MICE Target
Electronics
Paul J Smith
University of Sheffield
Fermilab 10th June 2006
P J Smith
University of Sheffield
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Presentation Overview
•Actuator Details
•Target Position Monitoring
•Control System
•Power Electronics
•DAQ (Briefly)
•Future Work/Conclusions
P J Smith
University of Sheffield
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Actuator Details
•Composed of 24 stacked coils each
~3mm thick
•From the ‘electronics’ point of view it
can be effectively be though of as 4
units of 6 coils
•The device can be driven in a similar fashion to a three
phase rotary motor
A
B’
C
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P J Smith
University of Sheffield
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•Presently all coils are wired in series as
a single ‘bank’
•The shuttle can be driven in two
modes
4A
4B
4C
Here, accurately knowing the position of 4A'
the shuttle is critical
4B'
4C'
- On Phase
- Off Phase
P J Smith
University of Sheffield
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2A
2B
2C
2A
2B
2C
2A'
2B‘
2C'
2A'
2B'
2C'
2 Bank
System
P J Smith
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University of Sheffield
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Modes Of Operation
P J Smith
PARK
NO POWER
HOLD
OFF-PHASE
3 Amps
ACTUATE
ENABLE
OFF-PHASE
3 Amps
ACTUATE
ON-PHASE
~80 Amps
University of Sheffield
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Position Monitoring
•Previously we had been using three hall switches
aligned to a set of small magnets embedded into the
shaft to give positional information
•This has now been replaced by a optical quadrature
system that uses three lasers to track a grating
attached to the shaft of the shuttle
P J Smith
University of Sheffield
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How does it Work?
Collimators
Lenses
Multi-mode
optical fibres
Single
Mode
Optic
Fibers
Grating – Slits
at 300
micron spacing
Receiver
LASER
Source
Shaft of Shuttle
P J Smith
University of Sheffield
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Multimode fibres –
collecting
P J Smith
Grating University of Sheffield
Single mode fibres –
transmitting
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Position Monitoring
Hall Switches
Optical
Position known to about 3mm
Position known to about 150 micron
Only provided modulo 6 positional
information
Absolute position is known
Questions about reliability of Hall
Switches in Radiation
Still Questions about Reliability – but
radiation hard components and
fibres can be used
Long signal cables 50m required in
electrically noisy environment
Effectively noiseless transmission
P J Smith
University of Sheffield
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Position Monitoring
•The system has proved to be a much better way of
ascertaining the shuttles position than the Hall switches
BUT there has been both hardware and software ‘bugs’:
this system is presently being developed and improved.
-Development of ‘flat’ windows to improve collimation
and light collection
-Upgrade of electronics to remove some problems with
the index channel
-Upgrade of software to ensure that position data is
accurately read by other boards
P J Smith
University of Sheffield
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Diagram of the System
Control
Current
Laser
Power
Electronics
Collimators
Board
Controller
Control
Board - P
Collimators
Optical Amplifier
Programmable
Index Offset P
Optical Amplifier
Quadrature
Optical Amplifier
P J Smith
University of Sheffield
Board - P
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Control System
•Output from the position system is input into the
controller
•Using PIC processors – Now that we are gaining some
experience with these processors we are able to
upgrade them. More Speed - 8MIPS. More memory
•This takes the positional information and other
status/inputs and decides what coils in the actuator
should be powered and at what current – Uses look-up
tables
•Different lookup tables can represent different
actuation depths or actuation profiles.
P J Smith
University of Sheffield
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Control System
•We are also in the process of upgrading the interface
between the controller and the power electronics from
an electrical interface to an optical one
• This is a reflection upon the decision to move the
power unit into the ISIS ring and also provides a
consistent interface
P J Smith
University of Sheffield
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MICE HALL
ISIS HALL
5 metres
Actuator
&
Power
Electronics
Control
Electronics
Optics
~50 metres
P J Smith
Cable
Optic Fibres
University of Sheffield
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Power Electronics
•In the lab we have been using a system that allows us
to pulse the actuator at up to 10A
•With this we have achieved an actuation depth of
28mm in 50ms.
•This was in free air and the coil timings have not yet
been optimised – possible room for improvement?
•The current to the actuator is controlled by
superimposing a 20kHz PWM signal onto the coil
switching signals. The duty cycle of the PWM
determines the ‘effective’ current that the actuator sees.
•An effective current of 2-3 Amps is sufficient to levitate
the shuttle
P J Smith
University of Sheffield
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 Power Electronics 
•BUT: 10 amps is not enough to actuate the shuttle to
specification! – We suspect that ~80 amps is the
minimum current that will be required to do this
•The design of a suitable power stage has been taken
on by Daresbury Laboratories in the UK – Steve
Griffiths, Jim Cartledge
P J Smith
University of Sheffield
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 Power Electronics 
•Daresbury design will centre around a trickle
charged capacitor bank as the high currents are only
required for a relatively short duty cycle
•As the current requirement is not yet well specified
they are using IGBTs (Insulated Gate Bipolar
Transistor) that are rated up to 300A @ 20kHz
•The idea here is to give us plenty of overhead so if
we should find that the actuators current requirement
is higher than expected then it will be relatively easy
to provide it without a major redesign.
•We should obtain the first of two power modules
from Daresbury by late summer – In time for tests at
RAL in October
P J Smith
University of Sheffield
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 Power Electronics 
•Much to do on the mechanical design to ensure that
the actuator can dissipate the heat when 80 Amps is
passed through it.
•Improve the thermal conduction away from the coils
•One electronic solution is to run the actuator coils as a
series of 2 or 4 banks
-This could reduce thermal loading by up to ~50%
-But significantly increases the complexity of the
controller
-Requires more Power Drivers
P J Smith
University of Sheffield
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DAQ
•DAQ was covered at Osaka in more detail by Lara
•DAQ write individual pulses to file
•Analysis of individual pulses
For each insertion the position is monitored to
~150 microns at 500ns time resolution
•Analysis of trends over time
•Future upgrade to an EPICS system so that the target
performance can be monitored and recorded by MICE
users
P J Smith
University of Sheffield
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10 Ampere Pulse –
38mm travel
P J Smith
10 Ampere Pulse –
28mm travel
University of Sheffield
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Current & Future Work
•Much of the electronics is being ‘upgraded’ at the
moment – Hence the lack of photos and video clips of a
working actuator!!
-Quadrature boards
-Controller boards
-Optical Links being installed
•Starting to take the issues of ‘noise’ more seriously as
the long term reliability of the electronics is important
-Wiring layout
-Appropriate shielding
•All of this should be completed before the July tests.
P J Smith
University of Sheffield
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Current & Future Work
•Redesign of optical block to remove alignment/light
collection problem
•This is something that we have only just started to
look at – doubtful that the present optical block will be
replaced for July – but certainly for the October tests
P J Smith
University of Sheffield
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Conclusion
•We have had hundreds of recorded pulses from the system with it
running at an actuation current of 10A
•It has been reliably(?) actuated for an average of 45 minutes
without dropout at 0.3Hz
•What we have learnt from this is being recycled back into the next
iteration of design for the electronics to make a system that is far
more robust and reliable
•The actuator is being moved from being actuated in open air to
being actuated in a vacuum system
•We are acquiring a Power Supply that should allow us to actuate the
shuttle through the required envelope for operation in ISIS –
Questions over coil heating yet to be resolved
•We need to prove the long term reliability of the electronics and the
optical system
P J Smith
University of Sheffield
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