m. barnes cern te/ abt contributions by j. holma (cern)

M.J. Barnes LεR2011, October 3-5, 2011 1

M. BarnesCERN TE/ABT

Contributions by J. Holma (CERN)

An Inductive Adder as a Low-Jitter, Ultra-Flat, DR

Extraction Pulser

Overview

Specifications for kickers for CLIC Damping Ring (DR) Extraction Kickers Striplines

Low beam coupling impedance Excellent field homogeneity

Pulse generator Schematic of an Inductive Adder Modulation schemes Status of R&D Measurement challenges

Summary

2M.J. Barnes LεR2011, October 3-5, 2011

CLIC General Layout

3

A total of approximately 300 kickers will be required for CLIC ! ; Damping Rings: one injection and extraction system per ring and per beam (8 kicker systems); Damping rings reduce beam emittance; hence kickers must be high stability (low ripple and droop)

with excellent integrated field homogeneity and very low beam coupling impedance.

TA kicker Loop phase compensation kicker

Phase measurement

Dump Dump

kicker

DR Extraction Kicker

M.J. Barnes LεR2011, October 3-5, 2011

DR Kickers: Selected CLIC, ILC & DAΦNE Parameters

CLIC Pre Damping

Ring

CLIC Damping

RingCTF3

Tail-Clipper ILC DAΦNE

Beam energy (GeV) 2.86 2.86 0.2 5 0.51Total kick deflection angle (mrad) 2.0 1.5 1.2 0.7 5Aperture (mm) ~40 20 40 24 (tapered) 54.8 (tapered)Effective length (m) 2*1.7 1.7 4*0.295 20*0.32=~6.4 0.94Field rise time (ns) 700 1000 ≤5 3 ~5Field fall time (ns) 700 1000 NA 3 ~5Pulse flattop duration (ns) ~160 ~160 Up to 140 NA NA

Input pulse duration (ns) 5.9 5.3

Flattop reproducibility ±1x10-4 ±1x10-4 NA 1x10-3

Flattop stability [inc. droop], (Inj.)per Kicker SYSTEM (Ext.)

±2x10-2

±2x10-3±2x10-3

±2x10-4 NA 1x10-4

1x10-4

Field inhomogeneity (%) [CLIC: 3.5mm radius] [CLIC: 1mm radius]

±0.1 (Inj.)±0.1 (Ext.)

±0.1 (Inj.)±0.01(Ext.) ±18 ±?? ±3 (x=±27mm @y=0)

±10 (y=±10mm @x=0

Repetition rate (Hz) 50 50 50 5 (3M burst) 50Pulse voltage per Stripline (kV) ±17 ±12.5 ±2.65 ±5 ±45Stripline pulse current [50 Ω load] (A) ±340 ±250 ±53 ±100 ±900Longitudinal beam coupling impedance (Ω) < 0.05*nTransverse beam coupling impedance (kΩ/m) < 200

4LεR2011, October 3-5, 2011 M.J. Barnes

The specifications for the pre-damping rings and the damping rings include: low longitudinal and transverse beam coupling impedances; high stability and reproducibility of the field; excellent field homogeneity; ultra-high vacuum.

Feedthru

Ceramic Support

Taken from: D. Alseni, LNF-INFN, “Fast RF Kicker Design”, April 23-25, 2008.

Beam

Elliptical cross-section (increases deflection efficiency).

DAΦNE Striplines (~0.9m) Note: each taper ≈ 30% of overall length.

• Stripline structures will be used for the beam-line kicker element;

• IFIC, in conjunction with CIEMAT & CERN, are carrying out a complete optimization of the design of the DR striplines (C. Belver-Aguilar: R&D on Striplines for the CLIC DR Kickers, LER2011);

• Spanish Industry (TRINOS) will produce manufacturing drawings and a set of prototype DR striplines;

• The striplines will be supplied with suitable high voltage vacuum feedthroughs.

Beam-Line Kicker Element


CLIC Damping Ring Pulse Definition

Rise time: time needed to reach the required flattop voltage (but includes settling time). DR extraction 1000 ns rise time allowed, ~100 ns desired;

Settling time: time needed to damp oscillations to within specification; Beam: 160 ns time window during which any ripple and droop (i.e. flattop stability)

must be within specification; Flattop stability: within ±2x10-4, for combined ripple and droop for DR extraction.

This corresponds to a maximum, combined, ripple and droop of ±2.5 V for a 12.5 kV output pulse for the DR extraction kicker;

Reproducibility: maximum difference allowed between any two pulses, of ±1x10-4; Fall time: time for voltage to return to zero. DR ext. 1000 ns allowed, ~100 ns desired. Minimizing rise and fall times reduces stress on kicker system. To minimize settling time, impedance of system has to be well matched.

20ms

Flat topFall time (losses)

Rise time (losses)

Reproducibility

Settling time

Droop

Beam


DR Kicker with an Inductive Adder

An extensive literature review of existing pulse generators has been carried out: an inductive adder is a very promising means of achieving the demanding specifications for the DR extraction kickers.

Two of the challenges of DR kickers Impedance matching of ALL parts/components over a wide

frequency range (… striplines are particularly challenging); Stability of ALL parts/components (with time, temperature,

….).

7LεR2011, October 3-5, 2011

Inductive Adder of 14 Layers½ Layer of an Inductive Adder

MOSFETor IGBTs

Capacitor

Gate Driver

M.J. Barnes

Schematic of CLIC DR Kicker System with an Inductive Adder

Beam upstream end of striplines

Inductive Adder (IA)Inductive Adder Semiconductor switches; Gate-drive circuit referenced to ground - no electronics

referenced to high voltage despite the high voltage output pulse of the Inductive Adder (IA);

Modularity: the same design can potentially be used for DR

and PDR kickers despite the different specifications. However the PDR version will require more layers in series;

the possibility to generate positive or negative output pulses with the same adder: the polarity of the pulse can be changed by grounding the other end of the secondary winding of the IA;

Source impedance is low, hence minimizing the number of layers required;

Output voltage can be modulated during the pulse; Redundancy and machine safety: if one switch or layer

fails, the adder still gives a significant portion of the required output pulse.

8LεR2011, October 3-5, 2011

Schematic of an Inductive Adder

M.J. Barnes

(N-2)layers

Constant Voltage Layers

Digital Modulation Layer

Analogue Modulation Layer

Gate Drive Circuit

Principle of IA Modulation LayersPROBLEM: During output current pulse charge is removed from capacitor banks, hence capacitor bank voltage reduces, causing droop of output pulse.o ANALOGUE MODULATION: layer is used to

compensate voltage droop of capacitors, and can also significantly reduce the required capacitance per layer.

o No energy storage capacitor on modulation layer, but there is a resistor Ra in parallel with the transformer core (magnetizing inductance Lm);

o Resistor Ra is effectively in series with the load; PASSIVE MODULATION: during the pulse,

current through Lm increases, hence current through Ra decreases (τ=Lm/Ra). Therefore, voltage over Ra decreases, compensating voltage droop caused by storage capacitor voltage droop of other layers.

ACTIVE MODULATION: a linear switch provides a shunt path for the current through resistor Ra. Therefore, the voltage over Ra can be controlled by controlling the current through the switch.

DIGITAL MODULATION: switching “On” and “Off” provides coarse modulation and hence will not be used for droop compensation. However turn-on of layers at different times may be used to reduce ripple.

.ci dt

9LεR2011, October 3-5, 2011

No capacitor hereLinear switch

ic

M.J. Barnes

Predictions for Various Modulation Schemes

o Without modulation 320 µF, per layer, is required to achieve 0.02% droop over 160 ns.

o An analogue modulating layer is very effective at controlling droop, even with a relatively small value of the capacitor banks;

o Critical design issues include: o low inductance for capacitor bank circuit, o small parasitic capacitances, o impedance matching (e.g. of pulse

transformer) to minimize reflectionso temperature stability of magnetic

characteristics of transformer cores and careful choice of material;

o For tape-would transformer cores, adequate interlaminar insulation;

o etc..o For a prototype inductive adder it is proposed to use ~80 µF, per layer.

Ripple may still be present at a level above ±0.02%: hence, a double kicker system may be required as well….. this will be better known once a prototype DR ext. system is tested.

10LεR2011, October 3-5, 2011

PSpice simulations of the effect of the value of the capacitance per layer upon the flattop droop, with:(i) no modulation, (ii) active analogue modulation (am);(iii) passive analogue modulation (pm).

99.66

99.7

99.74

99.78

99.82

99.86

99.9

99.94

99.98

100.02

Vlo

ad: N

orm

aliz

ed M

agni

tude

(%)

Time (s)

No modn layer, 320µF



Active modulation, 20µF

Passive modula tion, 20µF

Passive modula tion, 40µF

Δ=0.02 %

160ns

20µF

40µF

20µF - pm

320µF

40µF - pm160ns 20µF - am

M.J. Barnes

Status of the IA Design IA adder expert (Ed Cook – now “retired” from LLNL)

invited to collaborate in design and lab testing; Specifications have been defined for the main IA

components, based on existing applications, discussions with Ed Cook, and simulations;

Simulations on-going:

• Compensation of droop and ripple using analogue modulation;

Samples of main components ordered:

• Storage capacitors, MOSFETs (switch-type and linear devices) and transformer cores;

• Components will be tested starting autumn 2011 and the most suitable candidates will be chosen for the prototype;

The first prototype layers are scheduled to be ready for lab testing in the first quarter of 2012;

The goal is that one or more prototype adder(s) will be ready by the end of year 2012;

The prototype kicker system will be tested in a suitable facility, e.g. at ATF.

Sample components: transformer cores, capacitors, MOSFETs and their gate

driver circuits.


Measurement Challenges

• Se


The ±0.02 % requirement for the pulse flattop stability, for the DR extraction kicker, is an extremely demanding specification from both the design and measurement perspective.

Commercially available Current Transformers (CT) are promising for the measurement device, e.g.:

Short coaxial cables, terminated in their characteristic impedance, to minimize attenuation, dispersion and reflections.

But commercially available oscilloscopes are not capable of measuring shape of pulse flattop to required (relative) accuracy, e.g. because of ~1% amplifier droop over 200 ns.

o High speed, 14-bit, Analogue to Digital converter to be investigated…o Pulse measurement experts contacted (e.g. Technical Research Institute of Sweden

and ETH Zürich) and discussions commenced.o To confirm effect of analogue modulation by lab measurements (e.g. for droop compensation),

two systems, with output currents in opposite sense though a CT (~zero total field without modulation), will probably be required.

Ipeak > 250 A; Droop over 160 ns < 0.002%; Rise time < 10 ns, hence

measurement ripple introduced by CT is expected to be insignificant after 100 ns target rise-time.

+I or −I

I I

Summary1. The DR extraction kickers are particularly challenging as they require:

low longitudinal and transverse beam coupling impedances; good integrated field homogeneity; excellent stability (±0.02 % requirement for the pulse flattop stability).

2.An Inductive Adder is promising for both the PDR & DR kickers: for achieving a reliable design: multiple layers are good for machine

protection; for achieving adequately low ripple and droop – good predictions with a

circuit model of active analogue modulation.

3.Progress and plans: samples of main components ordered, to start testing in autumn 2011; a prototype layer scheduled to be ready for testing in the first quarter of

2012; discussions ongoing with experts and potential collaborators re IA design; experts and potential collaborators have been contacted re measurement

issues; the prototype kicker system (pulse generator and striplines) will be tested in

a suitable facility, e.g. ATF.13LεR2011, October 3-5, 2011 M.J. Barnes

Thank you for your attention.QUESTIONS ?


Double Kicker System: Concept (Extraction)

KEK/ATF achieved a factor of 3.3 reduction in kick jitter angle, with respect to a single kicker, with single-bunch measurements.

Bunches

Extraction with one kicker magnet: Requires a uniform

and stable magnetic field pulse.

Two “identical” pulses are required;

One power supply sends the pulses to 2 “identical” kickers.

Extraction with two kicker magnets:

1st Extraction Kicker Magnet

2nd Extraction Kicker Magnet

Extraction Line

Δθ1

Δθ2=Δθ1

Beam 1st kicker system for beam extraction; 2nd kicker system for compensation of jitter of

deflection angle (ripple & droop) from 1st kicker; Figure shows 1st and 2nd kickers separated by a

betatron phase of 2nπ: for a betatron phase of (2n−1)π the 2nd kick is in the other direction. (Kicker)

(Anti-Kicker)Time of flight


Example of Double Kicker System for DR Extraction

In order that beam bunches and kicker field are synchronized in time at the 2nd kicker system, the two kicker systems are powered in parallel. However, additional lengths of transmission line are required to compensate for the beam-of-flight between the 1st and the 2nd kickers.Potential problems Different attenuation & dispersion of stripline waveforms (due to length of transmission

lines); Differences between magnetic characteristics of kicker & anti-kicker; Imperfections in beam-line elements/alignment between kicker & anti-kicker.

1st kicker system (in damping ring) for beam extraction; 2nd kicker system (in extraction line) for jitter compensation.

HVDC Transmission line

Z=50W

Tapered stripline plates

BeamZ=50W

Z=50WZ=50W

First kicker

+veCopt

Z=50W

PFL Switch

RG220

-veCopt

RG220

Z=50W

Z=50W

Z=50W

Transmission line

Z=50W

Z=50W

Z=50W

Z=50W

Tapered stripline plates

Second kicker

BeamZ=50W

Z=50Wτfl≡(10m*3.33ns/m)

τ→long c.f. pulse width?

50W

50W

Z=50W

Z=50W

Z=50W

Z=50W

50W

50W

τ→long c.f. pulse width?

Beam Time-of-Flight compensation.


Stripline Design: Longitudinal Impedance

220

//22 2sin sin

2untapered cL LZ Z ic c

=

Longitudinal beam coupling impedance for untapered (Chao) and tapered stripline kicker (S. Smith, SLAC):

2

2// //

sintapered tapered

lcZ Z

lc

=

Virtual Ground

+ve

-ve

Beam pipe Ground

Striplines driven to same magnitude, but opposite polarity, voltage, to extract beam ODD mode characteristic impedance.Total capacitance (C) is given by: capacitance between a stripline and

virtual ground (C11) capacitance between a stripline and

beam-pipe ground (2C12)

+/-ve

+/-ve

Beam pipe Ground

Beam

Same polarity and magnitude of current / voltage induced on both striplines by beam. EVEN mode characteristic impedanceCapacitance (C) is given by: capacitance between a stripline and

beam-pipe ground (C11)

1cZ cC=Without dielectric or magnetic materials:


C11

C11

2C12

2C12

C11

C11

Stripline Design: Field Homogeneity

Contour plots of field inhomogeneity in the kicker aperture for the optimized design

2 mm

7 mm

20 mm

STR

IPL

INE

STR

IPL

INE

-25 -20 -15 -10 -5 0 5 10 15 20 25-0.00499999999999989

1.13624387676481E-16

0.00500000000000011

0.0100000000000001

0.0150000000000001

0.0200000000000001

0.0250000000000001

0.0300000000000001

0.0350000000000001

0.0400000000000001

apertureradiusheightedge lengthedge anglethickness

Parameter variation from the optimized value (%)

Fiel

d In

hom

ogen

eity

(%

)

Op-timum

Sensitivity of field homogeneity to parameter variations from the optimized design (Courtesy of C. Belver-Aguilar)

CLIC DR specifications: Field inhomogeneity: ±0.1 % (1e-3) for DR injection (over 3.5 mm radius); ±0.01 % (1e-4) for DR extraction (over 1 mm radius).


Other Issues

• Se

If only one of the two striplines is powered, beam will receive ~1/2

deflection; high intensity beam could cause considerable damage to other equipment. This could result if a “single” switch were used for each stripline: an inductive adder (multiple primary switches) will help to avoid this problem.

Fast rise and fall times of field are desirable; e.g. if beam is mis-timed, with respect to the kick pulse, a fast rise/fall time will result in beam being swept faster across downstream materials/devices, minimizing potential damage.


Tail Clipper: Deflection

From CTF3 CR

To CLEX

Beam (e-)

Strip-line at positive voltage

Strip-line at negative voltage

Fe

Deflection due to Electric Field:

From CTF3 CR

To CLEX

Beam (e-)

I

I

FmB

B

B

B B

B

Deflection due to Magnetic Field: Strip-lines fed from CLEX end+V

-V


m. barnes cern te/ abt contributions by j. holma (cern)

Documents