Transverse Emittance and Energy Spread Measurements for IFMIF-EVEDA

1. 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

2. Transverse emittance measurements • Low energy part E<5 MeV • High energy part E>5 MeV • Energy spread measurements • Future

3. Transverse Emittance Measurement

4. 1.1. Transverse emittance for low energy

5. Emittance Measurement E<5 MeV 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/cm2) Workshop on Emittance Diagnostics 5

6. IFMIF Injector: ALLISON scanner + WIEN filter Additional studies have been undertaken to only analyze D+ beam emittance with an Allison scanner associated with a Wien Filter (allows separated species analysis) • Possible Solution : Slit + Global WF  for a uniform magnetic field along the slit : 250 kg magnets • A small movable WF scanning along the slit Developped solution: Slit + Small Movable Wien Filter with Halbach magnetic configuration (magnetic simulations with Radia and Comsol) WF 2 3 1 1. Vertical Scan with the Slit 2. Horizontal Scan with the WF 3. Scan of beamlet with electric plates Allison- WF Workshop on Emittance Diagnostics

7. 1.2. Transverse emittance for high energy

8. Emittance Measurement E>5 MeV Different alternatives 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 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 Workshop on Emittance Diagnostics

9. Transverse Emittance Measurement 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 s0can 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 analysis • Use of variable quadrupole strengths: changing the quadrupole and measuring the beam size in a beam monitor located downstream Workshop on Emittance Diagnostics

10. Transverse Emittance Measurement • 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  Use of simulation codes Workshop on Emittance Diagnostics

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

12. Transverse Emittance Measurement Transverse emittance measurement using quad scan for IFMIF-EVEDA Size variation: 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 - Beam profile monitors located at the end of the DP to get enough size variation Q1= 4.36 T/m Q2=-13.84 T/m Q3= 9.97 T/m Q1= 4.36 T/m Q2=-12.84 T/m Q3= 8.97 T/m Workshop on Emittance Diagnostics

13. Transverse Emittance Measurement Evaluation of space charge influence For deuterons, I0≈ 62654 kA For IFMIF-EVEDA, during the diagnostic plate (nominal conditions):  space-charge can not be neglected Workshop on Emittance Diagnostics

14. Transverse Emittance Measurement Evaluation of space charge influence • 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 Workshop on Emittance Diagnostics

15. Transverse Emittance Measurement • Weak focusing • Beam size is deflected appreciably only by the space charge Workshop on Emittance Diagnostics

16. Transverse 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 forces Workshop on Emittance Diagnostics

17. Transverse Emittance Measurement Quad scan for different emittances 2-4 mm Enough for the beam profile monitor resolution?? Workshop on Emittance Diagnostics

18. Transverse Emittance Measurement Evaluation of space charge influence • 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 Workshop on Emittance Diagnostics

19. 2. Energy Spread Measurement

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

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

22. Energy Spread Measurement ¿ ? 3. Present status • 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 • Nominal configuration: Workshop on Emittance Diagnostics

23. Energy Spread Measurement Comparison of the betatron and dispersion contributions: • If we compare dispersion to emittance contribution: Dispersion contribution to betatroncontribution ratio 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 Workshop on Emittance Diagnostics

24. Energy Spread Measurement Optimization of the dispersion after the last triplet Dispersion contribution to betatroncontribution ratio Size/dispersion Workshop on Emittance Diagnostics

25. Transverse Emittance Measurement Future 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? • 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 Workshop on Emittance Diagnostics

26. Thank you!!!