Hard tube pulser for 150 MW klystron
The development of adequate modulators for high peak power klystrons is one of the focus points for linear collider R&D programs. For the DESY/THD Sband linear collider study 150MW RF pulse power at 50Hz repetition rate and 3mks pulse duration is required. Two different modulator schemes were in...
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| Дата: | 1999 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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| Назва видання: | Вопросы атомной науки и техники |
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| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Hard tube pulser for 150 MW klystron / P.A. Bak, A.D. Goncharov, I.V. Kazarezov, V.V. Leonov, B.A. Skarbo, A.D. Cherniakin, M. Bieler // Вопросы атомной науки и техники. — 1999. — № 4. — С. 42-44. — Бібліогр.: 5 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
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irk-123456789-815262015-05-18T03:02:33Z Hard tube pulser for 150 MW klystron Bak, P.A. Goncharov, A.D. Kazarezov, I.V. Leonov, V.V. Skarbo, B.A. Cherniakin, A.D. Bieler, M. The development of adequate modulators for high peak power klystrons is one of the focus points for linear collider R&D programs. For the DESY/THD Sband linear collider study 150MW RF pulse power at 50Hz repetition rate and 3mks pulse duration is required. Two different modulator schemes were investigated. One is the conventional line type pulser, using a pulse forming network and a step up transformer, the other one is a Hard Tube Pulser, using a DC power source at the full klystron voltage and a switch tube. The main advantages of a Hard Tube Pulser are short rise and fall times of the HV pulse, resulting in high efficiency and simpler design. 1999 Article Hard tube pulser for 150 MW klystron / P.A. Bak, A.D. Goncharov, I.V. Kazarezov, V.V. Leonov, B.A. Skarbo, A.D. Cherniakin, M. Bieler // Вопросы атомной науки и техники. — 1999. — № 4. — С. 42-44. — Бібліогр.: 5 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81526 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
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English |
| description |
The development of adequate modulators for high peak power klystrons is one of the focus points for linear collider R&D programs. For the DESY/THD Sband linear collider study 150MW RF pulse power at 50Hz repetition rate and 3mks pulse duration is required. Two different modulator schemes were investigated. One is the conventional line type pulser, using a pulse forming network and a step up transformer, the other one is a Hard Tube Pulser, using a DC power source at the full klystron voltage and a switch tube. The main advantages of a Hard Tube Pulser are short rise and fall times of the HV pulse, resulting in high efficiency and simpler design. |
| format |
Article |
| author |
Bak, P.A. Goncharov, A.D. Kazarezov, I.V. Leonov, V.V. Skarbo, B.A. Cherniakin, A.D. Bieler, M. |
| spellingShingle |
Bak, P.A. Goncharov, A.D. Kazarezov, I.V. Leonov, V.V. Skarbo, B.A. Cherniakin, A.D. Bieler, M. Hard tube pulser for 150 MW klystron Вопросы атомной науки и техники |
| author_facet |
Bak, P.A. Goncharov, A.D. Kazarezov, I.V. Leonov, V.V. Skarbo, B.A. Cherniakin, A.D. Bieler, M. |
| author_sort |
Bak, P.A. |
| title |
Hard tube pulser for 150 MW klystron |
| title_short |
Hard tube pulser for 150 MW klystron |
| title_full |
Hard tube pulser for 150 MW klystron |
| title_fullStr |
Hard tube pulser for 150 MW klystron |
| title_full_unstemmed |
Hard tube pulser for 150 MW klystron |
| title_sort |
hard tube pulser for 150 mw klystron |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
1999 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/81526 |
| citation_txt |
Hard tube pulser for 150 MW klystron / P.A. Bak, A.D. Goncharov, I.V. Kazarezov, V.V. Leonov, B.A. Skarbo, A.D. Cherniakin, M. Bieler // Вопросы атомной науки и техники. — 1999. — № 4. — С. 42-44. — Бібліогр.: 5 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-06T06:32:12Z |
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| fulltext |
HARD TUBE PULSER FOR 150 MW KLYSTRON
P.A. Bak, A.D. Goncharov, I.V. Kazarezov, V.V. Leonov, B.A. Skarbo, A.D. Cherniakin,
M. Bieler*
Budker Institute of Nuclear Physics, Novosibirsk, Russia,
*Deutches Elektronen – Sinhrotron DESY, Hamburg, Germany
INTODUCTION
The development of adequate modulators for
high peak power klystrons is one of the focus points for
linear collider R&D programs. For the DESY/THD S-
band linear collider study 150MW RF pulse power at
50Hz repetition rate and 3mks pulse duration is
required. Two different modulator schemes were
investigated. One is the conventional line type pulser,
using a pulse forming network and a step up
transformer, the other one is a Hard Tube Pulser, using a
DC power source at the full klystron voltage and a
switch tube. The main advantages of a Hard Tube Pulser
are short rise and fall times of the HV pulse, resulting in
high efficiency and simpler design.
A 25MW RF power test version of a Hard Tube
Pulser has been built up and tested at DESY. Fig. 1
shows the basic circuitry of a Hard Tube Pulser.
A high voltage power supply is used to charge a
capacitor (or some other storage element) to the full
operating voltage of the klystron. This storage element
is connected to the switch tube, a vacuum tube with a
gridded gun, that is able to switch the full operating
voltage of the klystron. If the grid is driven to a positive
potential with respect to the cathode, electrons are
emitted from the cathode, go through a hole in the
grounded anode and hit the collector, driving it negative
to almost the cathode potential. The collector of the
switch tube is connected to the cathode of the klystron,
supplying it with a HV pulse of the length of the switch
tube grid pulse. During the pulse the storage element is
discharged to about 90% of its initial voltage, and
between the pulses it is charged again.
As long as the cathode voltage of the switch tube
does not change by more than 10% during the pulse, the
switch tube delivers a constant current, resulting in a
constant klystron cathode voltage.
In order to evaluate the advantages and
disadvantages of a Hard Tube Pulser, a test setup with a
150kV switch tube was set up at DESY [1][2], a study
about a 600kV switch tube pulser was written at INP,
Novosibirsk [3], and a study about a 560kV switch tube
was written by CPI, Palo Alto [4]. In addition to the
tests theoretical investigations were carried out about a
Hard Tube Pulser for a klystron delivering 150MW RF
power. The results of these studies are presented. Fi-
nally the efficiencies of a Hard Tube Pulser and a line
type pulser for a 150MW klystron are compared.
Fig. 1: Basic Circuitry of a Hard Tube Pulser.
PROPOSAL FOR A 600 KV HARD TUBE PULSER
Fig. 2 shows the circuitry of a Hard Tube Pulser,
as proposed in [3].
Fig. 2: Circuit of a 600 kV Hard Tube Pulser.
HVS - high voltage source; Kl – klystron; ST – switch
tube; CT – current transformer; Rd – resistive divider;
Cd – pulse divider; L1 – protection choke; C1, C3, L2,
L3, R1 – elements of PFN; C4, C5 – spurious
capacitance; R2, R3 – limiting resistors; SG1, SG2,
SG3 – protection spark gaps.
The high voltage power supply, the storage
elements, the switch tube and the cathode of the
klystron are all in one oil tank. The filament power for
switch tube and klystron and the power for the switch
tube grid pulser are fed into the tank by insulating
transformers. The tank (without the klystron) has a
height of 2.25m, a width of 1.75m and a length of
3.75m.
HVS consists of a step-up transformer with a
closed core and a full-wave rectifier. The secondary
winding of the transformer is divided into coils, which
(together with diodes) form sections of the rectifier.
Twenty-five sections make a column, providing the
preset voltage. A one layer primary winding is conic in
shape to decrease the leakage inductance. Rectifier
diodes of SEMIKRON HSKE-14000/6300--0.4 type are
used for the rectifier. A high voltage choke capable of a
short time operation is used here to protect the rectifier
elements in a situation of a total voltage breakdown. It
inductance is 1 mH. The choke is equipped with a
resistive divider providing for a sufficient damping in
case of breakdowns. The choke connects the high-
voltage electrode of the HVS with the rest of the circuit.
The energy storage unit consists of a storage
capacitor C1 and a simple pulse forming network (Rl,
C3, L2, L3). High voltage capacitors PERTINOL ROK
200/V at an operating voltage of 210 kV and a
capacitance of 75 nF are used as energy capacitors.
Three capacitors are connected in series in a special
module with admissible dimensions to obtain a
specified voltage of 630 kV. PFN elements, excluding
the energy storage C1 are united into one assembly unit.
Taking into account the stray capacitance of switch tube
and klystron, the elements of the pulse forming network
can be optimized reaching a rise time of the klystron
voltage of about 500ns and a fall time of about 1 µs.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 42-44.
42
Function-unit principle is realized in design of
pulser box. Low current electronic plates are located in
a frame assembled of an aluminium profile, special
configuration VME type. The frame is located in a
hermetic container with necessary electrical connectors.
Other components of the unit are submerged in oil. All
components of the unit are placed in a square (but with
necessary rounds off) metal container which is at a high
potential. The container is installed on a support
insulator designed to operate at a high constant voltage.
There is a special connector on the wall facing the
switch tube. It allows to quickly replace the tube. The
unit is powered via an insulating transformer with its
primary winding located on the tank wall, and the
secondary one located on one of the container walls.
The protective spark gap of ST is located near
the ST cathode insulator. It is mounted on the tank wall
to be able to feed the gas mixture for blowing. The
protective spark gap of modulator is mounted on the
tank wall also for the purpose of blowing. Besides, such
a design allows to open the inside cavity of the spark
gap in order to check and restore the electrodes without
draining the oil from the tank. A resistor 12 Ohm
absorbing the energy at an action of the spark gap is
mounted at the spark gap end.
Fig. 3 shows the calculated waveforms of the
klystron cathode voltage and the voltage across the
switch tube. Trace shows a blowup of the klystron
voltage flat top. The ringing on the pulse is of the order
of ±0.6%.
Fig. 3: a) – pulse flat-top on klystron, b) – pulse voltage
on klystron and switch rube.
PROPOSAL FOR A 560 KV SWITCH TUBE
The design of a 560 kV switch tube has been
investigated by CPI (former Varian), Palo Alto. Fig. 4
shows the design of the proposed switch tube, the
preliminary specifications of the tube are given in
Table 1.
Table 1: Specifications of the Switch.
Cathode voltage, kV 622
Anode voltage, kV 0
Collector voltage, kV 560
Efficiency, % 90
Beam current, A 503
Microperveance, AV3/2 1.025
Pulse width, µs 3
Duty cycle 1.5 10-4
The insulator between cathode and anode is
divided into 6 ceramics and 5 intermediate electrodes to
keep the maximum hold off voltage between adjacent
electrodes below 110 kV. Experience with the switch
tube tested at DESY indicated that the voltage hold off
capability on the DC side of the switch tube is one of
the key problems of these tubes.
Fig. 4: Design of the proposed switch tube.
The electron beam, emitted from the gridded
gun, is electrostaticly focused, passes through the
grounded anode, widens up behind the anode and hits
the collector. Calculations of electron trajectories show
that the collector can be depressed to at least 91 % of
the cathode potential without the risk of returning
electrons, which might hit the anode and cause
breakdown.
With the switch tube investigated at DESY a
collector depression of 92 % could be reached.
EFFICIENCY OF A HARD TUBE PULSER
For a prediction of the efficiency of a Hard Tube
Pulser, the maximum collector depression of the switch
tube is an essential parameter. For further calculations a
maximum depression of a well-designed collector of
95% will be used as an upper limit.
Calculations of the losses in all modulator
components lead to an average input power (HV supply,
electronics and switch tube filament) of 74960 W. The
useful power, i.e. the power in the flat top of the switch
tube pulse (535 kV, 700 A, 3 µs, 50 Hz), is 56175 W.
These numbers lead to a total efficiency of the proposed
Hard Tube Pulser (useful power divided by input
power) of 75 %. This has to be compared with
efficiencies of 50-60 % of existing line type modulators
and 70% of proposed line type modulators [5].
Although the power efficiency of a Hard Tube Pulser is
of the same order as the efficiency of a well designed
line type modulator, the total operating costs of a Hard
Tube Pulser will be higher due to the limited lifetime
and high price of the switch tube. The lifetime of a
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 42-44.
42
switch tube will be of the same order as the lifetime of
aklystron (typically given by the cathode lifetime), and
the production cost will be at least as high as that of a
klystron (big ceramic, many intermediate electrodes).
This has to be compared with the lifetime and
production costs of thyratrons, which are the only major
parts of line type modulators that have to be replaced
regularly. It also should be mentioned that replacing a
thyratron is a much faster job than replacing a switch
tube, because the oil tank has to be drained and taken
apart to remove the switch tube.
With the efficiency of a Hard Tube Pulser being
not better than the efficiency of a line type modulator,
and with the remaining R&D necessary to transfer the
proposed Hard Tube Pulser and the proposed switch
tube into real hardware, for the required power level a
Hard Tube Pulser can not be recommended as an
alternative to a line type modulator.
REFERENCES
[1] M. Bieler et.all., Commissioning of the Hard Tube
Pulser Experiment at DESY, Proceedings of the Forth
European Particle Accelerator Conference, London,
1994, p. 1933.
[2] M. Bieler et.all., Final Report on Hard Tube Pulser
Activities at DESY, DESY M 98-04, to be published
[3] I. Kazarezov et.all., Switch Tube Pulser for a 150
MW Klystron, INP internal report, Novosibirsk, 1996,
and DESY M 97-03, Feb. 1997
[4] J. Atkinson et.all., 560 kV Linear Beam Switch
Tube Study Project, CPI internal report, Palo Alto, July
1996.
[5] R. Brinkmann, G. Materlik, J. Rossbach, A Wagner
(editors), Conceptual design of a 500 GeV −+ ee Linear
Collider with Integrated X-ray Laser Facility, DESYY J
997-048 and ECFA 1997-182, May 1997.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 42-44.
42
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