 300 32, Japan '
Received 21 September 1976 A pulse-operated polarized H - source o f the Lamb-shift type has been developed at the National Laboratory for High Energy Physics in J a p a n ( K E K ) for future acceleration o f polarized protons in the K E K 12 GeV proton synchrotron. A new spin selection principle proposed by Donnally has been adopted, in which only the hyperfine substate o f 2S1/z with zero total angular m o m e n t u m is selected by causing the transitions o f the other three substates o f 281/2 to 2Pt/2 by an rf electric field m a k i n g an angle of a b o u t 50 with the direction o f a weak static magnetic field. In the preliminary experiments, a 350 nA H beam o f about 60% polarization has been obtained.
Since 1975, a pulse-operated polarized H - source of the Lamb-shift type has been developed at the National Laboratory for High Energy Physics in Japan ( K E K ) for future acceleration of polarized protons in the K E K 12GeV synchrotronS). A new spin selection principle proposed by Donnally z' 3) has been adopted, in which transitions from the hyperfine-structure STATE NUMBER
~
F
1
Fz
substates of the 2St/2 state to those of the 2PI/2 state are induced by an rf electric field in a weak magnetic field. This scheme does not require such a long magnetic field of 575 G as used in conventional Lamb-shift type sources. Therefore, the distance between the cesium and argon charge-exchange canals decreases so as to make the overall length of the apparatus as small as 1 m. Fig. 1 shows the hyperfine splittings for the 2 S 1 / 2
0 1
1147 M H z 10 gauss
1.0
-1
2 2Slj 2
<
I
o rn
E T E 2 E~
n
tlJ Zhi
Z 0
11/.71~
T ~b---o
0.5 z
I
n,,"
EL
I
STATE NUMBER
hi >
F
Fz W3
0 2Pv 2
-1 ' ' ' 10 20 30
1=O B
210 ( gauss )
Fig. 1. Hyperfine splitting For the 2S~/z and 2Pz/2 states o f the hydrogen atom.
' ' ' 7'0 40 50 60 B ( DEGREE )
' 00 90
Fig. 2. Probability o f transition o f the substates 1 3 t o 2 P ~ / z a s a function o f an angle (0) between static magnetic field (B) and rf electric field (E). The value o f IBI is chosen as 10 G a n d the frequency o r E is 1147 MHz.
384
Y. MORI et al.
and 2P1/2 states of hydrogen atoms. If the substates 1-3 of 2Sj/2 transit to the substates of 2P1/2 by an rf electric field in a weak magnetic field and if then the remaining metastable hydrogen atoms in the substate 4 are selectively converted to H - ions by charge transfer in argon gas in a strong magnetic field ( ~ 2 0 0 G ) one can obtain an H - beam of 100% polarization. If a weak magnetic field is parallel to the direction of the rf electric field, the transition probability Wi ( i = 1 , 2, 3 or 4) from the ith state of 2S~/2 to 2P~/2 is proportional to
In fig. 3 is shown a schematic set-up of the pulsepolarized H - source of the Lamb-shift type which is under development at KEK. The H - beam was analysed by a 90" bending magnet at the exit of the argon charge-exchange canal and its intensity was measured with a Faraday cup of 32 mm in diameter. A duoplasmatron 4) developed at KEK was used for our polarized source. It was operated by an external trigger pulse. The pulse duration is 50/ts and the repetition rate 20 pulses per second. A high arc current of 20-30 A could be available which resulted in increases in intensity and proton ratio ( > 7 0 % ) in the (1) beam. A 500 eV H + beam was extracted by the accelE 272./[(E~- h~) ~ + (~,~p/2)~], decel system, both having a 20 mm aperture. A potenwhere o9 is the angular velocity of the rf electric field, tial of - 2 0 to - 3 0 kV was applied to the accelerating E its amplitude, El the energy level difference in the electrode. The positions of these electrodes are adjustatransition and Y2p the level width of the 2P1/2 state. ble along the beam axis in steps of 0.05 mm from the When the frequency of the rf electric field is 1147 M Hz outside of the vacuum chamber. and the strength of the magnetic field 10 G, the ratios The cesium charge exchange canal made of copper of W1, W2, W3 and W4 are was connected with the reservoir made of stainless steel through a 0.I mm thick stainless steel pipe. W~: 14/2:W3:W4 = 0.500: 1.000:02.74:0.035. Because of low thermal conductance, the temperature of the canal wall stayed at most around 60°C when the If a magnetic field is applied at an angle 0 with respect to the rf electric field, the transition probability IV,. reservoir was heated up to around 180°C. The cesium vapor jet from the reservoir did not directly escape out (i = 1, 2, 3) varies as a function of 0 as shown in fig. 2, of the canal but condensed on the canal wall. The while the transition probability W4 is kept unchanged consumption of cesium was about 5 gin 40 h. because the total angular momentum of the substate A pair of deflection plates of 13 cm in length and 4 is equal to zero. The transition probabilities of the 10 cm in width was placed at a distance of 1.5 cm from three substates are nearly equal in the neighbourhood the exit of the cesium charge-exchange canal to deflect of 50 °. With this value of 0, the transitions of the three substates 1-3 of 2S~/2 to 2P~/2 take place selectively, away unwanted charged components in the beam. most distinguishably from that of the substate 4, A positive and negative potential of about 40 V was I ~ a p p l i e d to each of the two plates. thereby enhancing the polarization. 3
6
10 1.
duo-plasmatron
6.
cesium charge exchange canal & reservoir
2.
plasma expans%on cup
7.
deflection plate R.F. cavity (1147 MHz) argon charge-exchange canal Ion and trans. Helmholtz coils
3.
accel, electrode
8.
&. S,
~ c e l . electrode focusing magnet
9. I0.
Fig. 3. Schematic set-up o f the pulse-operated polarized H
source of the Lamb-shift type at KEK.
POLARIZED H- SOURCE .
.
.
.
!
.
.
.
.
i
,
,
,
•
I
,
,
i
385
,
>-1.0 I.-
z LI.I I-z
F=I
LLI
>0.5 <[ .J
0
I0
20 RF-POWER ( d B )
30
40
Fig. 4. Relative intensity of the H - ( 2 S ) beam as a function of rf power. Closed circles and the solid lines show the experimental data and calculated values, respectively.
The argon charge-exchange canal of 20 cm in length and 6 cm in inner diameter was placed 34 cm apart from the exit of the cesium charge-exchange canal. Solenoid coils were wound around the canal to produce a homogeneous axial magnetic field of about 200 G. The cesium and argon charge-exchange regions were evacuated by 10" and 6" oil diffusion pumps respectively. The pressure in the cesium charge-exchange region was typically about (1.5-2) x 10- 5 torr and that in the argon charge-exchange region about (8 9)x × 10-5 tort. As described above an rf electric field should make an angle of about 50 ° with the direction of a weak magnetic field to induce effectively the transitions from the substates 1-3 of 2S1/2 to 2P1/2. The rf electric field was taken parallel to the beam axis and was produced by a TMo~o mode rf cavity of 20.0cm inner diameter and 5 cm overall length. The frequency was 1147 MHz corresponding to the energy difference between the relevant substates. The angle 0 of a weak magnetic field with respect to the beam axis was adjustable by superposing longitudinal and transverse magnetic fields with two pairs of Helmholtz coils as shown in fig. 3. The relative intensity of the H (2S) beam is shown in fig. 4 as a function of relative rf power. Closed circles in the figure represent the experimental data measured at an angle (0) of 50 ° and a magnetic field (B) of 10 G. A relative rf power of 0 dB corresponds to 39 pW in the absolute rf power fed into the cavity. The solid lines show the calculated values of the relative transition probability normalized to the experimental data at an rf power of 26 dB. The experimental and calculated values are in good agreement. At an rf
power of 26 dB almost all hydrogen atoms in the states F = 1 of 2S1/z have been quenched to the 2P1/2 state. At an rf power above 40 dB all the metastable hydrogen atoms ( F = I and 0) will be quenched and the H - beam will become unpolarized because the 2 P atoms transit promptly to the ground state. The polarization of the H - beam could, therefore, be evaluated from the following equation: P ~
(I---I~G)/I
(2)
,
where I - and /fig are the H - beam current at an rf power of 26 dB and that at an rf power of larger than 40 dB, respectively. A variation of the relative intensity of the H - (2S) f
i
i
i
~
i
l
RF-POWER
i
20 dB
0.5
Zo.4
~
0.3
w
~0-2 ._J
0.1
e (o)
Fig. 5. A variation o f the relative intensity o f the H-(2S) beam as a function of angle (0) between B and E. Closed circles and the solid lines show the experimental and theoretical values, respectively.
386
Y. MOR| et al.
beam is shown in fig. 5 as a function of the angle between B and E. Closed circles in the figure represent the experimental values measured at a n rf power of 20 dB and the bar indicates the error in measurement. The solid line shows the calculated values. Both are almost in agreement and at a r o u n d 0 = 50 c~, the intensity of the H - (2S) beam has a m i n i m u m . In a preliminary experiment, a 350 nA H - beam of a b o u t 60% polarization has been obtained, To increase the polarization, the argon pressure in the upstream of the a r g o n charge-exchange canal should be decreased. I m p r o v e m e n t of the evacuation system in this region is now in progress. The authors wish to express their appreciation to
Prof. T. Nishikawa for his continued interest and helpful discussions in this work. They are also greatly indebted to Dr. J. A r a f u n e for his valuable discussion a b o u t the theoretical estimation of the spin selection method and to Mr. K. Itoh for his cooperation during the experiments.
References ~) T. Nishikawa, Proc. 9th Intern. Conf. on High energy accelerators, SLAC (1974) p. 23. 2) B. L. Donnally, Bull Am. Phys. Soc. 12 (1967) 509. 3) R.N. Boyd, J.C. Lombardi, A.B. Robbins and D.E. Schechter, Nucl. Instr. and Meth. 81 (1970) 149. "~) M. Kobayashi, T. Nishikawa and A. Takagi, Proc. 2nd Syrup. on Ion sources and.formation of ion beams, Berkeley (1974) p. 11-5.