Download Rf power circuits: CERN perspective

A POSSIBLE CERN CONTRIBUTION TO THE
MICE RADIO FREQUENCY
M. Vretenar, AB/RF – April 21st, 2004
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1. Starting assumptions:
 CERN RF/Linac team is involved in the LHC
(Linac2 and Ions for LHC), and next priority is
the SPL  little or no resources are left for other
projects.
 However, there is still a certain inventory of RF
equipment recuperated from our old linacs,
which can be useful for MICE, but need a
thorough reconstruction and modernization.
 This reconstruction can be done outside CERN,
but it would be more efficient and probably less
expensive to do it at CERN, where some
expertise is available.
 In consequence, here we elaborate a scenario (to
be approved by CERN management) where an
old Linac RF amplifier is reconstructed and
modified at CERN, to possibly achieve 4 MW.
The RF tests are however left for the MICE RF
team (no manpower and no test stand available at
CERN).
In addition to this reconstructed amplifier, CERN
can contribute with a certain number of 400 kW
amplifiers to be used as drivers.
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2. The CERN Linac Amplifiers (old type)
Developed in the 50’s
(photo of 1959) for
the old Linac1.
Equipped with the
TH170R triode, can
deliver a maximum of
2.5 MW with an
anode voltage of
40 kV.
The tube is water
cooled, and can
operate at a maximum
of 0.3% duty cycle.
About 3.6 m high, 1m
x 1m base.
From the very beginning, these amplifiers experienced
problems in reaching the peak power (2.5 MW):
breakdowns in the power extraction system (presently a
single loop, used up to 2 MW) and in the anode
resonator.
The Linac2 amplifiers are an improved version of the
Linac1, with more clearance in the resonator and an
improved output loop. They can (sometimes…) reach the
2.5 MW.
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3. The last Linac1 Amplifier
All the Linac1 amplifiers have been reused since Linac1
decommissioning in 1992, except one:
It was a spare unit, “cannibalised” of many components
and stored in a hall for more than 20 years, now in quite
a bad status. However most of the mechanical parts are
there, and for the missing parts some drawings probably
exist to remake them.
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4. How can we possibly reach 4 MW with this
unit?
We propose 3 improvements:
1. Use the TH116 triode: the socket is the same as for the
TH170R, gain is higher and in the data sheet this tube
is rated for 5 MW. However, at 200 MHz the size of
the tube (≈/4) limits the anode current and thus the
power to about 4 MW.
2. Redesign the anode resonator, using a kapton
capacitor as anode blocker (presently the anode is
sitting on 3 teflon insulators) and possibly taking a
larger diameter external tube.
3. Use 2 output loops, to reduce to 2 MW the power per
output. The outputs can then either be recombined, or
feed separately 2 cavities.
A kapton capacitor,
built in 1995 for a
100 MHz amplifier
On top of that, we have to:
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1. apply a “standard” modernization kit for Linac1
amplifiers: improved contacts and socket design.
2. Use a cathode switch circuit, if the anode voltage is
not pulsed and/or introduce HOM suppressors (not
foreseen in the original design).
Example: The 100 MHz amplifier for the LIS RFQ
(kapton capacitor + improved socket, 100 MHz, 1 MW
power).
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5. Work organisation
Principle: the reconstruction is done at CERN, and then the
amplifier is transferred at another laboratory for the RF tests.
At CERN:
1. Collect drawings, design modifications.
2. Machine missing and new components.
3. Dismount, clean, reconstruct amplifier.
4. Assemble ventilation circuitry.
5. Assemble filament circuit and filament regulation
(PLC based, CERN standard).
6. Test filament and ventilation.
For these activities, we need the maximum of external support
(people or money) for: draftsman/designer, mechanic, wireman.
At MICE laboratory:
1. Install cathode switch and/or HOM suppressors.
2. Connect HV and RF loads.
3. Test with RF power.
Success is not guaranteed, and to reach 4 MW is a difficult task
that has to be taken over by the MICE RF team. This team must
be involved already in the design stage.
A TH116 tube from CERN can be used for the tests at CERN,
but can not be sent to RAL or elsewhere, due to the recent
difficulties in TH116 production.
The existing kapton capacitor developed for 100 MHz could be
probably used at least for a first test (available end 2004).
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6. Estimation of cost for CERN in this scenario:
Work unit definition for the CERN part (time in Man Week = MWK):
1
2
3
4
5
6
7
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10
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12
13
14
15
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Collect existing drawings,
documentation and parts
Design 200 MHz kapton
capacitor
Supervision of design and
construction
Prepare drawings of
missing/modified parts
Prepare general drawing
Dismount and clean
amplifier parts
Repair damaged parts
Machine missing parts
Machine capacitor parts
Prepare installation for
rolling capacitor
Roll and assemble kapton
capacitor
Assemble amplifer
Order components for
filament regulation
Cabling and mounting
filament regulation
Cabling and mounting
cavity base
Test filament and cooling
TOTALS
Equivalent in kCHF for
B,C,E
Total (kCHF) for material
and temporary labour
A
RF
engineer
B
Mechanical
designer
MWK
MWK
1
1
1
3
C
Mechanic
MWK
D
Electronics
Technician
E
Wireman
FSU
Material
cost
MWK
MWK
kCHF
2
4
3
1
4
2
4
2
5
15
10
2
5
1
4
0.5
1
5
12
19
25
45
10
0.5
1
10
1
1
1
3
2
55
5
50
130
Conclusion:
2 man.month of CERN staff + 8 m.m of support labor + 50
kCHF
or
2 man.month of CERN staff + 130 kCHF
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