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Desktop Publishing Instructions for Authors of Papers KOMAC Project

Y.S. Cho, P.K. Joo, K.R. Kim, J.Y. Kim, J.H. Lee, J.M. Han, H.J. Kwon, B.H. Choi
Proton Engineering Frontier Project
KAERI, Daejon, Korea

Abstract
The final objective of KOMAC (Korea Multi-purpose accelerator Complex) project is to
build a 20-MW (1 GeV, 20 mA, cw) high power proton linear accelerator to study basic
researches, industrial applications, and nuclear transmutation. It is planed that 20MeV,
100MeV, 250MeV and 1GeV proton beam will be supplied for the applications. Since 1997,
KAERI (Korea Atomic Energy Research Institute) has been developing high power proton
linac from injector to 3MeV RFQ with 1MW RF system in the KTF (KOMAC Test Facility).
For the second stage of the KOMAC project extended to 100MeV, a feasibility study and a
proposal had been accepted by Korean government, and the project is starting. The second
stage accelerator will deliver 20MeV and 100MeV proton beam for users. The simultaneous
beam sharing to many user is planed, and with the scheme, many proton beam line can be
installed in the user facility. Many spin-offs of the accelerator technologies for industrial
applications will be included in the KOMAC project in nano-technology, bio-technology, etc.
It is hoped that this accelerator will be useful for the nuclear data production with 100MeV
proton beam. The details of the KOMAC project status will be presented.
1. INTRODUCTION [1]
Since 1996, KAERI had proposed to build a high power proton linear accelerator of 1GeV
and 20mA under the KOMAC program. Figure 1 shows the accelerator structure and
parameters of KOMAC. The major H+ beam (18mA and 1GeV) will be used for nuclear
waste transmutation and nuclear physics experiments while utilizing the minor H- beam
(2mA) for the basic research and medical therapy study. As the 1
st
phase of the project,
KAERI had developed the proton accelerator technologies in KTF. In the KTF, 3MeV proton
accelerator have been constructed and tested. The 2
nd
phase of the project was approved by
the government, and will start in September 2002.

Figure 1: Schematic Layout of the KOMAC Linac 2. 1
ST
PHASE PROGRAM OF KOMAC
As the 1
st
phase of the project, we are developing cw accelerating structure up to 20MeV,
and operate the accelerator in 10% duty pulse mode. After the initial operation, we will
challenge the cw operation of the accelerator. The 20MeV proton accelerator is constructing
in the KTF (KOMAC Test Facility), and will be commissioned in 2005. After the
commissioning, KTF will provide the proton beam for the many industrial applications.
In the KTF, we are developing the proton injector, LEBT, 3MeV RFQ, 20MeV DTL, and
RF system. The proton injector is already developed, and the 3MeV RFQ will be constructed
in this fiscal year. Also we have a plan to develop the basic Super-Conducting cavity
technology in the KTF for the 2
nd
stage accelerator of the KOMAC.
2.1 Proton Injector [2]
For 20 mA proton beam at the final stage, KOMAC requires the ion source with the proton
beam current of 30 mA at the extraction voltage of 50 kV. Normalized rms emittance of less
than 0.3 mm mrad is also required for good matching of ion beam into RFQ.
The system is composed of an accelerating high voltage power supply, ion source power
supplies in a high voltage deck, gas feeding system, and vacuum system.
The injector has reached beam currents of up to 50 mA at 50 kV extraction voltage with 150
V, 10 A arc power. The extracted beam has a normalized emittance of 0.2 mm mrad from
90 % beam current and proton fraction of over 80 %. The proton fraction is measured with
deflection magnet and scanning wire.
The beam can be extracted without any fluctuation in beam current, with a high voltage
arcing in 4 hours. The cathode lifetime is about 40hr. To increase the filament lifetime, it is
necessary to lower the arc current or to change the tungsten filament to other cathode such as
oxide cathode.
2.2 LEBT
Low-energy beam transport (LEBT) consists of two solenoids, two steering magnets,
diagnostic system, beam control system, and funnelling system to transports and matches the
H
+
for 20mA and H
-
for 3mA, beams from the ion source into the RFQ. The main goal of the
LEBT design is to minimise beam losses. The design codes used are TRACE 3D and
PARMTEQM. The PARMTEQM-simulated solenoid settings are B=2800G and B=3900G,
the RFQ transmission rate is more than 90%. Two solenoid magnets constructed are 20.7cm-
long, 16cm-i.d., are surrounded by a low carbon steel and provide dc fields 5000G on the
axis. During the winter of 2000, we will test the LEBT to obtain a proper matching condition
with the RFQ.
2.3 RFQ [3]
The KTF RFQ bunches, focuses, and accelerates the 50keV H
+
/H
-
beams, and derives a
3.0MeV beam at its exit, bunched with a 350MHz. The RFQ is a 324cm-long, 4-vanes type,
and consists of 56 tuners, 16 vacuum ports, 1 coupling plate, 4 rf drive couplers, 96 cooling passages, and 8 stabiliser rods. The RFQ is machined of OFH-Copper, integrate from separate
four sections which are constructed by using vacuum furnace brazing. The fabricated RFQ is
shown in Figure 2.



Figure 2: Fabricated RFQ cavity.

2.4 High Power RF System
Two types of RFQ have been developed. The one is 0.45 MeV RFQ whose purpose is to
check the basic RFQ technologies such as tuning, beam matching and so on, the other is 3
MeV main RFQ which was fabricated and vacuum tight checked already. The required RF
power for 0.45 MeV RFQ is 110 kW CW and for 3 MeV is 417 kW CW respectively. The 1
MW, 350 MHz RF system has been developed to deliver a RF power to the RFQ. The high
power RF system consists of klystron, circulator, RF window, various waveguide components,
klystron power supplies and cooling system. Recently all components of the RF system were
prepared and are being tested.




Figure 3: 1 MW 350 MHz Klystron and RF window

2.5 low level RF System
The LLRF consists of a 350MHz signal generator, a 160W solid state amplifier,
amplitude/phase control loops, and RF interlocks. The designed field stability in the RFQ
cavity is within
±
1% amplitude and
±
1.4
°
phase using feedback control loops in the LLRF. For frequency control, another tuner controller module was used. The RF interlock signals
comes from excessive reflected RF power, circulator arcs and window arcs.
2.6 DTL [4]
DTL will accelerate the 3MeV 20mA proton beam to the energy of 20MeV. The structure
design of DTL is based on the 100% duty factor.
For 20MeV to 100MeV, CCDTL cold models are fabricated to check the design, the tuning
method, and the coupling coefficients and the fabrication method. The super-drilled coolant
path is well fabricated, and this type cooling method will be used for the CCDTL construction.
The field profile is measured with a bead perturbation method.
The design and fabrication technologies have been acquired, and the DTL for 2
nd
phase
accelerator will be fabricated from this year.
2.7 Power Supply System
The specifications of the high voltage power supplies for the KTF klystron are 100 kV, 20 A
with the conditions that the voltage peak to peak ripple and the voltage regulation are less than
1 %, and energy deposition in the klystron at the tube arc is less than 20 J. The power supply
that meets the above conditions has been designed, manufactured and tested. The main
components of the high voltage power supply are Induction-Voltage-Regulator, transformer &
rectifier tank for 12 pulses rectification, L-C filter, and ignitron crowbar. Voltage dividing
resistors and a tetrode tube were used to provide variable high voltage to modulating anode of
the klystron. The variable voltage modulating anode power supply gives the flexibility of
klystron operation.



Figure 4: High voltage power supply for Klystron

2.8 Cooling System
A 2 MW DI water cooling system for KTF RFQ and RF system was prepared as shown in
Figure 5 as KTF Facility. The required cooling loops for RF system are circulator, RF load,
RF window cooling loops and body, cavity, collector cooling loops for klystron. Because the
coolant of the RF load is a mixture of water and ethylene glycol, a separate cooling loop for
RF load with storage tank, pump and heat exchanger was installed. Also pump for pressurization was installed in klystron body cooling loop, because the pressure of the DI
water cooling loop was too low to supply enough flow to that cooling loop.



Figure 5: Facility for KTF

2.9 Status of KTF
In the KTF, we have developed the technologies for proton accelerators from low energy
part. As a result of this development, we have constructed and tested 3MeV proton
accelerator system. Figure 6 shows the status of KTF. The 20MeV accelerator in KTF will be
constructed and commissioned in 2005. The experiences in KTF will be a basis of the 2
nd

phase accelerator of 100MeV final energy.