Analog computation of transients in the power amplifier of DTL RF system
Some peculiarities of DTL pulse RF system operation are connected with its load – a high quality factor cavity.
 In case of coinciding of tank and feeder frequencies overvoltages may appear at the falling edge of RF pulse in the
 power amplifier anode-grid cavity. In the paper by mea...
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| Опубліковано в: : | Вопросы атомной науки и техники |
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| Дата: | 2004 |
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| Формат: | Стаття |
| Мова: | Англійська |
| Опубліковано: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2004
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| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Analog computation of transients in the power amplifier of DTL RF system / A.I. Kvasha // Вопросы атомной науки и техники. — 2004. — № 2. — С. 81-83. — Бібліогр.: 4 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860068472270094336 |
|---|---|
| author | Kvasha, A.I. |
| author_facet | Kvasha, A.I. |
| citation_txt | Analog computation of transients in the power amplifier of DTL RF system / A.I. Kvasha // Вопросы атомной науки и техники. — 2004. — № 2. — С. 81-83. — Бібліогр.: 4 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | Some peculiarities of DTL pulse RF system operation are connected with its load – a high quality factor cavity.
In case of coinciding of tank and feeder frequencies overvoltages may appear at the falling edge of RF pulse in the
power amplifier anode-grid cavity. In the paper by means of program Micro-Cap V an influence of the RF system at
an overvoltage value is investigated.
Особливості роботи систем імпульсного ВЧ живлення резонаторів із трубками дрейфу обумовлені
високою добротністю останніх. У випадку збігу власної частоти резонатора з однієї з фідерних частот в анодному контурі підсилювача можуть виникати неприпустимі перенапруги. У роботі за допомогою
програми Micro-Cap V досліджується вплив параметрів схеми ВЧ живлення на величини перенапруг.
Особенности работы систем импульсного ВЧ питания резонаторов с трубками дрейфа обусловлены вы-
сокой добротностью последних. В случае совпадения собственной частоты резонатора с одной из фидерных
частот в анодном контуре усилителя могут возникать недопустимые перенапряжения. В работе с помощью
программы Micro-Cap V исследуется влияние параметров схемы ВЧ питания на величины перенапряжений.
|
| first_indexed | 2025-12-07T17:09:29Z |
| format | Article |
| fulltext |
ANALOG COMPUTATION OF TRANSIENTS IN THE POWER
AMPLIFIER OF DTL RF SYSTEM
A.I. Kvasha
Institute for Nuclear Research RAS, 117312 Moscow, 60-th October Anniversary Prospect, 7a
E-mail: kvacha@rambler.ru
Some peculiarities of DTL pulse RF system operation are connected with its load – a high quality factor cavity.
In case of coinciding of tank and feeder frequencies overvoltages may appear at the falling edge of RF pulse in the
power amplifier anode-grid cavity. In the paper by means of program Micro-Cap V an influence of the RF system at
an overvoltage value is investigated.
PACS: 29.17.+w
1. INTRODUCTION
RF system of the Moscow Meson Factory (MMF)
DTL consists of six identical RF channels: five operat-
ing RF channels and one reserve channel [1], working
at the frequency 198.2 MHz with RF pulse length
300 μs, duty factor – 0.03, RF pulse power in the tank
up to 3 MW.
Every tank (excepting the fifth short one) is excited
by the two moving loops through a long (20...30 m)
coaxial transmission line with the mighty phase regula-
tor (PR) in it. The right adjustment of the RF channel,
loaded at a high-quality tank, has to provide:
• the given level of the accelerating field in the tank;
• the optimal operation of the PA and high efficiency
of the modulator amplitude control during the beam
load;
• the allowable level of overvoltages in the PA an-
ode-grid cavity. The main cause of overvoltage ap-
pearance is the RF energy stored in the tank and re-
leased in the PA cavity after cutting off the modu-
lator pulse.
Unfortunately, the listed above conditions frequent-
ly come in contradictions with each other. The proce-
dure of RF channel tuning, as usual, consists of the fol-
lowing main steps:
1. RF amplifiers are tuned in operation of the PA at the
matched RF load;
1. coupling between the tank and the CTL is adjusted
with the matched RF load, connected to the loop,
exiting the tank. The loops are simultaneously
moved till the tank quality factor is halved.
2. The transmission line CTL is connected to the tank
and the last one is tuned exactly (by changing the
tank cooling water temperature) to minimize a tank
reflected wave value in the CTL.
Thus, after fulfilling the above-described procedure
only one degree of freedom remains i.e. the length of
transmitting line between the RF power amplifier and
the tank. As a rule, changing of the CTL length is the
most-used method of the RF overvoltage damping in
the PA anode-grid cavity. In [2] it was shown, that a
magnitude of RF voltage in the PA cavity depends on
the order of so-called “feeder frequencies” (or side fre-
quencies [3]) relatively of the master-oscillator fre-
quency. In turn, the feeder frequency (FF) values are
the function of the CTL length and complex loads on
both their ends, in other words, the tank and PA cavity
tuning. In paper [2] the analysis of the generalized RF
system, loaded at a high quality cavity (tank), is con-
sidered. But expressions, obtained in the paper for the
FF values calculation, are rather complicated transcen-
dental equations and, moreover, any changes in the RF
system scheme parameters leads to the necessity of
solving the new transcendental equation. This process
is tough one and it takes a lot of time. That is why at-
tempts were made to use possibilities of the well-
known programs for RF circuit investigations, such as
Multisim, Microwave Office, Micro Cap V. It turned
out, that an analysis of RF system scheme is the most
convenient to carry out by means of MC-V [4], which
allows estimating not only a frequency response of the
scheme but also its transients. Below the equivalent
scheme of the RF system, loaded at the high quality
tank, similar to that of first part of the Moscow meson
factory DTL is investigated.
2. EQUIVALENT SCHEME
OF THE RF SYSTEM
The simplified equivalent schematic diagram of the
RF system connected to the tank is shown in Fig.1,
where the RF power amplifier is represented by the in-
dependent voltage source V2 and the internal resistance
R1, the value of which is estimated for the vacuum tube
GI-54A,
Fig.1.Equivalent scheme of the RF system
installed in the PA of the MMF RF system. The circuit,
consisting of C1 (vacuum tube plate-grid capacity), L1,
R2, represents the anode-grid cavity of the PA, the cir-
cuit C2, L4, R3 represents the DTL tank, the parameters
of which are determined from the measured shunt
impedance and the quality factor of the tank. Induc-
tances L2 and L3 are that of the loop couplers in the PA
cavity and the tank. Both circuits at the scheme are
tuned at the same frequency 200.04 MHz, close to the
resonance frequency of MMF DTL tanks. K1 and K2
values, as a matter of fact, reject relations between the
magnetic field flow, run through the loop, and the
whole magnetic field in the PA cavity and the DTL
tank. K2 value is determined from the matched condi-
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 2.
Series: Nuclear Physics Investigations (43), p.81-83. 81
mailto:kvacha@rambler.ru
tion between the tank input impedance and that of a
lossless transmitting line T1. Before investigation tran-
sients in the PA cavity it is necessary to determine K1
and K2 values.
2.1. DETERMINATION OF THE K2 VALUE
Fig.2 shows the scheme for finding of the K2 value.
It corresponds to the well-known procedure of the tank
exciting loop positioning, when the tank is excited by
means of the pickup probe from the low-power oscilla-
tor V1 and the loop is connected to the matched CTL.
Fig.2. Equivalent circuit for finding of K2 value
By means of the program MC-V (AC analysis), the
value of K2=0.0127, which corresponds to double de-
creasing of the tank quality factor, was found.
2.2. DETERMINATION OF THE K1 VALUE
Now when the K2 value is determined let us find the
K1 value. For that it is necessary to optimize the K1 val-
ue, which corresponds to the RF amplitude maximum in
the matched load, connected to the CTL instead of the
tank (see fig.1). This procedure is in agreement with the
preliminary that of PA tuning. As above the K1 value is
changed in some limits - from 0.1 to 0.9 with the step
value ΔK1=0,1. Results of AC analysis by means of MC-
V for parameters of the scheme in fig.1 allow choosing
the optimal value of K1=0,75, that corresponds to the
best delivery of the RF power to the matched load.
3. FEEDER FREQUENCIES
As it was shown in paper [2] a value of overvoltages
in PA cavity depends on the mutual position of so-
called “feeder frequencies” and the tank resonance fre-
quency (TRF). Program MC-V allows convenient and
fast estimating of FF values at any RF system parame-
ters. For illustration in fig.3 the results of AC analysis
of the scheme in fig.1 (node 1) are presented, R1 value
changing from 100 to 5 k. The last one corresponds to
the internal resistance of GI-54A without RF exciting
and plate supply, i.e. at the falling edge of RF pulse.
Fig.3. The nearest to TRF feeder frequencies (LCTL/λ=20.2)
In fig.4 the nearest to the tank resonance frequency
FF values as a function of the CTL relative length are
shown.
The more is the CTL length, the closer are FF val-
ues and the less is its slope, and on the contrary. But in
any case, there are always some CTL lengths at which
coincidence of feeder frequency and TRF takes place.
Just at these lengths the highest values of overvoltages
in PA cavity are appeared. It is necessary to have in
view, that variations in the K1 value and PA cavity tun-
ing have an affect on the mutual position of the tank
resonance and feeder frequencies. Really, as follows
from experiments, with any CTL length it is always
possible to achieve the overvoltage value maximum in
the PA cavity by means of appropriate tuning of it.
Fig.4. The nearest to TRF feeder frequencies as a func-
tion of LCTL/λ
4. TRANSIENTS IN THE DTL RF SYSTEM
Within the framework of the program MC-V there is
not a possibility to create a RF source at a frequency of
200 MHz. So for research of transients at the falling edge
of RF pulse in the PA anode-grid cavity the circuit in
fig.5 is offered. Formation of a required RF signal is car-
ried out with the help of two switches Part.1 and Part.2.
In beginning of process the switch Part.2 is closed, and
the switch Part.1 is open. After the capacity C2 will be
charged from a source V4, the first switch is disconnect-
ed and in some μs the second switch is closed; thus the
capacity, discharging, excites attenuated RF oscillations
in the tank at its resonance frequency (TRF).
Fig.5. The circuit for research of transients
The most dangerous situation arises when the coin-
cidence between TRF and one from FF takes place. In
this case in the PA cavity the amplitude of RF voltage
immediately after switching Part.1 might in a few times
exceed that of the steady state RF voltage Uao in excit-
ing the tank from PA. For estimation of real amplitudes
of RF voltage in the PA cavity the value of V4 in fig.5
corresponds to the steady-state RF amplitude in the
tank #2 of the MMF DTL. In turn, from AC analysis it
is not difficult to determine the RF voltage value Uao in
the PA cavity and to compare it with the value of volt-
age excited in the PA cavity from the tank. The situa-
tion is aggravated with, that after switching off PA (at
falling edge of the RF pulse) the vacuum tube internal
resistance R1 is increased almost by two orders. It is
connected with employing a grounded grid GI-54A, be-
82
cause of what the RF voltage, transmitting from the
tank in the anode-grid PA cavity, does not really excite
the PA cathode-grid cavity due to the low value of the
PA vacuum tube capacity Cak and low Roe of the cath-
ode-grid cavity. Only presence of the vacuum tube per-
meability maintains a small current through it. In fig.6,7
the most typical transients at the falling edge of RF
pulses in the PA cavity are given.
Fig.6. Envelopes of RF signal at the falling edge of RF
pulse in the PA cavity (LCTL/λ = 20)
Fig.7. Envelopes of RF signal at the falling edge of
RF pulse in the PA cavity (LCTL/λ = 20.25)
For convenience the envelopes of the RF signals at
the outputs of amplitude detectors D1 and D2 (nodes
10,13) are shown. From consideration of the transients
and AC analysis it follows:
- overvoltage value might be changed almost on the or-
der of magnitude depending on the CTL length. The
highest overvoltage value in tuning the tank and the PA
cavity at the same frequency takes place at
LCTL/λ=(2n+1)λ/4 and the lowest one – at LCTL/λ = nλ;
- beating frequency value between FF and TRF is the
highest at LCTL/λ = nλ, and is the lowest at
LCTL/λ=(2n+1)λ/4;
- transient duration at the falling edge of pulses in a few
times is less at LCTL/λ = (2n+1)λ/4 than at LCTL/λ = nλ.
5. CONCLUSIONS
The limited volume of the paper does not allow pre-
senting in the full volume all the aspects of the investi-
gations, which have been carried out with the use of the
program МС-V. Nevertheless, it is possible to suggest
that the results of simulation, qualitatively, well coincide
with results of experiments at the real equipment. So, at
unsuccessful tuning of the РА and choice of the CTL
length between the PA and the tank in the MMF DTL RF
system, the overvoltages in the PA cavity are so great,
that it is necessary to reduce in two - three times the PA
vacuum tube plate pulse voltage to pass this point. Other-
wise, overvoltages result in breakdowns in the PA cavity
and switching-off of the channel by the crowbar circuit.
In this case, the duration of the trailing edge of RF pulse
in the tank is reduced in a few times and is accompanied
by low-frequency modulation (see fig.7). What ways of
overvoltages decrease might be recommended?
As it was mentioned above, the mutual position of FF
and TRF strongly depends not only on the CTL length,
but also on the PA cavity tuning and its coupling with
CTL. Due to the sharp increasing of the PA cavity quali-
ty factor after PA vacuum tube plate pulse voltage cut-
ting (R1 in fig.5 is increased by two orders), PA cavity
detuning alongside with correct choice of the CTL length
are the most effective methods of overvoltage decreas-
ing. So, detuning of the PA cavity at 2 MHz decreases
overvoltages in 2...3 times, at the same time decreasing a
tank RF voltage only at 0.2...0.3%. Anyway, the control
of the CTL length and PA cavity tuning, providing an ar-
rangement of TRF symmetric concerning the nearest two
feeder frequencies, guarantees the minimum values of
overvoltages in the PA cavity [3].
REFERENCES
1. E.S.Esin, L.V.Kravchuk, A.I.Kvasha. Moscow Me-
son Factory DTL RF System Upgrade // Proceed-
ings of the 1995 PAC and ICHEA Conference.
1995, Dallas, Texis, p.1175.
2. A.I.Kvasha. Investigation of Overvoltages in the
Anode-Grid Cavity of the 200 MHz Pulse Power
Amplifier of the MMF // Proc. of the 2001 PAC
Conference, June 18-22. 2001, Chicago, Illinois,
p.1225.
3. Reinhold Hohbach. Investigation on Stabilizing the
92 MHz, 150 kW Booster Amplifier // TRIUMF
Design Note. TRI-DN-95-24.
4. Micro-Cap V. Electronic Circuit Analysis Program,
Spectrum Software 1993.
АНАЛОГОВОЕ ВЫЧИСЛЕНИЕ ПЕРЕХОДНЫХ ПРОЦЕССОВ В МОЩНЫХ УСИЛИТЕЛЯХ
А.И. Кваша
Особенности работы систем импульсного ВЧ питания резонаторов с трубками дрейфа обусловлены вы-
сокой добротностью последних. В случае совпадения собственной частоты резонатора с одной из фидерных
частот в анодном контуре усилителя могут возникать недопустимые перенапряжения. В работе с помощью
программы Micro-Cap V исследуется влияние параметров схемы ВЧ питания на величины перенапряжений.
АНАЛОГОВЕ ОБЧИСЛЕННЯ ПЕРЕХІДНИХ ПРОЦЕСІВ У ПОТУЖНИХ ПІДСИЛЮВАЧАХ
А.І. Кваша
Особливості роботи систем імпульсного ВЧ живлення резонаторів із трубками дрейфу обумовлені
високою добротністю останніх. У випадку збігу власної частоти резонатора з однієї з фідерних частот в
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 2.
Series: Nuclear Physics Investigations (43), p.81-83. 83
анодному контурі підсилювача можуть виникати неприпустимі перенапруги. У роботі за допомогою
програми Micro-Cap V досліджується вплив параметрів схеми ВЧ живлення на величини перенапруг.
84
ANALOG COMPUTATION OF TRANSIENTS IN THE POWER
AMPLIFIER OF DTL RF SYSTEM
REFERENCES
|
| id | nasplib_isofts_kiev_ua-123456789-79350 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T17:09:29Z |
| publishDate | 2004 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Kvasha, A.I. 2015-03-31T14:11:52Z 2015-03-31T14:11:52Z 2004 Analog computation of transients in the power amplifier of DTL RF system / A.I. Kvasha // Вопросы атомной науки и техники. — 2004. — № 2. — С. 81-83. — Бібліогр.: 4 назв. — англ. 1562-6016 PACS: 29.17.+w https://nasplib.isofts.kiev.ua/handle/123456789/79350 Some peculiarities of DTL pulse RF system operation are connected with its load – a high quality factor cavity.
 In case of coinciding of tank and feeder frequencies overvoltages may appear at the falling edge of RF pulse in the
 power amplifier anode-grid cavity. In the paper by means of program Micro-Cap V an influence of the RF system at
 an overvoltage value is investigated. Особливості роботи систем імпульсного ВЧ живлення резонаторів із трубками дрейфу обумовлені
 високою добротністю останніх. У випадку збігу власної частоти резонатора з однієї з фідерних частот в анодному контурі підсилювача можуть виникати неприпустимі перенапруги. У роботі за допомогою
 програми Micro-Cap V досліджується вплив параметрів схеми ВЧ живлення на величини перенапруг. Особенности работы систем импульсного ВЧ питания резонаторов с трубками дрейфа обусловлены вы-
 сокой добротностью последних. В случае совпадения собственной частоты резонатора с одной из фидерных
 частот в анодном контуре усилителя могут возникать недопустимые перенапряжения. В работе с помощью
 программы Micro-Cap V исследуется влияние параметров схемы ВЧ питания на величины перенапряжений. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Элементы ускорителей Analog computation of transients in the power amplifier of DTL RF system Аналогове обчислення перехідних процесів у потужних підсилювачах Аналоговое вычисление переходных процессов в мощных усилителях Article published earlier |
| spellingShingle | Analog computation of transients in the power amplifier of DTL RF system Kvasha, A.I. Элементы ускорителей |
| title | Analog computation of transients in the power amplifier of DTL RF system |
| title_alt | Аналогове обчислення перехідних процесів у потужних підсилювачах Аналоговое вычисление переходных процессов в мощных усилителях |
| title_full | Analog computation of transients in the power amplifier of DTL RF system |
| title_fullStr | Analog computation of transients in the power amplifier of DTL RF system |
| title_full_unstemmed | Analog computation of transients in the power amplifier of DTL RF system |
| title_short | Analog computation of transients in the power amplifier of DTL RF system |
| title_sort | analog computation of transients in the power amplifier of dtl rf system |
| topic | Элементы ускорителей |
| topic_facet | Элементы ускорителей |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79350 |
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