July 9-11 2014

LEReC Review 9 - 11 July 2014

Low Energy RHIC electron Cooling

Sergey Belomestnykh

SRF and RF systems

July 9-11 2014

Outline

• Scope• Parameters• Major Procurements• Relocated equipment

– used/borrowed/repurposed– Moved to make space

• Equipment installation location and conventional facilities requirements

• Timeline• Risk list• Summary

2

July 9-11 2014

Scope

• 704 MHz SRF photoemission gun providing a 1.6 to 2.0 MeV beam of electrons – requires some modification for LEReC.

• 130 kW CW RF system for the SRF gun – new high power RF amplifier.

• 704 MHz 5-cell SRF cavity operating at a voltage up to 0.9 MV for energy spread correction – relocated from R&D ERL.

• 20 kW CW RF system for the 5-cell cavity – shared with the CeC PoP linac.

• 2.1 GHz warm cavity operating at a voltage up to 460 kV cavity for further correction of the energy spread – new design.

• 20 kW CW RF system for the warm cavity – new RF system.

3

July 9-11 2014

Location in LEReC

4

704 MHz SRF gun

704 MHz 5-cell SRF cavity

2.1 GHz 7-cell warm cavity

July 9-11 2014

SRF Photoemission Electron Gun

5

The 704 MHz ½-cell SRF gun with an independently cooled (by helium gas) demountable cathode stalk uses a multi-alkali photocathode.

A quarter wave RF choke-joint supports the photocathode stalk and has triangular grooves for suppression of multipacting.

Two Fundamental Power Couplers (FPCs) are designed to deliver up to 1 MW of RF power. Will need only 100 kW for LEReC.

The gun’s Qext will have to be adjusted from 5.5e4 to 4.1e5. This will be accomplished with 3-stub waveguide transformers.

A high-temperature superconducting solenoid is located inside the cryomodule.

Frequency tuning range is 1 MHz (1 mm of cavity deformation).

HOM damping is provided by an external beamline ferrite load with a ceramic break.

CathodeisolationValveCathode

installationcart

Beam lineisolation valve

Top cover withfacilities feedthrough

Cavityassembly

InternalHelium dewar

Adjustable supports

Magnetic andthermalshielding

HOM Ferrite

Vacuum vessel

PowerCouplers (2)

InsulatingVacuum Port

HTS solenoid

July 9-11 2014

SRF Gun Parameters

6

RF frequency 703.6 MHz

Cavity active length 8.5 cm (0.4 cell)

Maximum energy gain 2.0 MeV

Maximum field at the cathode 26.7 MV/m

Eacc at 2 MV 23.5 MV/m

Installed RF power 120 kW

R/Q 96.2 Ohm

Geometry factor 112.7 Ohm

Cavity operating temperature 2 K

Cathode operating temperature 80 K

Cathode RF losses (80 K) at 2.0 MV 226 W

Qext 4.1x105

Required RF power 100 kW

Installed RF power 130 kWMore details on the SRF gun performance in“Commissioning Program of the 704 MHz SRF gun” by Wencan Xu

July 9-11 2014

Major Procurements for the SRF Gun

• Two 65 kW CW RF amplifiers

• Circulators, RF loads, transmission line components

• LLRF

• New cathode

• 3-stub WG transformers

7

More details on high power RF and LLRF in“Power amplifiers and low-level RF” by A. Zaltsman

July 9-11 2014

Relocated Equipment

• The SRF gun cryomodule and the cathode insertion setup will be relocated from the R&D ERL to IP2

8

July 9-11 2014

Location in LEReC

9

704 MHz SRF gun

July 9-11 2014

5-cell SRF Cavity

10

Fundamental mode resonates at 703.6 MHz.

Large (24 cm dia.) beam tubes allow all HOMs to propagate toward room-temperature ferrite HOM dampers.

The cutoff frequency of beam pipes is 790 MHz, while the first dipole mode is at 810 MHz.

50 kW CW fundamental power coupler of the SNS type with water cooled RF window.

First horizontal test was in March of 2009. Several more tests were carried out after that.

Mechanical tuner has 112 kHz tuning range, piezo provides 9 kHz fast tuning.

In CW operation the cavity is quench-limited to 11.5 MV/m due to to the AlMg3 seal located between the NbTi and stainless steel flanges on one of the beam pipes (on the FPC side). The cavity performance is more than sufficient for LEReC.

The cavity is used to “de-chirp” energy spread along the bunch.

July 9-11 2014

5-cell Cavity Parameters

11

Frequency 703.6 MHz

No. of cells 5

Geometry Factor 225 Ohm

R/Q 404 Ohm

Epk/Eacc 1.97

Bpk/Eacc 5.78 mT/(MV/m)

Length 152 cm

Beam pipe diameter 24 cm

Cavity voltage 900 kV

Qext 2x107

Required RF power 1 kW

Installed RF power 20 kW

July 9-11 2014

Major Procurements for the 5-cell Cavity

• RF transmission line components to connect the cavity to the 20 kW CW RF amplifier installed for CeC PoP

12

More details on high power RF and LLRF in“Power amplifiers and low-level RF” by A. Zaltsman

July 9-11 2014

Relocated Equipment

• The 5-cell cryomodule will be relocated from the R&D ERL to IP2

13

July 9-11 2014

Location in LEReC

14

704 MHz 5-cell SRF cavity

July 9-11 2014

2.1 GHz Warm Cavity

15

The third harmonic cavity is used to “fine-tune” the beam energy spread.

This is a 7-cell copper structure with magnetic coupling between cells.

The cavity is designed for an accelerating voltage up to 460 kV.

The dissipated power at this voltage will be 15.7 kW.

We plan to use a CEBAF-type RF window modified from 1.5 GHz to 2.1 GHz.

There will be two plunger-type frequency tuners operating in parallel.

Two ion pumps will be maintaining the cavity vacuum and one small pump will be located near the RF window.

The RF design is nearly complete as well as preliminary mechanical design.

Next step: ANSYS analysis (mechanical stresses & thermal).

July 9-11 2014

2.1 GHz Cavity Parameters

16

Frequency 2.11 GHz

No. of cells 7

Rsh 13.6 MOhm

R/Q 1.207 kOhm

Cavity voltage 460 kV

Required RF power 15.7 kW

Installed RF power 20 kW

Regular Cell

End Cell

July 9-11 2014

Major Procurements for the 7-cell Cavity

• Cavity

• Fundamental power coupler

• 20 kW CW klystron amplifier

• WR430 components, circulator, RF load

• LLRF

17

More details on high power RF and LLRF in“Power amplifiers and low-level RF” by A. Zaltsman

July 9-11 2014

Location in LEReC

18

2.1 GHz 7-cell warm cavity

July 9-11 2014

Timeline

• FY2014: finish detailed design of the 2.1 GHz cavity; commissioning of the SRF gun in pulsed/low current mode

• FY2015: engineering design reviews, place orders for the 2.1 GHz cavity, FPC, RF amplifiers, other RF components; commissioning of the SRF gun in pulsed/low current mode; SRF gun modification for CW operation

• FY2016: receive and inspect components; high-current commissioning of the SRF gun and 5-cell cavity in CW mode (bldg. 912)

• FY2017: install in IP2, commissioning

• FY2018: commissioning with RHIC beams and low energy Au operation

19

July 9-11 2014

Risk list

• Low risk– SRF Gun Cathode lifetime, as determined by ERL testing, is lower

than design specification. Likelihood: U. Mitigation: Cathode insertion system will have to be redesigned to allow the loading and remote changing of multiple cathodes for efficient RHIC operations. This load lock assembly must be designed to 10-11 Torr vacuum. Expiration: 4QFY15.

20

July 9-11 2014

Summary

• There will be three SRF/RF systems in LEReC: 704 MHz SRF gun and 5-cell cavity, and 2.1 GHz 7-cell warm cavity.

• The SRF gun commissioning with high beam currents in CW mode will have to be completed in bldg. 912: new cathodes; improved cathode cooling; new HTS solenoid leads.

• The gun’s FPC coupling will be modified using 3-stub waveguide transformers.

• The 5-cell cavity is ready for LEReC, just needs to be relocated.

• The new 7-cell third harmonic cavity operating at 2.1 GHz has its RF design complete. Mechanical design is in progress. The cavity will be straightforward to manufacture and there is a number of companies who can do this (AES, CPI, RI, Niowave, etc.). It also can be fabricated in collaboration with a national lab, e.g. SLAC.

21