Notes on the HIE-ISOLDE HEBT

Transcription

1 EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH HIE-ISOLDE-PROJECT-Note-13 Notes on the HIE-ISOLDE HEBT M.A. Fraser Abstract The HEBT will need to transfer the beam from the HIE-ISOLDE linac to up to four experimental stations over a wide range of energies from.45 MeV/u to 1 MeV/u, which equates to a maximum beam rigidity of 2 Tm for A/q = 4.5. As the linac will be installed in stages, so too will the HEBT, with the first two experimental stations being installed before a larger U-bend that will take the beam to a third experimental station and a spectrometer. The beam parameters at output from the linac are presented along with a preliminary scheme for the HEBT, which is consistent with the experiments footprints. The first beam optics calculations were carried out using TRACE3D. Supporting documentation can be found on the CERN EDMS under the HEBT Lines Optics & Layout Working Group in the HIE- ISOLDE Structure. Geneva, Switzerland October 211 This is an internal CERN publication and does not necessarily reflect the views of the CERN management.

2 1 Beam Parameters The energy of the beams at output from the linac is a function of A/q and will range from.45 to 17 MeV/u. There also exists the possiblity to transport the RF beam at.3 MeV/u. The heaviest beams will be accelerated up to a maximum energy of 1 MeV/u and have a rigidity of 2 Tm. The two main stages of the upgrade are shown in Figure 1. In addition, if a chopper line is installed the linac will be extended in Stage 2b by the length of one high energy cryomodule, i.e m, which can be seen in Figure 5. The beam parameters are given in Tables 2, 3 and 4 at the exit to the linac, i.e. at output from the final cryomodule, in each stage. The particle phase space distributions are shown in Figures 2, 3 and 4 from which the above mentioned beam parameters were extracted. The simulation tracked the realistic particle distribution from the RF exit through the realistic field maps of the linac s elements. The beam parameters vary with energy, although in all cases the beam exits the solenoid focusing channel of the linac at a waist and with reasonable symmetry in the vertical and horizontal phase space planes. Figure 1: REX linac with the HIE-ISOLDE upgrade in Stages 1 and 2b. The transverse beam parameters damp adiabatically with increasing energy and the longitudinal beam emittance reduces significantly on completion of the upgrade and installation of the low energy superconducting section. The requested beam parameters are summarised in Table 1. The exact specification is given in the minutes of the 3rd HIE-ISOLDE Physics Co-ordination Meeting. 2

3 Beam Parameter Table 1: Requested beam characteristics at HIE-ISOLDE Energy Beam spot diameter Beam divergence Micro-bunch structure a Description or Value continuous from <.7 to 1 MeV/u < 1 3 mm FWHM < 1 3 mrad FWHM no requirement of micro-bunching to bunched at < 1 ns with ns bunch spacing Energy spread <.1 % Absolute energy resolution no specific details given a The macro-bunch structure of the beam is determined by the charge breeder and the rf duty cycle of the REX front-end. 3

4 Table 2: Summary of the simulated horizontal HIE beam parameters Stage Simulation Energy αx βx ɛ geom x rms ɛ geom x 95% ɛ norm x rms ɛ norm x 95% Code (MeV/u) (mm/mrad) (π mm mrad) (π mm mrad) (π mm mrad) (π mm mrad) Stage 1 TRACK Stage 2b TRACK Stage 2b TRACK Table 3: Summary of the simulated vertical HIE beam parameters Stage Simulation Energy αy βy ɛ geom y rms ɛ geom y 95% ɛ norm y rms ɛ norm y 95% Code (MeV/u) (mm/mrad) (π mm mrad) (π mm mrad) (π mm mrad) (π mm mrad) Stage 1 TRACK Stage 2b TRACK Stage 2b TRACK Table 4: Summary of the simulated longitudinal HIE beam parameters Stage Simulation Energy αz βz ɛz rms ɛz 95% ɛz rms ɛz 95% Code (MeV/u) (ns/kev/u) ( /%) * (π ns kev/u) (π ns kev/u) (π %) * (π %) * Stage 1 TRACK Stage 2b TRACK Stage 2b TRACK * At MHz. 4

5 6 4 ε g =.81 π mm mrad x (rms) ε g = 3.95 π mm mrad x (95 %) ε g =.8 π mm mrad y (rms) ε g = 3.68 π mm mrad y (95 %) x (mrad) 2 1 y (mrad) α x =.27 β x = 1. mm/mrad x (mm) 4 α y =.4 β y = 1.3 mm/mrad y (mm) (a) horizontal phase space (b) vertical phase space ε z (rms) =.58 π ns kev/u ε z (95 %) = 3.8 π ns kev/u 2 2 W/A (kev/u) α z =.49 β z =.4 ns/kev/u φ (ns) (c) longitudinal phase space Figure 2: Beam phase space distribution at exit to the second high energy cryomodule in Stage 1 at 5.9 MeV/u, simulated with TRACK. 5

6 6 4 ε g =.6 π mm mrad x (rms) ε g = 3.14 π mm mrad x (95 %) ε g =.6 π mm mrad y (rms) ε g = 3.16 π mm mrad y (95 %) x (mrad) 2 1 y (mrad) α x =.3 β x = 1.55 mm/mrad x (mm) 4 α y =. β y = 1.21 mm/mrad y (mm) (a) horizontal phase space (b) vertical phase space ε z (rms) =.3 π ns kev/u ε z (95 %) = 2.1 π ns kev/u 2 2 W/A (kev/u) α z =.88 β z =.3 ns/kev/u φ (ns) (c) longitudinal phase space Figure 3: Beam phase space distribution at exit to the final high energy cryomodule in Stage 2b at 1.2 MeV/u, simulated with TRACK. 6

7 15 1 ε g = 3.4 π mm mrad x (rms) ε g = 2.2 π mm mrad x (95 %) ε g = 3.6 π mm mrad y (rms) ε g = 19.6 π mm mrad y (95 %) x (mrad) 5 1 y (mrad) α x =.32 β x =.51 mm/mrad x (mm) 1 α y =.37 β y =.8 mm/mrad y (mm) (a) horizontal phase space (b) vertical phase space ε z (rms) =.35 π ns kev/u ε z (95 %) = 2.6 π ns kev/u 2 2 W/A (kev/u) α z = 11.9 β z = 14.9 ns/kev/u φ (ns) (c) longitudinal phase space Figure 4: Beam phase space distribution at exit to the final high energy cryomodule in Stage 2b, with the low energy section phased to decelerate down to.45 MeV/u, simulated with TRACK. 7

8 2 Layout The HEBT design aimed to make the most of the limited space. The position of the experimental areas should stay fixed and just the transfer line manipulated as more cryomodules are added. Note that before Stage 2b, a third and fourth high energy cryomodule will be installed. The idea was to have a periodic FODO channel to transport the beam to each double bend achromat, of which periods could be removed in a modular fashion as cryomodules are added. However, it was not possible to find a FODO channel with the period the same length as the cryomodules because of the size of the dipole magnets required. Instead, a quasi-fodo channel was chosen (almost a doublet channel) where there are two drifts of different length per period. The total length of the period is 3.2 m. Inside of the long drift the dipoles magnets can fit and in the short drift a rebuncher or diagnostics/steerers could be placed. The difference in the lengths of the cryomodule and the transfer line period can be compensated by the matching section. A transverse phase advance of π/2 per period was chosen to match the phase advance in the linac and help any orbit correction routine that is placed periodically. Four quadrupoles were rather arbitrarily chosen to match into the FODO channel from the linac, although in most cases all four are not needed. The transfer line is sketched in AutoCAD for the two main stages in Figure 5, see the (a) HEBT for Stage 1. (b) HEBT for Stage 2b. Figure 5: HEBT layout in the extension of the ISOLDE experimental hall. 8

9 accompanying files or discuss with Didier Voulot. The design aimed to keep elements standardised. There are 8 rectangular dipole magnets each bending the beam through 45 and 2 bending the beam through 22.5, capable of directing beams with 2 Tm of rigidity. The number of quadrupoles vary and the specifics of the transverse matching to each experiment needs further iteration. Also shown in red is the possibility of translating the beam vertically by one floor to the proposed TSR storage ring. 3 Beam Optics Calculations The beam optics calculations were done using TRACE3D, see the figures below and the accompanying files. All the parameters of interest are held in these files. No studies of the stability of the designs or the orbit correction routine have been completed. A phase advance of π/2 results in quadrupole gradients of 11.1 Tm 1 at 1 MeV/u with a quadrupoles of an effective length of 2 mm. The gradients do not exceed this value at any point in the double bend achromats except for in the matching section. The beam optics calculations show that all beams can be kept inside a radial aperture of 1 mm, and an aperture diameter of 4 mm in the quadrupoles is specified. The energy and time structure of the beam is very important for the experiments. A rebuncher can be used in most cases to achieve the desired parameters shown in Table 1. The rebuncher is shown and needs significant voltages ( 1 MV) suggesting a superconducting cavity will be needed. 3.1 Stage 1 - Experiment Station 1 at 5.9 MeV/u BEAM AT NEL1= 1 H A=.27 B= 1. V A= 4.E 2 B= 1.3 H A=.27 B= 1. V A= 4.E 2 B= mm X 5. mrad I=.mA W= MeV FRE= 11.28MHz WL=296.4mm EMITI= EMITO= N1= 1 N2= 49 x. 1. y BEAM AT NEL2= 49 H A= E 2 B= 1.34 V A= E 2 B= H A= B= V A= B= mm X 5. mrad Z A=.49 Z A=.49 B= 3.3E 3 B= 3.3E 3 CODE: Trace 3 D v7ly FILE: miniball_stage1.t3d DATE: 1/3/211 TIME: 17:9:4 Z A= B= Z A= E 3 B= E 2 6. Deg X 3. kev 1. mm (Horiz) 9. Deg (Long.) 6. Deg X 3. kev NP2= G E E E E mm (Vert) 3. (Dispersion) Length= mm Figure 6: HEBT to Experimental Station 1 at 5.9 MeV/u with and without rebuncher (6ɛ rms envelopes). 9

10 3.2 Stage 1 - Experiment Station 2 at 5.9 MeV/u BEAM AT NEL1= 1 H A=.27 B= 1. V A= 4.E 2 B= 1.3 H A=.27 B= 1. V A= 4.E 2 B= mm X 5. mrad I=.mA W= MeV FRE= 11.28MHz WL=296.4mm EMITI= EMITO= N1= 1 N2= 52 x. 1. y BEAM AT NEL2= 52 H A= E 2 B=.8286 V A= E 2 B= H A= B= V A= E 2 B= mm X 5. mrad Z A=.49 Z A=.49 B= 3.3E 3 B= 3.3E 3 CODE: Trace 3 D v7ly FILE: helios_stage1.t3d DATE: 1/3/211 TIME: 18:5:11 Z A= B=.5634 Z A= E 2 B= E 2 6. Deg X 3. kev 1. mm (Horiz) 9. Deg (Long.) 6. Deg X 3. kev NP2= G E E E E mm (Vert) 3. (Dispersion) Length= 197.8mm Figure 7: HEBT to Experimental Station 2 at 5.9 MeV/u with and without rebuncher (6ɛ rms envelopes). 3.3 Stage 2b - Experiment Station 1 at 1.2 MeV/u BEAM AT NEL1= 1 H A=.3 B= 1.5 V A=. B= 1.2 H A=.3 B= 1.5 V A=. B= mm X 5. mrad Z A=.88 Z A=.88 B= 2.6E 3 B= 2.6E 3 I=.mA W= MeV FRE= 11.28MHz WL=296.4mm EMITI= EMITO= N1= 1 N2= 38 x.. y CODE: Trace 3 D v7ly FILE: miniball_stage2b.t3d DATE: 1/4/211 TIME: 15:14:58 BEAM AT NEL2= 38 H A=.2182 B= 1.18 V A= B=.9823 H A= B= V A=.1496 B= mm X 5. mrad Z A= Z A= B= E 2 B= E 2 3. Deg X 3. kev 1. mm (Horiz) 3. Deg (Long.) 3. Deg X 3. kev NP2= G E E E E mm (Vert) 3. (Dispersion) Length= mm Figure 8: HEBT to Experimental Station 1 at 1 MeV/u with and without rebuncher (6ɛ rms envelopes). 1

11 3.4 Stage 2b - Experiment Station 2 at 1.2 MeV/u BEAM AT NEL1= 1 H A=.3 B= 1.5 V A=. B= 1.2 H A=.3 B= 1.5 V A=. B= mm X 5. mrad Z A=.88 Z A=.88 B= 2.6E 3 B= 2.6E 3 I=.mA W= MeV FRE= 11.28MHz WL=296.4mm EMITI= EMITO= N1= 1 N2= 4 x.. y CODE: Trace 3 D v7ly FILE: helios_stage2b_reb.t3d DATE: 1/4/211 TIME: 14:16:57 BEAM AT NEL2= 4 H A= E 3 B=.13 V A= E 3 B=. H A= 1.945E 2 B=.4752 V A= E 2 B= mm X 5. mrad Z A= E 2 B= 2.46E 2 Z A= B= E 2 3. Deg X 3. kev 1. mm (Horiz) 3. Deg (Long.) 3. Deg X 3. kev NP2= G 1415 E E E 2728 E mm (Vert) 1. (Dispersion) Length= mm Figure 9: HEBT to Experimental Station 2 at 1 MeV/u (ɛ rms and 6ɛ rms envelopes). 3.5 Stage 2b - Experiment Station 1 at.45 MeV/u BEAM AT NEL1= 1 H A=.32 B=.5 V A=.37 B=.8 H A=.32 B=.5 V A=.37 B=.8 1. mm X 1. mrad Z A= 11.9 B= 12. Z A= 11.9 B= 12. I=.mA W= MeV FRE= 11.28MHz WL=296.4mm EMITI= EMITO= N1= 1 N2= 37 x.. y CODE: Trace 3 D v7ly FILE: miniball_stage2b_decel.t3d DATE: 1/4/211 TIME: 15:43:35 BEAM AT NEL2= 37 H A=.2278 B= V A=.1772 B=.9419 H A=.2278 B= V A=.1772 B= mm X 1. mrad Z A= B= Z A= B= Deg X. kev 2. mm (Horiz) 54. Deg (Long.) 54. Deg X. kev NP2= E E E E mm (Vert) 3. (Dispersion) Length= mm Figure 1: HEBT to Experimental Station 1 at.45 MeV/u (ɛ rms and 6ɛ rms envelopes). 11

12 3.6 Stage 2b - Experiment Station 3 at 1 MeV/u BEAM AT NEL1= 1 H A=.3 B= 1.5 V A=. B= mm X 1. mrad Z A=.88 B= 2.6E 3 I=.mA W= MeV FRE= 11.28MHz WL=296.4mm EMITI= EMITO= N1= 1 N2= 75 x y CODE: Trace 3 D v7ly FILE: U.t3d DATE: 1/25/211 TIME: 14:7:34 BEAM AT NEL2= 75 H A= B= V A= B= mm X 1. mrad Z A= 2.12 B= Deg X 3. kev 2. mm (Horiz) 9. Deg (Long.) 9. Deg X 3. kev NP2= 8 G G G E E E E E E E E mm (Vert) 3. (Dispersion) Length= mm Figure 11: HEBT to Experimental Station 3 at 1 MeV/u (ɛ rms and 6ɛ rms envelopes). This solution could be better matched. 3.7 Stage 2b - TSR at 1 MeV/u BEAM AT NEL1= 1 H A= B= V A= B= mm X 1. mrad Z A=. B= 2.E 3 I=.mA W= MeV FRE= 11.28MHz WL=296.4mm EMITI= EMITO= N1= 1 N2= 81 x y CODE: Trace 3 D v7ly FILE: TSR.t3d DATE: 1/25/211 TIME: 14:25:1 BEAM AT NEL2= 81 H A= B= V A= B= mm X 1. mrad Z A= B= Deg X 3. kev 2. mm (Horiz) 3. Deg (Long.) 3. Deg X 3. kev NP2= E E E E E B(v) E E B(v) E mm (Vert) 3. (Dispersion) Length= mm Figure 12: HEBT to TSR at 1 MeV/u. Further work is needed to match into the ring itself. 12