MMF linac high energy part LLRF system status
Accelerated beam quality and level of beam losses are strongly affected by accelerating field phase and amplitude stability and accuracy. Due to this a constant attention was paid to the Low Level RF systems of the MMF linac. During the last 4-5 years many components of LLRF system of high -energy p...
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| Published in: | Вопросы атомной науки и техники |
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| Date: | 1999 |
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| Language: | English |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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| Cite this: | MMF linac high energy part LLRF system status / S.I. Sharamentov, V.V. Edachev, V.V. Kuznetsov, V.V. Peplov // Вопросы атомной науки и техники. — 1999. — № 4. — С. 36-37. — Бібліогр.: 1 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860223361830879232 |
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| author | Sharamentov, S.I. Edachev, V.V. Kuznetsov, V.V. Peplov, V.V. |
| author_facet | Sharamentov, S.I. Edachev, V.V. Kuznetsov, V.V. Peplov, V.V. |
| citation_txt | MMF linac high energy part LLRF system status / S.I. Sharamentov, V.V. Edachev, V.V. Kuznetsov, V.V. Peplov // Вопросы атомной науки и техники. — 1999. — № 4. — С. 36-37. — Бібліогр.: 1 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | Accelerated beam quality and level of beam losses are strongly affected by accelerating field phase and amplitude stability and accuracy. Due to this a constant attention was paid to the Low Level RF systems of the MMF linac. During the last 4-5 years many components of LLRF system of high -energy part of MMF linac were significantly rebuilt and reconstructed, and as a result higher accuracy and longterm stability were achieved, along with the higher reliability and more simple maintenance. Besides, the time needed to carry out a procedure of linac accelerating cavities, longitudinal tuning (setting and adjusting of nominal values of amplitudes and phases in the accelerating cavities), was reasonably decreased. Also, a preamplifier feeding the input of the klystron amplifier was modified to get more reliable operation.
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| first_indexed | 2025-12-07T18:18:59Z |
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MMF LINAC HIGH ENERGY PART LLRF SYSTEM STATUS
S.I. Sharamentov, V.V. Edachev, V.V. Kuznetsov, V.V. Peplov
Institute for Nuclear Research of the Russian Academy of Science, Moscow, Russia
INTRODUCTION
Accelerated beam quality and level of beam
losses are strongly affected by accelerating field phase
and amplitude stability and accuracy. Due to this a
constant attention was paid to the Low Level RF
systems of the MMF linac. During the last 4-5 years
many components of LLRF system of high -energy part
of MMF linac were significantly rebuilt and
reconstructed, and as a result higher accuracy and long-
term stability were achieved, along with the higher
reliability and more simple maintenance. Besides, the
time needed to carry out a procedure of linac
accelerating cavities, longitudinal tuning (setting and
adjusting of nominal values of amplitudes and phases in
the accelerating cavities), was reasonably decreased.
Also, a preamplifier feeding the input of the klystron
amplifier was modified to get more reliable operation.
RF CHANNEL AND LLRF: STRUCTURE AND
SHORTCOMINGS
The structure of the rf klystron channel of high-
energy part of MMF linac along with the corresponding
LLRF system are well enough described in [1]. We
would like briefly remind that this structure was formed
in 1990-1991 and was in operation until 1995-1996
years.
Each accelerating cavity of the high-energy part
of MMF linac is fed from one multi-beam pulse
klystron with a maximum output power 4.5-5 MW,
maximum pulse duration and repetition rate 170 us and
100 Hz, respectively.
It requires 100-400 W of drive RF power, which
is produced by a three-stage lamp (metal-ceramic
triodes GS-31) preamplifier (PA). Nominal PA input
power is 10-30 mW.
To control (stabilize) the amplitude of cavity
accelerating field a method of klystron RF drive power
modulation, under constant value of klystron gun
voltage, was chosen. For making this, controlling
devices of the amplitude and phase feedback systems
are connected in series with klystron PA input. Both
amplitude and phase feedback systems are combination
of fast analog and slow analog-digital channels. Fast
channels use proportional low of regulation and work
within RF pulse duration. They use fast electronic
attenuator and fast strip-line phaseshifter as controlling
devices. Slow analog-digital channels use mechanical,
driven by stepping motors, coaxial attenuator and
trombone type phaseshifter. These channels are rather
slow and the work-off time in a case of relatively large
errors can be up to 5 – 10 minutes.
Fast electronic attenuator is built from two 3-dB
strip-line hybrids and two strip-line phaseshifters
(similar those used in phase feedback system). Principle
of operation of such attenuator is based on an opposite-
phase phase modulation of two vectors coming out from
the first hybrid and their following summing on the
second hybrid.
During the years of linac operation a number of
shortcomings inherent to LLRF scheme described above
were revealed. Main of them are following:
all stages of the lamp preamplifier are working at close
to their technical limits conditions
PA anode pulse modulator is not well matched to the
anode impedance of the amplification stages. It
leads to the 50% reverse voltage overshoot at the
rear edge of the HV pulse, thus increasing total
voltage applied to the anode isolating dielectric
gasket up to 4.5 kV. Due to this the isolating gasket
was destroyed in a relatively short time
low work-off time of the analog-digital channels.
Sometimes it can cause an additional time losses in
linac operation (for example, when cavity thermal
detuning is working off by phase and amplitude
feedback systems)
there is no fast electronic phaseshifter with the full
phase range not near 360 degrees, installed at the
input of rf channel. It makes no possibility to get
fast procedure of linac accelerating cavities
longitudinal tuning
fast electronic attenuator has relatively large rf signal
attenuation and two unstable point, due to his
control low described by following expression:
)sin( 0Φ+= ci SUUUo . In one of this point
the phase of output rf signal jumps at 180 degrees,
in other one the sign of amplitude feedback
becomes positive.
MODERNIZATION
To improve reliability and quality, simplify
maintenance and to get new possibilities of LLRF
system, a set of investigating and design works were
attempted during last years. Main ideas of this work can
be expressed as follows.
The most unreliable and having long repair time
is PA. To make his operation more stable one can
decrease the number of lamp stages (make 2 instead of
3) and decrease value of anode pulse voltage. Inevitably
decreasing output RF power can be compensated by
increasing of input RF power. In addition, to increase
lifetime of isolating dielectric gaskets, reverse voltage
overshoot at the rear edge of modulator pulse should be
eliminated.
To get more RF power at the PA input a new
electronic attenuator with reasonably less attenuation
should be designed. An existed attenuator had
attenuation at the operating point ~ -(15-10) dB.
To compensate low work-off time of analog-
digital channels of feedback controllers, one can
propose to add an integral channel to the fast analog
feedback, i. e. change proportional low of regulation to
proportional-integral low. Then wide-range amplitude
and phase errors can be fast compensated with high
accuracy. To do so, a new electronic attenuator with
smooth regulating curve needed, also.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 36-38.
36
The process of accelerating cavities longitudinal
tuning takes rather long time, due to the large number of
cavities. To make this process more effective, fast
electronic phaseshifter with more than 360 degrees
range should be designed.
FAST ELECTRONIC ATTENUATOR
As it was shown earlier, an electronic attenuator
should combine both low attenuation at operating point
and smooth control function and imply high stability
and reliability. Large experience accumulated by
authors of the paper in area of development and
manufacturing of miscellaneous semiconductor stripe-
line RF components made it possible to develop and
produce a required quantity of such devices able to
satisfy the technical requirements. It was decided to use
transistor RF amplifier as a fast electronic attenuator. To
control output power of such attenuator one can vary dc
collector voltage of the transistor (low parasitic phase
modulation is an advantage of this method). The
amplifier consists of two stages built of KT919B (first
stage) and KT942A (output stage) Russian industry
made bipolar transistors. It uses both stripe-lines and
“normal” circuit elements (resistors, inductances, and
variable capacitors) as matching circuits. Only the
output stage collector voltage is varied, first transistor
works at constant collector voltage 27 V. Amplifier has
close to linear controlling curve with input VSWR less
than 1.12:1 within the whole controlling range. At
nominal rf input power 0.2 W output power varies
within the range of 0.2-10 W, if collector voltage
changes from 3 to 30 V. At operating point output
power is typically around 2 W. Nominal amplifier
working frequency is 991 MHz, bandwidth +/- 5 %. The
construction of amplifier allows working even in dc
mode.
To control collector voltage, fast controlling
amplifier also was built. It made of fast operational
amplifier KP544UD2 and RF transistor KT928A and
provides more then 4 MHz bandwidth at real load
(measured on RF signal).
PREAMPLIFIER
A new electronic attenuator described above can
provide approximately 20 dB higher RF power at the
input of PA (2-3 W instead of 10-30 mW). It gives
possibility easily remove first lamp stage from the PA
and get even higher output power. Furthermore, this
extra RF power allows decreasing pulse HV anode
voltage of the rest two stages from 3 to 1.5-2 kV. Even
under this conditions, klystron input drive power well
enough satisfy required values, as it was measured at
large number of klystrons. One should mention that all
the connecting cable and elements in the line PA-
klystron were carefully checked and optimized from the
point of RF losses.
To provide best performance of PA anode pulse
modulator to a new load (less output voltage and
current), it was subjected to a complex modernization,
too. Mostly all elements of modulator scheme were
changed. It concerns the value of resistors, HV
transformers transformation coefficients, type of diodes,
etc. As a result much higher quality of modulator output
pulse were achieved, no reverse polarity overshoot
observed, modulator scheme thermal conditions became
much more light. Also, the working conditions for the
dielectric isolating gaskets in the lamp anode circuit
were considerably improved. It was very rare the
gaskets in a new PA were destroyed.
ELECTRONIC PHASESHIFTER
One of the main parameter taking into account
under development of electronic phaseshifter is a value
of RF power to be transmitted through the device. Study
of various existing LLRF system shows that maximum
transmitted RF power for the electronic phaseshifters
not exceeds some mW, typically. For our case 360
degrees phaseshifter should be installed before splitting
an RF signal coming from accelerator RF reference line
into a phase reference signal and PA driving one. RF
power in this point for linac high-energy part RF system
is around 3-4 W.
After changing an old electronic attenuator to
transistor regulator, two electronic phaseshifters for
each RF station become available, and it was very
tempting try to use them. A careful investigation and
calculation of these phaseshifters were made to define a
phase range, maximum transmitting power and signal
attenuation, and to understand whether these parameters
can be improved. The results of the investigation shows,
that the phase range is depended on the transmitted rf
power, and varies from 140 to 190 degrees, if
transmitted power decreases from 1 to 0.42 W. Signal
attenuation is independent from transmitted power and
lies near –1.5 dB.
From these data follows that to get phase range
more than 360 degrees one can connect two
phaseshifters in series and limit rf power transmitted
through the first phaseshifter at ~0.4 W. RF power at the
output of second phaseshifter will be around 0.2 W. But,
as it was mentioned above, we need 3-4 W at this point
of RF line. The only possible decision is to introduce
one more RF amplifier (similar the amplifier used as
electronic attenuator) and adjust his collector voltage to
get the required power.
According this idea a separate unit combined two
electronic stripe-line phaseshifters, RF amplifier and
some control electronics was built and installed at the
linac tunnel, near the RF reference line. This
phaseshifter-amplifier unit allows fast accelerating
cavity RF field phase changing, in a range more than
360 degrees. No additional RF instabilities were
observed.
To control this unit, a special DAC module
compatible with the linac control system equipment,
also was built.
FEEDBACK CONTROLLERS
Both phase and amplitude feedback controllers
have low work-off time for large phase and amplitude
errors. As it was suggested above one can improve the
situation by changing proportional low of regulation to
proportional-integral one. For amplitude feedback
system it become possible after new electronic
attenuator was installed.
To realize proportional-integral law of regulation
a new integrator module was built and installed both in
amplitude and phase feedback controllers. Output dc
signal from integrator module is added to the output
signal of proportional channel of feedback controller,
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 36-38.
36
thus changing operating point of electronic attenuator
(or phaseshifter). An integrating circuit has
equivalenttime constant near 0.2-0.3 sec. Dynamic
range of the integrator channel is chosen to be around
80% of full dynamic range of amplitude and phase
controlling devices. It provides effective operation of
fast proportional channels even at the edges of the
integrator range.
To get wider dynamic range of the feedback
controllers, an old mechanical amplitude and phase
controlling devices were retained, also. They start
working when integrator output voltage is approaching
to its upper and lower limits.
CONCLUSIONS
Several years of MMF linac operation show that
modernization of high-energy part LLRF system
described above have really improved quality of
accelerated high intensity proton beam. Much more
stable and better quality beam parameters were
achieved. The exploitation of high-energy part RF
system for linac technical personnel becomes much
easier, due to higher reliability and wide automatic
computer control of the RF system.
REFERENCES
1. S. I. Sharamentov et all. Progress of the Moscow
Meson Factory Linac RF Phase and Amplitude
Control System. Proceedings of the 1992 Linac
Accelerator Conference. Ottawa, Ontario, Canada,
August 24-28, p. 308.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 36-38.
36
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| id | nasplib_isofts_kiev_ua-123456789-81523 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T18:18:59Z |
| publishDate | 1999 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Sharamentov, S.I. Edachev, V.V. Kuznetsov, V.V. Peplov, V.V. 2015-05-17T16:29:43Z 2015-05-17T16:29:43Z 1999 MMF linac high energy part LLRF system status / S.I. Sharamentov, V.V. Edachev, V.V. Kuznetsov, V.V. Peplov // Вопросы атомной науки и техники. — 1999. — № 4. — С. 36-37. — Бібліогр.: 1 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/81523 Accelerated beam quality and level of beam losses are strongly affected by accelerating field phase and amplitude stability and accuracy. Due to this a constant attention was paid to the Low Level RF systems of the MMF linac. During the last 4-5 years many components of LLRF system of high -energy part of MMF linac were significantly rebuilt and reconstructed, and as a result higher accuracy and longterm stability were achieved, along with the higher reliability and more simple maintenance. Besides, the time needed to carry out a procedure of linac accelerating cavities, longitudinal tuning (setting and adjusting of nominal values of amplitudes and phases in the accelerating cavities), was reasonably decreased. Also, a preamplifier feeding the input of the klystron amplifier was modified to get more reliable operation. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники MMF linac high energy part LLRF system status Модернизация систем стабилизации амплитуды и фазы ускоряющего поля в резонаторах основной части линейного ускорителя ММФ Article published earlier |
| spellingShingle | MMF linac high energy part LLRF system status Sharamentov, S.I. Edachev, V.V. Kuznetsov, V.V. Peplov, V.V. |
| title | MMF linac high energy part LLRF system status |
| title_alt | Модернизация систем стабилизации амплитуды и фазы ускоряющего поля в резонаторах основной части линейного ускорителя ММФ |
| title_full | MMF linac high energy part LLRF system status |
| title_fullStr | MMF linac high energy part LLRF system status |
| title_full_unstemmed | MMF linac high energy part LLRF system status |
| title_short | MMF linac high energy part LLRF system status |
| title_sort | mmf linac high energy part llrf system status |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/81523 |
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