1. Present Status and Future Plans for the MKE Kicker Magnets
Acknowledgements: some slides are adapted from previous presentations by Fritz Caspers, Enrique Gaxiola, Tom Kroyer & Jan Uythoven.
M.J. BARNES, AB/BT
Mike Barnes, AB/BT
May 13, 2008

2. Transmission Line Kicker Magnets
The kicker magnets installed at LSS4 & LSS6 are travelling-wave type magnets, each consisting of 7 ferrite “cells”;
30 year old, recuperated, equipment;
Transition piece between vacuum tank and kicker magnet;
Tank length = 2174 mm;
Magnet length = 1700mm.
MKE magnet in the clean room
1 cell
Mike Barnes, AB/BT
May 13, 2008

3. Cross-section of MKE Magnet (prior to ~2003 at LSS4 and 2005/2006 at LSS6)
Ferrite “C” core constructed from three ferrites.
In general, ferrite used is type 8C11 from Ferroxcube.
Rectangular aperture for the beam.
Ferrite
Rectangular aperture
Mike Barnes, AB/BT
May 13, 2008

4. LSS4 LSS4 is used for extraction to CNGS/LHC;
LSS4 has 5 magnets, magnetically in series, each powered by its own PFN and terminated in a matched resistor;
Three of the magnets have “large” (L) apertures (147.7mm x 35mm);
Two of the magnets have “small” (S) apertures (135mm x 32mm).
Beam
No cells serigraphed,
Ferrite 8C11
Mike Barnes, AB/BT
May 13, 2008

5. LSS4 Parameters Voltage on magnet throughout pulse LHC CNGS Energy 400
(Protons)
Energy
400
450
GeV/c
Deflection
0.54
0.48
mrad
Nominal PFN Voltage 50
51.2 kV
Nominal Impedance 10 Ω
Available rise-time
≤1.1 μs
Measured rise-time* (1%99%)
1.1
Usable flattop length
10.5
7.9
|Flattop ripple|
 2
 1 %
* E. Gaxiola et al, “Upgrade And Tests Of The SPS Fast Extraction Kicker System for LHC And CNGS”, EPAC2004.
Mike Barnes, AB/BT
May 13, 2008

6. High Curie temp. ferrite (4E2),
LSS6
LSS6 is used for extraction to LHC;
As of 2006 LSS6 has 3 magnets, magnetically and electrically in series, powered by a single PFN and terminated in a short-circuit;
Two of the magnets have “large” (L) apertures (147.7mm x 35mm);
One magnet has “small” (S) aperture (135mm x 32mm).
Beam
7 cells serigraphed,
Ferrite 8C11
High Curie temp. ferrite (4E2),
No cells serigraphed
PFN
Short-circuit
2 cells serigraphed,
Layout as of ~2006
Mike Barnes, AB/BT
May 13, 2008

7. LSS6 Parameters
Before 2006, LSS6 consisted of 4 series magnets terminated in 10Ω. In 2005, proof of principle tests were carried out, in lab, for a short-circuit system;
Rise and fall time increased;
Reduced PFN voltage for same deflection;
BUT voltage reversal.
Voltage on magnet only during rise and fall time
LHC
(protons)
Energy
450
GeV/c
Deflection
0.429
mrad
Nominal PFN Voltage
33.1 kV
Nominal Impedance 10 Ω
Available rise-time
8.8 μs
Measured rise-time ~8
Usable flattop length
7.9
|Flattop ripple|
 1 %
Mike Barnes, AB/BT
May 13, 2008

8. Beam Induced Heating
2004: Need to reduce both beam impedance and losses.
The MKE (SPS extraction) kickers LSS4 & LSS6 are heated by the beam due to their beam coupling impedance. Ferrite heating is caused by coupling between beam and real part of ferrite impedance.
High intensity beam can result in high power deposition in ferrite.
Mike Barnes, AB/BT
May 13, 2008

9. Past Developments
Kicker magnets at LSS4 (~2003) & LLS6 (2005/2006) equipped with:
High thermal conductivity Aluminium-Nitride (AlN180) plates;
Water cooling;
PT100 temperature sensor.
Aluminium-Nitride cooling plate
Water cooling circuit
PT100 sensor
Mike Barnes, AB/BT
May 13, 2008

10. Measured Probe Temperature
“Design Space” simulations were carried out to determine the relationship between the highest ferrite temperature and probe (PT100) temperature (with water cooling).
“Validated” by machine measurements – for 8C11 ferrite kick strength diminishes above ~80˚C measured, which corresponds to ~125˚C highest ferrite temperature, i.e. Curie temperature of ferrite (AB-Note BT, section 5).
With water cooling, a power deposition of ~0.54kW/m results in a predicted highest ferrite temperature of 125˚C.
∆Thot≈(125*Power/0.68)
∆Tmeas≈(70*Power/0.68) 
∆Thot≈ ∆Tmeas*(125/70)
∆Tmeas
∆Thot
kW/m
25˚C
Mike Barnes, AB/BT
May 13, 2008

11. Summary of situation at 2006
Above about 120C the 8C11 ferrites loose their magnetic properties, this has been measured during the scrubbing runs.
Note: 4E2 ferrite has a Curie Temperature of ≥400C.
Additional risk is structural damage above about 150C.
For “normal operation” the beam is interlocked at ~70 C measured (~125C on the ferrites);
For “scrubbing runs” the beam is interlocked above 90C measured, which is about 140C on the ferrites.
The water cooling system allows the magnet to be operational with approximately double the beam power deposition in the ferrite (AB-Note BT, section 5).
Mike Barnes, AB/BT
May 13, 2008

12. Beam Coupling Impedance
Printed strips in MKE-L10
Interdigital comb structure 20mm spacing surface discharge
Beam coupling impedance can be reduced using conductive stripes (serigraphy), i.e. interleaved comb structure, directly printed onto the ferrite blocks and having a reliable contact to the metallic HV plates at either side;
Capacitive coupling between stripes (stripes carry beam image current).
Mike Barnes, AB/BT
May 13, 2008

13. Longitudinal Measurements (1)
Comparison between the two extreme cases:
MKE-L8, without any serigraphy on 8C11 ferrites;
MKE-L10, serigraphy on all seven 8C11 ferrite cells.
Significant reduction of longitudinal impedance from serigraphy.
Low frequency resonance directly linked to geometry of serigraphy.
Real part of Z
Imaginary part of Z
Note: Impedance based on 2.2m length (1.7m actual); hence should be increased by a factor of ~1.3 L8 L8
L10
L10
Mike Barnes, AB/BT
May 13, 2008

14. Dissipated Power
Calculated using beam spectrum measured during 2004 SPS scrubbing run (data from J. Uythoven), but theoretical beam coupling impedance;
2*72 LHC bunches in SPS at 450 GeV;
Comparison between fully shielded MKE-L10 and MKE-L8 (no shielding at all).
Serigraphy (painted stripes) reduce calculated power deposition by a factor of >4, for LHC beam.
Mike Barnes, AB/BT
May 13, 2008

15. Longitudinal Measurements (2)
Note: Impedance based on 2.2m length (1.7m actual); hence should be increased by a factor of ~1.3
7 cells serigraphed (L10)
2 cells serigraphed (S6)
High Curie temp. ferrite (L9)
No serigraphy (L8)
In a comprehensive measurement campaign data for all types of MKE magnets was collected.
Conclusions:
High Curie temperature ferrite (4E2) displays similar Real Impedance as 8C11 (Ferroxcube) ferrite.
“S-Type” & “L-Type” magnets, without serigraphy, display similar Real Impedance.
Mike Barnes, AB/BT
May 13, 2008

16. CNGS: Power Depositions
Calculated power deposition based on:
CNGS beam spectra measurements made by G. Arduini and T. Bohl (4.5 s period) – see Note ;
2.5x1013 protons per pulse;
A total cycle duration of 6 s.
From Jan Uythoven’s presentation to APC, 10 December 2004 (real part of beam impedance:
“2 x” 210 W/m  Thottest-equilibrium=107C
Replace theoretical beam impedance of SPS kicker by measured data, for MKE-L8 (see slide 13), scaled by 2.2/1.7:
“2 x” 178 W/m  Thottest-equilibrium=91C (based on 26C tunnel)
Replace theoretical beam impedance of SPS kicker by measured data, for MKE-L10 (see slide 13), scaled by 2.2/1.7:
“2 x” 25 W/m  Thottest-equilibrium=35C (based on 26C tunnel)
Therefore shielding stripes on MKE-L10 kicker reduce beam induced power deposition, attributable to nominal CNGS beam, by a factor of 7 c.f. MKE-L8.
For 1.7x1013 protons per pulse & 3 cycles per 39.6s, replace theoretical beam impedance of SPS kicker by measured data, for MKE-L10 (see slide 13), scaled by 2.2/1.7:
75 W/m  Thottest-equilibrium=40C (based on 26C tunnel)
Mike Barnes, AB/BT
May 13, 2008

17. Measured Temperatures (2007)
LHC type beam. No serigraphy (yet) at MKE4.
~70°C
∆T=43°C
Meas.
From slide 10: Meas. ∆T of 43°C  ∆T of 77°C for hottest part of ferrite  103°C maximum
From previous slide:
Ferrite hottest temp. of 91°C expected.
Expected peak is between measured (~70°C) and “corrected” measured (~103°C).
Conclusion
Calculation (91°C) underestimates heating (103°C).
Mike Barnes, AB/BT
May 13, 2008

18. Measured Temperatures (2007)
Serigraphy on L10 results in a factor of ~4 (37/9) lower temperature rise than L9 (with LHC type beam).
For S6, 2 of 7 cells serigraphed (first and last cell):
at exit, PT100 is on “normal” cell (no serigrapy);
at entrance, PT100 is on serigraphed cell.
LHC type beam. MKE6.
From slide 10: Meas. ∆T of 9°C  ∆T of 16°C for hottest part of ferrite  42°C maximum
∆T=37°C
Meas.
∆T=9°C
From slide number 16:
Ferrite hottest temp. of 35°C expected.
Expected peak is between measured (~35°C) and “corrected” measured (~42°C).
Conclusion
Calculation (35°C ) underestimates heating (~42°C).
Mike Barnes, AB/BT
May 13, 2008

19. Measured Temperatures (2007)
CNGS type beam. MKE6. Serigraphy on L10 results in a factor of 6.4 (9/1.4) lower temperature rise than L9 (factor of 7 expected – see slide 16).
∆T=9°C
Meas.
∆T=1.4°C Meas.
From slide 10:
Meas. ∆T of 9°C  ∆T of 16°C for hottest part of ferrite  42°C maximum;
Meas. ∆T of 1.4°C  ∆T of 2.5°C for hottest part of ferrite  28.5°C maximum.
Mike Barnes, AB/BT
May 13, 2008

20. HV Issues – Pulse Shape for MKE6
Beam
7cells serigraphed
2 cells serigraphed
High Curie temp. ferrite
PFN
Short-circuit
Terminating the series magnets by a short circuit: the magnet peak voltage is reduced in absolute value (33kV PFN = 16.5kV magnet voltage). However, because of the reflection from the short circuit, there is a full negative voltage
(-16.5 kV) on the magnet. If we consider peak to peak, the voltage is
2x16.5 = 33 kV. The magnets are designed for 30kV.
Mike Barnes, AB/BT
May 13, 2008

21. HV Breakdown in MKE6
The MKE6 magnets were tested one by one in the lab; only S6 (adjacent to short circuit) was therefore tested with the actual waveform shape.
After re-installation of magnets ( shut down), some conditioning (breakdown) problems with magnet L10 (closest, electrically, to PFN). But …
L10 magnet is exposed to the longest duration and dV/dt of both positive and negative voltage;
Before 2008, the DC conditioning was only made with positive polarity. During the past shut down ( ) we have also carried out conditioning with negative DC: so far it seems that such conditioning has had good effect – i.e. no HV problems with L10;
Last year, we had little time to condition in MKE6. Effort has been made, during shutdown, to take every opportunity to do conditioning, and progressive improvement has been observed.
Slightly negative effect due to the stripes is not excluded, but we have no evidence so far.
Mike Barnes, AB/BT
May 13, 2008

22. Summary
Aluminium Nitride plates and cooling system allows the magnet to be operational with approximately double the power deposition in the ferrite;
Serigraphy (painted stripes) reduces predicted power deposition, in ferrite, by a factor of >4, for LHC beam: this is consistent with temperature measurements made during October 2007 scrubbing run (slide 18).
Serigraphy (painted stripes) reduces predicted power deposition , in ferrite, by a factor of ~7, for CNGS beam: this is consistent with temperature measurements made during October 2007 (slide 19).
Mike Barnes, AB/BT
May 13, 2008

23. Transverse Impedance
Information re Transverse Impedance, and measurement techniques, can be found in:
Tom Kroyer’s presentation “Wire Measurements on the MKE Extraction Kicker Magnets” APC meeting 10/11/2006.
Shielding may increase transverse impedance at ~100MHz, but reduces transverse impedance above ~300MHz.
Mike Barnes, AB/BT
May 13, 2008

24. Future Plans
All 9 MKE magnets will be equipped (eventually) with serigraphy:
1 (and 2/7 !) of 5, installed, “L-Type” magnets equipped with serigraphy;
0 of 3, installed, “S-Type” magnets equipped with serigraphy;
We have 1 spare “L-Type” & 1 spare “S-Type” magnet (without serigraphy).
Spare Aluminium-Nitride plates ordered (expected delivery end of May 2008);
8C11 ferrite in stock (that can be prepared & serigraphed):
L-Type: 7 top, 13 middle; 8 lower. Therefore one complete magnets worth;
S-Type: 7 top, 10 middle; 7 lower (including 4 radioactive ferrites). Therefore one complete magnets worth;
Ferroxcube to manufacture and return following L-Type 8C11 ferrites: 6 top, 9 lower (date of expected return not yet known);
Plan is to replace one S and one L magnet at each SPS shutdown (using the normal operation year to convert the 2 spare magnets for the next shutdown) -- 4 shutdowns required!!
BUT potential problem of converting 2 spare magnets during operation: if problem is encountered with an installed magnet, there may not be an available spare;
If faster deployment is needed, we need to investigate the possibility to equip another 2 magnets during the shutdown. In which case a shutdown of at least 3 months is necessary (work includes: dismantling, machining of radioactive ferrite (radii), serigraphy (by another CERN service), mounting, vacuum tests, HV test and conditioning in lab, installation, vacuum, DC and pulsed conditioning in SPS).
Mike Barnes, AB/BT
May 13, 2008

25. Bibliography Mike Barnes, AB/BT May 13, 2008
T. Bohl, “CNGS Beam in the SPS: Beam Spectra”, Note
F. Caspers “Impedance Measurement of the SPS MKE Kicker by means of the Coaxial Wire Method”, PS/RF/Note
F. Caspers, “A Retrofit Technique for Kicker Beam-Coupling Impedance Reduction”, CERN-AB
F. Caspers et al, “The Fast Extraction Kicker System in SPS LSS6”, EPAC 2006
E. Gaxiola, “Upgrade and Tests of the SPS Fast Extraction Kicker System for LHC and CNGS”, PAC2004
E. Gaxiola et al, “Performance Of The CERN SPS Fast Extraction for the CNGS Facility”, PAC2005
E. Gaxiola et al, “Experience with Kicker Beam Coupling Reduction Techniques”, PAC2005 E. Gaxiola, “SPS Extraction Kicker Performance with Impedance Reduction Measures”,
T. Kroyer, “Wire Measurements on the MKE Extraction Kicker Magnets”,
T. Kroyer et al, “Longitudinal and Transverse Wire Measurements for the Evaluation of Impedance Reduction Measures on the MKE Extraction Kickers”, AB-Note
M. Timmins et al, “SPS Extraction Kicker Magnet Cooling Design”, AB-Note BT (Rev.2), TS-Note DEC (Rev. 2)
J. Uythoven, “MKE Heating and Measured Power Spectra: CNGS BEAMS” ,
J. Uythoven et al, “Beam Induced Heating of the SPS Fast Pulsed Magnets”, EPAC2004
Mike Barnes, AB/BT
May 13, 2008