ACCELERATION TEST OF 2MeV PROTON PROTOTYPE NEW IHQ LINAC

T.Hattori.~ Okamur~~Muto,

H. Suzuki",~Fukushima··

and N.Ueda···Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
Ohokayama, Meguro-ku, Tokyo, 152, Japan.

* National Institute of Radiological Sciences, Anagawa, Chiba-shi, Chiba-ken, 260, Japan.
** Sumi tomo

Heavy Industry, Ltd. Soukai -cho Ni ihama-shi. Ehime-ken, 792, Japan.

*** Institute for Nuclear Study, University of Tokyo,Midori-cho, Tanashi-shi, Tokyo, 188, Japan.

Abstract
Characteristics of an interdigital-H typelinac structure with focusing finger electrodes (IHQ)
have been studied. A prototype IHQ linac was designed
to accelerate proton from 0.8 to 2.0MeV with an operation frequency of 101. 5MHz. The geometrical dimensionof the linac tank is 54cm in inner diameter and 92cm
in length. The linac has been constructed and has successfully accelerated beams.,~,Table
Parameters of Prototype IHQ LinacIntroduction
In this structure design, the RF fields isfor focusing of ions as well as for acceleratiofl.
The resent success of RFQ linacs which use the RF electric field not only for acceleration but also for focusing has solved most problems associated with the acceleration of intense low velocity ions.
On the other hand, idea of spatially uniform
acceleration and focusing scheme of Kapchinsky and
Teplyakov• who have proposed the basic idea of RFQ
linac is known to be applicable only to the low energy
region of 2MeV or less, because of its low effective
shunt impedance. Boussard tried an RF acceleration andfocusing by attaching circular fingers to the face ofdrift tubes 9 • A similar configuration was proposed byR.W.M ller for his split coaxial structure 10 •We have begun to study an interdigital-H type linac
structure with Boussard's electrode configuration. TheIH type structure is well known for its high shunt
impedance at low and medium particle velocity". This
type linac has a high effective shunt impedance and isapplicable to the medium energy region.

~sed2MeV Proton Prototype Linac
Based on successful results of the low level RFmeasurements and numerical calculation of the beam
orbit, a prototype IHQ linac is constructed in order todemonstrate the operational capabilities of the newstructure.
For the design work of the cavity, a 1/2 scale model
resonator was made of brass. The resonance frequency
and the field distribution were checked by measurementson the model in term of the end cut of the ridge.

-86-Acceleration Particle
Energy Input
OutputProton0. 8 MeV
2. 0 Mev

Operation Frequency
Synchronous Phase
RF Power
Effective Shunt Impedance
Number of Cell
Focusing Sequence
Element

101. 5 MHz- 30"
16 kW
132 MQ /m
10FD
RFQ with Finger

16 mm

Drift Tube Bore Diameter
Outer Diameter
Stem Diameter
Distance
GapVoltage

24 mm
40 mm
145 kVTank Inner Diameter
Length

54 em
92 em

Ridge Width
LengthHeight6.4 em
72 em
27 em

Vacuum System

520 1/s TMP

48 mm

The particle trajectory was analyzed by mean of amodified computer program (LINOR) 12 in which the mostimportant input data were obtained from the modelexperiments.
The main parameters of the prototype IRQ linac aresummarized in table. The linac was designed to accelerate
protons from 0.8 to 2.0MeV with an operating frequencyof 101. 5MRz. The geometrical dimension of the I inactank is 54cm in inner diameter and 92cm in length.
The voltage distribution of the 1/2 scale model and theprototype l i nac are shown in fig. 1.

Acceleration Test Stand
A beam acceleration test stand was constructed
at INS' 3 • The injection is the RFQ I inac "'TALL'''' which
has capability accelerating up to 0.8MeV/u. The accelerated protons up to 2MeV are analyzed with an analyzer
magnet having a bending angle of 90• and a momentum
dispersion of 160cm. Slit systems, multiwire profile
monitors and Faraday cups are placed at the object andimage points of the magne~ A photograph of constructed
IRQ linac and its beam acceleration test stand areshown in fig. 2.

Fig.3

Block Diagram of Automatic
Tuning System of Two Linacs

Input beam current= 2.0 )JA

zetf = 132 M.lt/ mc~ 1-05uE~
co 0-50102030

RF power ( kW )

Fig.4

Fig.2

Intensity of 2MeV Proton vs RF power

Results of Acceleration Test 6 · 7

Photograph of constructed 2MeV IRQ linac andbeam acceleration test stand

RF Sources and Control Systems of Tandem Operation
The RF power sources are supplied from two power
amplifier systems connected with a master oscillater. Atetrode tube Eimac 4CW-25000A(8F) supplies to the prototype IRQ linac (injector RFQ linac) CW power up to 25kW
(8kW). The RF power is fed through a coaxial line WX-77D
to the IRQ linac (RFQ linac) cavity with a loop coupler.
CW and pulse operations are possible in two systems.
Two automatic gain control(AGC) are performed withan accuracy of ± 1%. An inductive tuner (4tuners) is used
for the automatic control of the resonance frequency
which shifts due to the change of temperature of the IRQ(RFQ) cavity. Two automatic frequency control (AFC) arestable within a phase shift of 3·. A phase shift between
the IRQ cavity and the injector RFQ cavity is stable byan automatic phase control (APC). A block diagram of
the automatic tuning system of two linacs is shown infig. 3.

A beam acceleration test was performed underpulse operation of two linacs having automatic tuningsystems with a duty factor of 5%. The pulse width andrepetition period were lms and 20ms, respectively. Beamtest was performed by proton from a SF-ECR' 5 ion source.
The intensity of 2MeV proton is shown in fig. 4 as afunction of the RF power. The effective shunt impedanceof the IRQ I inac was estimated to be about 132MQ/m fromRF power for proton (11.4kW at 7J>s=O).
The intensity of 2MeV proton is shown in fig. 5 asa function of the phase shift between the IRQ linac andthe injector RFQ linac. From this result, it is shownthat the automatic phase control (APC) is stable and isrequired within the phase shift of 10·.
The momentum distribution of accelerated particles
was measured as a function of the RF power as shown infig. 6. The acceleration characteristics agree well withcomputer simulation.

-87-flA

Acknowledgment

1.5cThe authors thank the member of the Accelerator
Research Division at INS for useful discussion andtheir helps. They thank people of the machine shop at
INS and Japan Steel Works, Handa-Sangyou, Asahi-Kent,
Yuukousha and Toshiba Corporation who manufactured
skillfully the prototype IHQ linac and acceleration
test stan d.

~::Juc 1.0.Q
IllIll.E
Illc~

I-0.5

References

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0.0

300°

360°

Phase of APC

Fig.5

Intensity of 2MeV proton vs APC phaseRFpower= 24.6 kW

270

280
1-82901-92.0300

BA (A J

2-1 (MeV)

Proton Energy

Fig.6

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