Transverse Emittance and Energy Spread Measurements for IFMIF-EVEDAC. OLIVER

Contributors: P. A. Phi NGHIEM, C. Marolles

ABI Workshop on Emittance DiagnosticsBad Kreuznach, 11th December 2008

Transverse emittance measurementsLow energy part E5 MeVEnergy spread measurementsFuture

Transverse Emittance Measurement

1.1. Transverse emittance for low energy

*IFMIF Injector Allison scanner for 15 kW beam powerIFMIF Injector will produce 15 kW CW deuteron beams.A dedicated Allison scanner is under study at CEA/Saclay (Cdric Marolles et al.) - Mechanical design - Thermal and hydraulic calculations (with Cosmos) are still in progressWater cooled copper block platted with tungsten would allow handling 15 kW CW beam (0.5 to 2 kW/cm2)Emittance Measurement E

IFMIF Injector: ALLISON scanner + WIEN filterPossible Solution : Slit + Global WF for a uniform magnetic field along the slit : 250 kg magnets1. Vertical Scan with the Slit2. Horizontal Scan with the WF3. Scan of beamlet with electric platesDevelopped solution: Slit + Small Movable Wien Filter with Halbach magnetic configuration (magnetic simulations with Radia and Comsol)Additional studies have been undertaken to only analyze D+ beam emittance with an Allison scanner associated with a Wien Filter (allows separated species analysis)A small movable WF scanning along the slitWFAllison- WF123

1.2. Transverse emittance for high energy

Different alternativesa) Interceptive methods Pepper pot, Slit wire scanAdvantages:Reduce space charge by separating the beam into many beamletsDrawbacks:Limited signal to noise ratio of the beam signal after passing the slit/pepper potHuge beam deposition in the mask

b) Non-interceptive methodsQuadrupole scan technique, multiple profile monitors, Limitations:Method becomes questionable when space charge cannot be neglected

IFMIF-EVEDA: 125 mA, 9 MeV, ~ 1.1 MW slits/pepper-pot masks will be destroyed by the beam

Only Non-Interceptive methods can be used in IFMIF-EVEDA at full current and cw

Emittance Measurement E>5 MeV

Non-Interceptive Methods for Transverse Emittance Measurement2D Trace space (x,x)

- Profile monitor determines- Other matrix elements may be inferred from beam profiles taken under various transport conditions downstream (knowing the transformation of the beam matrix, R) The elements of s0 can be deduced from a set of three measurements of s11 obtained from beam conditions described by three different transfer matrices More than 3 width measurements are taken Data subjected to least-squares analysisTransverse Emittance MeasurementUse of variable quadrupole strengths: changing the quadrupole and measuring the beam size in a beam monitor located downstream

Traditional emittance measurement techniques use the envelope equation ignoring space chargeThis assumption is not appropriate in our case except in a strongly focused waist Need of a beam envelope model that includes both space-charge and emittance

EnvelopeEquations

Ratio of space charge to emittance force:

Beams are space-charge dominated when R>>1 Defocusing term due to space charge

Focusing term due to the magnetic field

Transverse Emittance Measurement Use of simulation codes

Procedure of the Quad scan method for emittance measurement

Limitations:

To avoid losses in the vacuum chamber (attention to the distribution tails!!)To obtain big size variation a waist would needed (avoiding so big beam sizes in the quad scan and also it allows an easy fit to a parabola), but waist leads to halo which will affect to the rest of the line (losses or bigger vacuum chamber) Obviously, quadrupoles affect to both transverse directions and in both directions the beam must keep inside the vacuum chamber

Transverse emittance measurement using quad scan for IFMIF-EVEDATransverse Emittance MeasurementSize variation: Q1= 4.36 T/mQ2=-12.84 T/mQ3= 8.97 T/mQ1= 4.36 T/mQ2=-13.84 T/mQ3= 9.97 T/m - Beam profile monitors located at the end of the DP to get enough size variation

Evaluation of space charge influenceFor deuterons, I0 62654 kAFor IFMIF-EVEDA, during the diagnostic plate (nominal conditions): space-charge can not be neglectedTransverse Emittance Measurement

Evaluation of space charge influenceTransverse Emittance MeasurementEffect of space charge: Asymmetry in data about the waist Due to the fact that the beam evolution in the drift is very different for data points on opposite sides of the minimum Different relative contribution of emittance and space charge in each side

Weak focusingBeam size is deflected appreciably only by the space chargeTransverse Emittance Measurement

Stronger focusing A waist is produced in which the beam is thermal emittance dominated Emittance force applies an extra kick to the beam size Beam size is deflected by the combination of space charge and emittance forcesTransverse Emittance Measurement

Quad scan for different emittances 2-4 mmEnough for the beam profile monitor resolution??Transverse Emittance Measurement

Evaluation of space charge influenceTransverse Emittance MeasurementConsequences of space charge:

Linear transformation matrix formalism can not be used for IFMIF-EVEDA Fits to the numerical codes must be performed Points on different side of the curve are dominated by different terms difficult to obtain a correct emittance The beam size must be obtained from rms values and not from FWHM Asymmetry introduces a problem in the consistency of the result: Fit the data to a parabola fit parameters will depend on the portion of the curve used for the fit Fit using points only dominated by space charge will not lead to an accurate solution for the emittance due to the fact that the beam evolution in the drift is very different for data points on opposite sides of the minimum

2. Energy Spread Measurement

1. IntroductionEnergy spread is a crucial parameter to be measured Strongly related to beam dynamics issues

Energy Spread MeasurementEnergy spread ~ 0.6%Measurements: beam energy spread.Energy: 59 MeVAccuracy:

2. Different alternatives and final choiceInterceptive techniques: slits, pepper-pot masksPerformed in a dispersive locationSpatial and energetic contribution is separated

Non-interceptive technique:

Measurement of the beam size in a dispersive section

If emittance contribution is negligible compared to dispersion contribution:

Way to continuously verify that energy spread is below the requirementMaximum energy resolution for small beam size (at or close the waist) and dispersion largeOther alternatives: quad scan

Energy Spread Measurement IFMIF-EVEDA

3. Present statusIs this approximation valid for IFMIF-EVEDA?

Dispersion in a free drift is linearly increasing:(Dispersion depends on the dipole angle which was arbitrary fixed to 20)

However, quadrupoles affect to the dispersion function in the same way that to the beam size

Energy Spread MeasurementNominal configuration:

If we compare dispersion to emittance contribution:Dispersion contribution very small compared to betatron contribution Energy spread measurement method based in the size measurement in a dispersive location for the nominal configuration has not enough precisionComparison of the betatron and dispersion contributions:Energy Spread MeasurementDispersion contribution to betatron contribution ratio

Optimization of the dispersion after the last tripletEnergy Spread MeasurementSize/dispersionDispersion contribution to betatron contribution ratio

FutureTransverse emittance

Analysis of dependence of the results on the space-charge algorithm Comparison of results for several codes (different space charge terms) Different distributions Analysis of beam alignment through the quads during emittance measurement Error analysis of the quad scan data Code implementation of quad scan method

Energy spread

Effect of the space charge Other methods to improve the resolution?

Transverse Emittance MeasurementBut at full current and low duty cycle Best resolution is expected to be obtained Quad scan in these conditions has been analysed at present for transverse emittance measurement Quad scan in the dispersive section for energy spread measurement

Thank you!!!

*