1. D. Woog M.J. Barnes, J. Holma, T. Kramer
Magnetic core and semiconductor switch characterisation for an Inductive Adder kicker generator
D. Woog
M.J. Barnes, J. Holma, T. Kramer
David Woog - FCC Week 2017, Berlin
31/05/2017

2. David Woog - FCC Week 2017, Berlin
Content
FCC-hh injection
Inductive Adder concept
Magnetic core characterisation
Semiconductor switch characterisation
Preliminary prototype design
Milestones and next steps
David Woog - FCC Week 2017, Berlin
31/05/2017

3. FCC-hh injection system
LHC
SPS
FCC
Injection from high energy booster (HEB) into FCC
Injected bunch train needs to be deflected onto the circular orbit
Circulating bunches must not be kicked
Pulsed magnetic field in kicker magnet requires high power pulse generator
Kicker (pulse) generators
Septum magnets
Kicker magnets
Injected bunch train
Circulating bunch trains
David Woog - FCC Week 2017, Berlin
31/05/2017

4. David Woog - FCC Week 2017, Berlin
FCC-hh injection
Different high energy booster (HEB) options for FCC are in discussion, based on:
SPS (0.45 TeV, 1.3 TeV)
LHC (1.6 TeV, 3.3 TeV, 6.5 TeV)
FCC (3.3 TeV, 6.5 TeV)
In every case a reliable and fast injection kicker system is needed
Baseline HEB is LHC at 3.3 TeV
Parameter
Unit
Value
Kinetic Energy
[TeV]
3.30
Angle
[mrad]
0.18
Pulse flat top length
[µs]
2.00
Flat top tolerance
[%]
±0.50
Field rise time
0.425
Voltage
[kV]
15.70
Current
[kA]
2.50
System impedance
[Ω]
6.25
Parameters for FCC-hh injection
David Woog - FCC Week 2017, Berlin
31/05/2017

5. David Woog - FCC Week 2017, Berlin
FCC injection – generator options
Required field rise time: µs
→ µs of kicker magnet fill time
→ µs remain for pulse current rise time
For machine protection reasons high reliability of the kicker system is necessary!!
→ Thyratron pre-firing problems are unacceptable for FCC
~340mm
New pulse generator design is needed
Thyratrons must be avoided as switch
Semiconductor (SC) switches are a promising alternative
Two main pulse generator designs based on SC-switches under consideration:
Inductive Adder (IA)
Solid state Marx generator
see Poster on Tuesday
by A. Chmielinska «Solid-State Marx generator for use in the injection kickers of the FCC»
High voltage thyratron
David Woog - FCC Week 2017, Berlin
31/05/2017

6. David Woog - FCC Week 2017, Berlin
Inductive Adder concept
Stack of 1:1 transformers
Secondary windings are connected in series
Parallel branches of primary windings define max. output current
Parameters such as insulation properties, parasitic inductances, etc. define system impedance
𝐴 c
𝐼 sec
Stalk (secondary)
magnetic core
𝐼 prim
primary winding
insulation
parallel branches
PCB
Schematic drawing of an IA [4]
David Woog - FCC Week 2017, Berlin
31/05/2017

7. David Woog - FCC Week 2017, Berlin
Inductive Adder concept
Advantages and disadvantages of the IA compared to traditional pulse generators (PFN, PFL)
Pro
Con
Based on semiconductor switches
Ability to turn on and off current
Hence eliminate PFN/PFL
Output transformer necessary
Modular design
High energy storage in capacitors
All electronics ground referenced
Reduced maintenance
Larger dynamic range
Modulation of output pulse possible [5]
Simple replacement of components
Easy to adapt to different applications
Main components of the IA:
Magnetic core (following slides)
Semiconductor switches (following slides)
Pulse capacitor (tested and selected)
Insulation material (selected)
High voltage diodes
David Woog - FCC Week 2017, Berlin
31/05/2017

8. David Woog - FCC Week 2017, Berlin
Magnetic core
Important key component of the IA
Dimensions and material characteristics are important
Saturation of core must be avoided
Large core cross sectional area 𝐴 c needed
Pulse parameters
𝑡 pulse , 𝑉 layer
Magnetic flux density swing
∆𝐵 c
Core fill factor
η Fe
Security margin
𝛼 m
𝐴 c = 𝑡 pulse ∙ 𝑉 layer ∙ 𝛼 m ∆𝐵 c ∙ η Fe
Parameters of interest:
Equivalent loss resistance ( 𝑅 c )
Magnetizing inductance ( 𝐿 m )
B-H curve
Frequency behaviour
Biasing current ( 𝐼 bias )
Equivalent circuit of the core:
𝐿 m
𝑅 c
𝑉 out
David Woog - FCC Week 2017, Berlin
31/05/2017

9. David Woog - FCC Week 2017, Berlin
Measured B-H cures of different core types
Nanocrystalline tape wound core with 30 cm ruler
Thank you to Silvia Aguilera, Michal Krupa and Patrick Odier from CERN BE-BI group for assistance with measuring the B-H curves.
David Woog - FCC Week 2017, Berlin
31/05/2017

10. David Woog - FCC Week 2017, Berlin
Measurements on sample cores
Test setup for sample cores, based on the prototype for CLIC DR IA :
A MOSFET is discharging a capacitor over the primary winding of the core
The primary current is measured with a current sensor
The output voltage is measured on the secondary winding without load
On another test setup the B-H curves were measured
Equivalent circuit of test setup:
𝐿 m
𝑅 c
𝑉 out
𝐶 c 𝑆 A
Current sensor
Pulse capacitor
MOSFET
Core housing
(primary winding)
David Woog - FCC Week 2017, Berlin
31/05/2017

11. David Woog - FCC Week 2017, Berlin
Pulse characterisation of cores
𝑉 c =350 V
𝐼 0
𝑡 pulse =4.2us
∆ 𝐼 m
𝐿 m = 𝑉 c ∙ ∆𝑡 pulse ∆ 𝐼 m
𝑅 c = 𝑉 c 𝐼 0
Core 1 2 3 4 5 6 7 8
𝑅 c in Ω 55 50 65 75
150
160
230
200
𝐿 𝐦 in µH
282
367
191 56 42 30
30.6
B-H shape
square
linear
David Woog - FCC Week 2017, Berlin
31/05/2017

12. David Woog - FCC Week 2017, Berlin
Results of core measurements
Core 1 2 3 4 5 6 7 8 9 10
𝑅 c in Ω 55 50 65 75
150
160
230
200 70
𝐿 𝐦 in µH
282
367
191 56 42 30
30.6
28.8
B-H shape
square
linear
∆𝑩 𝐬𝐚𝐭 in T
2.4
2.1
2.0
𝑰 𝐛𝐢𝐚𝐬 in A 15 20
Cores 1-4 have been chosen as they best suit the requirements:
Highest inductance of all sample cores
Biggest ∆𝐵 sat
Low biasing current required
High inductance and ∆𝑩 𝐬𝐚𝐭 improve the IA design. The higher losses can be accepted.
David Woog - FCC Week 2017, Berlin
31/05/2017

13. David Woog - FCC Week 2017, Berlin
Considerations on Semiconductor Switches
Semiconductor (SC) switches to replace Thyratrons:
SiC MOSFETs seem promising
Advantages compared to Si components
Fast switching times
Lower values of 𝑹 𝐨𝐧 (<0.05 Ω)
Up to 1700 V available
Wide bandgap technology is a ‘rather’ new
Devices are still in development
Nevertheless there are already suitable devices available
Capability of devices has to be measured ( 𝑡 r,0.5−99.5 , 𝐼 D,pulse(2.5μs,1kV) )
Radiation hardness of SiC devices is of interest
Examples for SiC MOSFETs available on the market:
SiC devices 1 2 3 4
𝑉 DS
1200 V
1700 V
𝑡 r,10−90
32 ns
9 ns
20 ns
44 ns
𝑡 f,10−90
28 ns
22 ns
18 ns
𝐼 D,25°C
90 A
80 A
72 A
95 A
𝐼 D, pulse
250 A
190 A
160 A
237 A
𝑅 on
25 mΩ
40 mΩ
45 mΩ
22 mΩ
High 𝑉 DS is required to reduce number of layers
High 𝐼 D, pulse is required to reduce number of branches
High 𝑅 on causes increased voltage drop
Fast rise time is required
David Woog - FCC Week 2017, Berlin
31/05/2017

14. David Woog - FCC Week 2017, Berlin
Semiconductor switches characterisation
The capability of different sample devices has been tested
High current capabilities for ~2.5 µs pulse at 1 kV
Fast current rise times at high voltage from 0.5 to 99.5 %
The switching behaviour of the devices is strongly dependend upon the gate driver circuit
Device 1 2 3
𝑡 r,0.5−99.5
64 ns
100 ns
76 ns
𝐼 pulse,2.5µs
>200 A
Test results seem promising
PSpice simulations with measured values show a sufficiently fast rise time
Further measurements are ongoing
Radiation hardness is of interest – tests have not been successful yet
Any experience welcome!
David Woog - FCC Week 2017, Berlin
31/05/2017
Ruben Garcia Alia 16:30 same room, presentation about radiation hardness

15. David Woog - FCC Week 2017, Berlin
Preliminary prototype IA design
Based on the component characterisation a prototype IA has been designed:
21 constant voltage layers
2 special (modulation) layers for ripple and droop compensation
24 parallel branches per layer
Parameter
Unit
Value
Nr. of constant voltage layers - 21
Nr. of modulation layers 2
Nr. of branches per layer 24
Characteristic impedance Ω
6.25
Voltage per layer V
960
Current per branch A
105
Total height mm
~1200
Output voltage kV
15.62
Output current kA
2.5
David Woog - FCC Week 2017, Berlin
31/05/2017

16. David Woog - FCC Week 2017, Berlin
Milestones and next steps
Basic design steps
Definition of component requirements
Hardware design
First prototype (~5 layers)
Measurements
2019
2018
2017
2016
2015
Component selection
Characterisation of components
Start of hardware design
Optimisation
Final prototype (21+2 layers)
Final measurements
Contribution to FCC CDR
Next steps:
Production of hardware components (designed)
Core housing
Stalk
End caps
Development of final PCB (design ongoing)
Gate driver circuit
MOSFET switch
HV diode
Obtain outstanding parts and start prototype assembling
David Woog - FCC Week 2017, Berlin
31/05/2017

17. Thank you for your attention!
References:
[1] L.S. Stoel et al., “High Energy Booster Options for a Future Circular Collider at CERN”, proceedings, IPAC’16, Busan, Korea (2016).
[2] D. Woog et al., «Design of an Inductive Adder for the FCC Injection Kicker Pulse Generator», to be published in the IPAC’17 proceedings, Kopenhagen, Denmark (2017).
[3] M. J. Barnes et al., “Pulsed Power at CERN”, to be published in the EAPPC 2016 proceedings, Lisbon, Portugal (2016).
[4] T. Kramer et al., “Considerations for the injection and extraction kicker systems of a 100 TeV centre of mass FCC-hh collider”, IPAC’16, Busan, Korea (2016).
[5] J. Holma et al., “Measurements on prototype inductive adders with ultra-flat-top output pulses for CLIC DR kickers”, proceedings, IPAC’14, Dresden, Germany (2014).
David Woog - FCC Week 2017, Berlin
31/05/2017

19. David Woog - FCC Week 2017, Berlin
Backup
David Woog - FCC Week 2017, Berlin
31/05/2017

20. David Woog - FCC Week 2017, Berlin
BH curve measurement test setup from BE-BI-PI
Power supply
Oscilloscope
RC integrator to measure 𝑈 sec 𝑑𝑡 ~ 𝐵
Function generator
Current limiting resistor
Test core
Other required parameters:
Core dimensions, weight, fill factor, no of windings
Amplifier, incl. 1 Ω Shunt to measure 𝐼 prim ~ 𝐻
Thanks to S. Aguilera and M. Krupa
David Woog - FCC Week 2017, Berlin
31/05/2017

21. David Woog - FCC Week 2017, Berlin
Radiation hardness tests on SiC MOSFETs
Radiation hardness of power semiconductor devices is a real concern
High energy hadrons (HEH, >20 MeV) can cause single event burnouts (SEB) in power MOSFETs
SEBs cause short circuits between drain and source
The behaviour of Si semiconductors under radiation is known
Little experiences with SiC semiconductors as a new device technology
Radiation hardness tests in the CHARM facility at CERN have been successfully made with Si MOSFETs, GTOs and IGBTs
Using the existing test setup to test SiC MOSFETs was more difficult than expected
Reliable measurements were not possible with this setup until now
Over current protection needs to be adapted to SiC specification
Any existing experiences in this field are interesting
David Woog - FCC Week 2017, Berlin
31/05/2017