International Workshop on future linear colliders LCWS 2019

International Workshop on future linear colliders (LCWS 2019 ) October 28 - November 1, 2019 R&D Plan of Nb 3 Sn thin film SCRF gun at KEK TARO KONOMI KEK: HIGH ENERGY ACCELERATOR RESEARCH ORGANIZATION ACCELERATOR LABORATORY-CASA 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 1

Outline 1. Design of KEK Nb 3 Sn furnace 1. Design concept 2. Furnace design 3. Experimental area design 4. Schedule 2. Development of the pure Nb SRF GUN 1. Design concept 2. KEK SRF gun #1 3. KEK SRF gun #2 3. Plan of Nb 3 Sn SRF gun for UEM 1. Nb 3 Sn SRF gun for Microscopy 2. Ultrafast Electron microscopy (UEM) 4. Summary 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 2

Design of the KEK Nb 3 Sn Furnace 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 3

Nb 3 Sn • • SRF cavity with Nb 3 Sn film can be operated at 4 K, instead of 2 K. Nb 3 Sn would reduce the power consumption of refrigerator drastically. SRF accelerator system becomes greener. It would provide an operator free system. It can be use in small accelerator lab and small hospital, airport. The performance of Nb 3 Sn is well demonstrated. KEK also want to apply Nb 3 Sn to accelerators. 1. 3 GHz single cell cavity 22. 5 MV/m S. Posen, SRF 2019, THFUB 1 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 4

Cornell Nb 3 Sn Vapor Diffusion Furnace • KEK selected vertical type Nb 3 Sn vaper diffusion furnace based on Cornell design. • It is simple structure compared to horizontal type and well proved 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 5

Design concept of the KEK Nb 3 Sn furnace Roots + Cryopump SUS extension For Nb tube JISA 450 Oring flange • KEK furnace is designed based on Cornell one. Heater and reflector Water cooling jacket Single cell cavity Sn. Cl 2 Source Sn Source 3050 mm Roots + Cryopump <1500 mm (Space for Nb chamber) 1000 mm (soaking area ) • The maximum operation temperature of the furnace is 1400 K • Heater area and Nb 3 Sn vaper diffusion area are completely separated. Pumping system is also separated. • Only Nb, Mo, W can be used for high temperature zone (>200℃). • The maximum cavity size is assumed 3 cell 1. 3 GHz cavity. Nb chamber Heater for Sn Φ 450 mm (Space for Nb chamber) Φ 1000 mm (ID of furnace) 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 6

Design of the furnace • Nb 3 Sn diffusion chamber is mainly made of Nb. Ø Ti is used for flange. Ø Cu is used for gasket. Ø Stainless steal is used for low temperature (<200℃) parts. Ti Flange • Cavity and Heater sources are connected each other and suspended at same time. Mo heater Sn. Cl 2 + Radiation shield Sn Heater 2019/10/28 ~2300 mm • We are designing the Sn heater now. • Sn heater is 1 k. W and covered by Al. N. 3270 mm from ground SS chamber (Water cooling) Nb chamber Sn T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 7

Experiment area Lifter We will build Nb 3 Sn furnace in COI building. 2 nd floor will be construct to install the cavity. 2 nd floor is covered by clean booth. • Clean booth unit is Horizontal type to avoid the contamination come into the furnace. ISO Class 4 Clean booth 7 m 2 nd floor Lifte 1 m 6 m • • • Clean booth unit Stairs Furnace (ICF 356) Clean booth 4 m Flow of the clean air (horizontal) COI building 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 8

Schedule • We want to finish building all of Nb 3 Sn furnace until end of March 2020. 2019 Nov 2020 Dec Furnace Utilities Jan Feb Mar Fabrication Install to KEK Preparation of water, electricity, gas Nb chamber Connect to furnace Install to furnace Nb chamber fabrication Pump system fabrication Fabrication of Sn heater (not decided) 2 nd floor Clean booth Cavity lifter 2019/10/28 Design layout Constriction (not decide) Unit fabrication Design Fabrication (not decide) T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 9

Development of the pure Nb SRF GUN 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 10

Design of the pure Nb gun • We are developing the SRF gun for KEK ERL project. • The feature is transparent photocathode for simple transport line and easy laser spot control. • Cathode rod should be kept around 2 K because transit temperature of the transparent superconductor is 13 K. • Transparent photocathode can realize very small laser spot (~φ１ um) for small emittance. Photocathode SRF gun cavity Electron Beam Photocathode surface: K 2 Cs. Sb laser e- beam Tc=13 K AR coating: Mg. F 2 or Ta. O 5/Si. O 2/Ta. O 2 RF SRF cavity Thermal emittance: 2019/10/28 Transparent superconductor: Li. Ti 2 O 4 ~100 nm Transparent Substrate: Mg. Al 2 O 4 0. 5 mm RF Excitation Laser T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 11

Design of the KEK SRF gun #1 • KEK SRF gun #1 was developed to check the RF performance. • Cathode can be cooled directly by LHe. Acc. cell KEK SRF gun @2 K Choke cell Parameter Value Beam energy 2 Me. V Beam current 100 m. A Bunch charge 80 p. C Laser length (uniform) 10 ps Projected emittance 0. 6 mm. mrad Projected energy spread 0. 09% (1. 84 ke. V) Peak electric field 41. 9 MV/m Peak magnetic field 95. 2 m. T RF phase 55° Geometrical Factor 135. 6 Ω (TESLA 270 Ω) Target surface resistance 30 nΩ (ILC target) Target Q value 4. 5× 109 Target cavity loss 8 W 2019/10/28 Cathode rod T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 12

Vertical test result of the KEK SRF gun #1 • We already has the EP and HPR technique to achieve high gradient without field emission. EP HPR 5 o 70 o 90 o 110 o 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 13

Design of the KEK SRF gun #2 • We fabricating the KEK gun #2 for testing the demountable photocathode to test the K 2 Cs. Sb photocathode. • It will be tested in Horizontal cryostat Cathode rod Cathode holder Cavity #2 1. 5 cell cavity Cathode holder Helium jacket Cathode rod 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 14

Vertical test results of the KEK SRF gun #2 • • The maximum gradient without cathode rod reached to target value. We can shift the main target to cathode rod and holder development • Effective cooling structure to keep the cathode rod around 2 K. • Particle free cathode transport method. Target 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 15

Vertical test results of the KEK SRF gun #2 • • The maximum gradient without cathode rod reached to target value. We can shift the main target to cathode rod and holder development • Effective cooling structure to keep the cathode rod around 2 K. • Particle free cathode transport method. Cathode holder Cathode rod Target 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 16

Plan of Nb 3 Sn SRF gun for UEM 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 17

SRF gun for Microscopy • There are many applications using Nb 3 Sn can be considered. Light source, Water purification. Option LN 2 gas Return He gas Multi port 80 K shield • Nb 3 Sn technology enables operation in small facilities which don’t have a large refrigerator system. He level gauge 5 K shield Magnetic shield Tuner 4. 2 K He • We start designing of the SRF gun for microscopy in collaboration with Osaka university. • RF power is low (RF cable can be use). • Beam current is low (Metal (Nb) cathode can be use) 150 ㎜ 250㎜ RF input 1. 3 MV TEM@Osaka Univ. ISIR 2019/10/28 Liquid He T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK ~400㎜ RT All metal gate Valve 18

Ultrafast Electron Microscopy (UEM) • The RF design of the gun cavity is same as KEK SRF gun #1. • KEK SRF gun #1 is already achieved high gradient without filed emission. • The photocathode is metal Nb cathode. • We will try to coat the Nb 3 Sn on the KEK SRF gun #1 Required parameters for Nb 3 Sn gun Paramter Value Operation temperature 4. 2 K Beam energy 1~2 Me. V Pulse width 10 fs Charge 10 f. C Pulse repetition 100 MHz Current ~ 1μA Norm. Emittance 20 nm-rad Energy spread 10 -5 RF loss 8 W @Qo=4. 5 x 1010 2019/10/28 Nb SRF gun ⇒ Nb 3 Sn SRF gun 1. 3 GHz KEK SRF gun #1 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 19

Summary 1. Nb 3 Sn furnace • KEK start designing Nb 3 Sn furnace based on Cornell. • We want to finish construction until end of March 2020. 2. Nb SRF gun • KEK SRF gun #1 (metal cathode) was reached Esp=75 MV/m. • KEK SRF gun #2 K 2 Cs. Sb photocathode will be tested by using horizontal cryostat. 3. Nb 3 Sn SRF gun for UEM • We consider to apply Nb 3 Sn for Ultrafast Electron Microscopy (UEM). 2019/10/28 T. KONOMI: R&D PLAN OF NB 3 SN THIN FILM SCRF GUN AT KEK 20