Transverse Emittance and Energy Spread Measurements for IFMIF-EVEDA C. OLIVER Contributors: P. A. Phi NGHIEM, C. Marolles ABI Workshop on Emittance Diagnostics Bad Kreuznach, 11th December 2008

1.Transverse emittance measurements a)Low energy part E<5 MeV b)High energy part E>5 MeV 2.Energy spread measurements 3.Future

1.Transverse Emittance Measurement

1.1. Transverse emittance for low energy

December, 11th 2008 Workshop on Emittance Diagnostics 5 5 IFMIF Injector Allison scanner for 15 kW beam power IFMIF Injector will produce 15 kW CW deuteron beams. A dedicated Allison scanner is under study at CEA/Saclay (Cédric Marolles et al.) - Mechanical design - Thermal and hydraulic calculations (with Cosmos) are still in progress Water cooled copper block platted with tungsten would allow handling 15 kW CW beam (0.5 to 2 kW/cm 2 ) Emittance Measurement E<5 MeV

December, 11th 2008 Workshop on Emittance Diagnostics 6 IFMIF Injector: ALLISON scanner + WIEN filter Possible Solution : Slit + Global WF  for a uniform magnetic field along the slit : 250 kg magnets 1. Vertical Scan with the Slit 2. Horizontal Scan with the WF 3. Scan of beamlet with electric plates Developped 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 slit WF Allison- WF 1 2 3

1.2. Transverse emittance for high energy

December, 11th 2008 Workshop on Emittance Diagnostics 8 a) Interceptive methods – Pepper pot, Slit wire scan –Advantages: Reduce space charge by separating the beam into many beamlets –Drawbacks: Limited signal to noise ratio of the beam signal after passing the slit/pepper pot Huge beam deposition in the mask Different alternatives b) Non-interceptive methods –Quadrupole 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

December, 11th 2008 Workshop on Emittance Diagnostics 9 Non-Interceptive Methods for Transverse Emittance Measurement 2D 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    can be deduced from a set of three measurements of   obtained from beam conditions described by three different transfer matrices  More than 3 width measurements are taken  Data subjected to least-squares analysis Transverse Emittance Measurement –Use of variable quadrupole strengths: changing the quadrupole and measuring the beam size in a beam monitor located downstream

December, 11th 2008 Workshop on Emittance Diagnostics 10 Traditional emittance measurement techniques use the envelope equation ignoring space charge This 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 Envelope Equations 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

December, 11th 2008 Workshop on Emittance Diagnostics 11  x,  y RMS values Accelerator operation Quad current scan And beam profile measurements Input Beam Numerical code trying different Twiss parameters and emittance to reproduce the quad scan Simulation code To obtain Twiss parameters, emittance??? Twiss parameters and emittane Procedure of the Quad scan method for emittance measurement

December, 11th 2008 Workshop on Emittance Diagnostics 12 Transverse emittance measurement using quad scan for IFMIF-EVEDA Transverse 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 Size variation: Q1= 4.36 T/m Q2= T/m Q3= 8.97 T/m Q1= 4.36 T/m Q2= T/m Q3= 9.97 T/m - Beam profile monitors located at the end of the DP to get enough size variation

December, 11th 2008 Workshop on Emittance Diagnostics 13 Evaluation of space charge influence For deuterons, I 0 ≈ kA For IFMIF-EVEDA, during the diagnostic plate (nominal conditions):  space-charge can not be neglected Transverse Emittance Measurement

December, 11th 2008 Workshop on Emittance Diagnostics 14 Evaluation of space charge influence Transverse Emittance Measurement Effect 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

December, 11th 2008 Workshop on Emittance Diagnostics 15 -Weak focusing -Beam size is deflected appreciably only by the space charge Transverse Emittance Measurement

December, 11th 2008 Workshop on Emittance Diagnostics 16 - 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 forces Transverse Emittance Measurement

December, 11th 2008 Workshop on Emittance Diagnostics 17 Quad scan for different emittances 2-4 mm Enough for the beam profile monitor resolution?? Transverse Emittance Measurement

December, 11th 2008 Workshop on Emittance Diagnostics 18 Evaluation of space charge influence Transverse Emittance Measurement Consequences 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

December, 11th 2008 Workshop on Emittance Diagnostics 20 Energy spread is a crucial parameter to be measured Strongly related to beam dynamics issues 1. Introduction Energy Spread Measurement Energy spread ~ 0.6% Measurements: beam energy spread. Energy: 5÷9 MeV Accuracy: <0.3%ΔE/E. Rms precision: <0.1%ΔE/E. Frequency bandwidth: 0.5 Hz. Measurements: beam energy spread. Energy: 5÷9 MeV Accuracy: <0.3%ΔE/E. Rms precision: <0.1%ΔE/E. Frequency bandwidth: 0.5 Hz.

December, 11th 2008 Workshop on Emittance Diagnostics 21 1.Interceptive techniques: slits, pepper-pot masks –Performed in a dispersive location –Spatial and energetic contribution is separated 2.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 requirement –Maximum energy resolution for small beam size (at or close the waist) and dispersion large –Other alternatives: quad scan Energy Spread Measurement 2. Different alternatives and final choice  IFMIF-EVEDA

December, 11th 2008 Workshop on Emittance Diagnostics 22 -Is 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 20º) -However, quadrupoles affect to the dispersion function in the same way that to the beam size Energy Spread Measurement 3. Present status Nominal configuration:

December, 11th 2008 Workshop on Emittance Diagnostics 23 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 precision Comparison of the betatron and dispersion contributions: Energy Spread Measurement Dispersion contribution to betatron contribution ratio

December, 11th 2008 Workshop on Emittance Diagnostics 24 Optimization of the dispersion after the last triplet Energy Spread Measurement Size/dispersion Dispersion contribution to betatron contribution ratio

December, 11th 2008 Workshop on Emittance Diagnostics 25 Transverse 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? Future Transverse Emittance Measurement But 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

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