The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Design of the Kicker Systems for the JHF 50-Ge V Main Ring
Yoshihisa SHIRAKABE, Yoshihiro ISHI*, Shinji MACHIDA, Yoshiharu MORI, Masafumi MUTO, Shinji SHIBUYA**KEK(Tanashi), High Energy Accelerator Research Organization, 3-2-1, Midori-cho, Tanashi, Tokyo, 188 JAPAN*Mitsubishi Electric Co., 1-1-2, Wadasaki-cho, Hyogo-ku, Kobe, 652 JAPAN**Sumitomo Heavy Industry Co., 2-1-1, Yato-cho, Tanashi, Tokyo, 188 JAPANAbstract
The 50-GeV main-ring synchrotron in the JHF (JapanHadron Facility) uses three sets of kicker systems. They
include: ·injection kickers, ·abort kickers at the injectionenergy, and ·fast-extraction kickers for the neutrino
oscillation experiment line. All the kickers are of a fullaperture type and are energized by Blumlein PFN lines andthyratron switches. The designed parameters for the kickers
to fulfill required strength and speed are discussed.

1. Introduction
The main ring in the JHF (Japan Hadron Facility)
project[1,2] accelerates 3-GeV proton beams from thebooster to 50-GeV. The proton beams are injected into, andextracted from, the main ring by kicker magnets. Since themain ring has two fast-extraction lines, the one being an
abort line at the injection beam energy of 3-GeV and theother being a 50-GeV fast-extraction line to provide beams
to the neutrino-oscillation experiments, there are three setsof kicker systems in total.
The parameters of the· kickers are determined in order tomeet the required strength and time structure, the latterincludes a rise-time, a flat-top length and a fall-time. Thosenumbers are derived from the optical design of theaccelerator systems. In the next section, an overview todefine the parameters of three kicker systems are given. In
section 3, more detailed discussions on each kicker system
are described.

has sixteen small bunch-to-bunch intervals of 120nsec andone large interval of -400nsec. These intervals define therequired time structures of the kicker magnets.
There are three kicker systems in the main ring. Eachsystem has a different function, and, therefore, must be
designed with a respective optimized set of parameters.
These systems include:·Injection Kickers at 3-GeV,·Abort Kickers at 3-GeV, and·Fast-Extraction Kickers at 50-GeV.
The designed parameters for the kicker systems aresummarized in Table 1. In this table, the dimensions and thetime structures of the kickers are mainly defined by the
optical design of the ring. The other parameters are selected
to fulfill the required strength and speed within existing
technologies. In the following section, each kicker system
is described in further detail.

3. Detailed Parameters of the Kicker Systems
3-1 Injection Kicker Systems at 3-GeV

The proton beam from the 3-GeV booster is injectedvertically into the main ring using the short straightsections around the QFX magnet in one of the arc sections.
In order to inject four successive bunches from the booster,

2. Overview of the Main-Ring Kicker Systems
The requirements to the time structures of the kickers areschematically shown in Fig. 1. The booster accelerates fourbunches in each acceleration cycle. These four bunches areextracted from the booster and injected into the main ring.
After four injection cycles, numbered 1 to 4 in the figure,the main ring is filled with sixteen bunches and starts
acceleration. Since the harmonic number of the main ring isseventeen, one bucket is left open. This empty bucket gives
a longer bunch-to-bunch interval, and thus allows the kicker
magnets longer periods to establish or to extinguish thenecessary magnetic fields.
At injection of the main ring, the RF frequency is 3.43
MHz. One RF cycle is 292nsec, which includes one bunchand one bunch-to-bunch interval, as is shown in Fig.l.
Assuming that about 40% of each cycle is left unoccupiedby the bunch, the time interval allowed for the kickers
becomes around 120nsec. At extraction, the RF frequency isslightly increased to 3.51 MHz and the bunch-to-bunchinterval stays almost the same. Thanks to the abovementioned empty bucket, however, one full RF cycle can be
added to this 120nsec spacing. The main ring, accordingly,-389-

Main-Ring (3 to 50 GeV)

(1) Injection at 3 GeV
RF: 3.43 MHz (at 3 GeV)
Rise-time: 120 nsec
Flat-top: 1050 nsec
Fall-time: 400 nsec

I(2) Abort at 3 GeV
RF: 3.43 MHz (at 3 GeV)
Rise-time: 120 nsec
Flat-top: 4560 nsec
Fall-time: ignore(3) Fast-Extraction at 50 GeV
RF : 3.51 MHz (at 50 GeV)
Rise-time: 400 nsec
Flat-top: 4450 nsec
Fall-time: ignore

Fig. 1 Overview of the Main-Ring Kickers.

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

the injection kicker magnets keep a field flat-top for-1050nsec. To pack the next four bunches right after thefirst four, the kicker field rises within the short bunch-tobunch interval of 120nsec. At the end of the fourth injection
cycle, the long interval with the empty bucket arrives. The
kicker fall-time should therefore be shorter than 400risec.
In order to accept a vertically injected beam, the kickers
cover an area of 0.13m in horizontal and 0.12m in vertical.
Since the magnetic flux lies horizontally, the horizontal
0.13m span becomes the height of the kickers and thevertical 0:12m span the width. The effective length and thekick angle of each kicker unit are 0.6m and 3.0mrad,respectively. The injection system comprises four kicker
magnets, resulting in a 2.4m length and a 12.0mrad kick intotal.
The switching element is assumed to use a deuteriumfilled thyratron CX2171 from EEV Co. The maximum
voltage and current of the tube are 90 kV and 10 kA,
respectively. The pulse-forming network will comprises coaxial cables in a Blumlein line configuration. In order toavoid bulky low impedance cables, the co-axial cable isdesigned to have a moderate 20 Q impedance and a

Table 1. Designed Parameters for the Main-ring Kicker Systems.
Injection

Abort

Fast extraction

012tical r~uirements
Kinetic energy of beams
Momentum
Magnetic rigidity
Effective length
Kick angle
Number of kicker units
Total effective lengthTotal kick angle
Kick direction *Aperture height *Aperture width *

33.82
12.76
0.6
3.04
2.4
12.0
Vertical
0.13
0.12

3
3.82
12.76
1.2
6.0
3
3.6
18.0
Horizontal
0.10
0.13

50
50.9
169.9
1.5
0.6
11
16.5
6.6
Horizontal
0.11
0.12

[GeV]
[GeV]
[T·m]
[m]
[mrad]

Time structure
Rise-time (1% to 99%)
Flat-top (100% ±1%)
Fall-time (99% to 1%)

120
1050
400

4004560
ignore4004450
ignore[nsec][nsec][nsec]

Thyratron
Type
Model#Maximum voltage
Maximum current

Deuterium filledEEV/CX2171
9010

Deuterium filled
EEV/CX2171
9010

Deuterium filled
EEV/CX2171
9010

[kV]
[kA]

PFN
Type
Line configuration
Cable impedance
Parallel number of cables
Line impedance
Maximum voltage

Co-axial cable
Blumlein
20.0
2
10.0
100

Co-axial cable
Blumlein
20.0
1
20.0
100

Co-axial cable
Blumlein
20.0
1
20.0
100

[kV]

Full aperture
Transmission line
638
6.60
696
10.0
66.0
0.0086
69.6

Full aperture
Lumped
638
5.08
1960

Full aperture
Lumped
680
5.95
2056

[GauB]
[kA]
[nH]

50.8

59.5

49.0
22651.4237

Kicker magnets
Type (mechanical)
Type (electrical)
Field strength
Current
Total inductance
Impedance
Operational voltage
Transmission velocity
Transmission time
Time constant
99% rise/fall time[m][mrad]
[m]
[m]

[Q]
[Q]

[Q]

[kV]
[m/nsec][nsec][nsec][nsec]*When the 'Kick direction' is 'Vertical', the 'Aperture height/width' means the horizontal/vertical span of the kicker aperture.

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The II th Symposium on Accelerator Science and Technology, Harima Science Garden City, I997

maximum 100 kV insulation voltage. These two numbers,
impedance and voltage, define the inner and outer conductor
diameters as 20mm and 33mm, respectively, assuming thata polyethylene-insulated cable is used.
The kicker magnets are of a full aperture, transmissionline type. The current of the kickers to generate a necessary
field strength of 638 GauB is 6.60 kA. In order to keep theoperational voltage within a manageable range, the line
impedance is selected to be 10 Q. The PFN line comprises
two 20 Q cables in parallel. The operational voltage resultsin 66.0 kV.
The transmission velocity of the pulse inside the kickers
is 0.86 cm/nsec. An effective length of 0.60m of one kicker
unit requires 69.6nsec of transmission time for a pulse topropagate from the entrance to the exit of the kicker. The
transmission time is short enough, even when the thyratronrise-time is added, compared to the bunch-to-bunch intervalof 120 nsec.
3-2 Abort Kicker Systems at 3-GeV
The main ring provides a beam-abort system at theinjection energy. When an abort event occurs while theproton beam is being injected and circulated in the main ringat 3-GeV, the abort system fires at the large bunch-to-bunchinterval. The rise-time should be within -400nsec. In orderto eject all of the circulating bunches during one tum, theabort system has a 4560nsec flat-top. Once the main ring isevacuated, there is a sufficiently long time to extinguish thekicker field until the next injection cycle starts. The falltime requirement can therefore be ignored.
The beam simulation for the abort channel shows thatthe necessary aperture for the abort kickers is 0.1 Om in thevertical height and 0.13m in the horizontal width. The abort
kickers are at present designed to have the same kick angle
per unit length, 5mrad/m, as that of the injection kickers.
Each abort kicker has a kick angle of 6mrad and an effective
length of 1.2m, which result in almost twice the aperturevolume as that of the injection kickers. The long rise-timeof the abort system allows such a large aperture volume.
The number of the abort kicker magnets is three. Tha
abort channel accordingly has in total an effective length of
3.6m and a kick angle of 18mrad. The larger kicker volume
allows the smaller number of the kicker units to produce thesame total kick, resulting in the reduced sets of thyratrons,
PFN s etc. That is beneficial for saving the total
construction and operation costs.
The same components are used for the switching
thyratrons and for the PFN systems as in the injection
systems. Actually these components are designed to becommon among three kicker systems --- injection, abort andfast-extraction --- in the main ring. The basic idea is tominimize the variety of the employed components, and,thus, to avoid unimagined device malfunctioning as much as
possible.
Each kicker unit is a lumped-type magnet with a fullaperture. Since the kick strength per unit length is the sameas that of the injection kickers, the field strength is also thesame, 638 GauB. The smaller aperture height, however,requires a smaller current of 5.08 kA. When a lumped
magnet is connected to a PFN with a Blumlein
configuration, the effective voltage is doubled by reflection.

In the present case, the PFN with a 20 Q line impedance
results in an operational voltage of 5.08 kA x 20Q I 2 =50.8 kV. In order to avoid sparks at the magnet units, theabort kickers are charged to high voltage only when an abort
request occurs.
The lumped inductance, L, of one kicker unit is 1960
nH. With a Blumlein PFN with a line impedance Zo = 20n, the lumped magnetic field rises and falls exponentiallywith a time constant t = L!Zo/2 = 49.0nsec. With this time·constant, the field rises (falls) for 99% of its final (initial)
value in 4.6t = 226nsec.
3-3 Fast-Extraction Kicker Systems at 50-GeV
The fast-extraction line with a beam energy of 50-GeV
is equipped at the long straight section of the main ring.
The required time scheme for the fast-extraction kicker
system is almost the same as that for the abort systems.
The rise-time and the flat-top should be -400nsec and-4450nsec, respectively. The fall-time can be ignored.
In the present design, eleven kicker units are to bearranged in line. In order to keep a full aperture for both theinjected 3-GeV beam and the kicked 50-GeV off-axis beam,
the kickers must have a large aperture with a height ofO.llm and a width of 0.12m. Each unit has an effective
length of 1.5m and a kick angle of 0.6mrad. The fastextraction system occupies 16.5m in total effective lengthand has 6.6mrad in total kick.
The types of thyrartons, PFNs and kicker units are sameas that in the abort kicker systems described in the previous
sub-section. The kicker current and voltage necessary toproduce a field strength of 680 GauB are 5.95 kA and 59.5
kV, respectively. The large kicker volume of O.llm x
0.12m x 1.5m results in a large lumped inductance of 2056
nH. The time constant of the magnet, however, still stays
in a tolerable range of 1: = 51.4nsec. The 99% rise/fall timeis 4.61: = 237nsec. The sum of the thyratron rise-time andthe kicker rise-time can therefore be sufficiently shorter thanthe large bunch-to-bunch interval of 400nsec.

4. Conclusion
The parameters for the kicker systems in the JHF 50Ge V main ring is discussed. It is found that the required
speed and strength to the kicker systems can be realized
within existing kicker technologies. More detailed studies
on the structures of the kicker magnet units and the PFNsystems, along with the developments of preliminary testbenches, will be continued further.

Acknowledgment
The authors are thankful to professor T. Kawakubo in
KEK for his kind instructions on kicker technologies to us.

References[1] Y. Yamazaki, "The Japan Hadron Facility Accelerator",
KEK Preprint 97-98 (1997).
[2] JHP Beam Optics and Dynamics Working Group, "A
Preliminary Design of JHP Synchrotrons" (in Japanese),
JHP-30 (1996).

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