Transcript Maximum Power for Linac1 amplifiers

Refurbishment of CERN RF equipment for
MICE
M. Vretenar, CERN AB/RF
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MICE 23.02.2007
The CERN Linac1 Amplifiers
Developed in 1956-59 (photo of 1959)
for the old Linac1.
Frequency 202.56 MHz, 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.
The unit is about 3.6 m high, 1m x 1m
base.
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Linac1 amplifiers history
 From the very beginning, these amplifiers experienced problems in
reaching the peak power of 2.5 MW: breakdowns in the power extraction
system (later modified to a single loop and used up to ~1.5 MW) and in the
anode resonator.
Linac1 (protons, heavy ions) was decommissioned in 1992.
After Linac1 decommissioning a standard “modernization kit” (series of
mechanical modifications intended to improve reliability and easy
operation) has been developed for these units.
Most of the Linac1 amplifiers have been modernized and reused in other
installations: 2 + 1 spare for Linac3 (400 kW), 1 for Linac2 RFQ (1 MW), 2
at the AD-RFQ (0.3 and 1.6 MW).
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What is left of the Linac1 amplifiers?
Only 2 units left, one was
modified for 101 MHz and
then 88 MHz (gradient
test for bunch rotation
cavities in NF), the other
is a cannibalised spare,
stored in a hall for 50
years.
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Maximum Power for Linac1 amplifiers
 The maximum power achieved recently (1996) on these units was 1.7 MW
(AD-RFQ final amplifier, power limited by sparking and matching of the
output loop).
The first demand from MICE was for 4 MW out of a single unit equipped
with TH116. Discarded because required an expensive radical
reconstruction of the amplifier (anode blocker capacitor, HOM suppression,
double output, increased resonator diameter) and no guarantee of success
(bad experiences in the past at CERN with pushing TH116 to its limits).
Instead, preferred to prepare the 2 remaining amplifiers for 2 MW each.
Only minor modifications (together with standard upgrade kits) should be
required to go from the 1.7 MW measured in 1996 to 2 MW.
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Caveats
 The refurbishment of the linac amplifiers for MICE has
been authorized by the AB Department (Nov. 06), but there
are still some doubts concerning the level of UK support to
CLIC…
 The CERN Linac RF team is heavily involved in Linac4 and
from next year will work 100% on this project  it is now or
never, this year we still have a window for at least starting
refurbishing the amplifiers, from next year it will be very
difficult.
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Refurbishing details
2 “standard” upgrade kits will be applied to
the amplifiers:
1.
2.
Add neutralization circuit, improve RF
contacts and socket.
Modernize electronics: add industrial
filament regulator controlled by PLC, new
circuitry for transformer feeding.
+ replace the output loop with a “tapping”,
which should allow increasing power from
1.7 to 2 MW.
Work not going to be easy… many pieces have
to be remade, and few drawings exist!
We have to copy from our spare unit.
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What exactly we will do
It is not possible to test the amplifiers with RF
power at CERN (no anode supply, no RF drive).
They will be tested at CERN up to the “filament”
level: filament heating, test of cooling circuits.
The RF part (input matching, resonator tuning,
output matching) will be done to the “theoretical”
calculated values.
Input-outputs:
- 3 1/8” input connector
- 6 1/8” output connector (a bit at the limit for 2
MW…)
- RG220/U cable for HV connection
- electrical and water connections
Note that for a DC power supply, these unit need
a cathode switch circuit (not provided by CERN)
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Organisation of work
Principle: the reconstruction is done at CERN, up to the testing of filament. Then,
the amplifier is transferred to RAL or Daresbury for the RF tests.
At CERN:
1.
Collect drawings, and design modified parts.
2. Make inventory of existing and missing parts.
3. Machine mechanical parts.
4. Dismount, clean, reconstruct amplifiers.
5. Assemble ventilation circuitry.
6. Assemble filament circuit and filament regulation (PLC based, CERN standard)
7. Test filament and ventilation
These activities can be realized with minimum support of CERN staff if temporary
labor is used for: draftsman/designer, mechanic, wireman.
At MICE:
1.
Install cathode switch circuit (eventually also HOM suppressors).
2. Connect HV and RF loads.
3. Test with RF power.
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Status
The 2 units for MICE (blue) and the
spare CERN unit used as example (green)
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Other available RF equipment
We have 2 old Linac1 Modulators (=pulsed anode supplies)
for 25-30 kV, ~80 A, 1 Hz, 200 ms that we need to clear in
order to free space. If they can be useful, please show up,
otherwise at the beginning of March we will scrap them.
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