RF-Gun cavity for high charge electron generation Takuya Natsui

Introduction of Quasi-Traveling Wave Side Couple RF gun. Cavity design Beam study Plan Contents

Why we need advanced RF gun? Normal RF gun does not have focusing E-field. 5 nC beam charge has much higher space charge. We need advanced RF gun. Normal RF gun 5 nC beam tracking simulation. Beam size will be too large for our use.

4 normal cavitydeveloped cavity E-field E-field on-axis focusaccelerate focus accelerate Effective E-field on-axis E-field on-axis Effective E-field on-axis accelerate focus

5 focus: Weak focus ： Strong normal cavitydeveloped cavity E-field on-axis focusaccelerate focus accelerate Effective E-field on-axis E-field on-axis Effective E-field on-axis accelerate focus E-field Beam

Close nose make narrow acceleration field Long drift space causes the beam defocus Annular coupling cavities makes narrow accelerating gap 6 The close nose makes focus field. Side coupled cavity can be made the close nose. But, long drift space is problem. One solution is to use tow standing wave cavity.

Quasi traveling wave side coupled cavities Normal side coupled cavities

8 Avoid the E-field concentration Obtain strong focus field Prevent emittance growth ○ ☓ Prevent emittance growth by using a curved shape cathode 1 st Cavity Design (cathode cell) We need strong focus field. But strong focus field may cause emittance growth. We must avoid the electric field concentration.

9 First cavity (Cathode cell) Maximum E-field at surface: 120 MV/m Regular cell This RF gun has total of seven acceleration cavities. These are divided into two standing wave structure of 3 and 4 side coupled cavities respectively. Maximum E-field at surface: 100 MV/m Whole cavities design Emittance: nC This RF gun can generate 10 nC beam

Beam tracking simulation result （ 5 nC ） 5 nC 11.5 MeV parallel beam Emittance 5.5 mm-mrad Size 0.4 mm Energy spread 0.6% Bunch shape Gun Exit

Beam tracking simulation result （ 10 nC ） This RF gun can generate 10 nC beam.

３次元構造の詳細設計 Regular cell Coupler Cathode cell 12 k : 3.0 %

coupling cavities accelerating cavity cathode 3D design Cavity shape beam 90 deg hybrid RF 13

Cell fabrication 14

15 Brazing

Installed RF gun at A1 RF Cathode beam Laser port 90 deg Hybrid 16

Conditioning Target RF power is 20 MW, 1 usec. Maximum RF power : 14 MW, 600 nsec. Last one month is 13 MW, 600 nsec. vacuum pressure Klystron HV

Es:33.5kV Es:31.0kV Es:25.0kV Compared to 3-2 DAW RFgun vacuum pressure At 3-2 DAW gun, two weeks was enough conditioning term. A-1 gun had over a month conditioning time. RF power [MW] Maximum surface E-field [MV/m] A-1 target20120 A-1 achieved1485

Laser pulse streak camera measurement 30 ps

Electron beam streak camera measurement Compression at chicane 10 psec No compression 20 psec

Laser profile measurement (UV) It is not gaussian profile, not stable.

Emittance measurement Q scan method beam charge : 0.6nC beam energy : 30 MeV used screen Scan magnet

Emittance measurement Q scan method beam charge : 0.6nC beam energy : 30 MeV Normalized emittance X : /- 5.9 [mm-mrad] Y : / [mm-mrad]

Improvement plan Breakdown at cathode rod is one of the problem. New gun will be choke structure.

Improvement plan Simple cavity RF gun is designed. (not Quasi traveling wave ) Cut disk structure. Large coupling value, annular coupling, not so complex structure