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MKI Magnet Design, PT100 Sensor Locations & Heating Observations in 2011. M.J. Barnes Acknowledgements: H. Day, L. Ducimetiere, N. Garrel. An LHC Injection Kicker. PT100 Tube_Dn. PT100 Tube_Up. PT100 Mag_Up. Damping resistor (now at both ends). PT100 Mag_Dn.

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mki magnet design pt100 sensor locations heating observations in 2011

MKI Magnet Design, PT100 Sensor Locations & Heating Observations in 2011

M.J. Barnes

Acknowledgements:

H. Day, L. Ducimetiere, N. Garrel

M.J. Barnes

slide2

An LHC Injection Kicker

PT100

Tube_Dn

PT100

Tube_Up

PT100

Mag_Up

Damping resistor (now at both ends)

PT100

Mag_Dn

Screen conductors capacitively coupled to “ground”

Screen conductors soldered to “ground”

PT100

Tube_Up

ground

plate

HV plate

ground

plate

HV plate

ferrite

yoke

capacitor

PT100

Tube_Dn

Kicked Beam

PT100

Mag_Up

PT100

Mag_Dn

Beam impedance reduction ferrites

(lossy + low-loss)

Beam impedance reduction ferrite

(lossy + low-loss)

TMR connection

entrance box connection

M.J. Barnes

slide3

LHC Injection Kicker: Maximum Temperatures During Oct. 2011

  • Magnet PT100’s are mounted on ground plates: these plates contact the ground busbar and magnet capacitors;
  • Ground busbar does not contact ferrites – hence heat conduction to magnet PT100’s is mainly via magnet capacitors. Hence Mag_Up would be expected to measure a higher temperature than Mag_Dn, but ….
  • Tube_Up temperature > Tube_Dn temperature, maybe because of more cooling at “Dn” end (due to SS tube and “cage” around ferrites??).
  • The Power (W/m) shown is derived from impedance measurements – measured magnet temperature does not correlate with the power….

Screen conductors capacitively coupled to “ground” (metallization on ceramic tube)

NO

Capacitor

here

Screen conductors soldered to “ground”

(Ferrites mounted on SS tube)

PT100

Tube_Up

HV plate

ground

plate

HV plate

ground

plate

ferrite

yoke

capacitor

PT100

Tube_Dn

Kicked Beam

PT100

Mag_Up

PT100

Mag_Dn

Beam impedance reduction ferrites

(lossy + low-loss)

Beam impedance reduction ferrite

(lossy + low-loss)

TMR connection

entrance box connection

M.J. Barnes

slide4

LHC Injection Kicker: System Overview

Delay

TMR Current

LAB measurement: Magnet in vacuum tank; tank at atmospheric pressure; no bake-out jacket.

  • Lc is defined by the magnetic circuit, i.e. dimensions of aperture, but also deceases with reducing ferrite permeability;
  • Rise-time decreases with reducing Lc and/or Cc (~0.7ns reduction in rise-time, per 1% reduction in cell inductance).
  • Delay decreases with reducing Lc and/or Cc (~3.8ns reduction in delay, per 1% reduction in cell inductance).

M.J. Barnes

mki8 measured temperature magd dn rise time all 4 tmrs october 2011
MKI8 Measured Temperature (MagD_Dn) & Rise-Time (all 4 TMRs): October 2011

The rise-time of TMR current, for MKI8D, decreases at elevated temperatures (>~60˚C measured) for MKI8D_Dn.

M.J. Barnes

analysis of mki8 measurements
Analysis of MKI8 measurements

Initial permeability of CMD5005 increases to a max. at ~100°C, then starts to rapidly reduce.

Δ3ns Δ4% for Lc, & accelerating?

  • The above shows a fairly linear correlation between magnet temperature, made during SoftStarts in Oct. 2011, and rise-time up to 60°C (for MKI8D_dn).
  • The temperature dependence of the magnet capacitors (~−800ppm/°C), e.g. assuming the ground plate is at ambient temperature, is probably responsible for the initial slope (−0.04ns/°C for MKI8D_dn).
  • The slope of the reduction of the rise-time increases above 60°C measured for MKI8D_dn, indicating some of the ferrite yoke is at the Curie temperature.

The correlation between magnet temperature, made during SoftStarts in Oct. 2011, and absolute delay is noisy – probably due to thyratron jitter. The delay measurement should be improved, following the winter TS, by finding the delay w.r.t. thyratron cathode current.

M.J. Barnes

mki8 correlation between measured magnet temperatures
MKI8: Correlation Between Measured Magnet Temperatures

The above magnet temperature data, made during SoftStarts in October 2011, shows linear correlation between the measured magnet temperatures....

M.J. Barnes

beam impedance reduction ferrites
Beam Impedance Reduction Ferrites

Beam

  • Purpose of BIRF is to “encourage” image current of beam to flow through screen conductors. Rather than through the magnet tank.
  • Ideally image current of beam should flow through metallization/capacitive coupling/screen conductors/SS tube... Thus, ideally, there is no net field, due to beam current, which can couple into BIRFs.
  • In reality, BIRFs get hot (due to beam coupling) so there is field coupling into the BIRF’s, i.e. not all the beam image current is flowing in the ceramic tube metallization or SS tube.
  • BIRF heating may be partially attributable to non-perfect RF fingers – especially after bake-out. Note: ~50% increase in power deposition after bake-out!!
  • ALSO BIRF heating is probably also due to presence of capacitive coupling at one end….
    • ~200 pF @ 10 MHz  ~80 Ω (Note: 1 MHz  ~800 Ω)
    • ~3 µH (each BIRF) @ 10 MHz  ~400 Ω for 2 BIRFs

Assume ~3 µH with tank as return @ 10 MHz  ~200 Ω

Hence BIRF probably does not help at frequencies << 10MHz….

Ideally beam image current

flows, homogeneously within inside radius of ferrite.

M.J. Barnes

screen conductors
Screen Conductors
  • Ceramic has 24 slots for screen conductors: only 15 installed to decrease probability of HV breakdown. 15 conductors results in ~3x power beam induced power deposition, in the ferrite yoke, in comparison with 24 screen conductors.
  • Adding spheres to end of screen conductors will reduce electric field strength and, hopefully, allow 24 conductors to be installed.
  • Alternative idea for beam screen (beam impedance to be investigated by Hugo): connect only 2 of 24 screen conductors to ground, and capacitively couple others to ground  reduces peak voltages by ~2……….

BUT: low frequency impedance will increase…..

M.J. Barnes

conclusions
Conclusions
  • Mag_Up would be expected to measure a higher temperature than Mag_Dn, because of PT100 position, but this is not always the case….
  • Tube_Up temperature > Tube_Dn temperature.
  • Measured temperature of MKI8D_Dn reached 68˚C during October. The slope of the reduction of the rise-time increases above 60°C, measured for MKI8D_Dn, indicating some of the ferrite yoke is above the Curie temperature. Other MKI8’s do not yet show evidence of yoke being at the Curie temperature.
  • One BIRF measured temperature reached 102°C during October. BIRF (and a portion of ferrite yoke) heating is probably due to both non-perfect RF fingers (especially after bake-out) and the impedance of the capacitive coupling at frequencies << 10MHz.
  • Alternative beam screen configurations, which should allow 24 (c.f. 15 screen conductors) to be installed, are under consideration. The extra 9 screen conductors would reduce the expected beam induced power deposition by a factor of ~3.

M.J. Barnes

slide12

24 conductors capacitively coupled to beam-pipe ground

+16kV/-10kV

+27kV/-17kV

+16kV/-10kV

+23kV/-14kV

Connect to

beam-pipe ground

+16kV/-10kV

+16kV/-9kV

+16kV/-10kV

+11kV/-6kV

+16kV/-10kV

+1kV/-2kV

22 conductors capacitively coupled to beam-pipe ground

24 conductors capacitively coupled to beam-pipe ground

+7kV/-13kV

Connect to

beam-pipe ground

+4kV/-9kV

+6kV/-3kV

+16kV/-10kV

M.J. Barnes