Transcript 기본 이론 1
하전입자 (전자, 이온, 양전자, 반양성자…) 트랩 입문 울산과학기술원 물리학과 정모세 K-GBAR Meeting (2016. 7. 28@IBS) 연구 배경 화살표의 양방향 의미는? electrostatic quadrupole deflector GBAR Proposal (September 30, 2011) Reduce the p-bar energy from the MeV scale to the keV scale To shorten this pulse duration, it will be necessary to develop the technique to obtain a plasma length smaller than 1 cm and an effective way to extract it. ~ 0.5 mm ~ 100 ns Advice from Kurodo Sang 1. The in and out energies of pbar in the proposal(A) and new pbar trap for further cooling and recycling(B) are not the same. in : 100 keV(A) -> 1 keV(B) , out : 1 keV(A) -> 10 eV(B). Will the same trap work for both cases? If not what kind of changes should be needed ? 1. This scheme can work. The ASACUSA collaboration has established similar scheme (I also worked in the ASACUSA). However, the GBAR needs short bunch beams, < 100ns. To obtain such short bunch, axially compressed cloud of antiproton might be necessary. Or potential configuration at the extraction is needed to be tailored to compress the bunch length at the target. The latter may cause considerable energy spread, on one hand. We may need to find an optimal solution. So far, in ASACUSA, 20eV antiproton beam is used to form antihydrogen atoms. But the bunch length is the order of 10 micro-seconds... 2. I guess energy degrader for the incident pbar is not needed anymore for 1 keV beam. Am I right? 2. Yes, 1keV beam can be captured without energy degrader. In order to capture 1keV beam, HV switch driven by MOS-FET/IGBT/Thyratron can be used. 3. In the new scheme B, what will be the minimum magnetic field and inner radius of the solenoid ? I think this is critical for the cost. 3. Usually the bore size is 5-10cm in radius. If we take 10cm bore size, the inner radius of the solenoid becomes 10-15cm or so (4K-cold UHV bore is necessary between the trap and the solenoid). Several things should be considered. To capture 1keV beam, HV is needed to be applied to electrodes. If the size of trap electrodes is small, it would be difficult to keep margin to resist HV. Though it is difficult to say about the minimum size, but the trap electrode should have 4 cm in radius. Regarding the field strength, higher is efficient for electron cooling. At 2.5T, in ideal case, the synchrotron radiation cooling time constant is around 1s. But in actual case, it becomes longer (in ASACUSA, it is around 2s) because of external noise and so on. Thus it takes 30s or so to cool down a few keV antiprotons by electrons in the case of ASACUSA. The GBAR trap also needs to trap, cool, (compress), and extract antiprotons. I think the magnet should has 2-3T field strength at least. ATRAP uses 5T magnet with better catching efficiency. However higher magnetic field strength by solenoid has large stray magnetic field and divergence at the exit causes beam expansion... 4. Does rotating wall technique apply to B in the same way as A ? What will be radial beam size then? 5. At the extractor beam will be accelerated. What is the energy after the acceleration ? ( I guess I need an advice from Patrice too. as this will be the incident energy to positronium cloud) 4. Radial compression works for nonneutral plasmas in Penning-Malmberg trap. The frequency of the rotating wall defines the final radial size of the plasma. The plasma finally balanced between its self charge potential and the applied potential by trap electrodes. The final size often limited by alignment of the axis between the trap and the magnet. Because field error causes radial expansion of the plasma. In ASACUSA, the radial size of antiproton cloud becomes less than 1mm in diameter with larger halo (almost half of them in core). 5. As Patrice-san mentioned, at the target 10-1000eV kinetic energy is considered. 트랩의 종류 Penning–Malmberg trap (Cylindrical trap) - easier to manufacture and to align - easy access to the inside for particle injection and ejection Wolfgang Paul (Nobel Prize, 1989) Frans M. Penning Hans G. Dehmelt (Nobel Prize, 1989) 왜 이렇게 복잡한가? 정전기적으로 local potential minimum 을 만들 수 없음. Hyperbolic potential 은 Laplace equation 을 만족하면서, 물리적으로 구성하기 용이함. 어디에 쓰이는가? Precision tests of fundamental physics throughout the world ! 기본 이론 1: 힘의 균형 기본 이론 2: 3차원 평형 분포 ~균일 한밀도 Image charge 가 무시되는 경우 기본 이론 3: 각운동량 보존 Angular rotation frequency To the extent that the system’s total angular momentum L is conserved (perfectly symmetric case), its mean square should also be approximately constant. Only imperfections in the trap fields or vacuum can allow particles to eventually escape from the trap radially (i.e. small static field errors and background neutral gas exert a drag on the rotating plasma, causing slow plasma expansion and eventual particle loss) 기본 이론 4: Multi Ring Electrode Trap Self field potential Electrode 에서의 Potential 분포를 hyperbolic + self-field potential 로 맞춰주면, 마치 boundary 가 없이 자유공간 상에서 전하가 분포한 것 처럼 보임. 정리: 반양성자 트랩의 기본 원리 • Penning-Malmberg 트랩 – DC 자기장 (반경 방향 밀폐)과 DC 전기장 (축 방향 밀폐)을 이용하여 하전입자를 플라즈마 상태에서 공간적으로 가두어 놓는 장치 (주로 Cylinder 구조의 트랩을 지칭) – 반양성자를 비롯한 반물질 연구에 있어서 핵심이 되는 장치 (e.g., CERN의 ATHENA, ALPHA, ASACUSA 등) – 잔류기체와 반양성자와의 충돌 또는 결합에 의한 손실을 막기 위해, 매운 높은 진공도 필요 (~ 10-12 mbar) – 반양성자의 냉각을 위해, 반양성자와 전자와의 충돌에 의한 에너지 교환 및 전자의 싸이클로트론 복사 이용 전자 싸이클로트론 복사 시간의 자기장 의존성 + + Trap 관련 직접적 경험 Non-neutral Plasma Group @ Princeton Linear Paul Trap Electrodes Ion Source Vacuum and Electronics Operation Principle Trap 관련 간접적 경험 Penning-Malmberg Trap (by K. Morrison) Filaments Faraday Cup Phosphor Screen Temperature Diagnostics Diocotron Mode Diagnostics 시뮬레이션 선행 연구 반양성자 트랩 설계를 위한 선행 연구 트랩의 주요 설계 값 (자장, electrode 구조, 진공도, 운전조건) 산출을 위해서는 • 하전입자 사이의 전자기적 상호작용이 자기충족적으로 고려된 Particle-In-Cell (PIC) 시뮬레이션이 필요 • Multi-Ring Electrode (이온 뭉치의 전기적 평형을 위해), Rotating Wall (반경 방향으로 이온 뭉치를 압축하기 위해), Bunch Compression (이온 뭉치의 펄스 길이를 줄이기 위해), Cooling (이온 뭉치의 온도를 낮추기 위해) 등 여러 최신 이온 트랩 기술들이 고려된 시뮬레이션 필요 • 울산과기원(UNIST)에서 LBNL/LLNL 에서 개발한 WARP 도입 운영중 플라즈마 불안정성을 고려한 이온 트랩 과정의 수치모사 Rotating wall 기법을 이용한 이온 뭉치 제어의 수치모사 충돌 및 이온화를 고려한 이온트랩의 수치모사 RFQ Cooler 시뮬레이션 (by 유경훈) Injection Trapping Extracti on RFQ 안에서의 가스와의 충돌에 의한 시간에 따른 에너지 Cooling 효과 Geant4를 기반으로 한 G4beamline을 이용하여 시뮬레이션한 Ion trap 시간에 따른 입자의 y축 위치 변화 Warp코드를 이용한 Trap시뮬레이션 (by 유경훈) • Warp - Python과 Fortran을 이용한 Particle-In-Cell 코드 - Trap, Plasma acceleration등 다양하게 사용 가능 • Warp코드를 이용한 antiproton의 trap시뮬레이션 - Penning trap을 이용하여 trapping확인 - 각 장치의 모양등은 고려하지 않고 물리적인 부분만 Input으로 사용 - Background 는 진공으로 가정 Trapping Warp코드를 이용한 Trap시뮬레이션 (by 유경훈) • 시뮬레이션 조건 - 초기 입자 분포는 Gaussian분포를 가지는 하나의 bunch만 입사 - 초기 입자의 에너지는 임의로 설정 - Trap을 위한 electric potential 및 magnetic field 임의로 설정 • 향후 계획 - 구체적인 input beam 설정 - 적절한 magnetic field와 electric potential활용 - 장치 형태에 따라 변화되는 magnetic field와 electric potential 계산 - Background 물질과의 collision model을 계산하여 cooling 효과 계산 중이온 가속기 사업단 Electron Beam Ion Source (by 손혁준) EBIS – CARIBU at ANL SC Solenoid for CARIBU EBIS • • • Operating Temperature : 4.2 K Re-condensing type of cryostat A cold head and a motor of cyrocooler are connected by some kind of hose to minimize vibration. (PT-415RM) Drift Tube Structure for CARIBU EBIS Drift Tube Structure for RAON EBIS • UHV inside the ion trap : ~10 -11 mbar • Alignment of long structure (~1m) : ~100μm • Material - Non-magnetic electropolished 316 SS (Vacuum chamber, Drift tubes, scaffold, protection cup, potential lead, alignment fixture, differential pumping baffle / Fig1-1,2,3,4,6,7,9,10) - 99.8% pure alumina and/or zirconia (All isolation structure such as ceramic standoff / Figure1-5) • Thermal treatment - Vacuum firing @ 950℃ for 2 hours - In-situ baking @ 450℃ for 72 hours Proceedings of IPAC2016, Busan, Korea - ADVANCED EBIS CHARGE BREEDER FOR RARE ISOTOPE SCIENCE PROJECT* S. Kondrashev† , J.W. Kim, Y.H. Park, H.J. Son, Institute for Basic Science, Daejeon, Korea Index Component Name Material 1 Drift tube #1 Drift tube #10 (8 DTs are placed between DT1 an d DT10) Vacuum chambers SS 316L 2 3 4 Scaffold 5 Ceramic standoff Description SS 316L SS 316L SS 316L • NEG strip will be attached on outside of scaffold. • The drift tubes(DT#1~DT#9) will be assembled inside of the scaffold by the ceramic standoff. • There are some structures for alignment of assembled s caffold. • There are some holes on the surface of scaffold for vac uum. 99.8% pure alumi na and/or zirconi Supporting unit for drift tubes a 6 Protection cup SS 316L The ceramic standoff could be coated by ions or sperttere d conducting material. This kind of coating could generate discharging between DT and scaffold. Protection cup prev ent this kind of coating on ceramic standoff. 7 8 Potential lead NEG strip DT10 support and alignment fixtur e SS 316L NEG Appling voltage for each DT For vacuum 10 Baffle SS 316L 11 HV feedthrough - 9 SS 316L Differential pumping between "Ion trap section: and "Colle ctor section" Vacuum for EBIS • UHV inside the ion trap : ~10-11 mbar • Pumping system for the ion trap section Pump RISP : 1 more NEG pump E-Gun Section • Ion Trap Section Collector Section Q’t y Description TMP 2 480 l/s (N2) Cryo Pump 2 4000 l/s (H2O) NEG Strip 8 5000 l/s (H2) 2250 l/s (N2) 3mm*1mm*1700mm (W*H*L) Differential Pumping Section - E-Gun Section : ~10-10 Torr The volume of E-Gun section is small. One TMP is enough to get a goal vacuum level. - Ion Trap Section (DT Section) : ~10-11 Tor - Collector Section : ~10-9 Torr The collector section is high outgassing area, therefore we need a high pumping speed pump such as Cryopump. UNIST Electron Beam Ion Trap (UNIEBIT, 유니빛) 구축 계획 EBIT 개념도 EBIT 을 이용한 실험 구성도