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

1. MKI Magnet Design, PT100 Sensor Locations & Heating Observations in 2011 M.J. Barnes Acknowledgements: H. Day, L. Ducimetiere, N. Garrel M.J. Barnes

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. Spare Slides …….Status of Installed MKI Magnets M.J. Barnes

12. 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