1 July 11, 2008Mike Barnes, AB/BT Present Status and Future Plans for the MKD Beam Dump Kickers Acknowledgements: input gratefully received from Fritz Caspers, Enrique Gaxiola, Tom Kroyer, Viliam Senaj & Jan Uythoven. M.J. BARNES, AB/BT

July 11, 2008Mike Barnes, AB/BT CERN SPS & LHC Kicker Magnet Systems PS LHC SPS PS ComplexPS LHC SPS PS Complex 4 x MKI 2 x MKDV 3 x MKDH 4 x MKI 2 x MKDV 3 x MKDH

3 July 11, 2008Mike Barnes, AB/BT  When the beam can not be extracted: dumping of the beam using the MKD beam dump system (MD, emergencies...)  The system consists of:  Horizontal (MKDH) and vertical (MKDV) kicker magnets  Beam-dumps TIDV (E > 105 GeV/c) and TIDH (E < 37 GeV/c)  Function of the kicker magnets:  Sweep the beam to distribute the beam energy over a large volume of the absorbed block.  Function of the beam dumps:  Absorb the beam. II. MKD Beam Dump System

4 July 11, 2008Mike Barnes, AB/BT II. Principle of Beam Dumping

5 July 11, 2008Mike Barnes, AB/BT MKD Kicker Magnets  The MKD Beam Dumping System kicker magnets are installed in SPS LSS1;  Two MKDV magnets & three MKDH magnets provide vertical & horizontal deflection, respectively;  ~30 year old equipment;  No transition pieces between vacuum tank and kicker magnet. MKDV1 MKDV2MKDH1MKDH2MKDH3 Beam Simplified schematic of MKD magnet layout in LSS1 MKDV magnet in lab Ferrite PT100 sensor

6 July 11, 2008Mike Barnes, AB/BT MKD Magnet Parameters MKDV1MKDV2MKDH1MKDH2MKDH3 Kick direction Vertical - downwards Horizontal – inwards # Magnets # PFNs 3111 Magnet length 2.56m 1.256m Tank length 3.052m (~2.89m int.) 3.052m (~ 2.89m int.) 1.76m Horizontal aperture 75mm83mm96mm 105mm Vertical aperture 56mm 60mm Sections per mag Kick rise time (2%  98%) 1.1μs1.0μs23μs Magnetic material 8C11 Ferrite Laminated steel (0.35mm)

7 July 11, 2008Mike Barnes, AB/BT MKDV  MKDV1 & MKDV2 are 5 cell, transmission line, magnets constructed from (8C11) ferrite:  Each cell ~50cm long;  Above about 120  C, 8C11 ferrites loose their magnetic properties.  Three parallel PFN’s (3 Ω each) feed two, electrically parallel, magnets (2 Ω each) – this implies a failure in one magnet has an impact upon field in another;  Thyratron and ignitron switches are used for MKDV:  Thyratrons provide fast rise-time capability & the ignitrons conduct a significant duration of the high current;  Three PFNs were necessary for current sharing between switches;  Limited dynamic range of ~4.3 (~11 kV to ~46 kV on PFN) – for PS2 it will be necessary to dump at 50 GeV/c (or maybe even 26 GeV/c – TBD). Hence a dynamic range of 9 (or maybe 18) will be required.  Temperature probes not fitted to magnets installed in LSS1 (PT100’s fitted to magnet in lab);  No measures taken to reduce beam coupling impedance to ferrite;  No transition pieces, between magnet tank and magnet frame, installed in LSS1.

8 July 11, 2008Mike Barnes, AB/BT MKDH  MKDH1, MKDH2 & MKDH3 are lumped inductance magnets constructed from 0.35mm thick (or thinner), C-shaped, steel plates:  Thickness of the plate is parallel to the beam direction.  No problems with Curie temperature. Temperature limit will be due to mechanical constraints (150  C ??).  In the early 2000’s, ignitron switches were replaced with Fast High Current Thyristors (FHCT’s):  The FHCT’s permit magnet current to be proportional to the beam energy over a dynamic range of 30 (from injection at 15 GeV/c to a top energy of 450 GeV/c);  Each magnet has its own capacitor bank (precharge of 10 kV produces a magnet current of 21 kA amplitude);  Temperature probes not fitted to magnets installed in LSS1;  No measures taken to reduce beam coupling impedance to steel;  No transition pieces, between magnet tank and magnet frame, installed in LSS1.

9 July 11, 2008Mike Barnes, AB/BT Beam Induced Heating  Kicker magnets are heated by the beam due to their beam coupling impedance. Heating is caused by coupling between beam and real part of impedance.  High intensity beam can result in high power deposition.

10 July 11, 2008Mike Barnes, AB/BT Aperture Longitudinal Impedance: Analytical Calculation (1) From CERN-SL AP, by H. Tsutsui, pp7-10: Above equation is for 2D (infinite length) geometry. Analysis appears to allow for complex permeability and permittivity. Longitudinal impedance per unit length

11 July 11, 2008Mike Barnes, AB/BT Longitudinal Impedance: Analytical Calculation (2) Coding equation 27 (slide 10) in Mathematica format: Longitudinal impedance per unit length Longitudinal impedance depends upon frequency, horizontal aperture, vertical aperture, relative permittivity and relative permeability. Ferrite X hap vap Aperture

12 July 11, 2008Mike Barnes, AB/BT Applying equations from slide 11: MKDV2: 150Ω MKE-S: 3.4kΩ MKE-L: 3.2kΩ MKDH1,2: 1.6kΩ c.f. ~2.6kΩ meas. c.f. ~200Ω meas. Notes: Equations on slides 10 & 11 are for ferrite and hence not really applicable to a laminated steel MKDH magnet …. smooth nature of curves. Longitudinal Impedance: Analytical Calculation (3)

13 July 11, 2008Mike Barnes, AB/BT Longitudinal Measurements MKI: 15 screen conductors MKDV2: no beam screen or transition pieces. Spikes due to cell length ??? MKE (L10): stripes on all cells MKE: no stripes MKE (S6): stripes on 2 of 7 cells From presentation to SPSU Study Team meeting on May 13, 2008:  MKE: serigraphy (painted stripes) reduces power deposition, in ferrite, by a factor of:  >4 for LHC beam;  ~7 for CNGS beam. MKI: no screen Apertures (hap x vap): MKE-L: x 35mm; MKE-S: 135 x 32mm; MKI: 54 x 54mm; MKDV2: 56 x 83mm. Cell Length: MKE: ~24cm; MKDV2: ~50cm. (Note: impedance data in following plot is scaled according to length of tank rather than magnet length; therefore actual impedance per metre is larger than shown in plot)  MKI: 15 screen conductors reduce power deposition, in ferrite, by a factor of ~40 for LHC beam.

14 July 11, 2008Mike Barnes, AB/BT CNGS Beam: Power Depositions  Use measured Real Impedance Longitudinal Data, for MKDV2 (see slide 13), without “spikes” (200 MHz intervals used):  “2 x” 7 W/m  Use analytical calculation for Real Impedance Longitudinal Data, for MKDH1,2 (see slide 12), (200 MHz intervals used):  “2 x” 32 W/m  Note: for MKE-L10, using measured Real Impedance Longitudinal Data, (see slide 13), scaled by 2.2/1.7:  “2 x” 25 W/m  Thottest-equilibrium=35  C (based on 26  C tunnel) Calculated power deposition based on: CNGS beam spectra measurements made by G. Arduini and T. Bohl (4.5 s period) – see Note ; 2.5x10 13 protons per pulse; A total cycle duration of 6 s.

15 July 11, 2008Mike Barnes, AB/BT MKE: Beam Coupling Impedance Reduction  Beam coupling impedance is reduced using conductive stripes (serigraphy), i.e. interleaved comb structure, directly printed onto the ferrite blocks and a reliable contact to the metallic HV plates at either side;  Capacitive coupling between stripes (stripes carry beam image current). Printed strips in MKE-L10 Interdigital comb structure 20mm spacing surface discharge

16 July 11, 2008Mike Barnes, AB/BT MKI: Beam Coupling Impedance Reduction Z Metallization – to give coupling capacitance Note: 0.7 x 2.7 mm conductors implemented for HV reasons.

17 July 11, 2008Mike Barnes, AB/BT Transverse Impedance Measurements  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 increases transverse impedance at ~100MHz, but gives some reduction in transverse impedance above ~300MHz. MKE: no shielding MKE: stripes on all cells H V H V H V

18 July 11, 2008Mike Barnes, AB/BT Summary  MKDV2 longitudinal impedance, unshielded, is generally lower than that of MKE-L10 with full serigraphy (slide 13).  “Spikes” on measured longitudinal impedance (slide 13), which are not present in analytical calculation (slide 12), are probably attributable to magnet cell length.  Shielding increases MKE magnets transverse impedance at ~100 MHz, but reduces transverse impedance above ~300 MHz (slide 17).  No beam impedance measurements carried out on MKDH magnets: effect of laminated steel (permeability, permittivity, conductivity, plate thickness), versus ferrite, therefore not quantified.

19 July 11, 2008Mike Barnes, AB/BT Future Plans  Remove third PFN from MKDV installation, i.e. two PFN’s of 2 Ω each, each with an individual magnet (2 Ω each) [reliability issue];  For PS2 operation a dynamic range of 9 (or maybe 18) is required: development of a (fast) semiconductor switch for MKDV may be required;  What will be the available beam gap for field rise-time for the MKDV’s ?  Measure longitudinal and transverse impedance of MKDV magnet with transition pieces installed – measured impedance may be higher than without transition pieces, because of “bypass effect” without transition pieces;  Measure longitudinal and transverse impedance of MKDH magnet (effect of laminated steel ….);  Is beam shielding necessary for MKDV magnets since MKDV2 longitudinal impedance, unshielded, is generally lower than that of MKE-L10 with full serigraphy?  Beam shielding necessary for MKDH magnets?  Are transition pieces between magnet and tank necessary?

20 July 11, 2008Mike Barnes, AB/BT Bibliography  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  E. Gaxiola et al, “Experience with Kicker Beam Coupling Reduction Techniques”, PAC2005 E. Gaxiola, “SPS Extraction Kicker Performance with Impedance Reduction Measures”, div.web.cern.ch/ab-div/Meetings/APC/2006/apc061110/EG-APC pdf  P.E. Faugeras et al., “A Laminated-Iron Fast-Pulsed Magnet”, CERN-SPS/ABT/  T. Kroyer, “Wire Measurements on the MKE Extraction Kicker Magnets”, div.web.cern.ch/ab-div/Meetings/APC/2006/apc061110/TK-APC pdf  T. Kroyer et al, “Longitudinal and Transverse Wire Measurements for the Evaluation of Impedance Reduction Measures on the MKE Extraction Kickers”, AB-Note  H. Tsutsui, “Some Simplified Models of Ferrite Kicker Magnet for Calculation of Longitudinal Coupling Impedance”, CERN-SL AP,  J. Uythoven, “MKE Heating and Measured Power Spectra: CNGS BEAMS”, div.web.cern.ch/ab-div/Meetings/APC/2004/apc041210/uythoven.pdf  J. Uythoven et al, “Beam Induced Heating of the SPS Fast Pulsed Magnets”, EPAC2004