a new rfq cooler: concept, simulations and status trapped radioactive isotopes: icro-laboratories...
Post on 13-Dec-2015
217 Views
Preview:
TRANSCRIPT
A new RFQ cooler: concept, simulations and status
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
E. Traykov
• TRIP project and facility• Our concept• Prototype tests• Our design• Simulations• Conclusion
TRIP Group:G.P. Berg, U. Dammalapati, P.G. Dendooven, O. Dermois, G. EbberinkM.N. Harakeh, R. Hoekstra, L. Huisman, K. Jungmann, H. Kiewiet, R. Morgenstern, J. Mulder, G. Onderwater, A. Rogachevskiy, M. Sanchez-Vega, M. Sohani, M. Stokroos, R. Timmermans, E. Traykov, O. Versolato, L. Willmann and H.W. Wilschut
Krakow, 3-6 June 2004
TRIP project and facility
IonCatcher
RFQCooler
MOT
Beyond the Standard Model
TeV Physics
Nu
clea
r P
hys
ics
Ato
mic
Ph
ysic
sP
arti
cle
Ph
ysic
s
ProductionTarget
MagneticSeparator
MeV
meV
keV
eV
neV
AGORcyclotron
AGOR cyclotronIon catcher (gas-cell or thermal ioniser)
Low energy beam line
RFQ cooler/buncher MOT
MOT
D
D
DD
Q
Q Q
Q
Magnetic separator
Production target
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Wedge
Our RFQ cooler/buncher concept
Buffer gas pressure (He): ~10-1 mbar
RFQ ion cooler RFQ ion buncher10eV thermal
Trap position
U+Vcost
-(U+Vcost)
2 x 330 mm
Switching on end electrodes
• RF capacitive coupling• DC drag resistor chain
• Electronics designed for large range of isotopes• UHV compatible design and materials
• Standard vacuum parts (NW160)
~10-3 mbar
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
RFQ cooler prototype tests
• RFQ in vacuum• Transverse cooling• Velocity damping• With and without a drag voltage on the segments
133Cs+ beam, initial energy: 10eV
0
50
100
150
200
250
1.0E-03 1.0E-02 1.0E-01
Pressure [mbar]
Cu
rren
t [p
A]
.
Current through aperture Current on electrode Total current
Tests:
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Our RFQ cooler/buncher design
Pressure
cooler
: ~10-
1 mbar
~10-3 m
bar He b
uffer g
asSeparate connections
for trap segments
Changeable separation electrodeswith different aperture diameters
Buffer gas: Helium for light ions (i.e. Na-21)(Heavier gas may be considered for Ra ions)
Kapton foil12.5m 120 pF
Stainless steel rods
OFHC copper
Preset frequencies:0.5MHz, 1 MHz, 1.5 MHz
RF amplitude:150 V (peak-to-peak)
UHV compatible resistors for drag voltage:Uncoated, 2.2 k
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Simulations and calculation of E field
• Simulations• Real 3D geometry• Material properties • Geometry separated to smaller parts• Fine mesh and grid size• 3D electric field map (RF and DC)
RF electric potential DC drag potential
FEMLAB calculation examples:
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
F(x,y,z,t) = m*(dV(x,y,z,t)/dt) F(x,y,z,t) = E(x,y,z,t)*q
dV(x,y,z,t) =(E(x,y,z,t)*q/m)*dtdr(x,y,z,t) =dV(x,y,z,t)*dt
Program input:• Ion charge • Ion mass • KE • Phase space distribution• Electric field map (RF and DC)• fRF
• RF amplitude• Drag voltage step• Gas pressure• Standard ion mobility• Number of ions• Time step
Program output:• Single ion tracing• Phase space distribution• Confinement• Transmission through exit aperture
Ion tracing and distributions
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
0)2cos(22
2
uqad
uduu
2
t
Mathieu equation:
08
220
mr
zUau
220
4
mr
zVqu
aU
qV
qmax = 0.908
RF only (U=0)
• Ion tracing in RFQ guide• Buffer gas cooling + DC drag• Phase space distributions • Ion trapping and extraction• Confinement and transmission
Ion trajectories in vacuum
-3
-2
-1
0
1
2
3
0 25 50 75 100 125 150 175 200 225 250 275 300 325
z [mm]
x, y
[m
m]
Buffer gas cooling
-3
-2
-1
0
1
2
3
0 25 50 75 100 125 150 175 200 225 250 275 300 325
z [mm]
x, y
[m
m]
Transverse distribution after RFQ guide
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
x, y [mm]V
x, V
y [m
/s]
Optimization using the simulations • Main goal: collect all ions• Confinement and transmission• Optimize parameters (regions of stable operation):
• pressure and type of gas• aperture diameters• beam settings at entrance• drag voltage step• potentials on separation electrodes • accumulation time (buncher)• trap potential depth and shape
• Questions:• phase dependence (cooler-buncher)• phase dependence (switching)• where do we loose ions (why?)
Exit RFQ guide
-2000
-1500
-1000
-500
0
500
1000
1500
2000
-0.002 -0.001 0 0.001 0.002
x, y [m]
Vx,
Vy
[m/s
] .
Velocity distribution at exit of RFQ1
0
50
100
150
200
225 1125 2025 2925 3825 4725 5625 6750
longitudinal velocities [m/s]
nu
mb
er o
f io
ns
. ~ 2 eVq=0.5p=0.025 mbardrag voltage=0.5V
Buffer gas pressureRF: 1500 kHz, 21Na+, 10 eV 950 m/s maximum transverse velocity0.5 V drag voltage step
0
10
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
q parameter
%
0.1 mbar 0.1 mbar 0.15 mbar 0.15 mbar 0.075 mbar
0.075 mbar 0.05 mbar 0.05 mbar 0.025 mbar 0.025 mbar
Gas pressure drag voltage
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Drag voltage and pressure dependence
Drag voltage step21Na+, 10 eVPressure: 0.01 mbarRF: 1500 kHz 950 m/s maximum transverse velocity2 mm aperture
0
10
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
q parameter
%
0.5 V 0.5 V 0.1 V 0.1 V 0.2 V 0.2 V
0.01 mbar – too low, exit energy high
Drag voltage step21Na+, 10 eV
Pressure: 0.025 mbarRF: 1500 kHz
950 m/s maximum transverse velocity2 mm aperture
0
10
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
q parameter
%
0.5 V 0.5 V 0.1 V 0.1 V
0.025 mbar low pressure limit
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Frequency and focus dependence
0
10
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
q parameter
%
1.5 MHz 1.5 MHz 1 MHz 1 MHz 0.5 MHz 0.5 MHz
Frequency21Na+, 10 eV0.1 mbar buffer gas pressure950 m/s maximum transverse velocity0.5 V drag voltage step2 mm aperture
Higher frequency is preferred
0
10
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
q parameter
%
950 m/s 950 m/s 1450 m/s 1450 m/s 450 m/s 450 m/s
Maximum transverse velocity21Na+, 10 eV
1500 kHz radio frequency950 m/s maximum transverse velocity
0.5 V drag voltage step2 mm aperture
Beam properties at entrance: just focus
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
Cool and select (work in progress)
Mass selectivity for 23Na+ / 21Na+
Scan line:U/V = const=0.17
220
8
mr
zUau
220
4
mr
zVqu
m>M
Mm<M
mass resolution frequency
q
a
RF and DC operation: Mass filter
0.706
0)2cos(22
2
uqad
uduu
2
t
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
LEBL and optimization of parameters (work in progress)
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
• LEBL simulations:• Extraction tube • Einzel lenses• Electrostatic steerers • Quadrupole deflectors
Low energy beam line
RF
Q c
oole
r/bu
nche
rMOT
MOT
EL
EL
EL EL EL
EL
EL
EL EL
QD QD
ET
Ion catcher
Conclusion
• Novel RF coupling and DC resistor chain tested on prototype RFQ• Results from simulations in good agreement with experiment
• Mechanical, electrical and vacuum design completed• RFQ cooler and buncher system ready soon
• Continue with simulations (LEBL)
Trapped Radioactive Isotopes: icro-laboratories for Fundamental Physics
top related