M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Beam Chopper Development for Next Generation High Power Proton Drivers Michael A. Clarke-Gayther RAL / FETS / HIPPI

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008  Overview  Fast Pulse Generator (FPG)  Slow Pulse Generator (SPG)  Slow – wave electrode designs  Summary  Acknowledgement Outline

Overview M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Maurizio Vretenar (HIPPI WP Coordinator) Alessandra Lombardi (WP4 Leader) Luca Bruno, Fritz Caspers Frank Gerigk, Tom Kroyer Mauro Paoluzzi Edgar Sargsyan, Carlo Rossi Mike Clarke-Gayther (WP4 Fast Beam Chopper & MEBT) Chris Prior (WP Coordinator) Ciprian Plostinar (WP2 & 4 N-C Structures / MEBT) Christoph Gabor (WP5 / Beam Dynamics)

Overview M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 John Back (LEBT) Saad Alsari (RF) Simon Jolly, Ajit Kurup (RFQ) David Lee (Laser Diagnostics) Jaroslav Pasternack (UK-NF) Jürgen Pozimski (Ion source/ RFQ) Peter Savage (Mechanical Eng.) Mike Clarke-Gayther (Chopper / MEBT) Dan Faircloth, Scott Lawrie (Ion source) Alan Letchford (RFQ / FETS coordinator) Mike Perkins (Ion source power supplies) Jürgen Pozimski (Ion source / RFQ) Pierpaolo Romano (Beam stop) Philip Wise (Mechanical Eng.) Christoph Gabor (Diagnostics) Ciprian Plostinar (MEBT / DTL) Javier Bermejo (ESS) Jesus Alonso (ESS) Rafael Enparantza (ESS)

Overview M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Project History

Overview M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 The RAL Front-End Test Stand (FETS) Project / Key parameters

Overview M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 RAL ‘Fast-Slow’ two stage chopping scheme

Overview M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October MeV MEBT Chopper (RAL FETS Scheme A) Chopper 1 (fast transition) Chopper 2 (slower transition) ‘CCL’ type re-buncher cavities 4.8 m Beam dump 1 Beam dump 2

Overview M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 FETS Scheme A / Beam-line layout and GPT trajectory plots Losses: 0.1 input to CH1, 0.3% on dump 1 0.1% on CH2, 0.3% on dump 2 Voltages: Chop 1:+/ kV (20 mm gap) Chop 2:+/ kV (18 mm gap)

Overview M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 FETS KEY PARAMETERSSCHEME A ION SPECIESH- ENERGY (MeV)3.0 RF FREQUENCY (MHz)324 BEAM CURRENT (mA) NORMALISED RMS INPUT EMITTANCE IN X / Y / Z PLANES ( π.mm.mr & π.deg.MeV) 0.25 / 0.25 / 0.18 RMS EMITTANCE GROWTH IN X / Y / Z PLANES (%)6 / 13 / 2 CHOPPING FACTOR (%) CHOPPING EFFICIENCY (%)99.9 FAST CHOPPER PULSE: TRANSITION TIME / DURATION / PRF/ BURST DURATION / BRF 2 ns / 12 ns / 2.6 MHz / 0.3 – 2 ms / 50 Hz FAST CHOPPER ELECTRODE EFFECTIVE LENGTH / GAPS (mm)450 x 0.82 = 369 / 20 FAST CHOPPER POTENTIAL(kV)± 1.3 SLOW CHOPPER PULSE: TRANSITION TIME / DURATION / PRF/ BURST DURATION / BRF 12 ns / 250 ns – 0.1 ms 1.3 MHz / 0.3 – 2 ms / 50 Hz SLOW CHOPPER EFFECTIVE LENGTH / GAPS (mm)450 x 0.85 / 18 SLOW CHOPPER POTENTIAL (kV)± 1.5 POWER ON FAST / SLOW BEAM DUMPS (W)150 / 850 OPTICAL DESIGN CODE(S)IMPACT / TRACEWIN / GPT

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Open animated GIF in Internet Exploreranimated

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Fast Pulse Generator (FPG) development

FPG development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October x Pulse generator cards High peak power loads Control and interface Combiner 9 x Pulse generator cards Power supply 9 x Pulse generator cards 1.7 m FPG / Front View

FPG development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 FPG waveform measurement

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Slow Pulse Generator (SPG) development

M. A. Clarke-Gayther RAL/FETS/HIPPI SPG development HIPPI th October close coupled ‘slow’ pulse generator modules Slow chopper electrodes Beam SPG beam line layout and load analysis

M. A. Clarke-Gayther RAL/FETS/HIPPI SPG development HIPPI th October 2008 Prototype 8 kV SPG euro-cassette module / Side view Low-inductance HV damping resistors 8 kV push-pull MOSFET switch module High voltage feed-through (output port) Axial cooling fans Air duct 0.26 m

M. A. Clarke-Gayther RAL/FETS/HIPPI SPG development HIPPI th October 2008 SPG waveform at 3 kV peak & 50 ns / div. SPG waveform measurement / HTS GSM-CF-HFB SPG waveform at 3 kV peak & 1 μs / div. SPG waveform at 3 kV peak & 0.2 ms / div.SPG waveform at 3 kV peak & 5 ms / div. 256 ns33% 1.3 MHz PRF 1 ms burst 1 ms 50 Hz 3 kV

M. A. Clarke-Gayther RAL/FETS/HIPPI SPG development HIPPI th October 2008 Measured performance parameters / HTS GSM-CF-HSB Stability of SPG trigger input to pulse output delay time (1 hour) at 100 ps /div.

M. A. Clarke-Gayther RAL/FETS/HIPPI SPG development HIPPI th October 2008

M. A. Clarke-Gayther RAL/FETS/HIPPI SPG development HIPPI th October 2008 Pulse ParameterFETS RequirementMeasuredCompliancyComment Amplitude (kV into 50 Ohms)± Yes± 4 kV rated Transition time (ns)~ 12T rise : 11.1, T fall : 11.4Yes1316 pulses Duration (μs)0.23 – – 100YesFWHM Droop (%)00YesDC coupled Repetition frequency (MHz)1.3 Yes Burst 1.3 MHz0.3 – 1.5 ms1.0 msClose1.3 ms maximum? Burst repetition frequency (Hz)50 Yes1 ms 1.3 MHz Post pulse aberration (%)± 5≤ ± 5YesDamping dependent Pulse width stability (ns)± ns (n=1 to 2)Close Can be corrected Timing stability (ns over 1 hour)± 0.5± 0.4YesOver temperature Burst amplitude stability (%)+ 10, - 5< + 10, -5YesLimited by power reg. SPG measured parameters / HTS GSM-CF-HFB

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Slow-wave electrode development

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Where: Transverse extent of the beam: L2 Beam transit time for distance L1: T(L1) Pulse transit time in vacuum for distance L2: T(L2) Pulse transit time in dielectric for distance L3: T(L3) Electrode width: L4 For the generalised slow wave structure: Maximum value for L1 = V1 (T3 - T1) / 2 Minimum Value for L1 = L2 (V1/ V2) T(L1) = L1/V1 = T(L2) + T(L3) The relationships for field (E), and transverse displacement (x), where q is the electronic charge, is the beam velocity, m 0 is the rest mass, z is the effective electrode length,  is the required deflection angle, V is the deflecting potential, and d is the electrode gap, are: ‘E-field chopping / Slow-wave electrode design

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Why develop an alternative to the CERN electrode design?  To improve on the transverse field uniformity  To improve on the overall coverage factor  To investigate the upper frequency limit for a s-w structure  To address a possible differential thermal expansion issue Motivation

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 ‘On-axis field in x, y plane

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Phase space plot at entrance to chopper beam dump Kicked beam with uniform transverse chopper field

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Phase space plot at entrance to chopper beam dump Kicked beam with non-uniform transverse chopper field

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Phase space plot at entrance to chopper beam dump Kicked beam with non-uniform transverse chopper field requires Increase in chopper field and an increase in beam aperture and / or beam dump length

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Coaxial test assembly Planar test assemblyHelical test assembly Short length helical prototypeShort length planar prototype Planar or helical full length electrode Electrode development / Overview

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Electrode development / Overview

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Coaxial, planar and helical test assemblies The manufacture and test of these preliminary assemblies will provide important information on the following:  Accuracy of the 3D high frequency design code.  Construction techniques.  NC machining and tolerances.  Selection of machine-able ceramics and of copper and aluminium alloys.  Electroplating and electro-polishing.

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Coaxial test assembly

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Coaxial test assembly / Shapal-M version

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Helical test assembly

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Helical electrode / Short length prototype UT-390 semi-rigid coaxial delay lines

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Helical test assembly / CAD view 100 mm

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Helical strip-line Helical test assembly / Electro-polishing / T-domain

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Helical test assembly / Electro-polishing / T-domain

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Helical test assembly / Electro-polishing / F-domain

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Planar test assembly

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Planar short length prototype Boron nitride stripline support pillars

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Expansion joint BEAM 14 x 0.5 mm stripline Planar short length prototype

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 BEAM Expansion joint 14 x 0.5 mm stripline Planar short length prototype

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Expansion joint BEAM 14 x 0.5 mm stripline Planar short length prototype

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Expansion joint BEAM 14 x 0.5 mm stripline Planar short length prototype

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Expansion joint BEAM 14 x 0.5 mm stripline Planar short length prototype

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 RAL Planar / Short length prototype Expansion joint Coaxial assembly BEAM

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Expansion joint Coaxial assembly BEAM Planar short length prototype

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Coaxial assembly BEAM Planar short length prototype

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Coaxial assembly BEAM

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Planar test assembly

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Planar test assembly 230 mm

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Planar test assembly 230 mm

Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Planar test assembly 230 mm

Summary M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008  FPG Compliant with FETS requirements  SPG 4 kV version compliant with FETS requirements  Slow-wave electrode designs Measurements on coaxial and helical test assemblies have: Verified accuracy of high frequency modelling code Tested effect of mechanical tolerances Tested machining properties of selected ceramic materials Tested effect of strip-line tolerances and electro-polishing Probed limitations of NC machining practice

Summary M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008  Slow-wave electrode designs (continued): Planar test assembly – design almost complete – to test: Machining properties of ceramic support pillars Strip-line clamping and positioning tolerances Performance of expansion joints The design and manufacture of the subsequent planar and helical ‘short length’ prototype structures, will build on the experience gained from the preliminary test assemblies, and should facilitate the choice of a candidate design for the full scale structure. There is still much to do – and as always the devil is in the details – however we have addressed some challenging issues and I have confidence in a successful outcome!

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Acknowledgement

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Acknowledgement A successful and beneficial collaboration! CERNRAL Optical design Bipolar pulsing Compensating ‘grooves’ Coordination Coverage factor modelling Electrode & pulser technology

M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 Acknowledgement Coordination: Maurizio Vretenar Alessandra Lombardi Chris Prior Optical design: Frank Gerigk (RAL scheme A) Giulia Bellodi (RAL scheme B) Alessandra Lombardi Edgar Sargsyan Grahame Rees Ciprian Plostinar CERN electrode technology: Fritz Caspers Tom Kroyer CERN pulser technology: Mauro Paoluzzi RAL FPG technology: Jonathan Hares (Kentech UK) RAL electrode manufacturing:John Spencer (RAL MMT) Mathew Beardsley (RAL MMT)

References M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 HIPPI WP4: The RAL† Fast Beam Chopper Development Programme Progress Report for the period: January 2007 – June 2008 M. A. Clarke-Gayther STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK EU contract number RII3-CT CARE-Report HIPPI

References M. A. Clarke-Gayther RAL/FETS/HIPPI HIPPI th October 2008 M Clarke-Gayther, ‘The development of a fast beam chopper for next generation high power proton drivers’, Proc. of EPAC 2008, Genoa, Italy, 23 rd – 27 th June, 2008, pp M Clarke-Gayther, ‘Slow-wave chopper structures for next generation high power proton drivers’, Proc. of PAC 2007, Albuquerque, New Mexico, USA, 25 th – 29 th June, 2007, pp M Clarke-Gayther, G Bellodi, F Gerigk, ‘A fast beam chopper for the RAL Front-End Test Stand’, Proc. of EPAC 2006, Edinburgh, Scotland, UK, 26 th - 30 th June, 2006, pp M Clarke-Gayther, ‘Fast-slow beam chopping for next generation high power proton drivers’, Proc. of PAC 2005, Knoxville, Tennessee, USA, 16 th – 20 th May, 2005, pp M Clarke-Gayther, ‘A fast beam chopper for next generation proton drivers’, Proc. of EPAC 2004, Lucerne, Switzerland, 5 th – 9 th July, 2004, pp M Clarke-Gayther, ‘Slow-wave electrode structures for the ESS 2.5 MeV fast chopper’, Proc. of PAC 2003, Portland, Oregon, USA, 12 th - 16 th May, 2003, pp F Caspers, ‘Review of Fast Beam Chopping’, Proc. of LINAC 2004, Lubeck, Germany, 16 th – 20 th August, 2004, pp F Caspers, A Mostacci, S Kurennoy, ‘Fast Chopper Structure for the CERN SPL’, Proc. of EPAC 2002, Paris, France, 3 rd – 7 th June, 2002, pp