for proof-masses in space charging & charge...
TRANSCRIPT
Charging & Charge Controlfor Proof-Masses in Space�Effects of free charge
• Lorentz force
• Electrostatic forces from mirror charges
• Spring Constants
• Forces from applied voltages
�Charging Estimates
• Rates
• Timelines
�Charge Management
• Measurement procedures
• Discharge procedures
LISA Symposium – PSU 24/07/2002
Lorentz force noise
LISA Symposium – PSU 24/07/2002
BvQFl ∧= HallEQ−
MetallicEnclosure(Blaser)
BvQFl ∧=η
( ) ( ) ( )222 vBQBQva nnn ηδδη +=
Lorentz force noise
LISA Symposium – PSU 24/07/2002
)Hz(10 C 104 HzT/ 105.2 4-15
11−
−
×≤⇒×
= çQf
Bnδ
antinsignific term2 HzC/ 2
25.2 nd⇒≈
f
QeQn πδ
&
See later!
( ) ( ) ( )222 vBQBQva nnn ηδδη +=
Electrostatic forces
LISA Symposium – PSU 24/07/2002
FE
k
C
kV
Q
C
C
k
Q
CV
C
kki
i ii
i
n
= − = + −∑ ∑=
∂∂
∂∂
∂∂
∂∂
1
2 22
2
21
−∆≈
∂
∂+
∂
∂==
232
2
2
2
2
2 4
222 d
Ad
d
A
C
Q
k
C
k
C
C
Q
k
C
C
QF lrk
εδε∂∂
( ) spaceparameter - sconstraint 4
2 32
22
dTdd
A
mC
tQta d ∆⇒
∆≈⇒ε&
( ) ( )2
32
2
2
332
22 442
14
2
∆+
∆+≈⇒ dd
A
mC
QQdd
d
A
Cd
A
mC
Qa n
nn
εδδ
εε
( )
∆+≈⇒ 2
332
2 421
4
2d
d
A
Cd
A
C
Qk
εε
Electrostatic forces
LISA Symposium – PSU 24/07/2002
FE
k
C
kV
Q
C
C
k
Q
CV
C
kki
i ii
i
n
= − = + −∑ ∑=
∂∂
∂∂
∂∂
∂∂
1
2 22
2
21
( )
2
2
2
2
2
222
nr
cmr
rn
rnn
kk
CV
mC
Q
k
CV
k
C
mC
Q
k
CV
mC
Q
k
CV
mC
Qa
δ
δδ
∂
∂+
∂
∂∆
∂
∂+
∂
∂+
∂
∂∆≈⇒
Common-mode voltage effects disappear to first order in force
Differential-mode voltages used for charge measurement – see later
2
2
2 k
CV
C
Q
k
CV
k
C
C
Qk r
cmr
∂
∂+
∂
∂∆
∂
∂≈⇒
Summary of Charge Limits
LISA Symposium – PSU 24/07/2002
10 µV/√HzδVn
10µm∆d
Assumptions!!
3x10-11Potential (noise) (1Vcm)
10-24Potential (noise)
4x10-13Stiffness (1Vcm)
10-8Stiffness (∆Vdm)
3x10-12Stiffness (assymetry)
1.4x10-11 (10-4 Hz)Charge Noise (∆d)
4x10-11Displacement Noise
4x10-11 (10-4 Hz)Lorentz Noise
Limit (C)Effect
Charging Rates
Jafry, Sumner & Buchman - 96
Jafry & Sumner - 97 } GEANT3
~16 charges/sec
Modeling of Charging (LTP)
LISA Symposium – PSU 24/07/2002
•Compare rates using GEANT4 with low-E extension
•Get charging timelines
Modeling of Charging (LTP)
LISA Symposium – PSU 24/07/2002
Modeling of Charging (LTP)
LISA Symposium – PSU 24/07/2002
Modeling of Charging (LISA)
LISA Symposium – PSU 24/07/2002
Modeling ofCharging(LISA)
LISA Symposium – PSU 24/07/2002
‘…the hadron-inducedfluorescence isvery badlyimplemented.So we switchedit off …’
LISA Symposium – PSU 24/07/2002
Modeling of Charging (LISA)
LISA Symposium – PSU 24/07/2002
Modeling of Charging (LISA)
LISA Symposium – PSU 24/07/2002
Charge Management System
LISA Symposium – PSU 24/07/2002
�Charge Measurement using applied dither force intransverse direction with capacitive sensing of test-mass response.
�Discharge technique using differential illuminationof surfaces with UV illumination, with bias voltageenhancement if needed.
Cd
AQEFd
ε2=
Charge Measurement
Dither Technique•Different gaps in eachdirection give differentmeasurement authority
•Need to see ditherabove residual drag-freeposition noise
•Assume transversedither with 1nm/√Hzposition noise
2514
292/1 109.2
107.1
101dx
dxx w
wE ××≈
×
××≈
−
−
τLISA Symposium – PSU 24/07/2002
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E-03 1.E-02 1.E-01
Dither Frequency (Hz)
Res
po
nse
Tim
e (s
)
Charge Neutralisation
tpevcvcflfi TTLTR ηηηη=
LTiηlfTfηvc2Tvc ~ 3x1010 photons/s
Oxford Instruments HPSUV1000 fibre
Caburn FFTUV1000 (Special) secondper ronsphotoelect 103
later) (see surfaces real''for measuring
needsbut target is A 2537at 10
4
o6
×⇒
≈ −peη
LISA Symposium – PSU 24/07/2002
•Dual Surface Illumination with dc bias voltage tomodify ballistic trajectories
—2.1 V/m/eV gives δQ/δt ~ 15 charges/s
—80 V/m/eV gives δQ/δt ~ 6x103 charges/s
—500 V/m/eV gives δQ/δt ~ 3x104 charges/s
•Differential Surface Illumination usingindividual lamp currents to modify electron fluxes
—L(φ) and L(I)
Charge Transport - ηt
LISA Symposium – PSU 24/07/2002
•Polar Ouput
Charge Transport
Polar Output of 1mm Diameter HPSUV Fibre Optic Cable
0
5
10
15
20
25
0 5 10 15 20 25
Polar Angle (Degrees)
Ou
tpu
t (P
ho
ton
s/s/
sr
[Rel
ativ
e])
LISA Symposium – PSU 24/07/2002
•Lamp Ouput Against Power
Charge Transport
Output of UV Lamp As Function Of Power
y = 3.0778x - 1.8681
0
0.5
1
1.5
2
2.5
3
3.5
0.9 1.1 1.3 1.5 1.7
Power Into Lamp (W)
Ph
oto
n O
utp
ut
(Rel
ativ
e)
DC ROSAT Supply
Commercial Supply
LISA Symposium – PSU 24/07/2002
•Differential Surface Illumination
Charge Transport
Electrode:Housing:TM
1 : 1.3 : 0.1
1 : 1.1 : 13.1
-3.9x103< <+3.5x103 /sQ&
Add dc bias to driveharder when required
⇒ x5
LISA Symposium – PSU 24/07/2002
Charge TransportUV Lamp
LISA Symposium – PSU 24/07/2002
Photo-emissive surfaces•Tests have been done on sample surfaces made of Au and Au/MoS2
within LTP development programme.
Bias voltage on TM (V) vs time (s)
-12
-10
-8
-6
-4
-2
0
2
4
-500 0 500 1000
Time (s)
Bia
s vo
ltag
e on
TM
(V
)
19/06/02
25/06/02
MoS2/Au (CF2/02/9
Bias voltage on TM (V) vs time (s)
-10
-8
-6
-4
-2
0
2
4
-100 100 300 500
Time (s)B
ias
volt
age
on T
M (
V)
18/06/02
24/06/02
Au
η=0.2x10-5
LISA Symposium – PSU 24/07/2002
η=~0.7x10-5
LISA discharge in100secs!!
Team at ICSTM
• Henrique Araujo • Chris Lee
• Trevor Beek • Igor Liubarsky
• Arthur Bewick • Andy Rochester
• Chris Carr • Geoff Rochester
• David Davidge • Diana Shaul
• Alex Howard • Tim Sumner
• Manu Joshi • Ray Swain
LISA Symposium – PSU 24/07/2002