IPM development for LIPAc

CERN Workshop on Non-Invasive Beam... 1

IPM development for LIPAc

P. Abbon, J.F. Denis, J. Egberts, J.F. Gournay, F. Jeanneau, J. Marroncle, J.P. Mols, T. Papaevangelou, H. Przybilski

LIPAc: Linear IFMIF Prototype Accelerator

April 15th, 2013

J. Egberts’s PhD thesis defended on September 25th, 2012 at Orsay (France)“IFMIF-LIPAc Beam diagnostics: Profiling and Loss Monitoring System”

http://irfu.cea.fr/Documentation/Theses/


Overview

• IFMIF, LIPAc introduction

• IPM prototypedesign, tests at GSI and Saclay

• Space Charge effect

• Design of large and medium IPM aperture

• summary

April 15th, 2013

IPM: Ionization Profile Monitor


IFMIF (International Fusion Materials Irradiation Facility)

LMH2 cw accelerators, 2 x 125 mA, 2 x 5MW

Test CellLithium Target25 mm thick, 15 m/s

Beam profile200 x 50 mm2

deuteron source140/150 mA, 100 keV

RFQ 5 MeV

Superconductive Linac 40 MeV(Half Wave Resonators) Typical reactions

7Li(d,2n)7Be6Li(d,n)7Be6Li(n,T)4He

High > 20 dpa/y 0.5 lMedium > 1 dpa/y 6 lLow 1 dpa/y > 8 l

International agreement of the BA (JAEA+F4E in Feb. 2007) = IFMIF + IFERC + JT60-SA

IFMIF* : to test materials submitted to very high neutron fluxes for future Fusion Reactors.

Flux ~ 1017 neutrons/s

April 15th, 2013


LIPAc(Linear IFMIF Prototype Accelerator)

Validation phase: prototype accelerator LIPAc (Rokkasho – Japan)➝

LIPAc = 125 mA cw, 9 MeV, 1.125 MW, RF 175 MHz

100 keV 5 MeV 9 MeV

ionsourc

e

BeamDump

BeamExtraction LEBT RFQ MEBT HEBTSc HWR-Linac

12.5 kW 625 kW 1125 kW

Injector delivery: March 2013RFQ commissioning: June 2015

Very challenging Linear Accelerator:• highest intensity (125 mA)• highest beam power (1.125 MW)• highest space charge• very high radiation background, mainly due to neutron backscattered off the BD

April 15th, 2013

Rokkasho


LIPAc diagnosticsGlossary:

ACCT: AC Current TransformerBLoM: Beam Loss MonitorRGBLM: Residual Gas Bunch Length MonitorBPM: Beam Position MonitorDCCT: DC Current TransformerFC: Faraday CupFFC: Fast Faraday CupFCT: Fast Current TransformerIPM: Ionization Profile MonitorFPM: Fluorescence Profile MonitorµLoM: Micro Loss Monitor

4 grids analyser

FC

Emittance meter

Species fraction measurement

4 Profilers(CCD camera) ACCT

4 BPM (Stripline) 8 BPM (cryo)3 BPM

1 Slit (E.spread)

FPM

2 BPM

ACCT + FCT 3 x 8 µLoM SEM GridsACCT IPM

2 BPMs (stripline) 2 Slits (Emittance) RGBLM 1 BPM (Stripline) FPM

ACCT + DCCT SEM GridsIPMDiagnostic- Plate

Steerer for SEM

April 15th, 2013

∼ 20 BLoMs for the whole end-accelerator


LIPAc IPMs

1 IPM

2 IPMsDiagnostic- Plate

April 15th, 2013

FPM viewport

BPM

beam

Last HEBT part upstream to lead plug


IPM Prototype

April 15th, 2013


IPM

April 15th, 2013

Requirements, keeping in mind IFMIF• radiation hard materials neutrons: 7 kSv/h on beam axis at HEBT IPM location➞• fast FEE for monitoring beam footprint on the Li target

General aspect• Transverse size: 61 × 59 mm2 - depth 40 mm• 32 strips for charge collection (pitch = 1.25 mm 40 mm active width)➞• electric field uniformity Electric field simulation by FEM (SOLMAXP)➞• lateral degraders (150 MΩ) + 1 spire on top and bottom to reinforce the E-field homogeneity• movable slits in longitudinal direction for monitoring the active length of strips• typical applied voltage 5 kV E = 833 V/cm∼ ⇒

spire

DegraderSOLMAXP


Electric field: FEM simulation

April 15th, 2013

Finite Element Method• SOLMAXP (R. Duperrier, CEA Saclay, Irfu/SACM)

Ex component (V/m) in the transverse plane of the IPM• no spire inhomogeneity < 30%➞• spire (copper loop) inhomogeneity < 3%➞

J. Egberts – April 2010

inhomogeneity < 30% inhomogeneity < 3%


FEE & daq

April 15th, 2013

Front End Electronics• transimpedance and logarithmic cards

➞ continuously multiplexed every 2 µs, ie 1 strip ≡ 2000/32 = 62.5 ns• integration card (81 µs to 64 ms)

data Acquisition System• Acqiris card

➞ 8 bits ADC ➞ 1 GHz sampling rate with 2 MB memory

transimpedance card (oscilloscope )

2.1 s or 32 strips or 40 mm

Beam profile

Trigger signal set on channel 16


GSI tests, 2010

April 15th, 2013


GSI test

April 15th, 2013

Tests on the UNILAC of GSI (X2 branch devoted to GSI diagnostic team) ➞ May and November 2010 ➞ examples of beam conditions:

- 33 µA 48Ca10+ at 4.6 MeV/A @ 5ms/s- 1.6 mA 238U28+ at 4.8 MeV/A @ 100 µs/s

➞ Residual gas: adjustable pressure from 5 10-7 mbar to 5 10-5 mbar


Electric field uniformity (1)

April 15th, 2013

Beam conditions are kept frozen• Stepper motor ➞ accurate transversal displacement of the IPM• IPM ➞ calculation of the central position of the beam

Very good linearity (slope 1) ∼ ⇒ Good electric field uniformity

1 mA Xe21+

∆t=60 ms

Beam profile measured with the IPM

∆disp.=20 mm

∆disp.=500 µm


Electric field uniformity (2)

April 15th, 2013

Aperture variation of the sliding window• strip current rises linearly• weak σ enlargement

⇒ due to field inhomogeneity or to tilted strips?

3 8 13 18 23 283.4

3.5

3.6

3.7

3.8

slit aperture (mm)

σ (m

m)slit aperture

sliding windows

30 m

m

40 mm

s t r i p s

Conclusion: E field uniformity seems to be quite good on “inner” transverse plane

Aperture (mm)

Sign

al (m

m.m

V)


Accelerating field, Resolution, extrapolation

April 15th, 2013

Accelerating FieldProfile width• electron profile much broader than ion profile• profile width decrease with higher voltages

-5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 50003

4

5

6

7

8

9

10

accelerating voltage (V)

σ (m

m)

ResolutionFluctuation of beam center versus time acquisition (∆t)• σ << 100 µm for ∆t < 1 ms

σ (m

m)

time integration (µs)

120µA Xe21+, 10-5 mbar N2

Extrapolation GSI data to LIPAc ⇒ 8.4 mA with ∆t=5 ms at 5 10-8 mbar


Profile comparison IPM / FPM

April 15th, 2013

At the same location (cross):• IPM on 1 port• FPM or BIF on a port at 90°Note, walls were blackened to avoid reflection for CCD

Extracted from « GSI SCIENTIFIC REPORT 2010 »

FPM: Fluorescence Profile MonitorBIF: Beam Induced Fluorescence


Saclay tests, 2010

April 15th, 2013


Silhi tests

April 15th, 2013

Silhi source of Iphi• protons • dc: few 10-3 up to cw• Emax = 95 keV• Imax = 100 mA• P ~ 6 10-5 Torr

Silhi: Source of Light Ions at High IntensityIphi: Injector of Protons at High Intensity

0 500 1000 1500 2000 2500 30000

500

1000

1500

2000

2500

High Voltage [V]

Curr

ent C

onsu

mpti

on [µ

A]

Picture taken from a viewport

IPM was able to handle CW beam up to 21 mA.

Ibeam ~ 3 mA

CERN Workshop on Non-Invasive Beam... 19April 15th, 2013

Space Charge effect (SC)


Space Charge effect

April 15th, 2013

Ionization products experienced• IPM electric field• Beam electric field: Space Charge

➞ GSI: low I negligible effect⇒ ➞ IPHI: high I, low E big effect (profile distortion)⇒

How to counteract SC• magnetic field for guidance no space available➞• increasing the electric field limitation due to deviation➞• applying correction with an algorithm (developed by Jan Egberts)

Profile reconstruction with an algorithm

Theoretical

SC off

SC on

∆max ≈ 0.3 mm

∆max ≈ 5 mm


Space Charge Algorithm

April 15th, 2013

Generalized Gaussian distribution• µ: profile center• Two degrees of freedom

σ: 2nd momentβ: kurtosis, 4th moment

1- Hypothesis• D+

• round beam• beam charge distribution described by a generalized Gaussian Distribution (GGD)• Ibeam

2- Approach• • Matrix components Mij represent the probability that an ion collected on strip j has been create at the position i

➞ beam distribution (GGD) & ions trajectories• Set of matrices computed for various parameter combinations

Ibeam: 1 to 125 mA 35➞σ: 5 to 15 mm 21➞β: -0.25 to 0.25 3➞

total matrices: 2205

3- First parameter to initiate iteration process • fit of the experimental profile using a GGD to extract

Ibeam: given by Current Transformers ➞ σ0 = σexp

➞ β0 = βexp

• iterations

∙∙∙

until parameters converge (σn ≈ σn-1 ; βn ≈ βn-1) self consistent solution➞


Large aperture IPM for HEBT


IPM: HEBTLarge aperture: 15 × 15 cm2

Very high radiation background: 7 kSv/h neutrons on beam axis ⇒ Materials: ceramics (RO4350B), copper, resistors (CMS), Kapton (ribbon cable)

+ SAMTEC 80 micro coaxial cables (PVC, LCP, FEP ; halogen)Degraders (16×2): 230 MΩ Lorentz-3D for electric field uniformity➞FEE based on integrators; rate ≈ 10 Hz HVmax = 16 kV

Tests done at Saclay on SILHI source: Dec. 2011 - Feb. 2012 proton Emax = 95 keV, Imax = 100 mA, dc: up to cwMain test: SC algorithm

• frozen beam characteristics (conditions)• only variation of extracting field

15×15 cm2

HV: 1.65 to 6.5 kV


IPM: HEBT (cable test)


Medium aperture IPM for Diagnostic-Plate


D-Plate: IPM

April 15th, 2013

Medium aperture: 10 × 10 cm2

Low radiation backgroundDegraders (13×2): 400 MΩFEE based on integrators; rate ≈ 10 HzHVmax = 19 kV

Tests on SILHI: in progress


1st profile…

April 15th, 2013


Summary

April 15th, 2013

LIPAc is a challenging linear accelerator ➞ high intensity, high power, high SC, high radiation background

IPM prototype have shown very good behavior ➞ thanks to its good electric field uniformity (FEM simulation) ➞ very nice profile agreement with FPM

Nevertheless it is very sensitive to SC effect

An algorithm to correct SC was developed and tested with promising results

One large aperture IPM (15 × 15 cm2) has been already tested

A medium aperture IPM (10 × 10 cm2) is in test progress.

IF IFmif… ➞ the beam footprints on the Li target (20 × 5 cm2) would have to be monitored in a very

harsh environment. ➞ new materials and perhaps technics should have been inquired…

Very challenging issue!


Arigatou, merci… for your attention

April 15th, 2013

Thanks to:CEA Saclay colleagues

P. Abbon, J.F. Denis, J. Egberts, J.F. Gournay, F. Jeanneau, J.P. Mols, T. Papaevangelou, H. Przybilski

GSI diagnostics group and UNILAC GSI peopleSILHI – IPHI group at CEA Saclay

Organizing committee of this WS for the invitation


Challengeshighest intensity (125 mA cw)

highest beam power highest space charge

⇓↑ RFQ length to ↓ SC

for beam injection in the SRF Linac

⇓longest RFQ (0.1 to 5 MeV)

∼ 10 m

⇓Validation Phase: LIPAc

PAP Nghiem – Beam dynamics – CEA Saclay

LIPAc (9 MeV)

RFQ (5 M

eV)

April 15th, 2013


SC for Asymmetric beam

April 15th, 2013

σx = 6 mm - σy = 9 mm

Search algorithm find profile with a σxreconstructed = 5.5 mm


IFMIF

April 15th, 2013

Edeuteron = 40 MeV

Ibeam = 2 × 125 mA

HV = 12 kVAssumption:

• perfect electric field uniformity IPM with a large depth ➞• beam cross section: 25 × 100 mm2

⇒ Space charge effect for IPM aperture:• 200 mm (left)• 300 mm (right)


Radiation background

UNED (Madrid) - 2008

Shielding (polyethylene disks, plates…) ➟ neutrons

Fluence, calculated over 1 month cw

Electronic radiation hardness- high energy neutrons (~ MeV) electronic ⇒

trouble for Fluence > 1011 n/cm2

145

135

125

115

10595

65

55

75

85

4535 25

5

A. Marchix – January 2012 (only BD)

15

conc

rete

BD

beamaxis

CH2 – V shape

CH2 wall+roof

LinacSRF

Point # 5 15 25 145 115 85

n/cm2/s 7 108 6 108 5 108 4 107 6 106 4 106

Fluencen/cm2 2 1015 2 1015 1 1015 1 1014 2 1013 1 1013

April 15th, 2013

Documents

IPM development for LIPAc