Istituto Nazionale di Astrofisica
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Santa Fe, 2008
Istituto Nazionale di Astrofisica
IONS
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Santa Fe, 2008
Istituto Nazionale di Astrofisica
IONS
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Istituto Nazionale di Astrofisica1 grid fixed
1 grid oscillating @ 100zHz
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Istituto Nazionale di Astrofisica
Adjustable parameters that can be tuned during the mission are:
1. the piezo oscillation frequency 
2. The amplitude A.
Parameters that also affect the performances of the instrument and can be
optimized in the design phase are:
1. the angular resolution () of the instrument,
2. the width d of a slot unit
3. the ToF chamber length L
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The minimum detectable
velocity is related to the
maximum detectable time
of flight T which is:
1
T
2
since there are two apertures -START event- of the
entrance for each complete shuttering cycle. Particles
with longer TOF will arrive after a subsequent START
event occurs, and hence they will be targeted with
erroneous TOFs. To ensure that, during an oscillation, no
other opening is possible, the vertical repetition distance
(D, between two subsequent slots in the masks) must be
at least equal to:
D  A  2d
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The theoretical opening
time (t) can be estimated
as:
t 
which does not take into account of
the finite thickness of the grids. The
angular resolution of the instrument
is approximately 2°; the geometrical
factor at rest position (GF*) relative
to each angular sector is:
arcsin( d / A)

 d
GF*    S  f IR
 D
where fIR is the IR suppressor transparency (50%)
and S is the total entrance surface (1 cm2). If we
multiply GF* by the temporal duty cycle:
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2
t
r
T
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OSCILLATING
FIXED
Istituto Nazionale di Astrofisica
ENA
Angular
resolution
ENA
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OSCILLATING
FIXED
Istituto Nazionale di Astrofisica
ENA
ENA
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OSCILLATING
FIXED
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ENA
ENA
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Frequency: 45 kHz
Amplitude A=1 m
Slot width d200 nm
ToF L=12 cm
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t = 1.4 s
Max. detectable ToF corresponds to 10 eV (Na)
Slot repetition distance D = 1.4 m.
GF = 4 10–4 cm2 sr.
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