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DEVELOPMENT OF HIGH VOLATGE SUBSYSTEM AND COMPONENTS FOR
1 MW RF OF LEHIPA
Sandip Shrotriya*, Niranjan Patel, A. Shiju, Manjiri Pande and P. Singh
Ion Accelerator Development Division,
Bhabha Atomic Research Centre, Mumbai, India
*[email protected]
Abstract
Low energy high intensity proton accelerator (LEHIPA)
at BARC requires a total of around 2.9 MW of radio
frequency (RF) power at 352.2 MHz. This RF power is
generated by three klystron based high power RF
systems. Each of this 1 MW RF system uses high voltage
bias supplies that are floating at 100 kV for its operation.
Some of the bias supplies have been designed and
developed to operate in the CW and pulse mode.
Major high voltage bias supplies are (-) 100 kV /
20 A DC cathode supply and + 65 kV /10 mA (w.r.t
cathode voltage) anode supply and a filament power
supply floating at cathode voltage (-100 kV). The anode
and filament supply have been developed indigenously
whereas cathode supply is developed by IPR,
Gandhinagar. An high voltage interface system is
designed and developed indigenously to provide floating
arrangements and additionally houses a fast acting
crowbar, high voltage series resistors, insulating
transformers (dry type), high voltage dumping switch
with series dump resistor of 500 ohm, a high voltage
multi- distribution box and high voltage probes (divider
type) for HV measurement. All these components will be
housed in one single insulated rack. This paper gives
overview of development of all the high voltage
subsystem, results achieved and evaluation.
INTRODUCTION
High voltage subsystems and main components
for 1 MW klystron system require two floating bias
power supplies, high voltage crowbar protection system,
inclusive of dump switch and high voltage monitoring
signals. The basic block diagram of the klystron high
voltage system is given below in figure-1. In this paper,
details of each component, its function and test result are
given. The 1 MW klystrons will operate at -90 kV DC
(typical). Hence each component has been tested up to
120 kV DC.
A.
Filament supply
The filament power supply is 25 Volt / 25 Amp
(AC/ DC) floating on cathode voltage (-100 kV DC). The
isolation transform is used for filament voltage supply for
klystron. The primary voltage 230 Volt / 5 amp and
secondary voltage is 25 Volt floating at cathode voltage.
One end of the secondary winding of the isolation
transformer is connected to the cathode voltage which is 100 kV. To achieve this high voltage isolation, a dry type
isolation transformer uses epoxy resin for insulation.
Second end (secondary winding) of the isolation will be
connected to filament of the klystron. This isolation was
tested between secondary winding and core / primary
winding up to 150 kV and leakage current was observed
10 micro Amp. The load test was performed on isolation
transformer at 40 Amp / 25 Volt for 12 hrs. The
temperature rise of the core and secondary winging of
transformer recorded was 8 degree centigrade.
Figure 1: Block diagram of the high voltage system of
klystron
The filament voltage of the klystron will be
ramped to full voltage in 15 minutes to control the inrush
current of the klystron filament. The secondary voltage of
isolation transformer is controlled by controlling primary
voltage of the isolation transformer. For ramping the
primary voltage of the isolation transformer, a 230 Volt
SCR based control unit power supply was developed and
tested. This filament supply has remote/local mode and
fault signals for indication and over all interlock system.
B.
Anode power supply
The klystron current can be controlled by the
modulating anode voltage. The electrical configuration of
anode and cathode power supply for klystron is shown in
figure-1. The required anode and cathode voltage wave
forms are given in figure-2.
In order to have high efficiency in pulsed mode,
the rise- and fall-time of the beam pulse in the klystron
should be considerably less than 1μs. This goal was
achieved by using solid state modulating anode power
supply. The salient features of the modulator are, output
voltage + 65 kV variable (with respect to cathode voltage,
-100 kV) output current 10 m Amp, variable pulse
duration 5 micro sec to continuous wave (CW).
C.
Figure 2: Anode and cathode voltage requirement for 1
MW klystron
The power supply has been designed and
developed indigenously. Presently this supply is
undergoing tests on a high voltage dummy load that
simulates the klystron load. This power supply has a
voltage rms ripple 0.5 %, which was measured using high
voltage capacitors resistor set connected in parallel of
output terminal. The rise and fall time of the output
voltage was measured 1 micro sec in loading condition
using digital oscilloscope. The response time of the
power supply is 5 micro sec in fault condition. In remote
operation, the light signals (fiber optics) are used for
control and communicate to other external system. Fiber
optics signal has provided the isolation between high
voltage and low level control.
This 65 kV supply is floating on cathode voltage
(-100kV). This floated supply has been tested up to 100
kV in no load condition and 10 micro Amp leakage
current was observed. To test this power supply in full
load condition the 6.5 M ohm load floating load was
used. Two 150 kV high voltage divider / probe, one at
input terminal of the supply and second is at output
terminal of the supply was connected during testing. It
has been tested this power supply in pulse and CW mode.
The voltage wave-from is given in figure-3.
This being a dry type power supply, adequate
distance between each component has been provided
inside the power supply assembly so that air insulation is
sufficient thus avoiding the use of oil.
High voltage crowbar system
During the short circuit / arc condition inside the
klystron tube, the stored energy from the bias power
supplies may get dumped in klystron and this may cause
permanent damage to the klystron tube. Hence, klystron
needs to be protected in case of short circuit inside the
tube. This requires a fast processing circuitry that will
sense the fault current and bypasses the stored energy
from the power supply source. For this application, a 100
kV spark gap based crowbar protection system is used.
This gas pressure of the spark gap is adjustable and it
decided the operating voltage. The operating range of this
crowbar is from 50 kV to 100 kV. It has been tested for
full operating range. The static breakdown voltage and
response time of the crowbar system was measured using
high voltage capacitors as input high energy source.
Crowbar was triggered by external signal during the test.
The short current and voltage wave form was observed in
the oscilloscope.
D.
High voltage components
Dump switch and high voltage divider are also
part of the high voltage system. Dump switch was used in
the system to ground the high voltage connection during
OFF condition or maintenance condition. It has been
tested up to 120 kV and voltage discharge timing is
recorded on Digital oscilloscope. Two different type of
high voltage divider (analog/digital) are used in the high
voltage system. There have been tested up to 150 kV DC
voltage.
CONCLUSION AND FUTURE PLAN
The high voltage filament supply, anode power supply
and high voltage components required for 1 MW klystron
was ready and tested as per specifications. This high
voltage sub system is mounted in the single rack and high
voltage insulation test is also preformed for whole system
using CW HV tester and developed as per specifications.
In near future these sub systems will be integrated with
cathode power supply and 1 MW klystron.
ACKNOWLEDGEMENT
We would like to thank Dr. S. L. Chaplot,
Director Physics Group, BARC for his constant support
and encouragement.
REFERENCES
High Power RF Systems for LEHIPA for ADS", Manjiri
Pande*, Sandip Shrotriya, Sonal Sharma, BVR Rao, J.K.
Mishra and Dr. S. K. Gupta, 2 nd International Workshop
on ADS and Thorium Utilization, December-2011,
Mumbai.
[2] Klystron Based High Power RF System for Proton
Accelerator ", Manjiri Pande, Sandip Shrotriya, Sonal
Sharma, and V. K. Handu, IEEE-IVEC-2011 conference
held at Banglore.
[1]
Fig.-3 Output and input voltage wave form
Channel-2 and 3: 20 kV / division
Channel 2: input voltage - 100 kV w.r.t ground.
Channel 3: output voltage 20 kV w.r.t. input voltage