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A hybrid type undulator for far infrared FELs at the FELI
m
Nuclear Instruments and Methods in Physics Research A 375 ( 1996) ABS 80-ABS
82
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SectionA
d __ __
@ ELSEVIER
A hybrid type undulator for far infrared FELs at the FELI A. Zako*, Y. Miyauchi,
A. Koga, T. Tomimasu
Free Electron Laser Research Institute, Inc. (FELI). 4547-&f, Tsuda, Hirakata, Osaka 573-01, Japan
Abstract The development of a new type undulator is in progress. This undulator will cover the far infrared (20-60 pm) region, It is a unique hybrid type one with electro- and permanent (Sm-Co)-magnets. This report describes our undulator plan, its structure and the preliminary experiment on the trial model of the undulator.
1. Introduction
2. Fundamental
The Free Electron Laser Research Institute (FELI) has achieved first lasings at the infrared (20-l km) wavelength range with two halbach type undulators whose parameters are A, = 34 mm, N = 58, K = 0.5-1.5; and A, = 38 mm, N = 78, K = 0.5 1.4, in Oct. 1994 and in Feb. 1995 [ 1,2], and is now trying to lase the visible and ultraviolet (1.20.3 p,m) region with the third halbach type one (A, = 40mm, N = 67, K = 0.5-2.0) [3]. Recently, the FELI extended FEL research fields to the far-infrared range so it starts to develop the next undulator which covers the far infrared range of 20-60 pm [4]. In this report, we present a plan of our new undulator and a preliminary experiment on the trial model of the fourth undulator.
The main specifications of the undulator 4 are as follows, 1) to cover wavelengths of 20-60 km, 2) to tune the wavelength easily, and 3) to use the electron beam again after passing through the first undulator. Fig. 1 shows relations between the FEL wavelength and K value and Fig. 2 shows relations between small signal gain and K value. The small signal gain curves were calculated from the FELIX Group’s formula [5]. The main parameters of the undulator 4 are listed in Table 1. We chose SO-100 mm as the undulator period because the maximum gain is observed at the focused wavelength. Fig. 3 shows the conceptual structure of our undulator. This undulator is a unique hybrid type one whose magnetic field is generated by built-in permanent- and electro-mag-
design
0.1
0.08
s 7 M
3 T
0.06
?
s
2
5
0
0.04 ._,.... _ _
0.02
1
wavelength@III] ”
Fig. 1. K value vs. wavelength periods. * Corresponding
author.
0168-9002/96/$15.00 Copyright SSDI 0168.9002(95)01262-l
curves
with different
I
undulator
2
3
4
5
K value Fig. 2. Small signal undulator periods.
0 1996 Elsevier Science B.V. All rights reserved
gain
vs. K value
curves
with
different
A. Zako et al. I Nucl. Instr. and Meth. in Phys. Res. A 375 (1996) ABS 80-ABS
82
ABS 81
Dr iving
Magr,e
Fig. 3. Conceptual
Table 1 The undulator
and electron
Undulator periods Number of
periods Beam energy Peak current Beam emittance Energy divergence
A” [mm]
60
80
N
48
36
E [MeV]
28
I [Al E [n mm mrad]
50”
100
120
29
24
30”
AEIE [%]
a Cited as conservative Table 2 The parameter
beam parameters
1”
estimation.
structure
of our undulator.
nets that were first proposed by the Novosibirsk Group [6]. There are two reasons for the adoption of this type. First, the case of the halbach type undulator; it must change the undulator gap distance carefully against the attraction force of the permanent magnets to control the magnetic fields. At the manufacturing stage, however, this process costs the long tuning time, and the large size of the equipment increases the cost. Second, in the case of the simple electromagnet type undulator, it is difficult to induce sufficient magnetic field needed for the far-infrared FEL oscillations. The proposed model of the undulator has enough space for four magnetomotive coils installed
of the trial undulator
Undulator period A, Thickness of the permanent magnet Thickness of the pole Number of period N Permanent magnet material Gap distance g Coil ampere turn
magnetomotive force[kA .Tum/coil]
IOOmm -4
Gap length
[mm1 30 34 40 50
0
2.5
x + .
field
The gradient from the formula [kG/A]
0.107 0.093 0.078 0.053
0.134 0.118 0.101 0.080
-1
0
1
2
3
4
I,
I
, 0
3cmm 34mm 4Omm 5Omm
0
x
Ox
cl
ox
c 3 >
2.5 ,
+
2
~oo*oooooo*oooo~~ WXXXXXXXXXXXXXX++ 0
0
<
,t
>
-:
4
1.5 1
The gradient from Fig. 4 [kG/A]
-2
3
2 E m
Table 3 The relation between gap length and electromagnetic
-3
I ’ I I I, 1’11 undulator gap distancc(mm)
3.5
18mm 32 mm 3 Sm-Co [R26H; Shin-Etsu Co., Ltd.] 10-150 mm 4.8 kA turn/one coil
. -++++++++++++++++ . . . . . . . . . .
1.5
_!! y2
1 0.5
0.5 0
0 -30
-20
-10
0
10
20
30
1 [Al Fig. 4. Relations force of coils.
between the magnetic
field and magnetomotive
EXTENDED
SYNOPSES
ABS 82
A. Zako et al. I Nucl. Instr. and Meth. in Phys. Res. A 375 (I9961 ABS 80-ABS
outside of the undulator, independently periods, as shown in Fig. 3.
3. Preliminary
with the undulator
experiment
We had no data of this type of undulator so we constructed and tested a trial undulator for three periods as shown in Table 2. Fig. 4 shows relations between the magnetic field and magnetomotive force of coils. The peak magnetic field is measured at the center of the undulator with different undulator gap lengths. The magnetic field is formed with the permanent- and electro-magnets force. The original magnetic field caused by the permanent magnets and the increment of the magnetic field caused by the electromagnets. The magnetic field saturation begins at the maximum value of electromagnetic force because the magnetic field saturates near the pole inside. The negative magnetic force of the electromagnets can not decrease the magnetic fields. The magnetic field shortens as neighbor poles pass through the permanent magnets. Table 3 is a comparison between the gradient of the magnetic force which was obtained from Fig. 4 and a simple estimation of the gradient of the magnetic field by the bending magnet. The peak magnetic field B of the bending magnets is given
82
by B = p,,Nlld
where N is the number of the coil turns. I is the current of the coil and d is the gap length.
4. Summary The development of a new type undulator is in progress. This undulator will cover the far-infrared (20-60 Frn) region. It is a unique hybrid type one as the magnetic field generates with electro- and permanent (Sm-Co)-magnets. The trial model of the undulator (AU = 100 mm) could achieve a K value of 0.88 to 3.1.
References [II T. Tomimasu et al.. Proc. PAC ‘95. Dallas, May l-5. 1995, FAA30. PI E. Oshita et al., ibid., TAQ35. [31 T. Tomimasu et al.. these Proceedings (17th Int. Free Electron Laser Conf., New York, NY. USA, 1995) Nucl. Instr. and Meth. A 375 ( 1996) 626. [41 Y. Miyauchi et al., to be published in Proc. 2nd Asian Symp. on FEL. I51 P.W. van Amersfoort et al., The FELIX project status report, April 1988. I61 P.D. Vobly, private communication.
Nuclear Instruments and Methods in Physics Research A 375 ( 1996) ABS 80-ABS
82
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SectionA
d __ __
@ ELSEVIER
A hybrid type undulator for far infrared FELs at the FELI A. Zako*, Y. Miyauchi,
A. Koga, T. Tomimasu
Free Electron Laser Research Institute, Inc. (FELI). 4547-&f, Tsuda, Hirakata, Osaka 573-01, Japan
Abstract The development of a new type undulator is in progress. This undulator will cover the far infrared (20-60 pm) region, It is a unique hybrid type one with electro- and permanent (Sm-Co)-magnets. This report describes our undulator plan, its structure and the preliminary experiment on the trial model of the undulator.
1. Introduction
2. Fundamental
The Free Electron Laser Research Institute (FELI) has achieved first lasings at the infrared (20-l km) wavelength range with two halbach type undulators whose parameters are A, = 34 mm, N = 58, K = 0.5-1.5; and A, = 38 mm, N = 78, K = 0.5 1.4, in Oct. 1994 and in Feb. 1995 [ 1,2], and is now trying to lase the visible and ultraviolet (1.20.3 p,m) region with the third halbach type one (A, = 40mm, N = 67, K = 0.5-2.0) [3]. Recently, the FELI extended FEL research fields to the far-infrared range so it starts to develop the next undulator which covers the far infrared range of 20-60 pm [4]. In this report, we present a plan of our new undulator and a preliminary experiment on the trial model of the fourth undulator.
The main specifications of the undulator 4 are as follows, 1) to cover wavelengths of 20-60 km, 2) to tune the wavelength easily, and 3) to use the electron beam again after passing through the first undulator. Fig. 1 shows relations between the FEL wavelength and K value and Fig. 2 shows relations between small signal gain and K value. The small signal gain curves were calculated from the FELIX Group’s formula [5]. The main parameters of the undulator 4 are listed in Table 1. We chose SO-100 mm as the undulator period because the maximum gain is observed at the focused wavelength. Fig. 3 shows the conceptual structure of our undulator. This undulator is a unique hybrid type one whose magnetic field is generated by built-in permanent- and electro-mag-
design
0.1
0.08
s 7 M
3 T
0.06
?
s
2
5
0
0.04 ._,.... _ _
0.02
1
wavelength@III] ”
Fig. 1. K value vs. wavelength periods. * Corresponding
author.
0168-9002/96/$15.00 Copyright SSDI 0168.9002(95)01262-l
curves
with different
I
undulator
2
3
4
5
K value Fig. 2. Small signal undulator periods.
0 1996 Elsevier Science B.V. All rights reserved
gain
vs. K value
curves
with
different
A. Zako et al. I Nucl. Instr. and Meth. in Phys. Res. A 375 (1996) ABS 80-ABS
82
ABS 81
Dr iving
Magr,e
Fig. 3. Conceptual
Table 1 The undulator
and electron
Undulator periods Number of
periods Beam energy Peak current Beam emittance Energy divergence
A” [mm]
60
80
N
48
36
E [MeV]
28
I [Al E [n mm mrad]
50”
100
120
29
24
30”
AEIE [%]
a Cited as conservative Table 2 The parameter
beam parameters
1”
estimation.
structure
of our undulator.
nets that were first proposed by the Novosibirsk Group [6]. There are two reasons for the adoption of this type. First, the case of the halbach type undulator; it must change the undulator gap distance carefully against the attraction force of the permanent magnets to control the magnetic fields. At the manufacturing stage, however, this process costs the long tuning time, and the large size of the equipment increases the cost. Second, in the case of the simple electromagnet type undulator, it is difficult to induce sufficient magnetic field needed for the far-infrared FEL oscillations. The proposed model of the undulator has enough space for four magnetomotive coils installed
of the trial undulator
Undulator period A, Thickness of the permanent magnet Thickness of the pole Number of period N Permanent magnet material Gap distance g Coil ampere turn
magnetomotive force[kA .Tum/coil]
IOOmm -4
Gap length
[mm1 30 34 40 50
0
2.5
x + .
field
The gradient from the formula [kG/A]
0.107 0.093 0.078 0.053
0.134 0.118 0.101 0.080
-1
0
1
2
3
4
I,
I
, 0
3cmm 34mm 4Omm 5Omm
0
x
Ox
cl
ox
c 3 >
2.5 ,
+
2
~oo*oooooo*oooo~~ WXXXXXXXXXXXXXX++ 0
0
<
,t
>
-:
4
1.5 1
The gradient from Fig. 4 [kG/A]
-2
3
2 E m
Table 3 The relation between gap length and electromagnetic
-3
I ’ I I I, 1’11 undulator gap distancc(mm)
3.5
18mm 32 mm 3 Sm-Co [R26H; Shin-Etsu Co., Ltd.] 10-150 mm 4.8 kA turn/one coil
. -++++++++++++++++ . . . . . . . . . .
1.5
_!! y2
1 0.5
0.5 0
0 -30
-20
-10
0
10
20
30
1 [Al Fig. 4. Relations force of coils.
between the magnetic
field and magnetomotive
EXTENDED
SYNOPSES
ABS 82
A. Zako et al. I Nucl. Instr. and Meth. in Phys. Res. A 375 (I9961 ABS 80-ABS
outside of the undulator, independently periods, as shown in Fig. 3.
3. Preliminary
with the undulator
experiment
We had no data of this type of undulator so we constructed and tested a trial undulator for three periods as shown in Table 2. Fig. 4 shows relations between the magnetic field and magnetomotive force of coils. The peak magnetic field is measured at the center of the undulator with different undulator gap lengths. The magnetic field is formed with the permanent- and electro-magnets force. The original magnetic field caused by the permanent magnets and the increment of the magnetic field caused by the electromagnets. The magnetic field saturation begins at the maximum value of electromagnetic force because the magnetic field saturates near the pole inside. The negative magnetic force of the electromagnets can not decrease the magnetic fields. The magnetic field shortens as neighbor poles pass through the permanent magnets. Table 3 is a comparison between the gradient of the magnetic force which was obtained from Fig. 4 and a simple estimation of the gradient of the magnetic field by the bending magnet. The peak magnetic field B of the bending magnets is given
82
by B = p,,Nlld
where N is the number of the coil turns. I is the current of the coil and d is the gap length.
4. Summary The development of a new type undulator is in progress. This undulator will cover the far-infrared (20-60 Frn) region. It is a unique hybrid type one as the magnetic field generates with electro- and permanent (Sm-Co)-magnets. The trial model of the undulator (AU = 100 mm) could achieve a K value of 0.88 to 3.1.
References [II T. Tomimasu et al.. Proc. PAC ‘95. Dallas, May l-5. 1995, FAA30. PI E. Oshita et al., ibid., TAQ35. [31 T. Tomimasu et al.. these Proceedings (17th Int. Free Electron Laser Conf., New York, NY. USA, 1995) Nucl. Instr. and Meth. A 375 ( 1996) 626. [41 Y. Miyauchi et al., to be published in Proc. 2nd Asian Symp. on FEL. I51 P.W. van Amersfoort et al., The FELIX project status report, April 1988. I61 P.D. Vobly, private communication.