Time-of-flight spectroscopy at KATRIN with a
DC tagger and tagger-less with time-focusing
start by „tagger“
stop
stop
gating
time-focusing
see also N. Steinbrink et al., NJP 15 (2013) 113020
Christian Weinheimer
KATRIN Collaboration Meeting XXX, March 2016
1
Gain of differential versus integral:
avoid many steps in MAC-E-Filter mode
Integral – MAC-E-Filter method
Differential measurement
threshold
thresholds
energy
determination
by other means
with similar
energy resolution
need many retardation voltages
to obtain spectral information
N. Steinbrink et al. NJP 15 (2013) 113020
Christian Weinheimer
need one retardation voltage and
other means, e.g. TOF (TRISTAN-detector)
to obtain spectral information
→ TOF: Factor 5 improvement in mν2
w.r.t. standard KATRIN in ideal case !
KATRIN Collaboration Meeting XXX, March 2016
2
How to realize
time-of-flight spectroscopy @KATRIN
N. Steinbrink et al., NJP 15 (2013) 113020
start
stop
Stop: Can measure time-of-arrival with KATRIN detector with Δt = 50 ns → ok
Start: e--tagger: Need to determine time-of-passing-by of e- before main spectrometer
but after pre spectrometer to obtain handable rates
without disturbing energy and momentum by more than 10 (50) meV
Several ideas for implementation:
RF cavity tagger, DC tagger, Project 8-like tagging
→ strong background reduction possible
by requesting delayed coincidence
of start and stop signal
→ might be the way to beat the Rydberg background
or:
Use use tagger-less methods: „gated filter“ or „time-focusing time-of-flight“
Christian Weinheimer
KATRIN Collaboration Meeting XXX, March 2016
3
Proposals for an electron tagger at
KATRIN
RF cavity tagger
DC tagger
Project 8-like
tagging
ERF
RF tagger
main idea (H. Robertson):
electron exchanges energy ΔE
with the RF field: ΔE >> kBT
Christian Weinheimer
main idea (CW):
electron exchanges energy ΔE
with the DC field: ΔE >> kBT
can use MAC-E Filter naturally
KATRIN Collaboration Meeting XXX, March 2016
main idea (J. Formaggio,
B. Monreal):
electron radiates cyclotron
radiation in a homogenious
solenoidal field
→ need to shorten pre spec
4
Idea of the DC tagger
?
=
tof := Δt = l/v ! 1/"Ekin
tof
see also https://fuzzy.fzk.de/bscw/bscw.cgi/34381
Christian Weinheimer
→ Johnson noise of load resistor
gets smaller
than signal noise for large V0
KATRIN Collaboration Meeting XXX, March 2016
5
How to read out the very tiny signal with a dual SQUID amplifier from ECHo?
Discussions with L. Gastaldo, V. Hannen, P. Ranitzsch, K. Valerius, S. Wüstling
Signal:
DC
tagger
C
SQUID noise:
L
M
R
V0
LHe cold box
right side: P. Ranitzsch, PhD thesis, Heidelberg 2014
Christian Weinheimer
→ SQUID noise dominates
over signal
KATRIN Collaboration Meeting XXX, March 2016
6
Dual SQUID amplifier from ECHo
with an input transformer and a LC circuit
Discussions with L. Gastaldo, V. Hannen, P. Ranitzsch, K. Valerius, S. Wüstling
current in coil L:
ring down signal
analog circuit in Laplace space
ω0 = 10MHz, τ = RC‘ = 1ms , C = 10pF, L = 1mH
Christian Weinheimer
KATRIN Collaboration Meeting XXX, March 2016
Δt
7
Dual SQUID amplifier from ECHo
with an input transformer and a LC circuit
Discussions with L. Gastaldo, V. Hannen, P. Ranitzsch, K. Valerius, S. Wüstling
Signal:
SQUID noise:
analog circuit in Laplace space
ω0 = 10MHz, τ = RC‘ = 1ms , C = 10pF, L = 1mH
Christian Weinheimer
→ SQUID noise is smaller
than signal :-)
KATRIN Collaboration Meeting XXX, March 2016
8
Dual SQUID amplifier from ECHo
with an input transformer and a LC circuit
Discussions with L. Gastaldo, V. Hannen, P. Ranitzsch, K. Valerius, S. Wüstling
Signal:
SQUID noise:
analog circuit in Laplace space
ω0 = 10MHz, τ = RC‘ = 1ms , C = 10pF, L = 1mH
Christian Weinheimer
→ SQUID noise is smaller than
signal :-)
but what about stability of C or
external noise sources ?
KATRIN Collaboration Meeting XXX, March 2016
9
Is there a better way?
Have to measure tiny difference
Is there a way to make use of the
huge energy transfer eV0 = 18.6 keV ?
or how to make the charge change
to become the last straw ?
eV 0= 18.6 keV
Is this forbidden by 1st principles ?
How to precisely define that the glass is full ?
Christian Weinheimer
KATRIN Collaboration Meeting XXX, March 2016
10
Smearing of time-of-flight
in gated-filter mode
E0=18.575 eV, U0 =-18570V, last 3 eV
information
on mν
Gated filter:
T = ton + toff = 40 µs, ton = 16 µs,
E0 = 18.575 eV, qU=18.570 eV
Energy / eV
gate
length
time-of-flight / µs
time-of-flight / µs
Christian Weinheimer
→ mν-sensitive part of tof spectrum
is smeared out → loss of sensitivity!
KATRIN Collaboration Meeting XXX, March 2016
11
Avoid smearing by gated-filter:
“Time-focusing time-of-flight“
Idea: “Electrons starting behind/later
get a shortcut/inner track
or get accelerated (shortcut in time)
in order to arrive in time“
Pictures:
http://olympic.org
http://100milesisnotthatfar.com
Christian Weinheimer
KATRIN Collaboration Meeting XXX, March 2016
12
Time-focusing at KATRIN
ideal
detector
stop signal
energy filter
delay line, pulsed acceleration
more realistic
U = U0 + U1(t)
energy filter
some tests done at SDS2
detector
stop signal
delay line
pulsed acceleration
e.g. U1(t) = U10/2 * (1+sin(ωt))
for keV sterile ν search
energy filter
Christian Weinheimer
detector
stop signal
delay line, pulsed acceleration
KATRIN Collaboration Meeting XXX, March 2016
13
Conclusion
Time-of-flight spectroscopy at KATRIN would be advantageous,
because it provides additional information on the differential β-spectrum
above the retarding potential
with tagger (ideas: RF cavity, DC, Project 8, ...)
- close to ideal improvement (factor 5 on mν2)
- background can be suppressed by requesting delayed conincidence
- is the Penning trap between pre and main spectrometer a show stopper?
But also the DC tagger looks very, very challenging
taggerless: time-focusing TOF could give some improvement
An alternative method would be to measure directly the differential spectrum
above the retarding potential with an ultra-high resolution detector
but probably no background reduction
Christian Weinheimer
KATRIN Collaboration Meeting XXX, March 2016
14