litebird光学系の熱検討litebird.jp/wp-content/uploads/2012/03/hasebe_jps2017ver...4.5k 36.3k...
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LiteBIRD光学系の熱検討
長谷部孝、関本裕太郎、鹿島伸悟
他LiteBIRD WG
国立天文台
1
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Introduction
2
□ LiteBIRDは太陽と地球のラグランジュポイント L2 (太陽から約15万km)で三年間の観測を予定
□超伝導検出器 TES を0.1 K 以下に冷却しCMB偏光を超低ノイズで検出
□熱ノイズを抑えるため、放射冷却と機械式冷凍機の組み合わせにより望遠鏡全体を低温冷却
□検出器ノイズを抑えつつ効率の良い冷却系を検討する必要
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LiteBIRD低温ミッション部Sapphire HWP (5K)
200K
100K
30K
4K
Primary Mirror (5K)
Secondary Mirror (5K)
Aperture Stop (2K)
Focal Plane Detectors (<0.1K)+ Lenslet + Low Pass Filter (2K)
High Frequency Telescope (HFT)3
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Thermal Inputs to 200K Main Shell
Q2:Spacecraft BUS (300K) Q4:Cooler Mount
Q3:AFRP Truss
Radiator
MLI
Q1:SUNQ5:To space
Radiator for compressor
T = 205.7 K
4
Main shell : φ1920, h1758Radiator : φ2320
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K.Mitsuda, B-mode from space (2015)
ADR Cryocooler
5
4.5K
36.3K
215.7K (10K margin)
103.3K
左: 2段ST冷凍機 , シェル冷却 and JT 冷凍機予冷
右: JT 冷凍機 , 4K部冷却 and sub-K 冷凍機予冷ADR : 検出器用sub-K 冷凍機
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Open Structure Configuration
Reflective HWPLow Pass Filter
4K
Focal Plane Detectors+ Lenslet + Low Pass Filter
High Frequency Telescope (HFT)
4K Baffle
6
4K
30K
100K
200K
4K
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MLI
Truss
300K satellite IF
SUN
4K
30K100K200K
Radiator
To space
Thermal Inputs to 200K Main Shell
T = 187.8 K
Main shell : φ2500, h1600Radiator : φ2900
7
4K
φ550 Low Pass Filter
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Heat flow diagram (Open Structure)
4.5K
35.1K
Rad
iati
on
19
17
.7 m
W5
.4 m
W
Mai
n T
russ
to space
44
7.9
mW
2ST×3 (@50W EOL)
SQU
IDs
HW
P h
old
er
2475 mW
AD
R c
urr
ent
wir
e
Stage temperature 4.40K
14
91
.4 m
W5
.6 m
W2
28
.1 m
W
Sen
sor
Har
ne
ss1
2.3
mW
0.8
mW
5.6
mW
HK
Har
nes
s2
.8 m
W0
.2 m
W1
.3 m
W
80
.1 m
W1
.1 m
W2
7.3
mW
AD
R c
urr
ent
wir
eJo
ule
he
atin
g1
65
.0 m
W7
8.9
mW
1.1
mW
AD
R3
.0 m
W
3.0
mW
2ST×3 (@50W EOL)
4K-JT×1 (@50W EOL)
20.4 mW
197.8K(10K margin)
102.2K
Sup
po
rt T
russ
45
6.2
mW
17
6.4
mW
0 W
952.2m W
Low
Pas
s Fi
lter
0.3
mW
4K冷凍機1台で4.5Kを満たす (100% margin)
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Thermal Loading from Outer Shell
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Open型ではシェル内壁からの熱放射が検出器の大きなノイズ源となる
主鏡と副鏡間の背面、側面をミラー面で塞ぐことで高温の熱放射を遮蔽することが可能
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NEP Calculation
10
Δν/ν = 0.3No optical efficiency included
5K Mirrors Option 30K Mirrors Option
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NET Comparison
11
検出器1素子あたりの感度比較
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Summary以下の2種類の光学系について検討を行った。
①光学系全体を5K以下に冷却する。
②HWPと検出器部のみを5K以下に冷却する。
①4K冷凍機2台構成。
低ノイズ。
②4K冷凍機が1台構成。
熱放射遮蔽のためミラー形状に工夫が必要。12
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13
The shell size and the total mass of the satellite are also important parameters. K. Mitsuda
Incident angles of light from the Earth and Moon depend on the satellite obit.
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Moon: sun+44deg
4K shell
Earth: sun+30deg
1640mm
13
00
mm
Sun
520mm
11
90
mm
1700mm
345mm
α = 65°, β = 30° α = 45°, β = 50°
Sun to main shell : 890 W Sun to main shell : 911 W
Earth to 4K : 2.0 mW
Moon to 4K : 0.4 mW
Earth to 4K : 0 mW
Moon to 4K : 0 mW
On Halo orbit
Minimum size of the 4K shell
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On Lissajous orbit
15
Moon: Sun+20deg
4K shell
Earth: Sun+10deg
1610mm
Sun
1700mm
11
90
mm
11
00
mm
α = 65°, β = 30° α = 45°, β = 50°
Sun to main shell : 794 W Sun to main shell : 911 W
Earth to 4K : 0 mW
Moon to 4K : 0 mW
Earth to 4K : 0 mW
Moon to 4K : 0 mW
Minimum size of the 4K shell