TPC X-‐Ray Polarimeter Onboard GEMS Satellite

GEM-TPC X-ray Polarimeter onboard GEMS Satellite

Toru Tamagawa, A. Hayato, T. Kitaguchi, T. Enoto (RIKEN) K. Jahoda, K. Black, J. Hill (NASA/GSFC) and the GEMS team

MPGD2013 in Zaragoza（July 1-4, 2013） 1 OUTLINE

1. A brief Introducon to polarimetry 2. GEMS mission and GEM-TPC X-ray Polarimeter 3. Performance of the polarimeter 4. Onboard calibraon and lifeme esmaon 5. Summary and Outlook

MPGD2013 in Zaragoza（July 1-3, 2013） 2 1.1 Gas detectors used in space

(RIKEN/JAXA) l Gas Detectors 30 cm Ø key device in X-ray astrophysics for 50 yrs Ø easy to construct large-area counters Ø Ginga, RXTE, MAXI etc. Xe filled prop counter l Micro Paern Gas Detectors Ø JEM-X onboard INTEGRAL, the first mission employed MSGC Ø Some space applicaons proposed l X-ray Polarimeter Ø Ideal applicaon of gas detector (Sakurai+1995) Ø Suitable for MPGD (Costa+2000, Bellazzini+2003, Black+2007, Hayato+2007) JEM-X onboard INTEGRAL MPGD2013 in Zaragoza（July 1-4, 2013） 3/23 1.2 Open a new field in astrophysics

Imaging Spectroscopy Timing Suzaku

Tycho’s SNR

Polarizaon Polarimetry is technically easy l New dimension in radio and opcal, but not l Final froner in X-ray in X-ray/gamma-ray. We should know electric vector Astrophysics photon-by-photon.

MPGD2013 in Zaragoza（July 1-4, 2013） 4 1.3 What can we do with polarimetry?

l Explore strong magnec and gravitaonal Field l Geometry of plasma around high energy phenomenon

Electrons in strong magnec Scaering induces polarizaon. ﬁeld radiate with polarizaon perpendicular to B.

MPGD2013 in Zaragoza（July 1-4, 2013） 5 2.1 GEMS mission overview

X-ray grazing The Gravity and Extreme Magnesm Explorer (GEMS) mirrors • Selected by NASA in 2009 for launch in 2014 (NASA Small Explorer Mission). • GEM-TPC polarimeters at the focus of X-ray

opcs, on the rotang space cra (0.1 rpm).

4.5 m • Energy Band: 2-10 keV • Mission Lifeme > 9 months (goal 2 years) • Low Earth Orbit 565 km, inclinaon 28.5 deg. detectors • radiaon 3.6 krad over the life of the mission at focus • Project non-conﬁrmed in 2012 due to cost overrun, but we will propose the mission again in 2014 note: European group are proposing another polarimeter mission XIPE.

MPGD2013 in Zaragoza（July 1-4, 2013） 6 2.2 How to measure X-ray polarizaon

X-ray l GEMS polarimeters use the polarizaon sensivity E of the photoelectric effect. l As a result of an X-ray interacon, the φ photoelectron is ejected preferenally in the direcon of the electric field. l differenal cross secon ∝ cos2φ l quantum efficiency can be ε ~ 1 l Analyzing power µ=1 (intrinsic) but µ<1 (in reality) Auger Photoelectron electron l A gas detector is essenal to obtain a longer photoelectron track. l A micro paern gas detector is also essenal to reconstruct the track. relave count Figure of merit ∝ N − N µ = max min gas species N + N max min Opmizaon is needed. pressure effecve volume etc. photo-e azimuthal angle (rad) MPGD2013 in Zaragoza (July 1-3, 2013) 7 € 2.3 Design of GEM-TPC polarimeter

GEM-TPC as a photoelectron track imager (Black+2007) 50 nsec 120 microns

A me-projecon technique creates pixel images from a 1D readout. l Pure DME (C2H6O), 190 Torr to obtain longer photoelectron tracks l Longer (>30cm) eﬀecve volume along the opcal-axis for good detecon eﬃciency l Slow dri velocity of DME = spacing of strips (0.25cm/us * 20 MHz = 120 micron)

MPGD2013 in Zaragoza (July 1-4, 2013) 8 2.4 GEM-TPC Polarimeter

Detector Assembly: Field-cage and Dri Planes

32 cm

veto region

Eﬀecve Volume 2cm x 2cm x 7.8 cm (one unit)

MPGD2013 in Zaragoza (July 1-4, 2013) 9 2.5 Readout strip and GEM foils

Readout strip and ASIC (APV25) GEM foil 30 cm

3cm 7.8 cm

APV25

Readout strip GEM-Strip alignment l 128 strips (pitch 120, width 60 micron, 7.8 cm long) l veto region in both side l connecng to APV25 (20 MHz clock) GEM foil l LCP-GEM l 140 micron pitch, 70 micron hole 120 micron l 100 micron thick MPGD2013 in Zaragoza (July 1-3, 2013) 10/20 2.6 Thick-foil LCP-GEM

Tamagawa , SPIE 2006 Thick-foil GEM Hole 70um

100um

Pitch 140um eﬀecve gain

Ed=2.5 kV/cm l Laser Drilling (Tamagawa+2006) Ei=4-6 kV/cm l Liquid Crystal Polymer (LCP) Ar/CO2=(70%/30%) l Two mes thicker insulator foil than standard GEM Double standard Single LCP-GEM GEM conﬁg. Thick-foil GEM conﬁguraon

= eﬃcient way to get 50 µm V1

transfer region ΔVGEM higher gain at lower HV. 100 µm ΔVGEM =V1+V2 50 µm V2 MPGD2013 in Zaragoza (July 1-3, 2013) 11/20 2.7 LCP-GEM operaon in DME

Gain curve Gain stability 30x78 mm2 GEM P140/D70/T100um 30 cm 104 190 Torr LCP-GEM in 190 Torr DME

effective gain 1000effective

100

l We can easily achieve gain= l Gain is stable at the level of 40,000 in pure DME at 190 Torr. 0.5%. l requirement is around gain=1000-3000

MPGD2013 in Zaragoza (July 1-3, 2013) 12/20 2.8 Radiaon Tolerance of LCP-GEM l High Radiaon Environment p LCP is known as a radiaon tolerant material. p No degradaon in withstanding voltage was observed aer 5 G rad exposure where Kapton shows 80% degradaon of withstanding voltage from inial. (cf. Requirement is less than 10 krad over lifeme.) l Cosmic Radiaon Environment

p We performed heavy ion (Fe, (Iwahashi+2011) 500 MeV/n) and proton (160 MeV) irradiaon tests. p For Fe irradiaon, 100% of discharge was observed. but safely operate with appropriate protecon resistance

MPGD2013 in Zaragoza (July 1-3, 2013) 13/23 2.9 Detector Integraon

GEM-ROB assembly mounted on the baseplate Detector Assembly

Detector sub-assembly: 1 GEM-ROB and 3 GEM plates Cu Thermal Ti GEM Strap frames

14 3.1 Track image and modulaon curve

2.7 keV L=600um 4.5 keV L=1.5mm

Modulation curve Modulation curve

μ=32% μ=45% 3.2 Sensivity of polarimeter

MDP sensitivity minimum detectable polarizaon 4.29 r + b MDP = µ ⋅r T

mirror system

250cm2@2keV 70cm2@6keV

Our GEM-TPC will achieve two modulation µ order of magnitude higher sensivity than OSO-8. 4.1 Onboard Calibraon l Onboard calibraon is crucial part of the MXS & Collimator project Ø Energy Ø Dri Velocity A checking source (e.g. 55Fe) is not appropriate. l We employ the modulated X-ray source (Gendreau+2010)

12 10

8 6

time(us) 4 Edrift = 196 V/cm Ø Very good ming ~ nsec 2 pressure = 190 Torr v = 0.247+/-0.001 cm/us Ø Emission energy depends on target 0 material Ti (4.5 keV) is suitable. 0 0.5 1 1.5 2 2.5 distance (cm) 4.2 Lifeme of detector l Lifeme requirement Ø Variety of materials minimized to reduce Ø 6 months on ground number of outgassing species Ø 10 months on orbit Ø Materials carefully selected for DME and high vacuum compability l Limiter of detector lifeme Ø PEEK, LCP, Ceramic, Metals Ø Contaminaon (outgassing) Ø bake-outs components Ø Aging eﬀect Ø No epoxies used in assembly

Reducon of outgassing (mostly H2O) is essenal to prevent gas degradaon. outgassing from a chamber

H2O electron aachment coeﬃcient

keep monitoring α to evaluate gas degradaon

MPGD2013 in Zaragoza（July 1-3, 2013） 18 4.2 Lifeme of detector l Lifeme requirement Ø Variety of materials minimized to reduce Ø 6 months on ground number of outgassing species Ø 10 months on orbit Ø Materials carefully selected for DME and high vacuum compability l Limiter of detector lifeme Ø PEEK, LCP, Ceramic, Metals Ø Contaminaon (outgassing) Ø bake-outs components Ø Aging eﬀect Ø No epoxies used in assembly

Reducon of outgassing (mostly H2O) is essenal to prevent gas degradaon.

Alpha (1 yr)

MPGD2013 in Zaragoza（July 1-3, 2013） 19 5. Summary and Outlook l X-ray polarimeter is the best applicaon of MPGD in astrophysics. l We have fabricated semi-ﬂight detector of GEM-TPC polarimeter for the GEMS mission. l Operaon of LCP-GEM is ﬁne in pure DME at 190 Torr. Electric gain is achieved ~40,000 without any discharges. l We have the performance which we expected. Detailed performance study is ongoing. l Lifeme of the detector is mainly limited by outgassing. Current material selecon and bake-out protocols have been demonstrated to exceed the lifeme. l We propose the GEMS mission again in 2014.

MPGD2013 in Zaragoza (July 1-3, 2013) 20