Increase of the RF pulse width in the cavities of the main part of MMF linac
At the MMF linac for increasing an average beam current an rf pulse width in the accelerating cavities of the main part of the linac have to be increased. Pulse widths of a preamplifier modulator and a high voltage klystron modulator limited this value. Modification of these units allowed increasi...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2004
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| Цитувати: | Increase of the RF pulse width in the cavities of the main part of MMF linac / V.N. Leontiev, V.V. Peplov // Вопросы атомной науки и техники. — 2004. — № 1. — С. 71-73. — Бібліогр.: 3 назв. — англ. |
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irk-123456789-787012015-03-21T03:01:46Z Increase of the RF pulse width in the cavities of the main part of MMF linac Leontiev, V.N. Peplov, V.V. Элементы ускорителей At the MMF linac for increasing an average beam current an rf pulse width in the accelerating cavities of the main part of the linac have to be increased. Pulse widths of a preamplifier modulator and a high voltage klystron modulator limited this value. Modification of these units allowed increasing the rf pulse width at the klystron output to about 240 µs and the beam pulse duration to 200 µs. An estimation of the maximum possible rf pulse width and the results of an experimental exploration of the upgraded high voltage klystron and preamplifier modulators are presented. A possibility of the longtime stable work with a long pulse is shown. На лінійному прискорювачі ММФ для збільшення середнього струму пучка протонів треба було збільшити тривалість імпульсу ВЧ-поля в резонаторах основної частини прискорювача. Проведені роботи з модернізації устаткування каналів ВЧ-живлення дозволили збільшити тривалість, що обгинає ВЧ-імпульсу на виході підсилювального клістрона до 240 мкс, що дає можливість прискорювати пучок тривалістю 200 мкс. У роботі описані пророблені роботи, дані оцінки по обмеженню максимально можливих величин тривалості, представлені результати експериментальних іспитів устаткування каналів ВЧ-живлення при роботі з подовженим імпульсом і показана можливість стійкої роботи потужних модуляторів, попередніх підсилювачів, клістронів, елементів хвилевідно-фідерної системи і самих резонаторів, що прискорюють в експлуатаційному режимі зі збільшеною тривалістю імпульсу. На линейном ускорителе ММФ для увеличения среднего тока пучка протонов потребовалось увеличить длительность импульса ВЧ-поля в резонаторах основной части ускорителя. Проведенные работы по модернизации оборудования каналов ВЧ-питания позволили увеличить длительность огибающей ВЧ-импульса на выходе усилительного клистрона до 240 мкс, что дает возможность ускорять пучок длительностью 200 мкс. В работе описаны проделанные работы, даны оценки по ограничению максимально возможных величин длительности, представлены результаты экспериментальных испытаний оборудования каналов ВЧ-питания при работе с удлиненным импульсом и показана возможность устойчивой работы мощных модуляторов, предварительных усилителей, клистронов, элементов волноводно-фидерной системы и самих ускоряющих резонаторов в эксплуатационном режиме с увеличенной длительностью импульса. 2004 Article Increase of the RF pulse width in the cavities of the main part of MMF linac / V.N. Leontiev, V.V. Peplov // Вопросы атомной науки и техники. — 2004. — № 1. — С. 71-73. — Бібліогр.: 3 назв. — англ. 1562-6016 PACS: 29.17+w http://dspace.nbuv.gov.ua/handle/123456789/78701 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Элементы ускорителей Элементы ускорителей |
| spellingShingle |
Элементы ускорителей Элементы ускорителей Leontiev, V.N. Peplov, V.V. Increase of the RF pulse width in the cavities of the main part of MMF linac Вопросы атомной науки и техники |
| description |
At the MMF linac for increasing an average beam current an rf pulse width in the accelerating cavities of the
main part of the linac have to be increased. Pulse widths of a preamplifier modulator and a high voltage klystron
modulator limited this value. Modification of these units allowed increasing the rf pulse width at the klystron output
to about 240 µs and the beam pulse duration to 200 µs. An estimation of the maximum possible rf pulse width and
the results of an experimental exploration of the upgraded high voltage klystron and preamplifier modulators are
presented. A possibility of the longtime stable work with a long pulse is shown. |
| format |
Article |
| author |
Leontiev, V.N. Peplov, V.V. |
| author_facet |
Leontiev, V.N. Peplov, V.V. |
| author_sort |
Leontiev, V.N. |
| title |
Increase of the RF pulse width in the cavities of the main part of MMF linac |
| title_short |
Increase of the RF pulse width in the cavities of the main part of MMF linac |
| title_full |
Increase of the RF pulse width in the cavities of the main part of MMF linac |
| title_fullStr |
Increase of the RF pulse width in the cavities of the main part of MMF linac |
| title_full_unstemmed |
Increase of the RF pulse width in the cavities of the main part of MMF linac |
| title_sort |
increase of the rf pulse width in the cavities of the main part of mmf linac |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2004 |
| topic_facet |
Элементы ускорителей |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/78701 |
| citation_txt |
Increase of the RF pulse width in the cavities of the main part of MMF linac / V.N. Leontiev, V.V. Peplov // Вопросы атомной науки и техники. — 2004. — № 1. — С. 71-73. — Бібліогр.: 3 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
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| first_indexed |
2025-07-06T02:46:18Z |
| last_indexed |
2025-07-06T02:46:18Z |
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1836863957026996224 |
| fulltext |
INCREASE OF THE RF PULSE WIDTH IN THE CAVITIES
OF THE MAIN PART OF MMF LINAC
V.N. Leontiev, V.V. Peplov
Institute for Nuclear Research of RAS
117312, 60-th October Anniversary pr. 7-a, Moscow, Russia;
E-mail: peplov@inr.troitsk.ru
At the MMF linac for increasing an average beam current an rf pulse width in the accelerating cavities of the
main part of the linac have to be increased. Pulse widths of a preamplifier modulator and a high voltage klystron
modulator limited this value. Modification of these units allowed increasing the rf pulse width at the klystron output
to about 240 µs and the beam pulse duration to 200 µs. An estimation of the maximum possible rf pulse width and
the results of an experimental exploration of the upgraded high voltage klystron and preamplifier modulators are
presented. A possibility of the longtime stable work with a long pulse is shown.
PACS: 29.17+w
INTRODUCTION
At the MMF linac for providing physical experi-
ments and solving applied tasks an average beam cur-
rent have to be increased. One of the ways is a lengthen-
ing of the proton beam pulse duration in the linac. Ac-
cording to the project the maximum value was 100 µs. It
was limited by the parameters of the injector and rf-
feeding equipment of the high-energy part of the accel-
erator. The injector branch was upgraded in 1998 year
[1]. Use of the RFQ booster cavity, decrease of high
voltage at the injector and other modifications at the
first part of the accelerator provided a possibility to get
200 µsec beam pulse at the input of the main part of the
linac. The maximum value of rf pulse flattop in the cav-
ities of the high-energy part was only 120 µs.
A structure and the main parameters of 991 MHz rf
system are described in [2]. A pulse triode rf preamplifi-
er and a high-power klystron with anode modulators as
high-voltage supplies provide a necessary level of rf ac-
celerating field in the cavities. Modification of the
preamplifier and the klystron modulator for increasing
of the pulse width was done during last several years.
1. MODIFICATION OF THE
PREAMPLIFIER MODULATOR
The results of the works devoted to development of
a new type modulator for the rf preamplifier were pre-
sented in [3]. Briefly repeat them.
According to the project the 3-cascade triode pream-
plifier with 500 W rf power at its output was droved by
anode pulse modulator. A pulse-forming network (PFN)
consisting of 13 LC-links was charged up to 400…600V
and discharged through the primary of the pulse trans-
former with n=10. The maximum width of 2…3 kV out-
put pulse was about 140 µsec. It seems that the simplest
way to increase the pulse duration up to 200…220 µsec
is to add some LC-links into PFN, using old other ele-
ments and units of the modulator. But researches
showed impossibility to do this because of a saturation
of the pulse transformer. Some curves are presented in
Fig.1. One can see a nonlinear character of these depen-
dencies. The more pulse amplitude Ua is, the earlier sat-
uration takes place and the shorter maximum possible
duration of the pulse can be reached with the same
quantity of the links in PFN. For getting required output
power we need Ua =2.4 kV. In this case maximum pulse
width only T=155 µs can be achieved.
130
140
150
160
170
180
190
200
12 13 14 15 16 17 18 19 20
Numbers of LC-links
T
pu
ls
e
m
ax
.,
us
ec
Ua = 1.6 kV
Ua = 2 kV
Ua = 2.4 kV
Fig.1. Maximum pulse width of the preamplifier modu-
lator vs. numbers of PFN LC-links
This type of modulator has other disadvantages,
mentioned in [3]. By these reasons another type was
suggested and realized: cathode-grid modulator.
A new scheme has evident advantages. It uses
2.5 kV rectifiers with a capacitor for DC supplying an-
odes of the triodes. A low-voltage pulse former drives
the triodes through transistor switchers. A driving volt-
age is 50 V. Dimensions of the new unit are sufficiently
smaller. There are no high-current elements and no
heating inside the modulator unit. An efficiency of the
cathode modulator is twice better. A shape of the pulse
is practically ideal rectangular and it is very stable.
There is a possibility to adjust the pulse width from
120 µsec up to 250 µsec. The power of the high-voltage
transformer and accumulator capacitor limited this val-
ue.
2. LENGTHENING OF PFN
OF THE KLYSTRON MODULATOR
The high-power klystron modulator has a similar
electrical schematic. 4.5 kV adjustable thyristor rectifier
charges PFN, consisting of 3 parallel lines with 20 LC-
links in each, through a charging choke and a diode. The
parameters of the choke are like this to obtain a linear
type of the charging process at any pulse repetition rate
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.71-73. 71
mailto:peplov@inr.troitsk.ru
(PRR). PFN discharges through the thyristor switcher
and the primary of the pulse transformer with n=20. The
main parameters of the modulator are presented below:
U out max = 80 kV;
P pulse max = 15 MW;
P average max = 280 kW;
I rectifier max = 80 A;
T pulse (flattop) = 170 µsec;
T rise = 20 µsec;
T fall = 25 µsec;
∆ U (on flattop) ≤ 1.5%
PRR = 10,50,100 Hz.
One of the most important parameters is a voltage
ripple at the pulse flattop ∆ U. To satisfy the demands a
special procedure for adjusting exists. All PFN induc-
tances L are identical spiral coils disposed along a
straight axis on three floors. There is a possibility to
move each coil in transverse direction and to change the
mutual inductance for neighboring coils. As a result it is
able to make the amplitude ripple on the flattop after
two first oscillations less than 1.5%.
To increase pulse duration up to more than 200 µsec
minimum 3 additional LC-links have to be installed. All
the PFN are placed in special rooms. The dimensions of
these rooms are different and limited. It is possible to
arrange 5 additional links, but they can be installed at
the end of each PFN line in transverse direction only. In
this case an inductance coupling in the local point is suf-
ficiently different and a distortion on the pulse flattop
takes place. For example, some shapes of the pulses are
presented in Fig.2.
Fig.2. Shape of klystron modulator pulses (model)
This picture is a result of the transient analysis for
the simplified PFN model with real parameters. One
curve presents an ideal case, when all the LC links and
mutual inductances are similar, and the second curve
shows the case, when a jump of the coupling coeffi-
cients between 20 and 21 coils exists. To compensate
this oscillation one should move other coils and vary
magnetic coupling coefficients to get a desired shape of
the pulse flattop.
Experimental selection of the position of each coil in
11 modulators for adjusting PFN with additional 5 LC
links was done. Voltage ripple on the flattop (excepting
two first oscillations at the beginning) is less than 2%.
The duration of the pulse flattop is about 230 µs.
It should be mentioned that the maximum possible
pulse width for high voltage pulse transformer is about
240 µsec if the secondary voltage is about maximum
value. Then a saturation of the transformer iron starts.
3. TESTING OF THE MODIFIED
KLYSTRON MODULATOR
The first upgraded modulator was tested when it
worked to an active resistive load. A goal was to define
limits for existing electrical equipment.
The following parameters were obtained during test-
ing at PPR =50 Hz:
U load = 70 kV;
I load = 165 A;
I rectifier = 48 A;
T pulse (flattop) = 230 µsec;
P load (average) = 115 kW;
P load (pulse) = 10.5 MW.
From this table one can see that all modulator units
can work well at PRR=50 Hz without exceeding the
limit parameters.
In the case of PPR = 100 Hz an average power and a
rectifier current will be twice as much as before and the
rectifier current will exceed the maximum possible val-
ue 80 A. It is the main limit for working with 5 addi-
tional LC-links at the voltage level 70 kV. Routine
working points of klystron anode voltages are 60…
65 kV. Only 3 additional LC-links can be used in this
case. The maximum pulse width we can obtain at
100 Hz is about 210 µs.
4. TESTING OF THE KLYSTRON,
WAVEGUIDE ELEMENTS
AND ACCELERATING CAVITIES
After testing of the modulator it was necessary to
check a klystron, waveguide, accelerating cavities and
other elements of rf system working with a long rf
pulse.
According to the klystron technical data maximum
average power at its output is 100 kW and maximum rf
pulse width is 800 µsec. Basing on these demands one
can choose PPR and a pulse width for working point.
The following parameters were obtained when the
modulator with 3 additional LC-links worked with a
klystron as a load:
U klystron = 62 kV;
I klystron = 135 A;
PRR = 100 Hz;
I rectifier = 80 A;
T mod. pulse (at 0.5 level) = 215 µs;
Collector water flow, Q = 160 l/min;
T0 coll. in = 14 grad;
T0 coll. out = 30 grad;
P klystron beam pulse = 8.3 MW;
P klystron beam average = 180 kW.
Then an input rf signal was switched on. The param-
eters were the following:
T rf pulse = 200 µsec;
PRR = 100 Hz;
P rf klystron out (pulse) = 3.5 MW;
P rf klystron out (average) = 70 kW.
This is a typical running regime for getting a desir-
able level of the accelerating field in the accelerating
cavity. So it means that there is a possibility to work
72
successfully with PRR = 100 Hz and 200 µsec rf pulse
at the high-energy part of the MMF linac.
During the testing a heating of all the elements of
the waveguide feeder was controlled. A temperature of
regular parts of the cooper waveguide as well as temper-
atures of rf quartz windows, waveguide phase shifter
and ferrite isolator was completely acceptable. The
problem was an overheating of the steel bellow, which
has no silver cover on its inner surface. To solve this
problem bellows with good quality silver cover were in-
stalled in all working waveguide feeders.
We should make mention about very careful me-
chanical adjustment of the rotating parts of waveguide
switchers to except sparking on the inner specific gaps,
especially if working with a long rf pulses.
Due to lengthening of rf pulse a conditioning of all
the accelerating cavities was done. Sometimes the dura-
tion of this procedure was very long. It depended on the
quality of the inner cavity surface. In order to get a sta-
ble work without sparks inside the cavity, the pulse
width of rf signal was increased step by step to 200 µsec
during many hours.
Another problem was a choosing of the working
point for a system of stabilization of the cavity resonant
frequency. Power dissipated in the cavity walls increas-
es twice when the pulse repetition rate rises to 100 Hz
as compared to 50 Hz. Moreover losses in the walls are
increased sufficiently when we increase the rf pulse
width, and therefore an additional adjustment of the wa-
ter cooling system have to be done especially at
PRR=100 Hz.
5. CONCLUSION
To the moment 22 preamplifiers and 11 klystron
modulators have been modified and tested at the MMF
linac. During last two years the proton beam of 180-
185-usec-pulse width at 50 Hz PRR was accelerated
successfully up to energy 250 MeV and used for differ-
ent purposes. For example, the ordinary routine for iso-
tope program at the linac is 143…160 MeV beam with
maximum peak beam current up to 15 mA and the aver-
age beam current about 110 µA.
The future plans at the linac are the following:
1. To modify the other modulators for getting a
higher beam energy when working with a long
pulse.
2. To increase a peak current from the injector and
thereby to increase an average beam current.
3. To work at PRR = 100 Hz and thereby to in-
crease twice an average beam current
REFERENCES
1. S.K. Esin, L.V. Kravchuk et al. // Commissioning
of new injection line at INR proton linac. Proceed.
of the 18-th PAC, New York, March 1999.
2. Vysokochastotnye ustroistva uskoritelei zariajen-
nyh chastits // Trudy Radiotehnicheskogko instituta
AS USSR, #28. Moskva, 1977, (in Russian).
3. V.N. Leontiev, V.V. Peplov, S.I. Sharamentov. Ka-
todnyi moduliator predvaritelnogo triodnogo RF
usilitelia kanala RF pitania lineinogo uskoritelia
MMF // Trudy 16-go Sovetchania po UZCH.
Protvino 1999, tom 1, p. 215. (in Russian).
УВЕЛИЧЕНИЕ ДЛИТЕЛЬНОСТИ ИМПУЛЬСА ВЧ-ПОЛЯ В РЕЗОНАТОРАХ
ОСНОВНОЙ ЧАСТИ ЛУ ММФ
В.Н. Леонтьев, В.В. Пеплов
На линейном ускорителе ММФ для увеличения среднего тока пучка протонов потребовалось увеличить
длительность импульса ВЧ-поля в резонаторах основной части ускорителя. Проведенные работы по модер-
низации оборудования каналов ВЧ-питания позволили увеличить длительность огибающей ВЧ-импульса на
выходе усилительного клистрона до 240 мкс, что дает возможность ускорять пучок длительностью 200 мкс.
В работе описаны проделанные работы, даны оценки по ограничению максимально возможных величин
длительности, представлены результаты экспериментальных испытаний оборудования каналов ВЧ-питания
при работе с удлиненным импульсом и показана возможность устойчивой работы мощных модуляторов,
предварительных усилителей, клистронов, элементов волноводно-фидерной системы и самих ускоряющих
резонаторов в эксплуатационном режиме с увеличенной длительностью импульса.
ЗБІЛЬШЕННЯ ТРИВАЛОСТІ ІМПУЛЬСУ ВЧ-ПОЛЯ В РЕЗОНАТОРАХ
ОСНОВНОЇ ЧАСТИНИ ЛУ ММФ
В.Н. Леонтьєв, В.В. Пеплов
На лінійному прискорювачі ММФ для збільшення середнього струму пучка протонів треба було
збільшити тривалість імпульсу ВЧ-поля в резонаторах основної частини прискорювача. Проведені роботи з
модернізації устаткування каналів ВЧ-живлення дозволили збільшити тривалість, що обгинає ВЧ-імпульсу
на виході підсилювального клістрона до 240 мкс, що дає можливість прискорювати пучок тривалістю
200 мкс. У роботі описані пророблені роботи, дані оцінки по обмеженню максимально можливих величин
тривалості, представлені результати експериментальних іспитів устаткування каналів ВЧ-живлення при
роботі з подовженим імпульсом і показана можливість стійкої роботи потужних модуляторів, попередніх
підсилювачів, клістронів, елементів хвилевідно-фідерної системи і самих резонаторів, що прискорюють в
експлуатаційному режимі зі збільшеною тривалістю імпульсу.
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.71-73. 73
INTRODUCTION
|