35 MeV Beijing Proton Linac (BPL) was completed and put in operation in
1987. It is the first accelerator of its kind ever designed and built by
our country. It is used for basic and application research in many fields.
In 1989 it passed the technical appraisal organized by the Chinese Academy
of Sciences, which demonstrated that it had met or exceeded the designed
parameters and reached advanced international standard of the same kind of
accelerators. In 1991, it was awarded the First National Prize for Science
and Technology Progress.
Beijing Proton Linac
BPL belongs to a new generation of proton linear accelerators, containing the injector, the low energy beam transport line, the accelerating cavity, the RF power source, the water-cooling system, the vacuum system, the magnet power supply system, the computer control system, the beam measuring system and the intermediate energy beam transport line. Figure 1 shows the general layout of BPL.
It is a Cockcroft-Walton with the output energy of 750 keV and the current intensity of 200 mA. It is composed of the high voltage generator, the high gradient accelerating tube and the high current ion source. With the help of the low stability system, the high voltage can be stabilized to £ ± 0.1%. The accelerating tube has an inner diameter of 600 mm and is 2 m long. It is very difficult to fabricate and seal such large accelerating tubes. By controlling the hydrogen to be filled up in the accelerating tubes, they can maintain long stable operation. The ion source is of a double plasma type. Using oxidized cathode, its lifetime can be prolonged to 600 hours. The normalized emittance at the exit of the accelerating tube is £ 3.0 pmm-mrad. The local control of the ion source is realized through the optic fiber and computer using infrared.
Beam transport line 1
The low energy beam transport line
It constitutes the beam path between the injector and the linear accelerating cavity, which is 6.5m long. It consists of 17 quadruple magnets, 1 bunching cavity, 2 pairs of steering coils and many kinds of beam measuring probes. They make the beams to match the acceptance at the entry of the accelerator vertically and horizontally and ensure that the capture rate can reach 60%.
The RF Power
is a RF transmitter with the working frequency of 200 MHz and the output
power of 5MW – the RF transmitter with the highest output power at this
frequency band in our country. The RF signal coupled from
the crystal oscillator – the reference line, is sent to the final
amplifier after 4-step amplification. The final amplifier is an imported
TH 116 triode. The RF transmitter feeds power symmetrically to the
accelerating cavity from two paths. It has 3 servo control loops –
frequency, amplitude and phase. In recent years, modulation of the final
amplification of the RF power, in accordance with the characteristics of
TH 116 triode,
was changed to grid modulation from the joint hard tube plus grid
modulation with the hard tube modulation eliminated. Thus the complex high
voltage-floating platform was eliminated. And as a consequence, the
operation stability and reliability are further improved and the operation
cost is cut by a wide margin.
the RF power source
V. The Water-cooling System
is used to cool all the heated components. For the accelerating cavities
and drift tubes, constant temperature water-cooling system is adopted to
control the harmonic frequency of the accelerating cavities. The
temperature of the inner cooling water loop can be controlled within ±0.10c.
The working temperature of the accelerating cavity is about 18.90c
The Vacuum System
vacuum system of BPL consists of twelve 1000 l/s sputtering ion pumps,
twelve 450 l/s molecular pumps and a number of small ion pumps. The vacuum
of the accelerating cavity, with a diameter of 1m and a length of 22m, is
better than 5×10-7
torr. At the joint of beam pipes, fast detachable flanges are used for
easy installation and repair.
The Magnet Power Supply system
magnet power supply system consists of 100 odd quadruple magnets power
supplies, 20 steering coils power supplies, 8 bending and analyzing
magnets power supplies. The output of quadruple magnets power supplies is
200 – 500A, the top flat width of pulse is greater than 500 ms
and the stability reaches ±0.3%.
The steering coils adopt DC power supplies with the maximum output of 10A
and the stability being ±0.1%.
The bending and analyzing magnets also adopt DC power supplies with the
maximum output of 100A and the stability reaching ±0.01%.
Computer Control System
With the connection of the interface systems and the local stations of some sub-systems, a number of the main components can be tuned, monitored and
the central console
interlocked by the central console and the CAMAC system.The three terminals in the central console are used respectively to tune 100 odd power supplies, monitor the parameters of the RF power and adjust the parameters of the ion source. The adjustment of parameters of the ion source is realized through the optic fiber and computer using infrared laser. The ion source, the RF power, the magnet power supply system and the beam measuring circuits were made to operate synchronously by the timing system. Computer PDP11/34A had retired. Recently more
|compact PC system was adopted.
The Beam Measuring System
It consists of 16 beam current measuring meters, 2 interrupt type emittance measuring meters, 10 beam cross-section measuring meters and 1 energy spectrum measuring meter.
the beam measuring system
The beam current is measured with the beam transformer whose magnetic core is made of Bo – Mo alloy with high permeability. The average current at the end of the target is measured with the current integrator. The emittance of the 750 keV beam is measured with the stepping slit and multi-layer target. The beam cross-section and the emittance of the 35 MeV beam are measured with the multi-wire target. The energy and energy spread are
measured with the slit, analyzing magnet and
With the PC and the developed software, the beam measurement probes are
driven and the beam measurement data collected, analyzed and treated. This
set of beam measuring system can measure all the beam performances. It is
appropriately distributed and its measurement results are
of high quality.
Energy Beam Transport Line
It is 60m long, containing the common transport line, the transport line for the isotope production target, the transport line for the neutron production target and the energy spread the energy spread measurement line with the transport rate of 90%.
Beam transport line 2
sum up, BPL designed and developed by our own country has synthesized many
high technologies. It is a large scientific tool with sophisticated
technologies. Only a few developed countries in the world have built such
kind of accelerators. The completion of this accelerator is made possible
with the concern of our country and the painstaking efforts made by the
State Science and Technology Commission (now called the Ministry of
Science and Technology), the Chinese Academy of
departments concerned and dozens of factories and
research institutions in tackling the technical difficulties. More than
90% of the components are new products developed by our country. Its
completion has made important contributions to the development of
accelerator technologies in our country.
was intended to operate as the injector of the proposed 50 GeV Proton
Synchrotron. The first R & D project for BPL was a 10 MeV linac. In
order for this facility to produce more benefits in scientific research
and economic construction, it was decided later to extend it to 35 MeV.
10 MeV linac was awarded the First CAS Prize for Science and Technology
Progress in 1986. The RF power system was awarded the Second CAS Prize for
the Science and Technology Progress in 1987. The accelerator physics
design and the research result were awarded respectively the Second CAS
Prize for Science and Technology Progress in 1986 and the Third National
Prize for Science and Technology Progress in 1987.
May 1989, the 35 MeV BPL passed the technical appraisal organized by CAS
and was awarded the First CAS Prize for Science and Technology Progress in
the basic and application research, the Institute of Modern Physics
succeeded in synthesizing the new nucleon Ma235 for the first time in the
world using the 35 MeV proton beam, and this was awarded the Second CAS
Prize for Science and Technology Progress in 1997.
Institute of High Energy Physics 17/07/02