EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH HIE-ISOLDE-PROJECT-Note-0013 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 0.45 MeV/u to 10 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 2011 This is an internal CERN publication and does not necessarily reflect the views of the CERN management.
Transcript
EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
HIE-ISOLDE-PROJECT-Note-0013
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 fourexperimental stations over a wide range of energies from 0.45 MeV/u to 10 MeV/u, whichequates to a maximum beam rigidity of 2 Tm forA/q = 4.5. As the linac will be installed instages, so too will the HEBT, with the first two experimental stations being installed beforea 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 schemefor the HEBT, which is consistent with the experiments’ footprints. The first beam opticscalculations were carried out using TRACE3D. Supporting documentation can be found onthe CERN EDMS under the ‘HEBT Lines Optics & Layout Working Group’ in the ‘HIE-ISOLDE’ Structure.
Geneva, Switzerland
October 2011
This is an internal CERN publication and does not necessarily reflect the views of the CERN management.
1 Beam Parameters
The energy of the beams at output from the linac is a function of A/q and will range from 0.45 to17 MeV/u. There also exists the possiblity to transport the RFQ beam at 0.3 MeV/u. The heaviestbeams will be accelerated up to a maximum energy of 10 MeV/u and have a rigidity of 2 Tm. The twomain stages of the upgrade are shown in Figure 1. In addition, if a chopper line is installed the linacwill be extended in Stage 2b by the length of one high energy cryomodule, i.e. 2.62 m, which can beseen in Figure 5. The beam parameters are given in Tables 2, 3 and 4 at the exit to the linac, i.e. atoutput from the final cryomodule, in each stage. The particle phase space distributions are shown inFigures 2, 3 and 4 from which the above mentioned beam parameters were extracted. The simulationtracked the realistic particle distribution from the RFQ exit through the realistic field maps of the linac’selements. The beam parameters vary with energy, although in all cases the beam exits the solenoidfocusing channel of the linac at a waist and with reasonable symmetry in the vertical and horizontalphase 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 longitudinalbeam emittance reduces significantly on completion of the upgrade and installation of the low energysuperconducting section. The requested beam parameters are summarised in Table 1. The exact specifi-cation is given in the minutes of the 3rd HIE-ISOLDE Physics Co-ordination Meeting.
2
Table 1: Requested beam characteristics at HIE-ISOLDE
Beam Parameter Description or Value
Energy continuous from < 0.7 to 10 MeV/uBeam spot diameter < 1− 3 mm FWHMBeam divergence < 1− 3 mrad FWHMMicro-bunch structurea no requirement of micro-bunching to
bunched at < 1 ns with ∼100 ns bunch spacingEnergy spread < 0.1 %Absolute energy resolution no specific details givena The macro-bunch structure of the beam is determined by the charge breeder
and the rf duty cycle of the REX front-end.
3
Tabl
e2:
Sum
mar
yof
the
sim
ulat
edho
rizo
ntal
HIE
beam
para
met
ers
Stag
eSi
mul
atio
nE
nerg
yα
xβ
xεge
omx
rms
εgeom
x95%
εnor
mx
rms
εnor
mx95%
Cod
e(M
eV/u
)(m
m/m
rad)
(πm
mm
rad)
(πm
mm
rad)
(πm
mm
rad)
(πm
mm
rad)
Stag
e1
TRACK
5.9
0.27
1.00
0.81
3.95
0.09
0.45
Stag
e2b
TRACK
10.2
0.30
1.55
0.60
3.14
0.09
0.46
Stag
e2b
TRACK
0.45
-0.3
20.
513.
4020
.20.
110.
62
Tabl
e3:
Sum
mar
yof
the
sim
ulat
edve
rtic
alH
IEbe
ampa
ram
eter
s
Stag
eSi
mul
atio
nE
nerg
yα
yβ
yεge
omy
rms
εgeom
y95%
εnor
my
rms
εnor
my95%
Cod
e(M
eV/u
)(m
m/m
rad)
(πm
mm
rad)
(πm
mm
rad)
(πm
mm
rad)
(πm
mm
rad)
Stag
e1
TRACK
5.9
-0.0
41.
030.
803.
680.
090.
42
Stag
e2b
TRACK
10.2
0.00
1.21
0.60
3.16
0.09
0.47
Stag
e2b
TRACK
0.45
-0.3
70.
803.
5619
.60.
110.
61
Tabl
e4:
Sum
mar
yof
the
sim
ulat
edlo
ngitu
dina
lHIE
beam
para
met
ers
Stag
eSi
mul
atio
nE
nerg
yα
zβ
zε z
rms
ε z95%
ε zrm
sε z
95%
Cod
e(M
eV/u
)(n
s/ke
V/u
)(◦
/%)*
(πns
keV
/u)
(πns
keV
/u)
(π◦
%)*
(π◦
%)*
Stag
e1
TRACK
5.9
-0.4
90.
004
8.7
0.58
3.8
0.36
2.34
Stag
e2b
TRACK
10.2
0.88
0.00
312
.00.
302.
120.
110.
76
Stag
e2b
TRACK
0.45
11.9
14.9
2450
0.35
2.60
2.84
21.1
*A
t101
.28
MH
z.
4
∆x (mm)
∆x’ (m
rad
)
−5 0 5−6
−4
−2
0
2
4
6
50
100
150
200
250εg
x (rms) = 0.81 π mm mrad
εg
x (95 %) = 3.95 π mm mrad
αx = 0.27
βx = 1.00 mm/mrad
(a) horizontal phase space
∆y (mm)
∆y’ (m
rad
)
−5 0 5−6
−4
−2
0
2
4
6
50
100
150
200
250εg
y (rms) = 0.80 π mm mrad
εg
y (95 %) = 3.68 π mm mrad
αy = −0.04
βy = 1.03 mm/mrad
(b) vertical phase space
∆φ (ns)
∆W
/A (
keV
/u)
−0.4 −0.2 0 0.2 0.4−80
−60
−40
−20
0
20
40
60
80
100
120
50
100
150
200
250
αz = −0.49
βz = 0.004 ns/keV/u
εz (rms)
= 0.58 π ns keV/u
εz (95 %)
= 3.8 π ns keV/u
(c) longitudinal phase space
Figure 2: Beam phase space distribution at exit to the second high energy cryomodule in Stage 1 at5.9 MeV/u, simulated with TRACK.
5
∆x (mm)
∆x’ (m
rad
)
−5 0 5−6
−4
−2
0
2
4
6
50
100
150
200
250εg
x (rms) = 0.60 π mm mrad
εg
x (95 %) = 3.14 π mm mrad
αx = 0.30
βx = 1.55 mm/mrad
(a) horizontal phase space
∆y (mm)
∆y’ (m
rad
)
−5 0 5−6
−4
−2
0
2
4
6
50
100
150
200
250εg
y (rms) = 0.60 π mm mrad
εg
y (95 %) = 3.16 π mm mrad
αy = 0.00
βy = 1.21 mm/mrad
(b) vertical phase space
∆φ (ns)
∆W
/A (
keV
/u)
−0.1 −0.05 0 0.05 0.1 0.15−80
−60
−40
−20
0
20
40
60
80
50
100
150
200
250εz (rms)
= 0.30 π ns keV/u
εz (95 %)
= 2.1 π ns keV/u
αz = 0.88
βz = 0.003 ns/keV/u
(c) longitudinal phase space
Figure 3: Beam phase space distribution at exit to the final high energy cryomodule in Stage 2b at10.2 MeV/u, simulated with TRACK.
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∆x (mm)
∆x’ (m
rad)
−10 −5 0 5 10−15
−10
−5
0
5
10
15
50
100
150
200
250
αx = −0.32
βx = 0.51 mm/mrad
εg
x (rms) = 3.4 π mm mrad
εg
x (95 %) = 20.2 π mm mrad
(a) horizontal phase space
∆y (mm)
∆y’ (m
rad)
−10 −5 0 5 10−15
−10
−5
0
5
10
15
50
100
150
200
250εg
y (rms) = 3.6 π mm mrad
εg
y (95 %) = 19.6 π mm mrad
αy = −0.37
βy = 0.80 mm/mrad
(b) vertical phase space
∆φ (ns)
∆W
/A (
ke
V/u
)
−20 −15 −10 −5 0 5−4
−2
0
2
4
6
8
10
12
14
50
100
150
200
250εz (rms)
= 0.35 π ns keV/u
εz (95 %)
= 2.6 π ns keV/u
αz = 11.9
βz = 14.9 ns/keV/u
(c) longitudinal phase space
Figure 4: Beam phase space distribution at exit to the final high energy cryomodule in Stage 2b, withthe low energy section phased to decelerate down to 0.45 MeV/u, simulated with TRACK.
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2 Layout
The HEBT design aimed to make the most of the limited space. The position of the experimental areasshould stay fixed and just the transfer line manipulated as more cryomodules are added. Note thatbefore Stage 2b, a third and fourth high energy cryomodule will be installed. The idea was to have aperiodic FODO channel to transport the beam to each double bend achromat, of which periods could beremoved in a modular fashion as cryomodules are added. However, it was not possible to find a FODOchannel with the period the same length as the cryomodules because of the size of the dipole magnetsrequired. Instead, a quasi-FODO channel was chosen (almost a doublet channel) where there are twodrifts of different length per period. The total length of the period is 3.2 m. Inside of the long driftthe 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 thematching section. A transverse phase advance of π/2 per period was chosen to match the phase advancein the linac and help any orbit correction routine that is placed periodically. Four quadrupoles wererather arbitrarily chosen to match into the FODO channel from the linac, although in most cases all fourare 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.
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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 beamthrough 22.5◦, capable of directing beams with 2 Tm of rigidity. The number of quadrupoles vary andthe specifics of the transverse matching to each experiment needs further iteration. Also shown in red isthe 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 accompanyingfiles. All the parameters of interest are held in these files. No studies of the stability of the designs or theorbit correction routine have been completed. A phase advance of π/2 results in quadrupole gradientsof 11.1 Tm−1 at 10 MeV/u with a quadrupoles of an effective length of 200 mm. The gradients donot 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 10 mm, andan aperture diameter of 40 mm in the quadrupoles is specified. The energy and time structure of thebeam is very important for the experiments. A rebuncher can be used in most cases to achieve thedesired 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
5.000 mm X 5.000 mrad
60.000 Deg X 3000.00 keV
5.000 mm X 5.000 mrad
60.000 Deg X 3000.00 keV
NP2= 49
10.00 mm (Horiz) 90.0 Deg (Long.)
10.00 mm (Vert) 3.0000 (Dispersion)
NP1= 1
Length= 19796.59mm
1
2
Q
3
4
Q
5
6
Q
7
8
Q
9
10
Q
11
12
13
Q
14
15
Q
16
17
G
18
19
Q
20
21
22
Q
23
24
25
Q
26
27
E
28 29
E
30
31
Q
32
33
34
Q
35
36
E
37 38
E
39
40
Q
41
42
43
Q
44
45
Q
46
47
Q
48
49
H A= 0.27000 B= 1.0000 V A=−4.00000E−02 B= 1.0300
Z A=−0.49000 B= 3.30000E−03
BEAM AT NEL1= 1
H A=−2.70381E−02 B= 1.0304 V A=−3.33314E−02 B= 1.0179
Z A= 14.336 B= 0.54956
BEAM AT NEL2= 49 I= 0.0mA W= 265.5000 265.5000 MeV
