超伝導加速空洞のコストダウン T. Saeki (KEK) 24July 2016 2016 ILC 夏の合宿一ノ関厳美温泉
ILC Cost Breakdown (RDR) 1 ILC Unit ~ 1 US dollar(2007) ~ 117 Yen Detector: 460 560 Million ILC Units ~10 % of machine cost
超伝導空洞のコストダウン 冷凍機コストを抑える >>> 空洞の抵抗 あるいは消費電力を減らす >>> 空洞の Q 値を上げる トンネル長を短くする >>> 空洞の加速勾配を大きくする 標準の空洞内面処理過程のコストを抑える >>> 新しい空洞内面処理過程 あるいは改善
Polishing Inner Surface of Cavity 空洞内面の処理過程を変えると Q 値や加速勾配が改善される
Overview of Inner Surface Preparation Thick/Rough Removal (>100 um) Three alternative methods: Buffered Chemical Polishing (BCP) Electro-Polishing (EP) Centrifugal Barrel Polishing (CBP) Annealing / Degassing (750 800 C, ~3 h) Final Thin Removal (10 30 um) Two alternative methods: Buffered Chemical Polishing (BCP) Electro-Polishing (EP) High Pressure Rinse (>7 h) In-situ Baking (120 140 C, 48 h)
Electro-Polishing (EP) Current Oscillation occurs Sulfuric acid is not included in the reaction. It gives the viscosity to the electrolyte.
Electro-Chemical polishing inside 9-cell cavity Electro-Chemical Polish Use Sulfuric acid + HF mixture Apply voltage between center Al electrode and Nb cavity Optimize parameter for smooth surface without sulfur residual particle voltage and temperature are key parameter Successive rinsing is another key technology 8
Electro-polishing facility at STF/KEK Automatic Operation Console EP bed 9-cell cavity 1 st floor 2 nd floor EP solution reservoir tank EP facility at KEK EP acid: HF + H 2 SO 4, Aluminum anode, surface removal speed: 20µm/hour, V ~18V, I ~270A, T ~30degC (for 9-cell), cavity rotation: 1 rpm.
Annealing / Degassing Annealing / degassing furnace at KEK:Two 9-cell cavity can be processed at once. Designed to consider about the supper-structure (Super-structure is consisting of two connected 9-cell cavities with one input-coupler).
Annealing / Degassing Vacuum Furnce Cavity is set in a Ti box (gas getter) Ti box (gas getter)
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Q 値と加速勾配を同時に上げる アニール過程と窒素ドープを工夫して Q 値と加速勾配を同時に上げた結果が FNAL から発表されている ( 早野さんの発表参照 ) 多層膜を空洞内面に生成することで Q 値と加速勾配を同時に上げることができるかもしれない >>> 空洞ではなく サンプルで実験が繰り返されている
薄膜構造による加速勾配の向上 超伝導空洞内面に超伝導薄膜を生成することにより 空洞内面物質の臨界磁場が上がり 現状より数倍以上高い加速勾配が得られる可能性が指摘されている 従来の加速空洞では加速勾配 40~50 MV/m が限界 従来の加速空洞 加速空洞の内面に特殊な膜構造を生成することで加速勾配が上がることが期待される 空洞外面 空洞内面 空洞外面 空洞内面 空洞壁面の超伝導電流ニオブ金属 ( 厚さ2.8mm) 数倍の超伝導電流が可能 ニオブあるいは代替金属の内面に超伝導体 (NbN Nb 3 Sn など ) と絶縁体の多層薄膜を生成 基材ニオブへの磁場侵入を抑制
薄膜の研究 Gurevich 氏により 超伝導空洞内に薄膜を形成することで 高い到達電界に到達できる可能性が示唆された 空洞内面 バルク超伝導体 (Nb) 超伝導体薄膜 絶縁体薄膜
Electro-polishing (EP) process EP is thought to be the best final surface-polishing process of ILC 9-cell cavity to achieve high-gradient specification of ILC. EP is also most complicated/costy surface-preparation process in the cavity mass-production of ILC. The current standard EP method is called horizontal EP process, where a cavity is set up in a horizontal posture and the cavity is rotated during the EP process. In order to achieve simpler and more cost-effective EP process, vertical EP process is studied in many laboratories in the world, where a cavity is set up in a vertical and fixed posture. If EP electrolyte is HF free, the cost of EP facility and operation might be drastically reduced. HF-free EP process is also studied in many laboratories in the world.
VEP study with conventional EP solution at KEK / Marui Galvanizing Co. Ltd.
Horizontal EP (HEP) / Vertical EP (VEP) Rotation of cavity in HEP process. (HEP setup at KEK-STF) EP electrolyte is fully filled. Toxic EP electrolyte is half filled. Turning the EP-bed for draining Cavity is fixed Massive and complicated system No rotation of cavity in VEP process. (VEP setup at CEA/Saclay)
Horizontal EP / Vertical EP Horizontal EP (HEP) Asia: KEK-STF Europe: DESY, Saclay, RI, Zanon US: FNAL, ANL, Jlab, AES Vertical EP (VEP) Asia: KEK / Marui Galvanizing Co. Ltd. Europe: CEA/Saclay US: Cornell, JLab I will present these activities. Vertical electro-polishing (VEP) No need of large space No need of cavity rotation No need of horizontal-vertical conversion system More suitable for mass production Simple VEP is more cost-effective than HEP, but hydrogen-gas generation at cathode has a narrow way to escape at iris and top-cell. That is the main problem.
Development of retractable wing-shape cathode in collaboration with Marui Co. Ltd. EP electrolyte is circulated to remove hydrogen gas and for low temperature. The retractable-wing cathode to realize uniform flow of electrolyte and uniform distribution of electric current. Flow direction Rotation of cathode Al or insulator Side View Acid bath Pump Cavity is fixed Al Top View Opened Retracted Special Ninja cathode by Marui Galvanizing Co. Ltd.
Simple VEP setups at Marui Co. Ltd. in collaboration with KEK 1-cell cavity 9-cell cavity 9-cell cavity PAGE 23
VEP experiments with coupon single-cell cavity VEP experiments were carried out on 1cell cavity at 1rpm and 50 rpm.
VEP experiments with coupon single-cell cavity Continuous improvement of Ninja cathode concept makes it possible to improve the surface along the cavity surface
Slide by F. Furuta (Cornell Univ.)
VEP experiment with 9-cell cavity Water cooling system VEP setup for 9-cell cavity 9-cell cavity VEP condition (an example) Schematic view of VEP setup EP solution: H 2 SO 4 (98%):HF(55%)=9:1 Voltage: 11 V Flow rate: 5 10 L/min Rotation speed: 50 rpm Flow direction: Bottom to top Ninja with Al wings (old version) Cooling water: 8 L/min.
VEP experiment with 9-cell cavity with old-version Ninja cathode (Upper) cavity temperature (Lower) current density and voltage The removal thickness of lower cell tends to be slightly larger than upper cell.
VEP experiment with 9-cell cavity with old-version Ninja cathode Removal thickness of iris is 2 3 times larger than that of equator. We are fabricating the new 9-cell Ninja cathode (partial Al wings) with the feed back from 1cell cavity. Using the new Ninja cathode, we would like to perform VEP and vertical test of 9-cell cavity.
COI: Center-of-Innovation Building at KEK Vertical-EP As a model facility for ILC assembly & Testing Clean-room He Cryogenics EP(vertical-EP) Cavity Testing(4-cavities-test) Cryomodule Assembly(cantilever) Cryomodule Testing Cantilever30
New VEP setup in COI building at KEK Cathode motor Cathode insertion tool. EP bed EP bed is used both for HEP and VEP (2 ways). This enables the direct comparison of HEP and VEP processes. Manufacturer is MHI
HF-free EP study with alkaline solution at KEK / Jlab/ Nomura Plating Co. Ltd.
Periodic Reverse Electropolishing (PR-EP) with alkaline solution Conventional EP method Periodic Reverse EP with NaOH solution (1)Solution : H 2 SO 4 (60%)/HF(40%) Very dangerous Severe burn on skin Toxic gas(hf, H 2 S, SO x ) High cost By-product of Sulfar Performance degradation (1)Solution :NaOH (10~30%) Safer Low coat No by-product Degreasing effect of NaOH solution (2)Periodic Reverse (PR) voltage 2H 2 S + SO 2 2H 2 O + 3S (2)DC voltage with Nb anode and Al cathode Studies on PR-EP process (1) Parameter search and study about pulse-shape dependence in the creation of oxidation film. (2) Component analysis of generated gas.
PR-EP setups for parameter search Figure: Picture of setup In J lab. In Nomura plating co,.ltd
Parameter No. 1 2 3 4 5 6 Nb coupon picture Roughness (Ry) before EP Nb coupon picture Roughness (Ry) after EP Removal speed [μm/hour] NA NA NA NA 3.8 μm 5.4 μm 24.7 35.8 20.6 19.2 24.3 18.9 Solution 37% H 2 SO 4 30% NaOH Table: PR-EP parameters and results 3.5 μm 2.0 μm 5.1 μm 2.5 μm Best paramete 10% NaOH 10% NaOH 10% NaOH 0.05% 50% H 2 SO 4 0.05% 0.05% 0.05% (COOH) 2 (COOH) 2 (COOH) 2 (COOH) 2 Temperature [ 0 C] 20 50 20 20 50 50 Parameter Neg. Pos. Neg. Pos. Neg. Pos. Neg. Pos. Neg. Pos. Neg. Pos. 3.8 μm 1.6 μm PR wav e form Voltage [V] 9 3 9 3 9 3 9 3 9 3 9 3 Pulse width [ms] 2.5 2.5 2.5 2.5 3 3 3 3 3 3 3 3 T off [ms] 0 1 5 0 5 0 5 0 5 0 5 5
Wave-form study on oxidation process No.2 parameter is used for wave-form study Positive Current (voltage) on Nb Negative Current (voltage) on Nb Current / A 1.5 1 0.5 0-0.5-1 -1.5-2 -2.5-3 -3.5 0.004 0.006 0.008 0.01 Time / s PR current wave-forms
Component analysis of generated gas
No.6 parameter is used for wave form. Positive pulse 3 V, 3 ms, T off 5 ms Negative pulse 9 V, 3 ms, T off 5 ms Solution 50 % H 2 SO 4 10% NaOH + 0.05% (COOH) 2 10% NaOH + 0.05% (COOH) 2 Temperatur e 0 C 20 20 50 Gas O 2 H 2 O 2 H 2 O 2 H 2 Nb Pt No detection Detected (>24%) Results of Gas Analysis Detected (>2%) No detection Detected (<6%) Detected (>24%) Detected (>2%) No detection Detected (<6%) Detected (>24%) Detected (>2%) No detection It was found that on the Nb electrode the process of oxidation-film creation is dominating and reduction reaction of NaOH solution is suppressed. It was also found that on the Pt electrode reduction reaction of NaOH solution is dominating and electrolysis reaction is suppressed.
Bipolar EP at FNAL (U.S.) Slide by A. Rowe /FNAL
Bipolar EP at FNAL (U.S.) Slide by A. Rowe /FNAL
Summary of EP The R&D of Vertical EP (VEP) process is ongoing in collaboration between KEK and Marui Galvanizing Co. Ltd. Special cathode Ninja is developed by Marui Galvanizing Co. Ltd. for VEP process. The Ninja cathode has retractable-wings which realize uniform flow of electrolyte and uniform distribution of electric current. VEP experiments are performed with single-cell cavities, single-cell coupon cavity, and 9-cell cavities to optimize the parameters. New COI building will be equipped with VEP/HEP compatible setup by MHI, which was already delivered to KEK. The setup is under installation at the new COI building. The R&D of PR-EP with alkaline solution is ongoing in collaboration between KEK and Nomura Co. Ltd. We found that shorter width of positive pulse gave longer period of positive current form for oxidation process in the PR-EP process. Gas analysis was performed on Pt and Nb electrodes for PR-EP process. H 2 was not detected on Pt electrode.
プラズマ加速の原理により ILC 相当の 電子陽電子衝突型加速器を実現する 場合の技術的な課題について
プラズマ加速の原理 プラズマとは 気体の電子と原子核が分離した状態 ここにプラズマの固有振動に一致したパルス幅の電子ビームあるいはレーザービームを通すと電子が共鳴的に動かされてプラズマ波 ( 電子の濃淡 ) が発生し 外から投入した電子あるいは陽電子を加速することができる e - e - 電子ビームによってプラズマ波を発生するものを PWFA(Plasma Wakefield Accelerator) レーザーで駆動するものを LWFA(Laser Wakefield Accelerator) と呼ぶ マイクロ波加速の場合 電磁場エネルギーを閉じ込める金属境界が加速電場が高いと破壊されるが プラズマはもともと固体ではなく破壊されるものがないので マイクロ波加速の 100 倍もの加速勾配が可能になる
プラズマ加速で ILC を作る場合の課題 ビームの質について数 GeV 程度の単段加速について ビーム電流強度を約 100,000 倍にする必要がある また 多段加速について実証する必要があるが 現在のところ 2 段の実証実験が存在するのみである 加速の際にビームの取りこぼしがあると放射線をばら撒くため 99.99% のビーム加速効率が必要であるが 現在は数 % である これについて DOE のレポートでは 10 年後の達成目標を 90% としている (ILC 相当の加速器を実現するためには その後 90% をさらに 99.99% にする必要がある ) 陽電子の加速について陽電子を加速するアイデアは幾つかあるものの 原理実証を行っている段階である 衝突型加速器に使用できるような加速実験の成果は現段階ではない このため いつまでにできるとは言えない コスト 電力効率について少なくとも レーザー発生器について 約 100,000 分の 1 のコストダウンが必要である 電力効率について 約 50,000 倍の改善が必要である