Transcript RF systems for muon cooling ICTF WP7

NVEC 2014
RF systems for MICE
Andrew Moss
The MICE RF Group and the TIARA WP7 Team
Contributions include Daresbury, RAL, CERN, LBNL,
LANL, FNAL,
Strathclyde & Sheffield Universities, and Imperial
College
Contents
• The amplifier system for MICE
– Modernisation and recommissioning of amplifier
systems
– Operation of the amplifier systems towards
achieving high power operation
The amplifier chain
At Lawrence Berkeley National
Laboratory (LBNL) there existed
some amplifier systems from the
Bevelac last used ~1992
• 201MHz tetrode and
triode systems capable of
up to 2MW pulsed
operation
Input cavity
Amplifier
cavity
Cavity Socket
Cavity
4616 super power tetrode Tube
Output tuning stub
4616 Tetrode testing
Starting at 10kV
Grid one 250V
Grid two 1800v
1kW drive
1mSec 1Hz pulsed operation
Ideal 50 Ohm load
4616 data sheet
60db
directional
coupler
200kW CW
water load
Tetrode testing
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The tetrode has adjustments for
cavity frequency, output coupling
and input frequency tuning, all of
which effect each other
Initial setup using an old tube to
check that all systems were ok,
100kW achieved
With new tube fitted and
conditioned we were able to
optimise the output up to 234kW
at 1Hz 1mSec pulse operation
with good gain and electrical
conversion
Triode HT tank
HT input
Tuning stubs
Water input with steam output
Triode socket in HT tank
Heater terminal
Anode Tap
Ad hoc and undocumented
modifications had been made to
improve the operation of the systems
Considerable reverse engineering and
revision was required
RF capacitor
Grid
RF capacitor & resistor stacks
RF input and movable Grid tap
1 metre long
cooled with
compressed air
Parts ready for rebuild
The re-build process
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With the amplifier completely
stripped down we were able to
inspect all the components
Change from grid modulated to
cathode modulated operation
All the spring fingers needed to be
replaced as these are key to the
operation of the amplifier system
Many of the sections of the amplifier
were silver plated to improve the
surface condition of the parts
Motorisation of the operation of the
tuning sections, grid tap and anode
tap which tune the performance of
the amplifier system
HT blocking
capacitor
Anode section
Moveable coax sections
inside the amplifier
structure
Grid section with RF
input
HT tank under
modification
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HT input to tank had
become distorted
Reformed to correct shape
and position using a heat
and a 2 Ton winch
Inner surface of tank was
polished to remove high
points
Assembly
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The amplifier was assembled in
stages using many jigs that were
made to align the fragile spring
fingers into the coaxial structures
of the amplifiers
RF output 8 inch coax
Triode socket in HT tank
Motor drive anode tap
HT input
Water in
and out at
35kV
6 inch
coax
RF power
out
Output capacitor
We operate at
constant HT with
cathode modulation –
cathode switched by
IGBT between -400V
to earth to switch
tube into conduction
Triode tube socket
Moveable output
capacitor
TH116 triode
Triode testing June 2012
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•
With an old triode valve fitted (to
be safe) at 32kV 72A = 2.3 MW
electrical power per pulse we
achieved 1.0MW RF power into a
test dummy load
No significant microwave of X-Ray
hazard was observed from the
amplifier system while it was on
Triode tube in HT tank
HT and
water
Power supply problems
After a number of technical
issues, power supply trips at 32kV
• power supply tube protection
device (crowbar) was finally
identified as the problem
• 140uF Capacitor bank (110kJ
sorted energy) must be
discharged in 5uS to prevent
damage to tube in event of an
arc
• New crowbar had to be fitted
Crowbar
protection
device
Amplifier system running into test load
• June 2013 – MICE RF parameters archived
– First triode final stage amplifier had demonstrated 1ms pulses
at 1Hz, 2.06MW @ 201.25MHz
– Up to 34kV bias, operation with good gain achieved
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Performance achieved:
2.06MW output RF
34kV bias voltage
129A forward average current
h=46% (electronic)
Gain 10.8dB
Input port return loss -12.5dB
VSWR 1.6
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170kW output RF
18kV bias voltage
15.5A forward average current
h=61% (electronic)
Gain 19dB
– Drive from Tetrode
– Drive from SSPA
• 2.27kW
The challenge
has been
achieved
MICE experimental hall