Beam Dynamical Issues of Kolkata Superconducting Cyclotron

1
Beam Dynamical Issues of Kolkata Superconducting
Cyclotron

• J. Debnath
• (on behalf of Accelerator Physics Group)

Variable Energy Cyclotron Centre, 1/AF,
Bidhannagar, Kolkata-700 064
2
Plan of the Talk

• Operating Area
• Magnetic Field Features
• Beam Dynamical Calculations Related to
• Beam Injection
• Acceleration
• Extraction

Predict Cyclotron Operation Parameters For
Efficient Beam Extraction
1
3
Operating Region (in Charge State-Magnetic Field
Plane)
E/A
MeV/n

E/A
MeV/n

E/A
MeV/n

E/A
MeV/n

1 5 10 20 30 40 60 80
1 5 10 20 30 40 60 80
1 5 10 20 30 40 60 80
1 5 10 20 30 40 60 80
50
50
Bending Limit

Bending Limit Kb520
Kb 520
520
E/AKb (Q/A)2
45
45
Focusing Limit
Kf
160
Medium and Heavier mass ions, The Energy is
limited to 520.Q2/A2 MeV/A For Lighter Ions (Q/A
gt.312), The Energy is limited to 160.Q/A MeV/A
Focusing Limit Kf160




kG
kG
kG
kG
40
40
Bo
Bo
Bo
Bo
Q/A.5 Line
35
35
Low field limit at Bo30kG, due to ?r2 ?z3
resonance
Low Field Limit Bo30 kG
For Q/A gt 0.5 the coupling resonance ?r2 ?z3
resonance is encountered at internal radius
30
30
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Q/A
Q/A
Q/A
Q/A
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Energy-Field-Frequency Diagram
1
5
SCC With Beam Lines
1
6
Initial Operation
Initial Beam 16O 4 E 16 MeV/n, Bo34kG
Q/A.3 E30 MeV/n, Bo38kG Ar12, Ne6, O5
22 MeV/n
30 MeV/n
50 MeV/n
64 MeV/n
Q/A.5 E64 MeV/n, Bo33kG (He2,Ne10,
Deuteron)
7
Magnetic Field Characteristics
8
Beam Injection

• B?0.55 kG-m, e100 p-mm-mrad.
• Magnetic field along the cyclotron axis has been
  simulated by a series of solenoids with average
  field and appropriate length
• At Inflector Entrance xm2mm, xm90.5mrad,
  a52.
• At Inflector Exit, xm2mm, xm138mrad, ax50,
  ym4mm, ym187mrad, ax75

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Spiral Inflector

• Design Features
• Gap between the Dees and inflector hosing 10 mm
• Gap between inflector electrodes and housing 2
  mm
• Magnetic Radius, Rm 8mm,
• Height A 21 mm, k0 (untilted)
• Electrode Gap d4 mm
• ECRIS Extraction Voltage 20kV)

The operating voltages for representative points
covering whole operating range of the cyclotron
is shown
10
Central Region
Central region structures installed on the main
magnet.
Two orbits, corresponding to starting time t
240 and 270 RF degrees, Q/A0.249, B038.35 kG,
Vecr11.36 kV, E 20 MeV/n and Vdee58.9 kV.
Shows the phase width (30 RF degrees) selected by
the central region.
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Main Coil Trim Coil Settings
Ion 16O4 E 16 MeV/n
TrimCoilFit Adjusts the main coil and trim coil
currents to fit a given phase Vs energy curve
E/Emax
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TrimCoilFit Results
Ion 16O4 E 16 MeV/n
I b (A)
I a (A)
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Equilibrium Orbit Properties

• Behavior of ?r , ?z near extraction
• Any given nr below nr1 at a different radius
  depending on the particle Field
• Demands radially movable extraction system
• The total radial span at say ?r 0.8 which is
  typical value for extraction is 0.4.

nr
nr as a function of equilibrium orbit radius
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Tune Diagram and Resonance
Betatron oscillation grows at resonance
k, l and p are integers. kl is the order of
resonance, p is the symmetry of the driving term.
Resonance of order 1, 2 or 3 are driven by the
dipolar, quadrupolar and sextupolar component of
the guiding field respectively. Imperfection
Resonance k.?r p, l.?z p, depends on the
amplitude and radial extent of imperfection. Coupl
ing Resonance k, l ? 0, dangerous for large
radial oscillations
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Extraction Problem For Q/A gt 0.5

• The highest energy 96 MeV/A corresponds to
  Kf145, which is less than characteristic Kf of
  SCC.
• Hits the ?r2.?z 3 resonance at ?r 0.8. But
  extraction is impossible, since it requires
  electric field in the deflector higher than
  150kV/cm. (in present scheme, it can go 133 kV/cm
  max. in 6 mm gap)
• At lower energy resonance hits the beam very
  near to ?r 1. So extraction is difficult for
  inner extraction radius.

96 MeV/A
80 MeV/A
67 MeV/A

• 3He2 may be accelerated and extracted over a
  very short range of energy
• Acceleration and extraction of proton is not
  possible due to resonance being hit at very inner
  radius

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Precessional Extraction

• A controlled 1st harmonic field component will
  be used in proximity of the ?r1 resonance to
  excite the radial precession which allows the
  optimisation of the turn to turn seperation at
  the deflector entry. Adjustment of amplitude and
  phase of 1st harmonic will be done by TC 13.

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Effect of First Harmonic Field on Beam Extraction
Without bump, surrounding the equilibrium orbit,
there exists closed stabled region bounded by
unstable fixed points U1, U2 and U3 . The bump
opens the corner. This makes the EO unstable at
energies higher than ?r1 energy and induces
precession, which effectively increases the turn
separation
Static phase plot, radial position and momentum
for successive turns at deflector entry azimuth
(336?). (a) at 13 MeV/A without bump (b) at 13
MeV/A with bump (5 G) (c) at 13.12 MeV/A with
bump . Ion 4He1
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Median Plane View of SCC
Magnetic Channels Locally reduce magnetic field
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Electrostatic Deflectors
Insulator
High Voltage Electrode
Septum

• 2 Electrostatic Deflectors, 55o and 43o
• The High Voltage Electrode has special contour
  made of Titanium.
• Electrode is supported by 3 insulators
• Maximum applied Voltage 100 kV across 6 mm gap
• Septum Made of Tungsten, Very thin (0.25 mm),
• V-notch in the leading edge enhances radiation
  cooling

12 AWG (19/25) T.C
Insulating EPR
Braided Shield
PVC Jacket
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Magnetic Channels

• 8 Passive Magnetic Channel
• The magnetic channels have water-cooled copper
  blocks with iron embedded in them. Locally reduce
  magnetic field to facilitate Beam Extraction,
• Movable to suit dynamics of different ion
  species. M1, M2, M3, M5, M6 M8 have single
  drives. M4 M7 have Double drives.
• M3, M4, M7 can be given a 3 inch movement and
  others can be given a movement of 1 inch.
• One Active Magnetic Channel in the Yoke-hole

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Extraction Study
Table of Ion Specis
Extraction trajectories on Cartesian (R,?) Plot.
Dispersion parameters of investigated beams
The radial and angular dispersion of the
extracted beam generated by the energy spread in
the beam itself has to be known while designing
the optics of the external beam handling system.
These effects have been calculated up to the M9
slit (_at_ R 44.4, ? 317.5o) corresponding to
energy spreads of ?E/E ? 0.1 .
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Tracking through Extraction System
Area of the phase space ellipse30 mm mrad. At
deflector entry (-22o) eigen ellipse is obtained
form GENSPE1
at (a) deflector entry (b) M9 Slit for ions with
Q/A0.25, E56 MeV/n, Bo31 kG.
(a) deflector entry (b) M9 Slit for ions with
Q/A0.25, E30 MeV/n, Bo46 kG.
(a) deflector entry (b) M9 Slit for ions with
Q/A0.25, E20 MeV/n, Bo38.3 kG.
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Active Magnetic Channel M9
Centre Field (Bc) at 0 channel current at
different main coil excitation, where X I?I?
Median plane view of main magnet with the channel
inside the yoke hole
Radial phase space ellipse at entrance exit of
M9. Ion q/A.25 , E30MeV/n
Longitudinal field inside the channel
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Horizontal Beam Profile along the Extraction Path
Q/A 0.25, E 30 MeV/n, Bo 46. KG
Q/A 0.25, E 20 MeV/n, Bo 38 KG
Magnetic channels M1-M8 are passive. M9 is
active. For M1, M2 dB/dx 8.3 KG/in, M3-M5
dB/dx 13.3 KG/in, M6,M7 dB/dx 8.3 KG/in,
Q/A 0.5, E 56 MeV/n, Bo 31 KG
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Horizontal Beam Profile along the Extraction Path
High-field-case (B046.5 kG, E30 Mev/n,
Q/A-0.25)
Medium-field-case (Bo38 kG, E20 Mev/n,
Q/A-0.25)
The new design has higher radial field gradient
(13.3 kG/inch) compared to the others (8.3
kG/inch) and larger flat-gradient region near its
centre.
Figure 2 Radial beam-envelope for high-field
case.
Gradient (kG/inch)
X (inch)
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External beam handling system layout with Building
Faraday Cup Beam Viewer Vacuum Pump
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Thank You
ACKNOWLEDGEMENT C. Mallik, M K Dey, G Pal, S.
Paul, U. Bhunia, J. Pradhan, Md. H. Rashid, Md.
Z. A. Naser, V. Singh, A. Dutta, P Y Nabhiraj and
R. K. Bhandari
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Charged Particle Tracking Results

• q/m 0.5, Bo3.45 T
• Without solenoid (Bsol0), beam diverges due to
  fringing field above yoke (fig. 1)
• A solenoid (50 cm) is placed at z1.8m for
  confining the beam (fig. 2)
• A double waist is achieved at the injection
  point (z3.2m) for Bsol560G (fig 3)
• Lower filed (Bsol460G) gives rise to a
  converging beam and higher field (Bsol660G)
  causes a diverging beam (fig. 4)

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Optimization of the Injection System Using
TRANSPORT Code

• Beam profile optimisation (from I.P. to
  inflector exit) using TRANSPORT for B?0.64 kG-m,
  e100 p-mm-mrad.
• Magnetic field along the cyclotron axis has been
  simulated by a series of solenoids with average
  field and appropriate length
• Spiral inflector transport matrix has been
  calculated with the code INFLECTOR.
• At Inflector Entrance xm2mm, xm90.5mrad,
  a52.
• At Inflector Exit ex ey 144 p-mm-mrad, xm2mm,
  xm138mrad, ax50, ym4mm, ym187mrad,
  ax75, which may be acceptable by cyclotron.

Figure 14
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Stability of the Beam E.O Study

• Concept of Equilibrium orbit
• Particles displaced from EO oscillate around it
• Coherent and incoherent oscillations

• Behavior of ?r , ?z near extraction
• Radially movable deflector system at ?r 0.8

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Turn Separation

• Due to acceleration

• Increasing coherent oscillation amplitude by
  field bump
• ?xb1R/B(?r2 1)
• Due to precession max. turn separation 2?(?r
  1)x

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