Andrew MossDaresbury Laboratory

Collaboration Meeting 3514th -16th February 2013

Coseners House

MICE RF HP System

rprogress

Contents• System Overview

– MICE Hall System– Test System at Daresbury

• Amplifier update and status– Amplifier testing

• LLRF• Layout

– Will be presented by Alan Grant

• ConclusionAndrew Moss

RF system components

Andrew Moss

2 MW Amplifier

2 MW Amplifier

Master OscillatorControls etc

201 MHz Cavity Module

2 MW Amplifier

2 MW Amplifier

201 MHz Cavity Module

LBNL CERN

250 kW Amplifier

250 kW Amplifier

250 kW Amplifier

250 kW Amplifier

HT Supplies

HT Supplies

Daresbury

DL Test SystemAt present

Auxiliary Systems

Auxiliary Systems

NEW

Amplifier layout

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Test system at Daresbury

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Status of Amplifier s and power supplies

• Test bay at DL is operational and able to test amplifiers and power supplies as they become available

• New 250 kW amplifier has been bought, and has been under test at the manufacturers

• First 250kW amplifier has operated at 100kW with old tube, then 240kW with new tube fitted during 2012

• First TH116 high power amplifier has operated at 1MW during 2011 using an old RAL tube – new MICE tube fitted, has operated at 1.2MW for short time

• Two further 250kW amplifiers are being refurbished now• Two 2MW CERN amplifiers circuits refurbished but awaiting assembly

and high power test• Still need to build 3 more sets of power supplies – including set for TIARA

tests in experimental hall September 2013

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New amplifier in test bay at Photonis USA

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New 250kW amplifier enclosure

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New amplifier operating at 240MHz (driver low on gain at 201MHz)

Delivered to Mississippi on 8th June 2012

New tetrode tube in DL test amplifier number 1

•Tube needed to be conditioned after spending 3 years on shelf• Input matching required careful tuning as new valve presents different RF load eventually this was optimised at around 20dB•After 20 hours running, with a lot of adjustments to amplifier and electrical parameters, system is stable and predictable with linear response• Still some issues with screen power supply to sort out – loading of screen is moving with beam current and output loading

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250kW amplifiers numbers 2 and 3 • One amplifier is now completed and assembled in rack• Small number of parts left to source from the manufacturer because they are missing – may need modification to suit much older design of amplifier enclosure• final 250kW amplifier will be assembled back into rack in the next few months

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CERN amplifiers• Need assembly with the support

of CERN • Very similar electrical design

philosophy for the heater and control functions etc

• Addition of cathode switch electronics needed and possible small modifications so that they can be operated by the power supplies we already have – will be done as we find issues

• Already have additional coax sections (for twin output couplers) and second test load

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RF and power supply testing• Operation at 1.2MW with good conversion efficiency and gain

• Overload of power supply resistors during a crowbar caused system stop, replaced with higher power units, testing underway, but now problematic – repeated crowbar events

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Forward power into load

Current status HP Tests• Testing of the amplifier system continued into late 2012

– However performance above 300kW proved to be very difficult

• After a period of diagnosis on the power supply and amplifiers it was decided to remove the new tube and revert back to the old used tube to re-establish settings on the amplifier system

• As the power tube was removed it became clear that sparking had occurred around the valve which clearly indicated the source of the problems we had experienced– This would have triggered the initial crowbar event– Would have inhibited further increases in output power

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116 triode removal

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Evidence of arcing on HT connection

HT top box• HT top box is where high voltage

is applied to the anode• Water coolant is supplied to the

valve using insulating glass rods• On the original LBNL amplifier,

coolant passed out of the system as steam

• CERN HT top box with ability to pass both coolant flow and return pipes, which is why it was used

• Original LBNL HT top box with small inlet for only one coolant pipe

• HT box to tube interface is slightly different and is where fault is created

• LBNL HT top box is being converted to two water pipes and with correct spacing should remove issue that created arcing

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HT Top Box

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• The seating of the valve in the HT top box has caused the arcing

• The HT box actually belongs to another amplifier and was swapped in to speed up the commissioning process

• However there are some dimensional and location differences that obviously have caused the issues that we can see when the tube is removed

HT connection• Picture shows the correct spring

finger arrangement that is required for the LBNL amplifier

• Using the CERN top box allowed the valve to be pressed too far down into the socket causing the incorrect alignment

• All parts are being machined now ready for fitment to the amplifier in the next 5 weeks

• Amplifier testing will then proceed again with the old Triode tube first to 1MW

• The Triode tube will then be swapped for the new device and tested to 2MW

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Coax power and Losses • Assuming 2MW from the amplifier and 500kW for each cavity

coupler• Using calculations obtained from MEGA, the peak standoff for 6

inch coax with MICE parameters is 3MW, for 4 inch coax it is 1.4MW

• With N2 gas at 1.5Bar this rises 3.6MW and 1.68MW respectively• Using slow cavity filling technique the reflected power from the

cavity can be substantially reduced (P forward + P reflected = P total) we expect P reflected to be less than 20% of P forward = peak standoff will not be exceeded at start of each pulse

• Calculations of attenuation and hence power loss though coax is 10% per cavity coupler, which will reduce gradient available, overdriving amplifier maybe possible with reduced reliability – still need to test this

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RF to beam synchronisation• Cavity phase and amplitude will be stabilised to 0.5 deg and

1% with the ability to run as high a gradient as possible• Muon particles will arrive randomly in the cooling channel for

acceleration at various phase angles • Cavity phase angle will have to be measured for each muon

and time stamped for analysis after a period of running• Time of flight detectors along the cooling channel will be used

to trigger electronics to measure and digitise the state of the cavity phase angle to < 15 pS

• Groups from Sheffield and Strathclyde University’s in conjunction with DL and LBNL are working on possible solutions for this area of the experiment

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Digital low level RF Control• To control and regulate

cavity amplitude and phase angle during the RF pulse

• DL able to build up hardware ~ 3months

• Systems in use already with EPICS control, feedback, feedforward, resonance control etc

• Ramped pulse structure to limit reflected power tested on bench with 1.3GHz cavity

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AmplifierMice cavities

RF system monitoring and protection

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Summary• Progress on all three 250kW amplifiers including new system in USA• Tested first MICE high power tube and system to 1.2MW, some issues to

resolve before 2MW – Arc on anode HT plate identified– Probably the cause of the crowbar events– Modification to HT circuit completed, re-assembly completion imminent– Problems with crowbar circuit resolved

• High power testing to resume at DL as soon as resources allow– 2MW peak power objective

• Tests in MICE hall by September• We plan to replicate the power supplies and install and test them at DL –

this will allow testing to continue, then move one set of amplifiers and power supplies to the MICE hall for September 2013

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Extra Slides

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Page 24Page

24

Cavity Progress at LBNL/FermiLab • 1st Cavity Electropolished

• Now at FermiLab• 9 Cavities to be polished• New Coupler Design

• Nearing Completion• 6 Actuators to be built

• For the tuning arms• FermiLab/MTA have other

required components • Ready to move to clean

room• Assembly of 1st cavity• Install into single cavity

test chamber• Testing initially in fringing

field• ~1T

Cavity section view

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25

Revision to RF layout

• Proposed change to layout• Pairing of identical amplifier

assemblies• Should afford efficiency in

running up• Two hybrids move to the

amplifier side of the shield wall

• Line lengths re-matched by sections lying along the top of the shield wall

• No interference with crane service

Cavity section view

Original Arrangement

Revised Arrangement

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26

Revision to RF layout

Cavity section view

Preparation for TIARA & Procurement• Plan for installation of STEP IV allows for amplifier installation in 1st

slot• To meet TIARA deadline, September 2013

• Procurement of co-axial components, new tetrode and amplifier modulator components

• New Tetrode procured• Component list for co-axial and modulator components ready• Procurement of components required for TIARA prioritised

View over top of shield wall

• Mounting clamps and hangers for co-axial lines designed

Review of the RF system• Review meeting held in December 2011 to assess all aspects of current RF system design and

strategy - praise for the design work we had done and the results with the amplifiers • The main concern of the review panel was of the RF coax layout, the panel suggested a

different layout that would improve access to the amplifiers and simplify the coax runs. • This was taken on board and a new layout designed

Previously a lot of RF components were placed behind Shield wall

TH116 Triode amplifiers

4616 tetrode amplifiers

RF phasing

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Andrew MossAmplifier order changed so that experience of LBNL amplifiers will be consistent

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Coax system distribution

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RF coax parts list

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All RF coax parts identified and designed to fit between the amplifiers and the cavities

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RF distribution• RF coax distribution system has been finalised in 3D

CAD so that line lengths are matched• Enough flexibility has been built into the system to

take up small random errors• Purchasing of components has begun• System will be pressurised with 2 Bar of nitrogen to

help voltage standoff and use RF pulse shaping to minimise RF reflected power during the cavity filling period – this will increase reliability

Andrew Moss