1 July 11, 2008Mike Barnes, AB/BT Present Status and Future Plans for the MKD Beam Dump Kickers...

1 July 11, 2008 Mike Barnes, AB/BT

Present Status and Future Present Status and Future Plans for the MKD Beam Plans for the MKD Beam

Dump KickersDump Kickers

Acknowledgements: input gratefully received from

Fritz Caspers, Enrique Gaxiola, Tom Kroyer,

Viliam Senaj & Jan Uythoven.

M.J. BARNES, AB/BT

July 11, 2008 Mike Barnes, AB/BT

CERN SPS & LHC Kicker CERN SPS & LHC Kicker Magnet SystemsMagnet Systems

PS

LHC

SPS

PS ComplexPS

LHC

SPS

PS Complex4 x MKI

2 x MKDV

3 x MKDH

4 x MKI

4 x MKI2 x MKDV

3 x MKDH


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 SystemMKD Beam Dump System


II. Principle of Beam DumpingPrinciple of Beam Dumping


MKD Kicker MagnetsMKD 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 MKDV2 MKDH1 MKDH2 MKDH3

Beam

Simplified schematic of MKD magnet layout in LSS1

MKDV magnet in labMKDV magnet in lab

Ferrite

PT100 sensor


MKD Magnet ParametersMKD Magnet ParametersMKDV1 MKDV2 MKDH1 MKDH2 MKDH3

Kick direction Vertical - downwards

Vertical - downwards

Horizontal – inwards



# Magnets 1 1 1 1 1

# PFNs 3 1 1 1

Magnet length 2.56m 2.56m 1.256m 1.256m 1.256m

Tank length 3.052m

(~2.89m int.)

3.052m

(~ 2.89m int.)

1.76m 1.76m 1.76m

Horizontal aperture 75mm 83mm 96mm 96mm 105mm

Vertical aperture 56mm 56mm 56mm 56mm 60mm

Sections per mag. 5 5 1 1 1

Kick rise time (2%98%)

1.1μs 1.0μs 23μs 23μs 23μs

Magnetic material 8C11 Ferrite 8C11 Ferrite Laminated steel (0.35mm)

Laminated steel (0.35mm)

Laminated steel (0.35mm)


MKDVMKDV MKDV1 & MKDV2 are 5 cell, transmission line, magnets

constructed from (8C11) ferrite: Each cell ~50cm long; Above about 120C, 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.


MKDHMKDH 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 (150C ??). 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.


Beam Induced HeatingBeam 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.


Aperture

Longitudinal Impedance: Longitudinal Impedance: Analytical Calculation (1)Analytical Calculation (1)

From CERN-SL-2000-04 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



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

Ferrite

Xhap

vapAperture


Applying equations from slide 11:

MKDV2: 150Ω

MKE-S: 3.4kΩMKE-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 MeasurementsLongitudinal 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: 147.7 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.


CNGS Beam: Power CNGS Beam: Power DepositionsDepositions

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=35C (based on 26C tunnel)

Calculated power deposition based on:• CNGS beam spectra measurements made by G. Arduini and T. Bohl (4.5 s period) – see Note-2004-39;• 2.5x1013 protons per pulse;• A total cycle duration of 6 s.


MKE: Beam Coupling MKE: Beam Coupling Impedance ReductionImpedance 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


MKI: Beam Coupling MKI: Beam Coupling Impedance ReductionImpedance Reduction

Ceramic beam pipe with beam screen

A beam screen consisting of either painted silver stripes (left), or 0.7 mm by 2.7 mm conductors (right)

has been tested.

The outside diameter of the ceramic beam pipe is metallized, at one end, over a length of 150 mm and

connected to ground.

38 mm

ZMetallization – to

give coupling capacitance

Magnet in the vacuum tank with ceramic beam pipe

Note: 0.7 x 2.7 mm conductors implemented for HV reasons.


Transverse Impedance Transverse Impedance MeasurementsMeasurements

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


SummarySummary 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.


Future PlansFuture 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?


BibliographyBibliography T. Bohl, “CNGS Beam in the SPS: Beam Spectra”, Note-2004-39 F. Caspers “Impedance Measurement of the SPS MKE Kicker by means of the Coaxial Wire

Method”, PS/RF/Note 2000-004 F. Caspers, “A Retrofit Technique for Kicker Beam-Coupling Impedance Reduction”, CERN-AB-

2004-048 E. Gaxiola et al, “Experience with Kicker Beam Coupling Reduction Techniques”, PAC2005 E.

Gaxiola, “SPS Extraction Kicker Performance with Impedance Reduction Measures”, http://ab-div.web.cern.ch/ab-div/Meetings/APC/2006/apc061110/EG-APC-10-11-2006.pdf

P.E. Faugeras et al., “A Laminated-Iron Fast-Pulsed Magnet”, CERN-SPS/ABT/77-16. T. Kroyer, “Wire Measurements on the MKE Extraction Kicker Magnets”, http://ab-

div.web.cern.ch/ab-div/Meetings/APC/2006/apc061110/TK-APC-10-11-2006.pdf T. Kroyer et al, “Longitudinal and Transverse Wire Measurements for the Evaluation of

Impedance Reduction Measures on the MKE Extraction Kickers”, AB-Note-2007-028 H. Tsutsui, “Some Simplified Models of Ferrite Kicker Magnet for Calculation of Longitudinal

Coupling Impedance”, CERN-SL-2000-004 AP, http://doc.cern.ch/archive/electronic/cern/preprints/sl/sl-2000-004.pdf

J. Uythoven, “MKE Heating and Measured Power Spectra: CNGS BEAMS” , http://ab-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

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1 July 11, 2008Mike Barnes, AB/BT Present Status and Future Plans for the MKD Beam Dump Kickers...

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