# [Superconducting RF Cavities]{.smallcaps} 

> **19.d. [Background]{.underline}**
>
> The Accelerator Division and the Technical Division are coordinating
> efforts on Fermilab\'s superconducting cavity (SCRF) program. At
> present this program has two cavity development efforts under way;
> both efforts focus on cavities operating at 3.9GHz. The deflecting
> mode cavity originally designed for operation in the kaon separated
> beam line will now be used for upgrade of the FNAL-NICADD
> Photo-injector Laboratory (FNPL). It will provide beam slice
> measurement capability, as the head and tail of the beam can be
> deflected by different amounts and directions. The accelerating mode
> "Third Harmonic" cavity will also be used for the photo-injector
> upgrade. It will compensate for longitudinal nonlinear beam energy
> curvature correlation with time due to the finite length of the
> electron beam accelerated by the sinusoidal RF field. Because the
> longer bunches help to reduce space charge effects, this will allow
> significant reduction of the emittance of electron bunches produced by
> long laser pulses (20-40ps) and allow for very short bunch
> compression. Injection systems of free electron lasers and linear
> colliers can use results of this R&D.
>
> The basic infrastructure for SCRF cavity development has been
> developed over the years. This includes ultra pure water (UPW), high
> pressure rinsing (HPR), an oven for high temperature bake and a
> vertical dewar. Collaboration with Argonne on a chemical etching
> facility is under way.
>
> **19.f. [Accomplishments in FY04]{.underline}**

# [Deflecting Mode System]{.smallcaps}

System tests of the 3.9 GHz cavity horizontal module start this year.
These tests will look toward operation in the module with the necessary
vibration suppression and explore just what bandwidth will be necessary
for stable operation. They will verify the field flatness tuning
algorithm, cryogenic heat load estimates, and ultimately show the field
level capacity of the first 13 cell prototype. Operation of the cold
tuner and piezoelectric tuner will be tested.

> 3.9 GHz cavity fabrication, RF field measurement, cavity tuning, and
> vertical dewar tests continue in order to provide prototype cavities
> that (one hopes) will meet field strength and power dissipation
> specifications. Design studies of HOM and LOM (higher/lower order
> mode) couplers have been initiated in order to make the cavity
> suitable for operation with bunch trains. Cavity fabrication will be
> mostly through U.S. vendors, increasing commercial capacity in this
> technology.
>
> A cryomodule for the deflection mode cavity is being designed for
> installation in the FNAL/NICADD photoinjector. A low level RF system
> for integrated operation of all the cavities in the upgraded
> FNAL-NICADD facility is being designed. A high power RF supply for the
> deflecting mode cavity will be assembled from parts on hand.

## [Third Harmonic System]{.smallcaps}

Two copper models of the 3.9 GHz accelerating mode superconducting
cavity have been fabricated and tested. A three-cell Nb cavity has been
fabricated and will be tested in vertical cryostat. A nine-cell
prototype cavity is being fabricated. This cavity will include HOM
couplers. The fabrication of prototypes of the Third Harmonic
superconducting cavities is followed by RF field measurements, cavity
tuning, and cold measurement.

> The design of a cryostat for the Third Harmonic cavity with power
> input coupler and HOM coupler is in progress. A klystron, modulator,
> and control system are in procurement.
>
> **[Cavity Fabrication Infrastructure and Materials
> Investigation]{.smallcaps}**
>
> As a part of the FNAL-ANL facility for cavity surface treatment,
> process compartment development is ongoing at the Technical Division.
> After a process review, the equipment will be mounted in the
> designated hall at ANL.
>
> Materials investigation studies have started. These include activities
> in collaboration with University of Wisconsin on properties of
> Niobium, measurements of RRR and eddy current measurements of Nb
> sheet.

## [Piezoelectric Technology]{.smallcaps}

> Piezoelectric materials have been used to provide fast frequency
> adjustment of the very narrow resonances that are characteristic to
> superconducting cavities. The state of the art is to use these
> materials as mechanical activators that are cycled according to a
> fixed pattern, usually determined by Lorentz pressure distortions of
> the cavity as it is filled and emptied of energy. We are attempting to
> extend the state of the art to handle less predictable patterns using
> adaptive filtering. In particular, RF power supply costs for a range
> of SCRF applications would be reduced if we can compensate for ambient
> microphonic vibrations.
>
> **[US Collaboration on a SCRF Module Test Facility
> (SMTF]{.smallcaps}[)]{.underline}**
>
> Initial discussions have started amongst interested US laboratories as
> to the possibility of a joint facility to develop SCRF technology and
> fill the gaps in our knowledge. Such a facility could be a test bed
> for both high gradient pulsed cavity operation and CW operation at
> high Qo and high Qext.
>
> **19.g.1. [Accomplishments Expected in FY05]{.underline}**

###### **[Deflection Mode System]{.smallcaps}**

> A deflection mode cavity will be installed in the FNPL photoinjector
> and tests with beam initiated. Fabrication and test of cavities will
> continue with emphasis on using the system for the purpose of beam
> diagnostic in FNPL

##### [Third Harmonic System]{.smallcaps}

> Fabrication of the Third Harmonic cavities will be in progress.
> Preparation for installation of a cavity in FNPL will continue.
> Complete systems tests of single cavity system with input and HOM
> couplers, tuner, etc will proceed.
>
> Design and construction of a cryomodule suitable for operation in a
> higher energy photoinjector will be under way. This module will be
> designed to interface to TESLA-type accelerating modules.
>
> Room temperature high power coupler tests will start.
>
> **[Cavity Fabrication Infrastructure]{.smallcaps}**
>
> The collaboration with Argonne National Laboratory on cavity surface
> treatment will continue. After the system commissioning at ANL, a
> small clean room for cavity rinsing will be added.
>
> The R&D program to optimize cavity fabrication procedure will
> continue.
>
> **19.g.2. [Future Accomplishments Expected in FY06 and
> Beyond]{.underline}**

###### **[Deflection Mode System]{.smallcaps}**

> The deflection mode cavity will be in use as a part of FNPL for
> diagnostic purposes. Further work plans will be contingent upon the
> results of this operation.

#### 3rd Harmonic System

> Accelerating mode cavity will be fabricated, tested and assembled into
> a cryostat for use as a part of a Third Harmonic system at FNPL. Work
> will continue on a four cavity module suitable for interface to a
> standard TESLA module.
>
> Power system will be assembled and tested.
>
> Test of the system will start.
>
> **[Cavity Fabrication Infrastructure]{.smallcaps}**
>
> The collaboration with Argonne National Laboratory on cavity surface
> treatment will continue. If sufficient funds are available,
> fabrication of TESLA cavities and module will start with U.S.
> industrial participation. These cavities will be used in the High
> Brightness Photoinjector (HBPI) or SRF Module Test Facility (SMTF).
> Experience in this area will give Fermilab and U.S. industry know-how
> and a test bed for development of Linac structures and systems for
> linear collider, proton driver, or FEL.

######### *TECHNICAL DIVISION'S CONTRIBUTION TO*

#########  *ACCELERATOR RESEARCH AND DEVELOPMENT*

#### Superconducting RF Cavities

> **19.d. [Background]{.underline}**

The Accelerator Division and the Technical Division are coordinating
efforts on Fermilab\'s superconducting cavity (SCRF) program. At
present, this program has two cavity development efforts under way; both
efforts focus on cavities operating at 3.9GHz. The deflecting mode
cavity originally designed for operation in the CKM kaon separated beam
line will be used for upgrade of the FNAL-NICADD Photo-injector
Laboratory (FNPL). It will provide beam slice measurement capability, as
different amounts and directions can deflect the head and tail of the
beam. The accelerating mode "Third Harmonic" cavity will also be used
for the photo-injector upgrade. It will compensate for longitudinal
nonlinear beam energy curvature correlation with time due to the finite
length of electron beam accelerated by the sinusoidal RF field. Because
the longer bunches help to reduce space charge effects, this will allow
significant reduction of the emittance of electron bunches produced by
long laser pulses (20-40ps) and allow for very short bunch compression.
Injection systems of free electron lasers and linear colliders can use
results of this R&D.

The basic infrastructure for SCRF cavity development has been developed
over the years. This includes ultra pure water (UPW), high pressure
rinsing (HPR), an oven for high temperature bake, a vertical Dewar, etc.
Collaboration with Argonne on a chemical etching facility is under way.

## 19.f. [Accomplishments in FY04]{.underline}

# [Deflecting Mode System]{.smallcaps}

System tests of the deflecting-mode cavity horizontal module start this
year. These tests will look toward operation in the module with the
necessary vibration suppression and explore just what bandwidth will be
necessary for stable operation. They will verify the field
flatness-tuning algorithm, cryogenic heat load estimates, and ultimately
show the field level capacity of the first 13-cell prototype. Operation
of the cold tuner and piezoelectric tuner will be tested.

Deflecting-mode cavity fabrication, RF field measurement, cavity tuning,
and vertical Dewar tests continue in order to provide prototype cavities
that (one hopes) will meet field strength and power dissipation
specifications. Design studies of HOM and LOM (higher/lower order mode)
couplers have been initiated in order to make the cavity suitable for
operation with bunch trains. Cavity fabrication will be mostly through
US vendors, increasing commercial capacity in this technology.

A cryomodule for the deflection-mode cavity is being designed for
installation in the FNAL/NICADD Photo-injector Lab. A low level RF
system for integrated operation of all the cavities in the upgraded
FNAL-NICADD facility is being designed. A high power RF supply for the
deflecting mode cavity will be assembled from parts on hand.

#### Third Harmonic System

Two copper models of the 3.9 GHz accelerating mode superconducting
cavity have been fabricated and tested. A three-cell Nb cavity has been
fabricated and will be tested in a vertical cryostat. A nine-cell
prototype cavity is being fabricated. This cavity will include HOM
couplers. The fabrication of prototypes of the Third Harmonic
superconducting cavities is followed by RF field measurements, cavity
tuning, and cold measurement.

The design of a cryostat for the Third Harmonic cavity with power input
coupler and HOM coupler is in progress. A klystron, modulator, and
control system are in procurement.

###### **[Cavity Fabrication Infrastructure and Materials Investigation]{.smallcaps}**

As a part of FNAL-ANL facility for cavity surface treatment, process
compartment development is ongoing at TD. After a process review, the
equipment will be mounted in the designated hall at ANL.

> Materials investigation studies have started. These include activities
> in collaboration with University of Wisconsin on properties of
> Niobium, measurements of RRR and eddy current measurements of Nb
> sheet.

###### **[Piezoelectric Technology]{.smallcaps}**

> Piezoelectric materials have been used to provide fast frequency
> adjustment of the very narrow resonances that are characteristic to
> superconducting cavities. The state of the art is to use these
> materials as mechanical activators that are cycled according to a
> fixed pattern, usually determined by Lorentz pressure distortions of
> the cavity as it is filled and emptied of energy. We are attempting to
> extend the state of the art to handle less predictable patterns using
> adaptive filtering. In particular, RF power supply costs for a range
> of SCRF applications would be reduced if we can compensate for ambient
> microphonic vibrations.
>
> **[US Collaboration on an SRF Module Test Facility
> (SMTF)]{.smallcaps}**

Initial discussions have started amongst interested US laboratories as
to the possibility of a joint facility to develop SCRF technology and
fill the gaps in our knowledge. Such a facility could be a test bed for
both high gradient-pulsed cavity operation and CW operation at high Qo
and high Qext.

## 19.g.1. [Accomplishments Expected in FY05]{.underline}

###### **[Deflection Mode System]{.smallcaps}**

A deflection-mode cavity will be installed in the FNPL Photo-injector
and tests with beam initiated. Fabrication and test of cavities will
continue with emphasis on using the system for the purpose of beam
diagnostic in FNPL.

###### **[Third Harmonic System]{.smallcaps}**

Fabrication of the Third Harmonic cavities will be in progress.
Preparation for installation of a cavity in FNPL will continue. Complete
systems tests of single cavity system with input and HOM couplers,
tuner, etc will proceed.

Design and construction of a cryomodule suitable for operation in a
higher energy photo-injector will be under way. This module will be
designed to interface to TESLA-type accelerating modules.

Room temperature high power coupler tests will start.

**[Cavity Fabrication Infrastructure]{.smallcaps}**

The collaboration with Argonne National Laboratory on cavity surface
treatment will continue. After the system commissioning at ANL, a small
clean room for cavity rinsing will be added. The R&D program to optimize
the cavity fabrication procedure will continue.

## 19.g.2. [Future Accomplishments Expected in FY06 and Beyond]{.underline}

###### **[Deflection Mode System]{.smallcaps}**

> The deflection-mode cavity will be in use as a part of FNPL for
> diagnostic purposes. Further work plans will be contingent upon the
> results of this operation.

#### 3rd Harmonic System

Accelerating mode cavity will be fabricated, tested and assembled into a
cryostat for use as a part of a Third Harmonic system at FNPL. Work will
continue on a four-cavity module suitable for interface to a standard
TESLA module.

Power system will be assembled and tested. Test of the system will
start.

###### **[Cavity Fabrication Infrastructure]{.smallcaps}**

> The collaboration with Argonne National Laboratory on cavity surface
> treatment will continue. If sufficient funds are available,
> fabrication of TESLA cavities and module will start with US industrial
> participation. These cavities will be used in the High Brightness
> Photo-injector (HBPI) or SRF Module Test Facility (SMTF). Experience
> in this area will give Fermilab and US industry know-how and a test
> bed for development of Linac structures and systems for linear
> collider, proton driver, or FEL.